Satellite News Gathering
FOR BEGINNERS and NON-TECHNICIANS
By: Eddie Maalouf - VP of Engineering - PACSAT International
emaalouf@starstream.net
FOR BEGINNERS and NON-TECHNICIANS
By: Eddie Maalouf - VP of Engineering - PACSAT International
emaalouf@starstream.net
BEFORE WE START
This text was designed as a basic training course for SNG “beginner” technicians, but anyone wishing to learn the basics of Satellite News Gathering would benefit from reading it.
Although the information here is simplified, there are supplemental appendixes with expansions on various topics (for those interested) towards the end of the text. Since the majority of the technical jargon and formulas are almost never used in the field, very little was included here.
An SNG technician’s job is one of the most demanding in the broadcast world. If you work for a service provider (instead of a TV station), expect lots of traveling, holiday and weekend work, being away from home for lengthy periods of time and lots of stressful episodes.
Most of the stress comes from the un-yielding deadlines and customer demands. The first year will be the hardest, customers will demand and expect way more than you can deliver primarily because you’re still learning and they’ll sense that. But, after mastering the art and learning to run your platform blindfolded, they will worship you, literally.
When everything goes well in the SNG world the producer and crew take the credit, when things fail, the “uplink” aka the SNG technician is the first to blame. True, if it’s not your fault and you can prove it, they’ll let you live another day, but that depends on how good you are. So basically, although your customers could be your worst enemies, positive interaction with them is priority number one.
The upside to all of that is the job itself. It takes you places you would never think of visiting on your own, it’ll expose you to people with the most diverse backgrounds, and at times, it will literally place you amidst historical, world changing events.
IMPORTANT TO KNOW
The list below contains some of the most important elements that should be learned, memorized and practiced while operating a satellite uplink platform. Pay special attention to the components highlighted in RED and feel free to add more that apply to “YOUR” situation.
1 Learn the proper use of a Voltmeter. It could save your life.
2 DO NOT STAND IN FRONT OF THE DISH WHILE TRANSMITTING. EVER. UNLESS YOU NO LONGER NEED YOUR EYE SIGHT OR WANT TO HAVE CHILDREN.
The satellite broadcasting field utilizes non-ionizing microwave radiation, and although not radioactive, it could still cook soft skin such as the cornea of the eye (goes first) and testicles (if not covered)
3 Make sure the truck has a first aid kit.
4 Always carry drinking fluids and snacks on assignments and don’t forget to hydrate, especially on hot days.
5 If you drive a diesel vehicle in cold, snowy weather, add anti-gelling additives to every fill up. Otherwise, the diesel may freeze and gel up in the hotel parking lot while you’re taking that desperately needed nap after a long overnight assignment.
6 Devise and maintain a schedule for checking all fluids on the truck engine and generator.
7 If your wheels/tires have “locking security” nuts on them, keep track of the key’s location. You will get a flat tire in the middle of nowhere and will need it.
8 Carry emergency reflective triangles and flares for when you break down on a dark highway.
9 Carry an orange reflective vest and ALWAYS wear it when you break down and have to pull off to the side of a busy road, especially at night.
10 Carry and maintain snow chains. Learn how to put them on and take them off by yourself. Practice doing it in the summer. Don’t wait until you need them.
11 Know the height, width and weight of your vehicle. The information is most useful when you have to drive under freeway bridges, into covered fueling stations or onto someone’s lawn.
12 Maintain “jump start” battery cables and learn how to jumpstart the truck or generator batteries.
13 Maintain replacement fuses for the all fuse boxes and the “DC” power distribution panel for the uplink platform.
14 If both truck and generator batteries die, you will need to recharge them. Most SNG trucks have on-board battery chargers. Devise a way to connect the charger to an external outlet to re-charge the batteries.
15 Learn to deploy and polarize the antenna manually so you could deploy or stow it in case of antenna controller or generator failure. THIS IS VERY IMPORTANT.
16 Maintain an updated list of mobile mechanics’ contact numbers. Write down the location of the tire jack and devise (if possible) a quick and safe method to change a tire in an emergency in the middle of the desert or a snow storm.
17 Maintain an emergency contact list that includes “un-lock” codes for cell and satellite phones on it.
18 PRACTICE. PRACTICE. PRACTICE. Nothing helps more. Go over your weak skills whenever you have down time.
THE PURPOSE
The primary purpose of an SNG platform, be it a van, a truck, a hybrid trailer or a flyaway, is to provide a path, a link, a pipe to move information from point A (transmit site) to point B (receive site) or point A to multiple receive sites.
Satellites are nothing more than microwave repeaters in space. They take a signal from a satellite truck then repeat it to a single or multiple locations. In effect, any SNG platform (with more than one dish) can perform the same functions as a satellite. It could take a signal down from any visible satellite then re-peat it (re-transmit it) back up on another satellite.
A basic uplink platform requires very little equipment. In some cases, flyaway kits that deploy in war zones have one audio/video encoder, one SSPA (Solid State Power Amplifier) with a built in BUC (Block Upconverter -- Traditionally with a maximum power output of about 20 watts) plus 1 (one) meter, or smaller satellite dish.
This text was designed as a basic training course for SNG “beginner” technicians, but anyone wishing to learn the basics of Satellite News Gathering would benefit from reading it.
Although the information here is simplified, there are supplemental appendixes with expansions on various topics (for those interested) towards the end of the text. Since the majority of the technical jargon and formulas are almost never used in the field, very little was included here.
An SNG technician’s job is one of the most demanding in the broadcast world. If you work for a service provider (instead of a TV station), expect lots of traveling, holiday and weekend work, being away from home for lengthy periods of time and lots of stressful episodes.
Most of the stress comes from the un-yielding deadlines and customer demands. The first year will be the hardest, customers will demand and expect way more than you can deliver primarily because you’re still learning and they’ll sense that. But, after mastering the art and learning to run your platform blindfolded, they will worship you, literally.
When everything goes well in the SNG world the producer and crew take the credit, when things fail, the “uplink” aka the SNG technician is the first to blame. True, if it’s not your fault and you can prove it, they’ll let you live another day, but that depends on how good you are. So basically, although your customers could be your worst enemies, positive interaction with them is priority number one.
The upside to all of that is the job itself. It takes you places you would never think of visiting on your own, it’ll expose you to people with the most diverse backgrounds, and at times, it will literally place you amidst historical, world changing events.
IMPORTANT TO KNOW
The list below contains some of the most important elements that should be learned, memorized and practiced while operating a satellite uplink platform. Pay special attention to the components highlighted in RED and feel free to add more that apply to “YOUR” situation.
1 Learn the proper use of a Voltmeter. It could save your life.
2 DO NOT STAND IN FRONT OF THE DISH WHILE TRANSMITTING. EVER. UNLESS YOU NO LONGER NEED YOUR EYE SIGHT OR WANT TO HAVE CHILDREN.
The satellite broadcasting field utilizes non-ionizing microwave radiation, and although not radioactive, it could still cook soft skin such as the cornea of the eye (goes first) and testicles (if not covered)
3 Make sure the truck has a first aid kit.
4 Always carry drinking fluids and snacks on assignments and don’t forget to hydrate, especially on hot days.
5 If you drive a diesel vehicle in cold, snowy weather, add anti-gelling additives to every fill up. Otherwise, the diesel may freeze and gel up in the hotel parking lot while you’re taking that desperately needed nap after a long overnight assignment.
6 Devise and maintain a schedule for checking all fluids on the truck engine and generator.
7 If your wheels/tires have “locking security” nuts on them, keep track of the key’s location. You will get a flat tire in the middle of nowhere and will need it.
8 Carry emergency reflective triangles and flares for when you break down on a dark highway.
9 Carry an orange reflective vest and ALWAYS wear it when you break down and have to pull off to the side of a busy road, especially at night.
10 Carry and maintain snow chains. Learn how to put them on and take them off by yourself. Practice doing it in the summer. Don’t wait until you need them.
11 Know the height, width and weight of your vehicle. The information is most useful when you have to drive under freeway bridges, into covered fueling stations or onto someone’s lawn.
12 Maintain “jump start” battery cables and learn how to jumpstart the truck or generator batteries.
13 Maintain replacement fuses for the all fuse boxes and the “DC” power distribution panel for the uplink platform.
14 If both truck and generator batteries die, you will need to recharge them. Most SNG trucks have on-board battery chargers. Devise a way to connect the charger to an external outlet to re-charge the batteries.
15 Learn to deploy and polarize the antenna manually so you could deploy or stow it in case of antenna controller or generator failure. THIS IS VERY IMPORTANT.
16 Maintain an updated list of mobile mechanics’ contact numbers. Write down the location of the tire jack and devise (if possible) a quick and safe method to change a tire in an emergency in the middle of the desert or a snow storm.
17 Maintain an emergency contact list that includes “un-lock” codes for cell and satellite phones on it.
18 PRACTICE. PRACTICE. PRACTICE. Nothing helps more. Go over your weak skills whenever you have down time.
THE PURPOSE
The primary purpose of an SNG platform, be it a van, a truck, a hybrid trailer or a flyaway, is to provide a path, a link, a pipe to move information from point A (transmit site) to point B (receive site) or point A to multiple receive sites.
Satellites are nothing more than microwave repeaters in space. They take a signal from a satellite truck then repeat it to a single or multiple locations. In effect, any SNG platform (with more than one dish) can perform the same functions as a satellite. It could take a signal down from any visible satellite then re-peat it (re-transmit it) back up on another satellite.
A basic uplink platform requires very little equipment. In some cases, flyaway kits that deploy in war zones have one audio/video encoder, one SSPA (Solid State Power Amplifier) with a built in BUC (Block Upconverter -- Traditionally with a maximum power output of about 20 watts) plus 1 (one) meter, or smaller satellite dish.
EXAMPLE OF CARRY ON FLYAWAY CURRENTLY OFFERED BY AVL TECHNOLOGIES WWW.AVLTECH.COM
All the equipment is usually integrated and configured into a suitcase size package, small enough to fit into a passenger’s jet overhead carry-on luggage compartment.
A flyaway offers a quick, low grade, audio, video and data transmissions. But to provide and maintain “higher” quality broadcasts, large SNG platforms are needed. They carry more processing and monitoring equipment, higher power transmitters and of course, larger antennas.
TYPICAL ASSIGNMENT FLOW LIST
1 A call comes in requesting an uplink vehicle. The call is processed, a truck and a technician are assigned then a work order is issued.
2 The technician reviews the work order to confirm all the details are CLEAR. The work order will have directions to the site, satellite transponder listing, editing, playback, cable and IFB needs plus all contact information for on and off-site producers and downlink locations.
3 The technician performs a PTI (Pre-Trip Inspection) to confirm the vehicle is in good drivable condition, then inspects and locates all needed electronic components within the truck that will be needed for the assigned uplink.
4 The technician drives to the site.
5 Prior to permanently parking the SNG truck, the technician performs an impromptu site survey. The survey will reveal the best parking location with the best view of needed satellites and the shortest cable run to the venue.
6 The technician parks the vehicle and connects it to shore power (if not available, will use on-board generator).
7 The satellite is located, peaked and polarized.
8 All parameters (digital rates and frequencies) are programmed then a full system test on all equipment is performed. The test confirms that all the electronic equipment is in good operating condition.
9 A quick satellite/test loop is performed to confirm the satellite ID and to make sure the video, audio and RF stages are fully functional.
10 The technician notifies the on-site producer and the downlink sites of the success of the test and/or of any equipment failure. If there are faulty pieces of equipment, the technician will contact headquarters and inform the desk of the problems. Set-up procedures and tests consume about :45 minutes to 1:00 hour of time after arriving on site.
11 Cables are then stretched to the venue and contact is made with the EIC (Engineer In Charge) on site (if a production venue is taking place).
12 Audio and video are tested and all levels are equalized and confirmed.
13 A full test loop is performed with incoming signals within the uplink to confirm all equipment is functional with the external signals.
14 Quick break for the technician before the event.
15 The event takes place.
16 Breakdown and return to headquarters.
SIGNAL FLOW
Typically, most uplink platforms will follow a similar path as they ingest, equalize and transmit signals. Below is a rough signal flow breakdown within an uplink truck and the equipment involved in the process.
A live camera or a production platform sends a video and an audio signal to the truck via a coaxial or a fiber cable.
The video and audio cables are then connected into designated ports on the I/O (Input/Output) panel on the side of the truck.
The audio and video are sent to DA’s (Distribution Amplifiers) to have their levels adjusted and equalized while simultaneously are displayed and routed to various audio and video monitoring, mixing and switching components.
From the DA’s, the audio and video signals are sent to an exciter (if the signal is to be transmitted in analog) or an MPEG-2 Codec (if the signal is to be transmitted digitally).
If the audio and video signals are sent to an exciter, they are processed further within the exciter then they are placed onto a 70MHz IF (Intermediate Frequency) carrier.
If the audio and video signals are sent to an MPEG-2 Codec, they are digitized, compressed then placed on a 70MHz IF carrier.
Regardless whether you are using an analog exciter or a digital Codec, either one becomes the first step of converting the audio and video signals from electrical pulses traveling on a wire to an actual RF (Radio Frequency). From there, the IF (Radio frequency within the RF spectrum known as Intermediate Frequency) signal is sent to an upconverter where it is upconverted from 70MHz to the required C or KU frequency.
From the upconverter, the signal is sent to an HPA (High Power Amplifier) or an SSPA (Solid State Power Amplifier).
The HPA (or SSPA) amplify the signal to the required satellite transponder power levels (various from 10 to hundreds or watts) depending on the signal, bandwidth and the satellite being used. The power leaves the amplifier via a metal tube called: Waveguide. The waveguide carriers the RF signal from the output of the transmitters to the feedhorn/dish where it is magnified further then transmitted (Propagated) to the satellite.
It’s worth noting here that the actual signal itself, the electrons and neutrons never leave the dish and travel to the satellite, if they did you would see a light beam traveling into space from the dish. Instead, the signal originating from the satellite truck “propagates” (free flowing electrons bump each other and exchange states of energy (at the speed of light) all the way to the satellite).
Propagation is the act of exchanging or duplicating energy between electrons. The power being pumped into the signal from the amplifiers provides the energy continuum (the excitation that’s needed to reach the satellite). In effect, the “original” audio and video signal being processed at the truck, never actually leave the truck, a copy of it or a facsimile is transmitted all the way to the satellite. When we discover how to send “physical” signals (electrons and neutrons) to the satellite, we won’t need airplanes or the space shuttle any longer.
There are two main types of uplink choices in use today for commercial broadcasting; C or KU band and sometimes both on the same platform. The main difference between the two is frequency range and wavelength. KU caries an advantage over C band due to the high frequency it utilizes. That fact allows manufacturers to integrate smaller platforms with smaller antennas.
Domestic (USA) KU uses a 500MHz spectrum from 14.00GHz to 14.50GHz with an average wavelength of 2.2 cm. Domestic C-band uses 500MHz spectrum from 5.925 to 6.425 GHz with an average wavelength of 4.5 cm.
So what you say? Why do I give a hoot about wavelengths?
Here is where tradition meets innovation. Traditionally, the C-band spectrum had and still is being used by local telecom (telephone companies) and some terrestrial TV stations for microwave links/hops. So when C-band was converted over for satellite use, due to its wavelength and dispersion characteristics, depending on the location its being used, it tends to interfere with terrestrial links or vise-versa (the links interfering with C-band uplinks).
In short, due to the already existing infrastructure, it’s not easy to use C-band everywhere because it may interfere with older, terrestrial microwave links. For that reason, every time a new location is selected for C-band transmissions, a “Frequency Clearance Study” has to be conducted prior to using the location and frequencies.
KU on the other hand was invented specifically for SNG use and is in a band of its own so no frequency clearances are needed. However, (and here’s where the wavelength issue comes in) due to the high frequency and wavelength (shorter than C-band) of KU, it is more susceptible to moisture/rain fade. Turns out that under certain conditions (heavy rain mostly), the 2.2 cm wavelength is short enough to be attenuated by raindrops (moisture) beyond recovery at times, for as long as the heavy rain cloud persists.
Both C and KU bands could be used for sporting and pre-planned events but C band is requested and preferred by vendors especially in heavy rain regions.
Both C and KU could also be used for newsgathering but KU is preferred for quick deployment at breaking news events.
DISH SIZE
In RF, size does matter.
Non ionized microwave radiation which is what the dishes put out, As I mentioned earlier, although the waves are not radioactive, they could still cook soft skin such as the cornea of the eyes and the testicles.
For that reason, the FCC publishes radiation hazard specification for dish compliance. The hazard goes up with the amount of power being transmitted and sprayed around the dish.
The "band" (or frequency spectrum) being used (C or KU), the dish size and amp power combinations dictate what amount of ERIP (Effective Radiated Isotropic Power) RF density is being sprayed in the air and is authorized by the FCC in regulations (not to be hazardous to people within a certain distance/diameter from the dish).
Example: In order to transmit a 36MHz QPSK HD carrier in C-band on a 2.4Meter dish on an old satellite like SBS 6 (always calculate the worst case scenario), you will need about 746 watts of power (the power figure was derived from published transponder flux densities to perform a small link budget). The power figure above reflects a proper Eb/No (Energy bits per Noise bits), BER (Bit Error Rate, EVM (Error Vector Magnitude) and MER (Modulation Error Ratio) that's acceptable at the receive end.
The problem:
In order for the 2.4Meter dish to deliver such values (in C-band), the transmit site has to generate 746 watts of power which increases the "Excess" side lobes bleed-through performance on the dish and pushes it higher than the 10% maximum allowed by the FCC.
In plain English, it means that in addition to spraying everyone around the dish within 30 meters and up to 600 meters directly in front with hazardous microwave radiation, the uplink will most likely interfere with similar frequencies on adjacent satellites within 2 degrees of the satellite being transmitted on. NOT GOOD.
The FCC stipulates that the maximum feed horn flange power allowed anywhere is -50.90 dBw per Hz. With the amount of power being transmitted, the dish will spray at -46.37 dBw per Hz, clearly higher than allowed therefore breaking the FCC rule and spraying harmful microwave radiation to the public in the area and on adjacent satellites.
DISH TYPE
There are two types of dishes being used on SNG platforms. They are the center feed and the Offset feed.
The center feed will have the feedhorn placed above the center of the antenna and is usually supported by struts.
The Offset feed antenna (picture below) will have the feedhorn placed below or above the center of the antenna (usually about 15 degrees offset).
The Offset dish is usually more efficient and has a “higher gain” because the feedhorn is not in the way of the transmitted signal.
Typical components that make up an SNG antenna are:
Reflector, OMT (Orthomodel Transducer – transmit/receive feed assembly), Waveguide, LNB (Low Noise Block - for signal receiption), and the Dish positioning base (Azimuth / Elevation control) etc..
PRE-TRIP INSPECTION
One of the most important tasks to perform prior to leaving on assignment is a PTI (Pre-Trip Inspection). Especially, if the vehicle had been parked for a lengthy period of time.
* Inspect all tires for damage and un-usual wear and tear.
* Search for fluid leaks under the vehicle, particularly under the transmission and the fuel tank(s).
* Look for lose cables, hoses, nuts and bolts.
* If your vehicle has it, follow the manufacturer’s specifications to inspect and test the air brake system.
* Confirm that the rear break, parking, driving, towing and headlights work.
* Test the windshield wipers.
* Check all engine fluid levels; Transmission, Power steering, Master Cylinder and coolant.
* Fill out and maintain a driving log.
Note any damage (in writing) and report it immediately.
CAUTION
SNG VEHICLES ARE HEAVIER THAN REGULAR AUTOMOBILES. MAINTAIN POSTED HIGHWAY SPEEDS AND PROPER DISTANCES FROM THE VEHICLES IN FRONT OF YOU.
MOST ACCIDENTS HAPPEN WHEN THE SNG VEHICLE IS SPEEDING TO GET TO A SITE.
THE CORRECT HEADING.
Once you arrive on site and prior to doing anything, make contact with the on-site producer/coordinator. Newsgathering is fluid and dynamic, things may have changed while you’re on route. The on-site producer and crew may have moved to a different location? If there are no on-site personnel to assist you, telephone the client’s assignment desk and inform them of your arrival and re-confirm that all coordinates are still valid and the site has not changed.
If all is still the same and this is a pre-planned event, you may want to find the on-site electrician and inform him/her of your electric needs at this point. They can start hooking your cables (pig tails) up while you park and run your on-board generator to find and identify the satellite.
After you make contact and confirm your parameters, you must make sure that the satellite you are booked on is visible from your location
(no obstructions such as trees and buildings in the way).
Often, at questionable, pre-planned venues, where the client requests a specific satellite, a site survey is conducted days or weeks ahead of the event. A site survey entails sending a technician with a compass to the site or at times even taking an SNG vehicle, deploying the dish and physically finding and identifying “accessible” satellites. A site survey also includes planning for parking, production facilities and cable runs.
Since all geostationary satellites are placed in orbits over the equator, your main concern lies in aiming your truck (actually the dish) facing the proper heading. That would be roughly due “South” if you are in the Northern hemisphere (North America), and “North” if you are in the Southern hemisphere (Australia).
Although geostationary satellites appear motionless to an SNG platform (or any earth station), the reality is that they are constantly moving in space. After being placed in an “orbital slot” about 37,000 Kilometers in space and due to various forces such as the Earth’s gravitational force, the satellites hurl through space at 11,000 Kilometers per hour following the Earth’s rotational spin to maintain the same orbital slot, hence appearing stationary from the Earth’s surface.
For more details on satellite orbits, perform a search on the Internet under: “Geosynchronous satellites” or visit this link:
http://en.wikipedia.org/wiki/Geostationary_orbit
GPS and military (spy) satellites traditionally occupy MEO’s (Middle Earth Orbits) and LEO’s (Low Earth Orbits) which are much lower than 37,000 Kilometers and are never stationary, those satellites orbit the earth numerous times per a 24 hour period (earth day). For now, and for the sake of simplicity, we will limit our discussion to broadcast satellites in geostationary (equatorial) orbits.
Let’s assume you don’t operate a platform with the latest GPS satellite finding equipment and need to find your heading manually. So, for now, we’ll focus on finding satellites from the “Northern” hemisphere. Let’s also assume that we will be transmitting from Sacramento, California and are looking for satellite: “X” at 74 degrees West orbital slot (the name of the satellite does not matter as long as you know the orbital slot location, in which case, SBS-6 used to live at 74 degrees West). The best place to start is to find 180 degrees (South) on your compass (or GPS) and park your truck facing that direction (the dish should be deployable in the southerly direction after you finish parking).
DISH DEPLOYMENT WARNING:
BEFORE DEPLOYING THE DISH, EXIT THE TRUCK AND “VISUALLY” SURVEY FOR ANY DISH DEPLOYMENT OBSTICLES SUCH AS TREE BRANCHES, BALCONIES AND PARTICULARLY LOW ELECTRICAL WIRES.
DO NOT DEPLOY THE DISH UNTIL YOU PERFORM THIS VISUAL SURVEY, ESPECIALLY IF YOU ARE DOING THIS AT NIGHT AT A STRANGE SITE.
IF THE DISH MAKES CONTACT WITH HIGH VOLTAGE ELECTRICAL WIRES SUCH AS LOW HANGING TROLLY WIRES ON THE STREETS OF SAN FRANCISCO, SERIOUS INJURY AND/OR DEATH COULD RESULT.
IF THE DISH MAKES CONTACT WITH TREE BRANCHES, LOW BALCONIES OR OVERHANGS THEN, AT MINIMUM SOME DISH DAMAGE COULD OCCUR.
FINDING THE SATELLITE.
All domestic satellites visible from Sacramento will start in the Eastern sky and move up to the right (West), they start at a low elevation (12 degrees – Amazonas satellite) and work their way up into the sky (mid 40 degrees – AMC_7). It would be useful to carry a satellite chart, and/or a transponder guide to reference your location in the arc.
There are numerous sources of satellite charts and transponder guides available on the Internet, here’s one example:
http://testced.cahners1.com/ced/2005/0305/orbit-arc-0305.pdf
If your truck has a Satellite GPS unit built into the dish controller, turn your controller on and let it find the satellite you need. If not, read below.
It’s impossible to teach someone how to find satellites without hands on participation. They have different footprints, beacon frequencies and transponder characteristics. At times two or more satellites may look alike which may make it more difficult to identify the correct spacecraft. Even the same satellite may have different types of carriers at different times of day. Learning to identify them and even memorizing the patterns will prove useful under deadlines.
Some technicians use digital cameras to take screen shots of each satellite they identify to compare when needed, many others draw charts, grids and even draw traces of the actual image off the spectrum monitor. If you chose to do any of the above, make sure to update your drawings regularly.
Even after finding a certain satellite, it is advisable that you call the satellite access center and try to talk them into allowing you to “pop” a test carrier for few seconds on the transponder you will be using. That way, they can, without a shadow of a doubt confirm that you are looking at the right spacecraft.
There are numerous sites on the Internet that will give you any satellite look angle from anywhere in the world. All you have to do is enter the Longitude, Latitude of your site and the desired satellite. Example: http://www.satellite-calculations.com/
You can get the Longitude and Latitude of any
location off the Internet or you can invest in a hand held GPS unit like the “e-Trex”, Garmin Vista (for hikers) that can, amongst many other things such as saving way points, pointing out restaurant locations, highways and city maps, display the Longitude and Latitude of any site around the globe. http://www.garmin.com/
PEAK AND POLARIZE THE DISH
After visiting the satellite look angles web site above and entering Longitude: 121.5 West and Latitude: 38.55 North for Sacramento, California, amongst other information the program yielded, were the look angles. Satellite “X” at 74 degrees can be found at 24 degrees elevation and 119 degrees Azimuth (the program takes into account the magnetic deviation of the site and calculates the output accordingly). So, the look angles should be, theoretically, “SPOT ON”.
Now, all I that needs to be done is to use a compass to find 119 degrees azimuth then aim the antenna in the same direction. Once the antenna is there, move the elevation up to 24 degrees, scan the sky back and forth a few times and with any luck, you should find the satellite. This is normally a bit difficult the first time but with practice it becomes a second nature.
After you find the satellite, if your controller peaks and polarizes automatically, you may skip this section otherwise, read below.
Once you find the satellite, you need to optimize the transmission path. Place the dish controller in the “SLOW” mode, find a nice stable carrier then peak your Azimuth and Elevation angles for optimum signal levels. When done, center the same carrier you peaked on, switch to the opposite polarity and inspect for any remnants of that carrier. If you are polarized properly, there should be none visible.
If you see any of the carrier bleeding through the other side (pole), use the POL switches CCW and CW on your controller to null out (flatten the noise bleeding through).
Summary:
The purpose of using a stable carrier to peak the Azimuth and Elevation angles is to, obviously obtain the maximum signal levels.
The purpose for nulling that same carrier completely on the opposite polarity is to minimize spraying the opposite pole with the same frequency you will be transmitting and possibly interfering or washing another customer off the spacecraft.
The overall purpose of peaking and polarizing is to optimize your transmit and return signal levels, otherwise, the majority of your amplifier power will be lost into space during transmission and your return carrier level will not be strong enough for the client’s or your receiver to lock up on.
POWER HOOK UP
With the satellite in site, it may be time to hook up to shore power. Turn everything off including your generator and find the electrician.
Some of the latest satellite platforms offer “Dual band”, “Multi path” uplink capability in Analog, Standard Definition and/or High Definition, simultaneously.
Every broadcast platform needs electricity to run, it either uses it’s own onboard generator(s) or draws shore power from the venue, the power they draw varies accordingly. Make sure you know what your platform power requirements are.
Typically, most platforms require a single-phase connection with two hot wires and one ground at 240 Volts with a 50 amps breaker. It connects to the venue using pre-fabricated 50’ to 150’ cables, usually with bare ends affectionately known as “pig tails” or cam lock connectors. Traditionally, the electrician on site is responsible for hooking the bare ends or cam locks to their system (or on site venue generator) before allowing you to connect your truck. Most platforms use the majority of their electricity for the transmitters and the air conditioners (needed to keep all the equipment cool in the summer and winter).
The operator must always confirm that correct voltages are drawn to a platform. That’s accomplished by using a high voltage test-meter which most platforms carry in their tool kits. Always and without exceptions test the leads the electrician hands you on site for proper voltages prior to hooking it up to the truck. After confirming the voltages, ask the electrician (actually, watch him do it) to shut the breaker off so you could connect the wires to your distribution panel. Even if the electrician assures you that your cable has the correct voltage(s), you must still use your meter to confirm his information.
EVERYONE MAKES MISTAKES. IT’S BETTER TO OFFEND THE ELECTRICIAN THAN DIE.
To perform the testing, connect your meter between the two hot wires (usually Black and Red) and measure the voltage(s), they should read between 208 to 240 depending on what the electrician has available. Measure each hot wire (black or red) separately against the ground wire to insure the same voltage exists on both. If your truck requires a fourth White wire (neutral), measure the electricity between the Neutral and Green (ground) wire… There should be none – Zero electricity. The only electricity you should read should be between the two hot wires and between each hot wire to ground.
Again, no electricity should be present between the Green (ground) and the White (neutral) wires (if White is required).
If your platform requires 220 to 240 volts to run and you are handed 208 volts, use your tap transformer to boost the voltage up to the required level. Most if not all platforms will have at the very least a tap transformer and/or a regulating transformer installed onboard to compensate for voltage differences. Learn how to read the voltages and tap them up or down on your transformers.
Example, if the venue has 208 volts at 100 amps, the tap transformer onboard the truck can be switched to 208 (usually before hooking up the cables to the truck) to boost the power up to the required voltage (220--240 volts). Take the time to learn your truck’s power system and distribution panel, particularly the location and the current position of your tap transformer (usually they are installed behind the racks or in one of the storage compartments) plus all the selections it offers for shore power hookups.
Turn the main breaker(s) “ON” (to power the truck and equipment) only after you are certain all voltages and grounding has been validated.
ELECTRIC HOOKUP WARNING
READ AND ALWAYS FOLLOW
NEVER, NEVER, NEVER CONNECT OR DISCONNET THE TRUCK TO SHORE (ON SITE VENUE) POWER WITH *LIVE* CABLES. MAKE SURE THE BREAKER THE CABLES ARE ATTACHED TO IS *OFF* FIRST.
Apply power to all racks and systems only after confirming all hookups and configurations are correct.
SERIOUS INJURY OR LOSS OF LIFE MAY OCCUR.
EXITERS AND ENCODERS
There’s no need to learn everything about exciters and encoders at this stage. But, it is important to learn what they do and how they are utilized in the SNG platform.
For now, remember this:
Exciters are used to transmit analog carriers. Digital video encoders are used to transmit digital carriers.
Even if the exciter came in one enclosure, internally, it is made up of two basic stages. The first stage processes the audio and video signals, the second stage places the signals on an IF (Intermediate Frequency) carrier, usually 70MHz.
By the same token, even if the encoder came in one enclosure, internally, it is made up of two basic stages also. The first stage takes analog or SD (Serial Digital) audio and video, digitize and compress the signal, then sends it on an ASI (Asynchronous Serial Interface) stream to the second stage (modulator) which places it onto an IF carrier, usually 70 MHz.
Although most transmissions are moving towards digital, some clients still request and feel more comfortable with analog transmissions. On the long run, to save bandwidth and transmitter power on the satellite and within the SNG platform, the majority of transmissions will most likely move to and stay in the digital mode.
If your assignment is analog, adjust and equalize the audio and video levels via the DA’s then send them to your exciter. At this time, you should also program your upconverter with the proper frequency. For additional information on analog exciters see Appendix Z.
If your assignment is digital, you will need to program your encoder and IRD (Integrated Receiver Decoder) with the proper symbol or data and FEC rates. See Appendix AA on encoder basics and IRD’s. If you are not an SNG technician and are reading this text for general knowledge, continue reading.
SATELLITE CONFIRMATION.
You should now turn your amplifiers on and give them a few minutes to warm up. Instead of waiting until the actual transmit window to put up a carrier, and find out that there may be a problem somewhere in the system, we will now perform a quick “pop” up, or “access” test on the satellite. This test is being done solely to confirm that we are indeed looking at the correct spacecraft.
For this test we will use a digital encoder. Program your modulator, encoder, codec (whichever you have in the truck) with symbol, data and FEC rates then enter the satellite frequency on your upconverter.
Remember, the sole purpose of this “test” transmission is to identify the spacecraft. No video or audio will be transmitted or is needed at this time, in fact, keep your modulator or codec in “CW” (Clear Wave) mode.
When your amps warm up, place them in “High Voltage” mode, make sure you are switched into the load then apply drive to confirm that your codec, upconverters and amplifiers are working properly. Apply enough power so the amps are showing about 5-10 watts.
Contact the satellite provider and explain that you are at a new site and are supposed to be transmitting on satellite “X” transponder “Y” at time “Z” but you want to make sure that you are actually looking at the correct spacecraft. Sometimes, if they’re really busy, they will deny you the test access. If that happens, you will have to wait and hope you are on the right spacecraft when your window opens.
Often however, they will allow you to access for the test. Just in case they happen to be in a good mood or slow that day, make sure to pre-tune your IRD so you could decode your signal if they allow you to stay up for a few minutes and even modulate.
Once that’s done, cool your amps down and turn them off (usually 5-10 minutes). Contact your on-site producer or telephone the assignment desk and inform them that you have found, identified, test accessed and locked on your return off satellite X. The news will undoubtedly make them very happy.
CABLING THE SITE
At this point, you should start cabling your truck to the actual live camera or production facility position.
Various types of multi bundles aka “Siamese” cables (bundles with one or two video and 3 to 6 audio cables) have traditionally been used for analog audio and video signals. These cables served well until the introduction of SD (Standard Definition) and HD (High Definition) transmissions. Uncompressed SD streams run at 270 Mb/s, HD streams run at 1.485 Gb/s (Giga), such specs superseded the traditional cables and demanded a higher-grade method of transfer. For short runs with embedded audio, Belden 1694F for example serves the purpose but for runs beyond 300 feet, a fiber links is advisable.
Cables are often snaked through rose bushes and flown over busy boulevards with no regard to the commodity they carry. The fact is that a cable with faulty connectors (wrong impedance, short or missing center pins) could handicap a link. Take the time to evaluate and mark your cables properly, long cable runs could attenuate a digital signal and throws it off the “digital cliff”.
Perform a loop test at the I/O panel prior to stretching your cable to the designated location (live camera, production trailer etc…). Hook one end of the cable into an input and the other into an output then send color bars through it. Watch for video art effects on your waveform monitor. This step could save you lots of time and most importantly a stressful headache.
For redundancy, always test and run two cables to live events. If one fails you won’t have to run like a chicken with it’s head cut off to replace the faulty cable. After stretching the cable, confirm immediately that you are receiving proper levels. If not, pursue and fix the problem immediately.
If you’re transmitting in analog, route the audio and video signals to the waveform monitor and adjust all the levels on the corresponding DA’s.
A properly equalized video signal will have the Chroma and gain at 100 units above the zero line (as in the picture on the next page - left) and Sync will be 40 units below the zero line. Color burst will occupy 40 units, 20 above and 20 below the lines.
Sync and Burst at 40 units
100 units of Chroma over 40 units of Sync
If you’re transmitting a digital signal, the production platform will send you an SD (Serial Digital) stream, most likely uncompressed. The stream could have audio imbedded on it or separate on additional audio cables. Furthermore, the audio could be in analog or AES/EBU (digital) format, clarify and confirm all of that prior to plugging the cables into the truck.
For this example let’s assume that you are getting digital video and audio separately from the production source. Plug the cables into the proper ports on the I/O panel then route the video to the digital waveform monitor. Instead of equalizing Chroma, sync and gain like you would for analog, you will need to examine the eye pattern.
As shown in the picture above, the eye pattern displays jitter, noise and timing faults. The best way to see how these three parameters change with video quality is to compare a good vs a bad video signal. Use color bars from the truck first to establish what a good signal looks like then switch to a bad video source (color bars over a very long cable without going through a DA), you will be able to immediately spot the difference in quality. The lines will vibrate and oscillate (jitter increases), their width or girth (noise level) will increase (gets wider) and the overall pattern will shrink down from the level it’s at to below +.8 volts (timing).
All the above parameters could be adjusted via the digital re-clocking DA.
The “gamut” is another way to gauge your video signal. It displays color information within the signal and as displayed, most of the color congregates close to the letter they represent. Deviating from that represents a bad video signal.
As shown in the lower left quad (drawing below), most digital SNG trucks will have digital audio passing through the waveform monitor after the DA’s in order to at the very least adjust the volume.
Something to always ponder when you have digital video and audio being ingested separately into the truck. There always exists a chance that they may not be synched up together (lip sync problems). You or the production venue may need to adjust the delay/timing on the audio (via the encoder) so the two sources are synched up.
It is near impossible to simplify waveform equalization but enough information has been covered to allow you to manipulate and adjust to needed parameters. You will need to study waveform adjustments further on your own.
In summary: You should use the proper cable for the proper assignment. Confirm the cable is working by performing a test loop prior to stretching it from the truck and lastly, make sure the levels being received at the truck are equalized properly.
Analog video signals could degrade greatly (after a long cable run – without a DA) but never actually go away. Digital signals on the other hand will reach a certain attenuation point and drop off completely (never make it to the other end of the cable).
Make sure the camera or the production trailer is sending you audio and video then test all your cables for continuity and proper levels.
DO NOT WASTE TIME.
Do not rest until you identify and confirm all signals are proper and valid as soon as possible.
AUDIO BASICS
IF YOU’RE NOT A SATELLITE TECHNICIAN OR WANT TO BECOME ONE, SKIP THIS SECTION.
There are three “main” types of audio that can be ingested into the uplink platform. Analog, AES/EBU (Digital) and Embedded. Each type of audio has sub-parameters that could be manipulated for a desired service.
For example; Up to 4 analog audio channels can be ingested into the MPEG-2 encoder (or analog exciter). Those channels can be manipulated so they are transmitted in two stereo pairs or in mono (each channel on it’s own). Each exciter / encoder may have different options depending on model and software installed on the units. Scroll through your equipment to find out what options are available for you.
All analog exciters will accept up to 4 analog audio channels. MPEG-2 encoders on the other hand, come from the factory with the ability to handle up to 4 audio channels but unlike analog exciters, additional cards can be added so the encoder could handle up to 8 audio channels in analog or up to 16 AES/EBU (digital) or embedded channels.
It’s not simple to cover all audio standards and parameters that could be processed or have to be dealt with during a transmission. There are numerous books on the subject but most are un-readable due to heavy use of technical jargon. To keep things simple, I’ll provide basic explanations plus links and or book titles to whom ever is interested in pursuing the subject further.
ANALOG AUDIO
Analog audio is the simplest to ingest. Some of the parameters to be aware of is injection levels and pre-emphasis. Injection levels on analog exciters mean that the audio sub-carriers should be 18 to 21 dB’s below the main (video) carrier. Pre-emphasis deals with noise on audio carrier. Visit this web site for an explanation on pre-emphasis and what it does for analog broadcast audio.
http://etvcookbook.org/audio/ntsc.html
AES/EBU (DIGITAL) AUDIO
The AES/EBU (Audio Engineering Society / European Broadcasting Union) digital audio format is used for carrying audio between various devices. This audio format is also known as AES3. Unlike analog audio, AES/EBU audio does not need digitization after entering the encoder. For a more “technical”, in depth explanation visit this web site:
http://en.wikipedia.org/wiki/AES/EBU
EMBEDDED AUDIO
http://www.embedded.com/columns/technicalinsights/201202515?cid=RSSfeed_embedded_news&_requestid=259506
DOLBY DIGITAL OR AC-3 AUDIO
http://en.wikipedia.org/wiki/Dolby_Digital
Since audio uses smaller amounts of data, it is digitized faster than the video, if certain settings are omitted on the encoder, lip synching problems could occur. Learn your encoder’ settings and study how you could manipulate audio delays to match the incoming video.
TEST LOOPS
After confirming the signal integrity, the next step is to perform a test loop within the truck with the actual signal (audio and video) running all the way through the encoder and the RF chain.
Some trucks will have a sample port on the amplifiers that could be downconverted to L-band from C or KU then decoded via an IRD to analyze the integrity of the signal.
Other trucks will only have the ability to sample the 70MHz IF carrier out of the encoder and decode that by upconverting it to L-Band then sending it to an IRD.
The RF test method is a better way to perform a test loop simply because it allows the technician to sample and validate the signal flow all the way through the amplifiers prior to leaving the truck therefore discovering any faults or problems if any.
At this point it doesn’t matter which way your truck performs a test loop, one should be performed and we’ll go over both.
Before we go further, you must take the time to program and confirm (again) all the correct parameters have been entered on the Codec and the upconverter. Then, program your second (back up chain) with the same parameter. You should have both your primary and back up chains ready for this test with audio and video from the venue running through both.
THE RF METHOD
This is done by taking an RF sample from the on air amplifier or a cross guide coupler installed within the waveguide run while the amp is running with drive and power on (use about 20 watts) into a load or into space – off satellite. The signal is downconverted to L-band then it is sent to an IRD. If your truck is designed and set up to do that, it will have some kind of a panel with all the connections and switching already installed. Stop reading, familiarize yourself with that panel and perform a test loop at this point.
THE IF METHOD
Most Codecs will have an “IF MONITOR” port in addition to the main IF output port that usually goes to the upconverter. That port is sent to an IF to L-band upconverter then to an IRD.
If your truck is designed to use IF for test loops, it will have a panel with all the necessary ports to accomplish that. Stop reading, familiarize yourself with that panel and perform a test loop now.
In summary, test loops are very important because they provide signal integrity information and equipment operational status. You don’t want to wait until the actual feed time to find out that your codec, for some reason is not happy with the video coming from the field.
After performing the test loop with your main (primary) chain (codec, upconverter and amplifier), switch to the back up (secondary) chain and perform the same test. Do not omit this step you may need it if you encounter an on-air failure with your primary set up.
If the tests are satisfactory and you still have a long time before going on the air, cool and power down your amplifiers. You are ready for the transmission.
Now would be a good time to visit the bathroom and/or find something to eat, once the transmission starts you won’t be able to leave your post in the truck.
TRANMISSION TIME
You should by now have carried out all the steps necessary to make the actual transmission effortless and are ready to transmit the actual event.
Turn the amplifiers “ON” at least ½ hour prior to the transmission window then go over all the rates and settings one last time.
Send drive to the amplifiers and place them into their perspective loads at around 10 watts each.
Most DVR’s (Digital Video Recorder) have 4 video and one audio inputs if your truck has one route your two incoming and two received signals into it, you should record the signals throughout the event. If a problem arises, you can use the information to trace it.
Contact the satellite access center at least 5 minutes prior to the window and access the satellite.
After accessing, set up your redundant path and place it into the load with about 5-10 watts of power. If a failure occurs you don’t want too much power going through the RF/waveguide switch, it may cause high reflective power to bounce back to the amp and possibly damage it.
A better way to run a redundant uplink (if you have the ability) is to place your RF system (both amplifiers) into a phase combiner. Run both amplifiers to the satellite with equal amounts of power, if one fails, the second amplifier will take over, all you need to do is a slight adjustment to the power level but at least you won’t come off the satellite. Phase combining should always be used for important live events where failure is not an option and a satellite signal drop is detrimental.
On most live events, the client will book the satellite window with at least ½ to 1 hour of test time prior to the actual event. So, after placing the redundant (back up) system in place start the DVR recording then call the client’s downlink site immediately to perform a “check in” so signal reception and integrity could be confirmed.
The downlink site will walk you through various requests that may include having you send your own (truck) color bars to compare to the venue’s color bars. If they know what they’re doing, they will also ask to see your redundant path so they can set levels to it in case you encounter a failure and switch to it.
After accessing, you should always acquire the following reading from the downlink site and your own site then write them down on a piece of paper, they will come in handy during troubleshooting and searching for problems.
C/N = Carrier to Noise level (in dB’s) when in CW
S/N = Signal to Noise level (in dB’s) after saturation
Eb/No = Error bits in Noise bits (in dB’s)
BER = the amount of “Bit Error Rate” in a transmitted stream shows as errors per million bits. For example: 1 in 10-
(1 in 10 to the minus 7 means 1 error bit in every ten million bits -- 10 followed by 6 zeros.
Some downlink sites monitor “EVM” and “MER” also, ask them for the readings if they do.
EVM = Error Vector Magnitude is the ratio of RMS – Root Mean Square – It displays the error magnitude to maximum symbol magnitude – it is measured in percent and a good signal yields below 18%)
MER = Modulation Error Ratio (Transmitted symbol vector versus received symbol vector)
Don’t forget to also write down your amplifier output power readings.
Only when the “check in” is done that you can relax, sit back and watch the event.
Keep a watchful eye on the spectrum and waveform monitors. NEVER LEAVE THE PLATFORM DURING A TRANSMISSION except for quick bathroom runs or emergencies.
DIGITAL SIGNAL SATURATION
A digital transmission link like an MPEG-2 signal does not have to saturate a transponder, all that is needed is a required "Signal to Noise" level on the satellite which is usually between 15 to 18 dB's for an SCPC (Single Channel Per Carrier) uplink.
The extra power will not contribute to the signal strength, instead it may interfere with other carriers and usually shows up as " noise floor shoulders" on either side of the digital carrier causing additional distortion in some cases.
Always cooperate with the satellite access centers to resolve any power or carrier balancing issues. A good “Signal to Noise” carrier produces a required “Eb/No” (Energy bits per Noise bits) on the receive end. The higher the received “Eb/No” the better the quality of the signal will be.
An 8448000 Mb/s data rate (equals to 6111319 Symbol rate) with 3/4 FEC coding signal requires a minimum of about 6 dB's of “Eb/No” on the receive end. Every link should allow extra power (3 dB’s more power) on top of the minimum required “Eb/No” to compensate for rain, transmit and receive dish pointing errors, waveguide and cable losses, atmospheric signal dissipation and electronic threshold such as a high noise LNB or IRD.
Some IRD's utilize an Eb/No count while others display BER readings. Since the Eb/No is a measurement of the overall received signal performance, you need it to be as high as possible. Since BER measures the average bit errors in a stream, you want it to be the lowest possible.
In summary we should remember that a good digital signal should yield a high “Eb/No” and/or a Low “BER” at the receive site.
CONDITIONAL ACCESS
At the beginning, every manufacturer developed a proprietary conditional access or digital signal scrambling system, but due to market pressures everyone is now moving towards “BISS” (Basic Interoperable Scrambling System) standard.
Although a digitally compressed signal is sort of scrambled, anyone with an IRD and the correct settings can decode it. So, for more protection it is possible to scramble a digitally compressed video signal and allow only certain IRD's or clients to receive it.
Tiernan’s original proprietary scrambling system for example allows their encoders to be programmed via a computer with the IRD identification numbers. Only the programmed IRD's will be capable of receiving and decoding a scrambled Tiernan signal. The BISS method allows the operator to enter a code up to 7 digits long, the code is then given to the receive sites to be entered on the IRD’s, no computer hookup or complicated programming is needed.
HD TRANSMISSIONS
By now you probably have a very good grasp on analog and SD transmissions so let’s bring in HD (High Definition) links.
Unlike analog and SD the High Definition format is in a class on it’s own. In addition to Symbol/Data, FEC and sampling rates, HD offers different frame aspect ratios, resolution and frame rate scanning methods plus various modulation schemes. On top of all that, with current technology (DVB-S – MPEG-2) HD requires a much higher bandwidth.
A standard full transponder NTSC or PAL analog carriers occupy anywhere from 17 MHz (half transponder) up to 72 MHz. The actual NTSC color information signal is only 4.5 or 5.5 MHz.
A standard, uncompressed SD signal could occupy up to 270 Mb/s. Clearly, such a signal cannot be transmitted on a satellite transponder without compression. There would only be enough bandwidth on the satellite to handle a little less than 2 uncompressed SD carriers.
A standard, uncompressed HD signal on the other hand could occupy up to 1.485 Gb/s. At that rate, one uncompressed HD signal would need three satellites (each satellite has 500 MHz of bandwidth). Even when HD is compressed at the rate of 36:1 (1.485 divided by 36) the data rate remaining (with the proper FEC), 41 Mb/s is still large enough to occupy a full 36 MHz transponder. A lower data rate (higher compression of 40:1) will yield a lower resolution.
Let’s take an HD transmission being sent in 1080i at 41 Mb/s. That would mean the transmission might have the following parameters to be entered on the encoder.
41 Mb/s with QPSK modulation (40.963725 to be exact)
27 Ms/s (26.670000 Mega Symbols per second to be exact)
DVB-S (Digital Video Broadcasting Standard 1)
5/6 FEC
16:9 Aspect ratio
1080i format --- “i” = Interlaced scanning
1080 = Vertical lines by 1920 Horizontal lines of resolution
59.94 frame rate (drop frame)
4:2:2 sampling
Frame rate of 15 GOP (Group of Pictures)
As you can see, HD requires a few additional parameters that an SD transmissions does not need.
Additionally, all the parameters above could be altered or changed on the HD encoders depending on the results sought after by the client.
If we change the QPSK modulation to 8PSK (8 Phase Shift Keying), we could then raise the data rate value up to 60 Mb/s with 5/6 FEC. That decreases our compression ratio down to 24:1 but still allows us to occupy 36MHz of bandwidth.
If we change to DVB-S2, we could use 16APSK (Amplitude Phase Shift Keying) and be able to increase our data rate much higher but still transmit on a 36MHz transponder.
HD offers a multitude of options that cannot possible be covered in this text. Learning your encoder’s capabilities and parameters is important.
HD AUDIO
The same goes for HD audio, HD encoders offer analog, AES/EBU or embedded audio that could be in Dolby E 5.1 or AC-3. Again, the type of audio the encoder ingests depends on the client’s needs and application.
APPENDIX Z
ANALOG VIDEO EXCITERS
Analog exciters ingest one video and up to four audio inputs, process them then places the signals on an IF carrier to be sent to an upconverter. Traditionally, audio sub-carriers have been placed on 5.76 MHz, 6.2 MHz, 6.8 MHz and 7.4 MHz.
7.1 MHz is usually used for an ATIS signal (Automatic Transmit Identification System). The ATIS is a Morse code signal that beeps the uplink phone number with the main video and audio carriers. It is there primarily for the benefit of the satellite service providers to contact the uplink in case of emergency.
Some of the analog exciter’s processing functions are:
IF (INTERMEDIATE FREQUENCY) ON/OFF
Must be on to transmit.
IF DRIVE LEVEL
This is the actual signal drive output that drives the upconverter and amplifier to achieve a high power output (300 – 400 watts).
CLEAR WAVE (CW) OR MODULATED (TRAFFIC) SETTINGS
Allows placing the modulator in CW mode to access the satellite then into Modulate mode when instructed to do so after reaching the required power (saturation) settings on the satellite.
VIDEO AND AUDIO CARRIER LEVEL ADJUSTMENTS
Allows the adjustment of the actual video and audio sub-carriers to meet required specifications for analog transmissions. Usually, the audio sub-carrier levels are set about 18 dB’s below the video sub-carrier.
MAIN CARRIER DEVIATION ADJUSTMENT
Allows adjusting the actual bandwidth (width) of the entire analog carrier (including the audio sub-carriers) being transmitted to meet satellite bandwidth requirements. Uses 36 MHz, 27 MHz or half transponder 17 MHz settings.
AUDIO DEVIATION ADJUSTMENTS
Adjusts audio deviation settings from 25 KHz up to 200 KHz. This is the actual bandwidth (width) of the audio sub-carriers.
ENERGY DISPERSAL ON/OFF
When turned on, this function helps disperse excess signal harmonics to prevent them from interfering with adjacent satellites that are using similar frequencies.
VIDEO EMPHASIS
This function selects the video standard being used such as NTSC (for USA), PAL (for Europe), Flat (if no emphasis is needed) and MAC (if the signal is being transmitted and encrypted in B-MAC).
AUDIO EMPHASIS
Allows 50 or 75 microseconds plus J17 or FLAT emphasis to the audio carriers. Pre-emphasis and de-emphasis are used in the transmit and receive chains to help improve high frequencies. For a better description of what pre-emphasis does and how it does it exactly, visit the link below.
http://www.batlabs.com/predemp.html
APPENDIX AA
MPEG-2 BASICS
MPEG is an acronym for "Moving Picture Experts Group", the unit was formed by the I.S.O. "International Standards Organization" to help develop and deploy digital transmission standards
An MPEG encoder with a built in modulator and an IRD (Integrated Receiver Decoder) is called a “Codec”, this is an acronym for “Co” der and “dec” oder.
MPEG-1 was developed first, it compresses audio and video into a maximum of about 1.5 Mb/s (Megabits per second). Clearly, that does not reproduce a sufficient quality product for commercial television broadcasting.
When MPEG-2 was developed, it allowed broadcasters more flexibility by introducing higher profiles and levels which translates to better sampling capabilities and higher resolutions which produces better pictures on the receive end. Since MPEG-2 is a subset of MPEG-1, MPEG-2 IRDs are manufactured to often be able to decode MPEG-1 streams also.
THE IRD
The “IRD” (Integrated Receiver Decoder) requires a minimum of five basic parameters whether you are sampling your own or decoding a satellite signal. IRD’s by different manufacturers may have additional needed settings, but the following five parameters will most likely be always similar and sufficient to cause a signal lock.
The five parameters are: The “Data” or “Symbol” rate, the “FEC” code rate, the actual “RF” frequency of the satellite transponder and the “IRD’s” built in “LO” frequency. The fifth parameter is turning the “DC” power “ON” or “OFF” to energize an LNB or the 70 MHz “IF” to “L-band” upconverter being used for a test loop.
ASYMMETRICAL ?
The way data is transmitted in one-direction from one encoder to one or more receivers forms an “Asymmetrical” link. It simply means that the encoders, although manufactured by different firms (Tandberg, Tiernan etc…) they have to comply with pre-set MPEG-2 data stream outputs regardless of how the internal electronics achieve that. Basically, each manufacturer is free to build the encoder in whichever way they like as long as it’s output complies with the MPEG group specifications for DVB (Digital Video broadcasts).
At the receive sites the IRDs have to also be DVB compliant in order to receive the signal and decode the streams. This infrastructure allows manufacturers to fabricate “dumb” IRDs, all they need to be able to do is follow instructions from the encoders to paste together the necessary video images. The nature of satellite broadcasting creates a need for much more IRDs than encoders to deliver events therefore encoders are smarter, more complicated and more expensive.
COMPRESSION
Compression has been around for a while; it was even being used in analog color transmissions. Without compression it would be difficult to move a digitized signal on an RF link economically from one site to another, simply because digitally uncompressed signals take up lots of bandwidth.
There are two types of compression: "Loss less" compression, which is what computers use to save data. And, "Lossy" compression, which is what MPEG-2 encoders utilize. "Lossy” compression is a process where all duplicate information is discarded.
Let’s assume you have a live shot beaming in from the field with a reporter standing in front of the police department. There are 30 frames per second in the NTSC system, each frame is looked at by the encoder, digitized, compressed then sent out to the satellite.
Since the reporter is standing in front of the police station and is not moving much, most likely, only the reporter’s facial expressions move but not much changes in the back ground. The encoder learns that fact by comparing successive frames from the camera then it actually stops encoding and digitizing the frames, it only encodes and digitizes the movements within the frame which is not as demanding as the whole frame.
In effect, it sends information to the receiver telling it to change the mouth movements but not to change the background because it’s still the same.
The encoder sends new information only when the entire frame changes, otherwise it repeats the instructions to the receivers until the event ends. This process results in what is called GOP’s (Group of Pictures) and is a basic description of Lossy compression.
Let’s assume you have a 9 MHz satellite segment you want to use. Since an SD signal occupies up to 270 Megabit stream, a 30:1 ratio produces approximately a 9 Megabit stream we got that by dividing 270 by 9. If you had a 6 MHz segment to use we would then have a compression ratio of
45:1. Obviously a 45 to 1 ratio is higher than 30 to 1, if the event being transmitted have lots of action and motion on it such as automobile racing or a basketball game, it is more than likely that the higher compression ration will encounter more error bits and produce unwanted art-effects on the final program output. We see here how important it is to use a proper compression ratio with a proper satellite bandwidth to deliver various programs.
In summary, by using digital transmissions, we save on satellite bandwidth resources in space and on transmitter power resources on the ground. The minor limitations digital transmissions present could easily be overcome with proper planning.
For more details on Lossy compression and the method frames are grouped, read Appendix FF.
SERIAL DIGITAL VIDEO
A digitized, uncompressed serial digital video signal could occupy a large bandwidth (up to 270 Mb/s). Satellite bandwidth resources are limited, so compression is utilized to allow the transmission of multiple digital carriers.
The first generation SD (Standard Definition) MPEG-2 encoders required many parameters the new ones only need four. Often the encoder parameters are supplied by the customer, if not, they can be calculated by the uplink engineer.
The first parameter is the data or symbol rate, if you enter one of them, the encoder will automatically calculate the other. A standard Data rate being used for a 9 MHz bandwidth slot is 8448000 which yields a symbol rate of 6111319, this rate is best utilized by using a ¾ FEC code.
Appendix GG contains more details on the difference between Symbol and Data rates.
The second parameter is the FEC (Forward Error Correction) code. This code is needed to help the receiver retrieve enough data off the stream to reconstitute a legible picture. Typically, the FEC is calculated when the Data and symbol rates are being devised. If you are interested in playing around with bandwidth and Data/Symbol figures, send an email to: emaalouf@pacsat.com with the words Data/symbol spreadsheet in the subject line. I will send you my homemade Data/symbol/FEC calculator. Read Appendix HH for more details on FEC codes and their meanings.
The third parameter to set is the sampling rate, 4:2:0 or 4:2:2. Often, for most quick news shots, 4:2:0 is used because it delivers sufficient details/resolution on a small amount of bandwidth. For sporting events with lots of moving action and wider bandwidth (18 MHz for example), 4:2:2 is a better option to use. It’s not easy to describe the difference between them in a short paragraph, all you have to remember to program the encoder is if the data rate or bandwidth being used is between 4 to 15 Megabits, use 4:2:0 sampling. If the data rate is above 15 Megabits, use 4:2:2. And, yes, a better, slightly lengthy explanation is available in Appendix II.
The forth parameter is the modulation scheme being used which will often be QPSK (Quadrature Phase Shift Keying). Since newer Codecs come with 8PSK (Eight Phase Shift Keying) modulation also you need to make sure the correct option is selected. For a better explanation on QPSK and 8PSK see Appendix JJ.
APPENDIX FF
MPEG-2 GOP’s
GOP's are the results of MPEG-2 Lossy compression. GOP’s are the end product of inter-frame and intra-frame compression states. Most GOP structures within the encoder, for most transmissions are set to IBBP with the frame lengths at 12 or 15. The reason these rates are used is because they offer the most quality video pictures for a reasonable or acceptable delay at the receive site(s).
Longer frame groups may introduce a lower quality video return at the receive site and shorter frame groups may introduce higher compression and encoding algorithms at the encoder resulting in longer delays at the receiver.
Longer delays could cause problems on live talk back programs. A "LIVE" reporter on site will not be able to respond to an IFB question in timely manner because it will take longer to digitize and compress the generated video signal on site and transmit it than it took for the IFB audio to be heard in his ear.
To understand what IBBP means, we have to break down what each letter stands for within the GOP frames structure.
"I" = Intra-coded frames. This is an originally digitized and compressed frame - Specially coded "anchor" frame, the beginning of a GOP structure.
"B" = Bidirectional frames. These frames relay the difference in information changes from the "I" and/or the "P" frames.
"P" = Predictive frames. These frames are sent after a few repetitions of identical frames (like color bars), the encoder stops encoding the video and sends "P" frames only which are in reality information only “data” frames directing the receiver to repeat the last frame it displayed with no changes. A 12 GOP frame structure leaving the encoder would look like this to the receiver.
APPENDIX GG
Data/symbol rates
Like just about any form of digital transmission, the receiver has to know the rate at which the transmitter is sending information. In the computer world, we call this the bit rate. For example, PCs can transmit from their serial ports at up to 115,200 bits per second. Lets get something straight before going forward with this explanation. A bit aka “Data” rate and a baud aka “Symbol” rate are not the same. The bit rate specifies how many bits per second are carried across the channel (phone line, serial cable or satellite transponder), however, the baud rate describes the rate that data is sent within the channel.
Let’s take a modem that transmits at 50 bps (Baud/Symbol rate) by using two tones. One tone could signal a 1 needed to be sent and the other would signal a 0.
Now imagine that you wanted to double the transfer rate across the channel. By using four tones instead of two, you could signal two sets of bits at the same time by switching various combinations of the four tones. The baud rate is still 50 baud (i.e. the tone pairs change 50 times per second), however, the bit (Data) rate is now 100 bps. The combination of the sets of tones is called a "symbol" because too many people are confused by the term baud.
APPENDIX HH
FEC codes
Every step of an uplink transmission, from the camera, cable, playback deck, DA's, encoders, upconverters, amplifiers, dish misalignment, terrestrial interference and particularly satellite transmit/receive components can and do introduce additional noise to a transmitted signal.
MPEG-2 encoded transmissions travel "Asymmetrically" that means; only the encoder sends information (one way) to one or multiple receivers. Since the receiver cannot send a signal back to the encoder saying for example: "I didn't get that last piece of information, please re-transmit it" an error correction scheme had to be implemented.
FEC (Forward Error Correction) allows the encoder to insert error correction information along with the actual data stream so the information could be used to re-constitute/re-generate a frame or a part of a frame in case errors occur.
There are two forms of Forward Error Correction. The first is "Viterbi coding" and is quoted as a fraction.
Let’s take ¾ FEC as an example. The fraction represents the amount of bits entering the encoding engine versus the amount coming out onto the stream. So, 3/4 means that 3 bits entered and 4 came out. The four represent the three original bits plus one correction bit.
One draw back of the "Viterbi" error correction code is that it introduces bursty cluster of errors when it is unable to correct a strain of errors on the stream so a second error correction scheme is implemented to smooth out the bursts.
The Reed-Solomon code corrects by assigning “parity bits” to the overall packets generated by the original encoding algorithm. MPEG packet bit length are 188/204, the Reed-Solomon code raises the value to 192/208, the extra bits are used by the IRD to correct any remaining errors resulting form the Viterbi code.
Additionally, the FEC scheme also uses interleaving of the data stream to prevent noise bursts from interrupting the flow of data in much the same way that CDs use it to prevent scratches from causing dropouts.
Consider the following example:
We’re coming to you live from Tokyo
If interleaved, it might look like:
Kuwcovi emgtyemo ronol eify ot
Should an error occur and say wipe out the 'eify' part of the message, the de-interleaved message will now read
We’r* com*ng to you live *rom Tok*o
As a result, only single characters are missing from the message (shown here as an astrix), rather than an entire word in the case of non-interleaved data.
As a final step, the QPSK symbols are scrambled (not the same as scrambled video) to ensure that long “same” symbol runs which could cause a change in the phase of the carrier do not occur.
Since the QPSK demodulator obtains its signal clocking directly from the signal itself, a large number of phase changes is necessary to re-generate the clock which is accomplished by scrambling the symbols.
APPENDIX II
4:2:0 vs 4:2:2
When MPEG-2 encoders process video (color and picture information), they sample the analog picture (from the field camera for example) at certain resolution, both as horizontal and vertical pixels, but they do it separately as color (chrominance/hue) and brightness (luminance).
Since the human eye notices "luminance / brightness" changes in the picture much more than "chrominance / color / hue" information, the DVB standard specifies that the "luminance" be sampled more times than "chrominance" so a valid, broadcast quality reproduction can be achieved.
So, a 4:2:0 sample mode on the encoder designates that the "luminance" be sampled 4 times and the "chrominance" or color differences between Red, Blue and Green (the three main TV colors) be sampled 2 then 1 time each... I know what you're saying now... Where did the 1 come from? I thought it was 4:2:0... Not 4:2:1?? Well in their infinite wisdom, the MPEG engineers working on the standard designated a 0 to a single sample because in math, a Zero is an actual number... In math, 0 (zero) does not mean the absence of a number it simply represents a position of a number.... We can go on discussing this but just take my word for it... 4:2:0 is actually 4:2:1, otherwise, why would they go to 4:2:2 from 4:2:0?
Basically, in 4:2:0 encoding, the resolution of the color information is one quarter of the resolution of the video information. 4:2:0 quickly proved inefficient for production work so a better quality than DVB system was developed and offered 4:2:2 sampling which increased the color information and in turn increased the quality of the re-produced pictures. This system doubles the amount of vertical color information being transmitted.
Another format exists that is in very common use today but not used much in SNG, called HHR - Half Horizontal Resolution, this part of the MPEG-2/DVB standard transmits only half of the normal 720 pixel horizontal resolution while maintaining normal vertical resolution of 480 pixels (although, since it's 4:2:0 format, the color information is only encoded at 240 pixels vertically and 176 pixels horizontally.
A lot of the smaller DBS (like the ethnic packages on IA5 etc) use HHR format since it dramatically reduces the bandwidth needed for channels - of course at the expense of picture quality (VHS quality). Special logic in the (home version) video decoder chip within the set top box re-expands the picture to its normal horizontal size by interpolation prior to display.
The diagram on the next page shows the ratios of 4:2:0, 4:2:2 and HHR resolutions.
Here's a good book on MPEG-2: Digital Video: An Introduction to MPEG-2 by Barry Haskell, Atul Puri and Arun N. Netravali - ISBN 0-412-08411-2.
APPENDIX JJ
Digital modulation schemes
When satellite transponders are used to transmit MPEG-2 signals, some form of Phase Shift Keying in this case QPSK (Q=Quadrature or 4) is used to modulate the digital information onto an RF carrier.
Rather than using the amplitude or frequency of the carrier to convey the information, QPSK modulates the phase of the carrier signal. Depending on the data being modulated, the carrier is forced into one of four different phase states, known as a symbol. The great advantage of this method is that each symbol contains two data bits, thus doubling the potential amount of data that is transmitted over conventional amplitude or frequency modulation (AM or FM) techniques.
The diagrams below illustrate a typical implementation of QPSK:
Figure 1 shows that each possible pair of data bits is represented by a different phase angle and figure 2 shows an example of a QPSK waveform.
This is a simplified way of expressing digital modulation using QPSK, other forms of modulation include 8PSK, 16QAM, 32QAM, 64QAM (up to 256QAM) and 16APSK with the upcoming DVB-S2 standard are available and in use on various transmission mediums.
FEC (Forward Error Correction) contributes to the actual data/symbol rates being used.
APPENDIX HH
WHAT ARE PIDs?
MPEG-2 transmits its data in packets of 188 bytes each. A package identifier (or PID) is inserted at the top of each packet that tells the receiver what to do with the packet.
If the MPEG-2 data stream is a part of an MCPC transmission, the receiver searches for the packet of the channel selected on its menu and passes those packets on to the Decoder portion of the receiver then simply discard all other PIDs.
Typically, four types of PIDs are used by satellite receivers.
The VPID is the PID for the video stream, the APID is used for the audio stream. Occasionally, a PCR PID (Program Clock Reference) is used to synchronize the video and audio packets by utilizing a Presentation Time Stamp (PTS), however, most of the time, this data is embedded into the video stream and is handled automatically via the receiver.
The forth PID, System Information (SIPID) is used for data such as the program guide, information about other frequencies that make up the total package etc... The SIPID is usually assigned a number between 0000 and 0014 (hex).
The "V" and "A" PIDs are what the receiver identifies first and displays to confirm reception of a certain program.
APPENDIX II
WHAT IS DVB?
DVB stands for Digital Video Broadcast and is a standard based upon MPEG-2 video and audio. DVB covers how MPEG-2 signals are transmitted via satellite, cable and terrestrial broadcast channels along with how such items as system information and the program guide are transmitted along with the scrambling system used to protect the signal.
With the exception of the United States of America, Mexico, Canada, South Korea and Taiwan, DVB has been adopted by just about every country in the world for digital TV & radio.
DVB-S, is the current satellite format of DVB - DVB-S2 is destined to replace it within 1-2 years.
DVB-C is the specification for DVB/MPEG-2 over cable.
DVB-T is DVB/MPEG-2 over terrestrial transmitters such as your local TV station.
DVB-H is the specifications for DVB/MPEG-2 / 4 over handheld devices such as mobile phones.
QAM
Quadrature Amplitude Modulation (QAM) is the cable version of QPSK.
Using many different symbol phases (the initial standard for the US is 64 different phases - 64QAM), a given 6MHz of cable bandwidth will be able to carry the same amount of data as a single 30MHz transponder.
A 125 channel cable system @ 6MHz per channel = 750MHz bandwidth. With 64QAM modulation the cable company will be able to carry up to 625 (Standard Definition) video and audio programs (assuming compression levels where five video services are sent on a single RF channel).
VSB
Vestigial Sideband modulation (otherwise known as VSB-8) is the technique that will be used in the US for terrestrial ATSC transmission (TV station over the air broadcasts). VSB-8 uses AM transmissions with phase information within one of two sidebands. The other sideband is almost totally suppressed except for a pilot carrier inserted to help receivers initially acquire the signal.
No need to delve further into VSB, it is not used in satellite transmissions (as of yet anyways). It is worth mentioning because most of the newer MPEG encoders will have that function and you need to understand where it would be implemented.
THE MPEG-2 TRANSPORT STREAM
MPEG-2 transmissions are either transmitted as SCPC or MCPC feeds. However, at an individual channel level, both techniques use the same method for building a data stream containing the video, audio and timing information. We will concentrate on MCPC because once this is understood SCPC becomes obvious. This combination of compressed video and audio is called the PES or Packet Elementary Stream and is built as follows:
The time field isn't the actual time that the encoding was done, but timing information to allow the audio and video to stay synchronized together. This part of the PES is called the PCR (Program Clock Reference) and may be sent either as part of the video stream or as a separate stream.
Multiple PES streams get multiplexed together into a faster stream and the System Information or SI stream gets added, resulting in the final MPEG-2/DVB multiplex that gets uplinked to a transponder on the satellite:
The SI is responsible for telling the receiver all kinds of useful information about the data stream, so that the receiver can write the appropriate data into its program guide. The first part of the SI is called the Program Association Table or PAT. The PAT is always transmitted on PID 0000 and contains a list of Program Map Tables or PMTs that are part of the data stream. For example:
PAT (PID 0000) = 0100, 0200, 0300, 0400
PMT 1 (PID 0100) = Video PID 0101, Audio PID 0102, Audio PID 0103, PCR 01FF
PMT 2 (PID 0200) = Video PID 0201, Audio PID 0202, PCR 01FF
PMT 3 (PID 0300) = Video PID 0301, Audio PID 0302, PCR 02FF
PMT 4 (PID 0400) = Video PID 0401, Audio PID 0402, PCR 0401
Given this information, the receiver knows that the DVB transport on the current frequency contains four programs. The first channel contains two audio services and all of them except for the fourth program contain separate timing information - the fourth has the PCR timing embedded into its video stream.
The reason that the PCR might be transmitted separately from the video stream is in the case of multiplexed channels which were encoded with a common clock reference. In this case, it would be redundant to send the PCR again, since the receiver would always use the same clock reference for all the signals within the multiplex.
Obviously, the PMT contains other information, such as pointers to the name of the channel in the SDT table and things like information about data services that might be multiplexed in as part of the PES. But in addition to the PAT and PMT, there are a few more interesting ones. The Network Information Table (NIT) on PID 0010 contains a list of associated transponders that make up the package along with their SR and FEC values, which can be different.
There are few other PIDs that make a DVB receiver work the way it does. The optional BAT or Bouquet Association Table tells the receiver about programs of the same type (such as sporting events, movies, news etc.) that are part of a "Sports" package on a DBS bird for example. The EIT or Event Information Table on PID 0012 contains a list of the programs (or events) that when interpreted by the receiver's firmware, make the program guide. The EIT allows for up to two weeks worth of programming to be sent ahead of time.
And finally, if you wondered how MPEG-2/DVB receivers know what the time is, the TDT (Time and Date Table) tells the receiver what the date and time is in Universal Time - the IRD contains the UTC offset, so that you see local time on the screen.
ENCRYPTION
Many types of encryption algorithms exist. The ones being used in satellite transmissions these days are usually B-MAC for analog and BISS for digital.
In B-MAC (Multiple Analog Component) type “B” each line of video information is delayed by several microseconds, creating B-MAC's characteristic diamond-hatched pattern. Only those terminals equipped with decoders that are addressed by a packet of data contained in the vertical blanking interval of the B-MAC signal can descramble the video. B-MAC's horizontal blanking interval contains up to six digitally-encrypted audio channels and one utility data channel.
B-MAC is a setting that used to come standard on most analog exciters, now days a B-MAC encoder will have to be placed in line to scramble the signal.
At the onset of MPEG-2, most encoder manufacturers developed and incorporated their own proprietary encryption techniques. Tiernan had PGCA which required inputting all identification codes of every IRD intent on receiving the programming into the encoder prior to the transmission.
Tandberg (NDS back then) developed the “SNG key” which is a 7 digit number that was programmed into the encoder which had to be entered on every IRD at the receive end to decode the programming.
Regardless of which system was being used, the encoders and IRD’s had to be by the same manufacturer… I smell a monopoly here… Don’t you?
Eventually the EBU helped develop BISS encryption (Basic Interoperable Scrambling System). BISS provides three levels of encryption complexity and allows any encoder to be decoded by any IRD regardless of the manufacturer as long as both have the needed “BISS” software/hardware on board.
GOOD PRACTICE
Digital signals require precise settings. They don’t tolerate imperfections and will not put up with unusual input levels.
Digital transmissions are difficult to troubleshoot when they fail. Due to inherent characteristics, they don’t fade or show “Sparklies” like analog signals, they just drop off completely. Locating the precise cause could be challenging, time consuming and will require numerous inquiries into many variables.
Below are a few suggestions to follow if digital problems are encountered.
VIDEO AND AUDIO CABLES
Always draw good video and audio levels from the production venue. If you are ingesting an analog signal, run the video signal thru a “Frame Synchronizer” (when possible). A Frame Synchronizer will help maintain and/or re-constitute the integrity of the video.
Inspect and confirm that the video and audio cable runs from the source to you are free and clear of EMF (Electro Magnetic Field) interference. EMF could induce hum and unwanted effects into audio and video cables when they run close to it – An example of an EMF source is a high voltage wire (truck’s power cable).
Basically, in addition to maintaining a proper well grounded single power source for your equipment, pay special attention to high voltage cables crossing or coiled over your video and audio runs.
DIGITAL EQUIPMENT INITIALIZATION
Always run a complete software factory initialization on the encoder and IRD before entering any new settings. Confirm that all the settings on the IRD match the settings on the encoder, check transmit and receive frequencies, Data and/or Symbol rates, FEC coding, video data rate too low or too high (too high uses up too many bits, too low produces lower video resolutions on the receive end). Check audio settings not to be too low or too high, extreme variations could yield amongst other effects a tinny sound on the receive end.
Replace Codecs, upconverters and transmitters if necessary to test a path that keeps exhibiting problems. Some Codecs or IRD's could have faulty chips, small error buffers or software faults. These units may experience problems under certain circumstances and never display a fault indicator (light) on the front panel.
BNC AND F CONNECTORS
Inspect and test all in rack (internal) cables that run into and out of the encoder, modulator and onto the RF chain. Confirm that the 70 MHz IF (Intermediate Frequency) cable from the codec (modulator module) to the upconverter is of proper length and impedance (usually 75 Ohm). Check for old or non-broadcast cables in the system.
SMA AND N CONNECTORS
Confirm that the RF cable run between the upconverter and the HPA is free of kinks and the SMA or N connectors are mounted and screwed on tight. Inspect all SMA, N, L or T shaped connectors and splitters within the path, they all go bad and cause signal degradation or loss.
UPCONVERTERS
Confirm that your upconverters are digital capable. If a non-digital grade upconverter is being used, it may function OK for low data rate carriers but will introduce unstable, spurious effects on high data rate signals. The unstable carriers will suffer from constant timing corruptions that will effect the overall signal and cause intermittent or permanent loss of lock at the receive site.
Watch out for wide band transmitters, they may harbor inherent intermodulated products that could under some circumstances or frequencies cause undetected high bit errors right at the transmission port (amplifier output). An IF sample loop will never detect such errors, a cross guide coupler within the waveguide is needed to sample the RF stage and look for problems.
WAVEGUIDE
Inspect all waveguide runs for hot spots. Look at the input and output flanges for flattened rubber washers, moisture build up, kinks, unusual twisting, loose screws and rust. DO NOT perform any waveguide repairs or dish inspections while transmitting.
SPECTRUM AND WAVEFORM MONITORS
Keep your spectrum monitor tuned to the satellite receive frequency, if your signal drops you’ll be able to see it immediately. A waveform monitor will prove useful in detecting ground loops and unusual effects in the ingested signals use it to confirm your incoming video quality and levels.
DISH
Inspect the dish surface and feed horn aperture clearance at least once a month. Prior to setting up and deploying the antenna, always confirm that the path in front of it is clear of obstacles such as trees, buildings and people standing directly in front of it. Re-peak and re-polarize when in doubt to correct for dish pointing errors, inspect your deviation and polarization often.
TRANSMISSION PATH
Watch for other carriers bleeding into or sitting too close to your signal on the satellite. Digital carriers that are stronger in amplitude could cause interference to lower signals.
Even though geostationary satellites move within a designated orbital box, as it ages, the movements will eventually take the satellite farther away from the center of the box. To compensate, the satellite access center intervenes by firing the satellite thrusters and guiding it back into its correct orbit. If you are directly under the satellite while its orbit is expanding and contracting, you could experience a brief "Doppler" (abrupt signal timing change) effect that could corrupt the digital signal timing and cause temporary problems.
THE RECEIVE SITE
Confirm that the LNB, LNC or LNA being used is rated for low noise and is digitally stable.
Pay special attention to lengthy cable runs between the receive dish and the IRD. Long cables will cause signal attenuation that could lead to data corruption and a noticeable Eb/No drop. If possible, use good grade cable with heavy shielding like an RG6 or RG11.
TERRESTRIAL INTERFERENCE
Other factors that could cause disruptions are TI's (Terrestrial Interference) from microwave and local cellular towers, sun spots and various television or military facilities in the area of the transmit and receive sites.
MCPC VIA IF COMBINING.
This can only be done with encoders that have 70 MHz offset capability.
In order to perform IF combining, the two signals must be on the same polarity and within 40 MHz of each other. If signal one is at 14250 and signal two is at 14260. Set the IF on Codec 1 to 70 MHz and Codec two to 80 MHz.
A digitally stable upconverter is needed, the analog modulator is not used for digital transmissions.
To receive a good signal, a digital grade LNB is recommended.
Use the drive on the Codecs’ modulator to manipulate the power output levels on the satellite.
70 MHz TEST LOOP
USEFUL TERMS
ASI: Asynchronous Serial Interface. The final stage of a digital signal before it is fed to a modulator.
Bit rate: The number of bits of data sent over a set time.
BPS: Bits per second
DVB: Digital Video Broadcasting - A standard providing specifications for transmitting and receiving digital video broadcasts.
FIFO. First in first out, a type of data buffer within the MPEG encoder.
GOP: Group of pictures, a product of lossy compression representing video frames.
IRD: Integrated Receiver decoder
LNB. LNC. LNA. Low Noise Block, Low Noise Converter, Low Noise Amplifier. Usually mounted on the antenna’s feed horn to provide a return signal to an analog or a digital receiver.
LO: Local Oscillator
MCPC: Multiple Channel Per Carrier
PID: Packet Identifier, data used within a packet to identify it.
QPSK: Quadrature Phase Shift Keying. A form of digital modulation implemented with MPEG-2.
SCPC: Single Channel Per Carrier
Symbol: An identifiable electrical state linked to a signal element within a set period of time. The Symbol rate is also referred to as the Baud rate.
UNCOMPRESSED VIDEO DATA RATES
HDTV = 1485 Mbps
SD video 10-bit CCIR 601 = 270 Mbps
SD video 8-bit CCIR 601 = 216 Mbps
SD video 8-bit 601 (active only) = 167 Mbps
Digital Betacam (R) ~90 Mbps
MPEG PARAMETERS
MPEG-2 4:2:2 P@ML 10-50 Mbps
MPEG-2 4:2:0 MP@ML 2-15 Mbps
MPEG-1 constrain. Parameters between 0.5-1.8 Mbps
MPEG-4 H.261 videoconferencing 64 Kbps - 1.5 Mbps
MPEG-4 H.263 videoconferencing 4 Kbps - 0.5 Mbps
PICTURE SIZE / RESOLUTION
CCIR 601 525/30/2:1 720 x 486
CCIR 601 625/25/2:1 720 x 576
MPEG-2 422P@ML 30fps 720 x 512
MPEG-2 422P@ML 25fps 720 x 608
MPEG-2 30fps (quasi-std) 704 x 480
MPEG-2 25fps (quasi-std) 704 x 576
SIF (30fps, 25fps) 352 x 240,288
CIF (always 30fps) 352 x 240
HHR, 2/3-HR, 3/4-HR 352,480,528 x 480,576
SIF (30fps, 25fps) 176 x 128,144
QCIF (always 30fps) 176 x 144
SAMPLE DATA, SYMBOL AND FEC RATES.
8448000 Data rate with 3/4 FEC yields 6111319 symbol rate – 9 MHz bandwidth
8134380 Data rate with 2/3 FEC yields 6620000 symbol rate- 9 MHz bandwidth
7148000 Data rate with 3/4 FEC yields 5170894 symbol rate – 7 MHz bandwidth
SYMBOL RATE CALCULATOR
Here’s a formula to calculate the symbol rate if the client provides the data rate only.
This applies to most of the SNG work done in the field. This formula assumes that external MPEG framing is set to 188 byte frames (default SNG).
8448000 X 1 X 204/188 X 4/3 X ½ = 6.111319 symbol rate
8448000 = Data rate (supplied by the client)
1=MPEG external framing (default factor for QPSK)
204/188=Reed Solomon rate (RS)
4/3=FEC rate inverted from 4/3 for use with this formula.
1/2=Modulation index for QPSK (use 1/3 for 8PSK and 1/4 for 16QAM)
BANDWIDTH CALCULATOR
Symbol rate (6.111319)X1.38=8.43362022 MHz or about 8.5 MHz used on the satellite leaving ¼ MHz on either side as guard bands.
IRD AND LOCAL (LO) FREQUENCY SETTINGS
If your satellite frequency is between:
10950 and 12050 IRD LO frequency to be used is 10000 MHz
If your satellite frequency is between:
11700 and 12800 IRD LO frequency to be used is 10750 MHz
If your satellite frequency is between:
12250 and 13350 IRD LO frequency to be used is 11300
If your signal is in C-band then your IRD Local Oscillator frequency will usually be: 5150 MHz
DOMESTIC (USA) FREQUENCY CONVERSIONS
Take any uplink frequency in KU band and subtract 2300 MHz, you will have the downlink frequency.
Example: 14250 – 2300 = 11950 MHz
Take any downlink frequency in KU and subtract 10750 MHz, you will have the L-band equivalent frequency.
Example: 11950 – 10750 = 1200 MHz
Take any uplink frequency in C band and subtract 2225 MHz, you will have the downlink frequency.
Example: 6150 – 2225 = 3900 MHz
Take the C-band LO frequency and subtract any downlink frequency from it, you will have the L-band equivalent frequency.
Example: 5150 – 3900 = 1250 MHz
This works on all satellites domestic and global as long as you know the LO and the conversion factors to use.
MINIMUM Eb/No AND VITERBI RATES
Viterbi rate Minimum Eb/No (dB’s)
1/2 4.5
2/3 5.0
3/4 5.5
5/6 6.0
7/8 6.4
Use this table as a benchmark; actual results will vary depending on link conditions.
STANDARD RATES TO USE FOR EVENTS
Resolution Bit rate range Suggested use
704 ppl above 7 Mbps sports
544 ppl 4 to 7 Mbps movies & shows
352 ppl 2 to 4 Mbps talking heads
SIF 1 to 2 Mbps multimedia
ppl = pixels per line
Parts of this text were collected, compiled and edited from articles found on the World Wide Web. Academic credit was granted when the author was posted.
This manual and all its contents are the property of Eddie Maalouf. Use, sharing and/or reproductions are encouraged as long as credit is given/posted.
Eddie Maalouf – Director of Engineering – PACSAT – 916/446-7890
emaalouf@pacsat.com
www.pacsat.com
Typically, most uplink platforms will follow a similar path as they ingest, equalize and transmit signals. Below is a rough signal flow breakdown within an uplink truck and the equipment involved in the process.
A live camera or a production platform sends a video and an audio signal to the truck via a coaxial or a fiber cable.
The video and audio cables are then connected into designated ports on the I/O (Input/Output) panel on the side of the truck.
The audio and video are sent to DA’s (Distribution Amplifiers) to have their levels adjusted and equalized while simultaneously are displayed and routed to various audio and video monitoring, mixing and switching components.
From the DA’s, the audio and video signals are sent to an exciter (if the signal is to be transmitted in analog) or an MPEG-2 Codec (if the signal is to be transmitted digitally).
If the audio and video signals are sent to an exciter, they are processed further within the exciter then they are placed onto a 70MHz IF (Intermediate Frequency) carrier.
If the audio and video signals are sent to an MPEG-2 Codec, they are digitized, compressed then placed on a 70MHz IF carrier.
Regardless whether you are using an analog exciter or a digital Codec, either one becomes the first step of converting the audio and video signals from electrical pulses traveling on a wire to an actual RF (Radio Frequency). From there, the IF (Radio frequency within the RF spectrum known as Intermediate Frequency) signal is sent to an upconverter where it is upconverted from 70MHz to the required C or KU frequency.
From the upconverter, the signal is sent to an HPA (High Power Amplifier) or an SSPA (Solid State Power Amplifier).
The HPA (or SSPA) amplify the signal to the required satellite transponder power levels (various from 10 to hundreds or watts) depending on the signal, bandwidth and the satellite being used. The power leaves the amplifier via a metal tube called: Waveguide. The waveguide carriers the RF signal from the output of the transmitters to the feedhorn/dish where it is magnified further then transmitted (Propagated) to the satellite.
It’s worth noting here that the actual signal itself, the electrons and neutrons never leave the dish and travel to the satellite, if they did you would see a light beam traveling into space from the dish. Instead, the signal originating from the satellite truck “propagates” (free flowing electrons bump each other and exchange states of energy (at the speed of light) all the way to the satellite).
Propagation is the act of exchanging or duplicating energy between electrons. The power being pumped into the signal from the amplifiers provides the energy continuum (the excitation that’s needed to reach the satellite). In effect, the “original” audio and video signal being processed at the truck, never actually leave the truck, a copy of it or a facsimile is transmitted all the way to the satellite. When we discover how to send “physical” signals (electrons and neutrons) to the satellite, we won’t need airplanes or the space shuttle any longer.
There are two main types of uplink choices in use today for commercial broadcasting; C or KU band and sometimes both on the same platform. The main difference between the two is frequency range and wavelength. KU caries an advantage over C band due to the high frequency it utilizes. That fact allows manufacturers to integrate smaller platforms with smaller antennas.
Domestic (USA) KU uses a 500MHz spectrum from 14.00GHz to 14.50GHz with an average wavelength of 2.2 cm. Domestic C-band uses 500MHz spectrum from 5.925 to 6.425 GHz with an average wavelength of 4.5 cm.
So what you say? Why do I give a hoot about wavelengths?
Here is where tradition meets innovation. Traditionally, the C-band spectrum had and still is being used by local telecom (telephone companies) and some terrestrial TV stations for microwave links/hops. So when C-band was converted over for satellite use, due to its wavelength and dispersion characteristics, depending on the location its being used, it tends to interfere with terrestrial links or vise-versa (the links interfering with C-band uplinks).
In short, due to the already existing infrastructure, it’s not easy to use C-band everywhere because it may interfere with older, terrestrial microwave links. For that reason, every time a new location is selected for C-band transmissions, a “Frequency Clearance Study” has to be conducted prior to using the location and frequencies.
KU on the other hand was invented specifically for SNG use and is in a band of its own so no frequency clearances are needed. However, (and here’s where the wavelength issue comes in) due to the high frequency and wavelength (shorter than C-band) of KU, it is more susceptible to moisture/rain fade. Turns out that under certain conditions (heavy rain mostly), the 2.2 cm wavelength is short enough to be attenuated by raindrops (moisture) beyond recovery at times, for as long as the heavy rain cloud persists.
Both C and KU bands could be used for sporting and pre-planned events but C band is requested and preferred by vendors especially in heavy rain regions.
Both C and KU could also be used for newsgathering but KU is preferred for quick deployment at breaking news events.
DISH SIZE
In RF, size does matter.
Non ionized microwave radiation which is what the dishes put out, As I mentioned earlier, although the waves are not radioactive, they could still cook soft skin such as the cornea of the eyes and the testicles.
For that reason, the FCC publishes radiation hazard specification for dish compliance. The hazard goes up with the amount of power being transmitted and sprayed around the dish.
The "band" (or frequency spectrum) being used (C or KU), the dish size and amp power combinations dictate what amount of ERIP (Effective Radiated Isotropic Power) RF density is being sprayed in the air and is authorized by the FCC in regulations (not to be hazardous to people within a certain distance/diameter from the dish).
Example: In order to transmit a 36MHz QPSK HD carrier in C-band on a 2.4Meter dish on an old satellite like SBS 6 (always calculate the worst case scenario), you will need about 746 watts of power (the power figure was derived from published transponder flux densities to perform a small link budget). The power figure above reflects a proper Eb/No (Energy bits per Noise bits), BER (Bit Error Rate, EVM (Error Vector Magnitude) and MER (Modulation Error Ratio) that's acceptable at the receive end.
The problem:
In order for the 2.4Meter dish to deliver such values (in C-band), the transmit site has to generate 746 watts of power which increases the "Excess" side lobes bleed-through performance on the dish and pushes it higher than the 10% maximum allowed by the FCC.
In plain English, it means that in addition to spraying everyone around the dish within 30 meters and up to 600 meters directly in front with hazardous microwave radiation, the uplink will most likely interfere with similar frequencies on adjacent satellites within 2 degrees of the satellite being transmitted on. NOT GOOD.
The FCC stipulates that the maximum feed horn flange power allowed anywhere is -50.90 dBw per Hz. With the amount of power being transmitted, the dish will spray at -46.37 dBw per Hz, clearly higher than allowed therefore breaking the FCC rule and spraying harmful microwave radiation to the public in the area and on adjacent satellites.
DISH TYPE
There are two types of dishes being used on SNG platforms. They are the center feed and the Offset feed.
The center feed will have the feedhorn placed above the center of the antenna and is usually supported by struts.
The Offset feed antenna (picture below) will have the feedhorn placed below or above the center of the antenna (usually about 15 degrees offset).
The Offset dish is usually more efficient and has a “higher gain” because the feedhorn is not in the way of the transmitted signal.
Typical components that make up an SNG antenna are:
Reflector, OMT (Orthomodel Transducer – transmit/receive feed assembly), Waveguide, LNB (Low Noise Block - for signal receiption), and the Dish positioning base (Azimuth / Elevation control) etc..
PRE-TRIP INSPECTION
One of the most important tasks to perform prior to leaving on assignment is a PTI (Pre-Trip Inspection). Especially, if the vehicle had been parked for a lengthy period of time.
* Inspect all tires for damage and un-usual wear and tear.
* Search for fluid leaks under the vehicle, particularly under the transmission and the fuel tank(s).
* Look for lose cables, hoses, nuts and bolts.
* If your vehicle has it, follow the manufacturer’s specifications to inspect and test the air brake system.
* Confirm that the rear break, parking, driving, towing and headlights work.
* Test the windshield wipers.
* Check all engine fluid levels; Transmission, Power steering, Master Cylinder and coolant.
* Fill out and maintain a driving log.
Note any damage (in writing) and report it immediately.
CAUTION
SNG VEHICLES ARE HEAVIER THAN REGULAR AUTOMOBILES. MAINTAIN POSTED HIGHWAY SPEEDS AND PROPER DISTANCES FROM THE VEHICLES IN FRONT OF YOU.
MOST ACCIDENTS HAPPEN WHEN THE SNG VEHICLE IS SPEEDING TO GET TO A SITE.
THE CORRECT HEADING.
Once you arrive on site and prior to doing anything, make contact with the on-site producer/coordinator. Newsgathering is fluid and dynamic, things may have changed while you’re on route. The on-site producer and crew may have moved to a different location? If there are no on-site personnel to assist you, telephone the client’s assignment desk and inform them of your arrival and re-confirm that all coordinates are still valid and the site has not changed.
If all is still the same and this is a pre-planned event, you may want to find the on-site electrician and inform him/her of your electric needs at this point. They can start hooking your cables (pig tails) up while you park and run your on-board generator to find and identify the satellite.
After you make contact and confirm your parameters, you must make sure that the satellite you are booked on is visible from your location
(no obstructions such as trees and buildings in the way).
Often, at questionable, pre-planned venues, where the client requests a specific satellite, a site survey is conducted days or weeks ahead of the event. A site survey entails sending a technician with a compass to the site or at times even taking an SNG vehicle, deploying the dish and physically finding and identifying “accessible” satellites. A site survey also includes planning for parking, production facilities and cable runs.
Since all geostationary satellites are placed in orbits over the equator, your main concern lies in aiming your truck (actually the dish) facing the proper heading. That would be roughly due “South” if you are in the Northern hemisphere (North America), and “North” if you are in the Southern hemisphere (Australia).
Although geostationary satellites appear motionless to an SNG platform (or any earth station), the reality is that they are constantly moving in space. After being placed in an “orbital slot” about 37,000 Kilometers in space and due to various forces such as the Earth’s gravitational force, the satellites hurl through space at 11,000 Kilometers per hour following the Earth’s rotational spin to maintain the same orbital slot, hence appearing stationary from the Earth’s surface.
For more details on satellite orbits, perform a search on the Internet under: “Geosynchronous satellites” or visit this link:
http://en.wikipedia.org/wiki/Geostationary_orbit
GPS and military (spy) satellites traditionally occupy MEO’s (Middle Earth Orbits) and LEO’s (Low Earth Orbits) which are much lower than 37,000 Kilometers and are never stationary, those satellites orbit the earth numerous times per a 24 hour period (earth day). For now, and for the sake of simplicity, we will limit our discussion to broadcast satellites in geostationary (equatorial) orbits.
Let’s assume you don’t operate a platform with the latest GPS satellite finding equipment and need to find your heading manually. So, for now, we’ll focus on finding satellites from the “Northern” hemisphere. Let’s also assume that we will be transmitting from Sacramento, California and are looking for satellite: “X” at 74 degrees West orbital slot (the name of the satellite does not matter as long as you know the orbital slot location, in which case, SBS-6 used to live at 74 degrees West). The best place to start is to find 180 degrees (South) on your compass (or GPS) and park your truck facing that direction (the dish should be deployable in the southerly direction after you finish parking).
DISH DEPLOYMENT WARNING:
BEFORE DEPLOYING THE DISH, EXIT THE TRUCK AND “VISUALLY” SURVEY FOR ANY DISH DEPLOYMENT OBSTICLES SUCH AS TREE BRANCHES, BALCONIES AND PARTICULARLY LOW ELECTRICAL WIRES.
DO NOT DEPLOY THE DISH UNTIL YOU PERFORM THIS VISUAL SURVEY, ESPECIALLY IF YOU ARE DOING THIS AT NIGHT AT A STRANGE SITE.
IF THE DISH MAKES CONTACT WITH HIGH VOLTAGE ELECTRICAL WIRES SUCH AS LOW HANGING TROLLY WIRES ON THE STREETS OF SAN FRANCISCO, SERIOUS INJURY AND/OR DEATH COULD RESULT.
IF THE DISH MAKES CONTACT WITH TREE BRANCHES, LOW BALCONIES OR OVERHANGS THEN, AT MINIMUM SOME DISH DAMAGE COULD OCCUR.
FINDING THE SATELLITE.
All domestic satellites visible from Sacramento will start in the Eastern sky and move up to the right (West), they start at a low elevation (12 degrees – Amazonas satellite) and work their way up into the sky (mid 40 degrees – AMC_7). It would be useful to carry a satellite chart, and/or a transponder guide to reference your location in the arc.
There are numerous sources of satellite charts and transponder guides available on the Internet, here’s one example:
http://testced.cahners1.com/ced/2005/0305/orbit-arc-0305.pdf
If your truck has a Satellite GPS unit built into the dish controller, turn your controller on and let it find the satellite you need. If not, read below.
It’s impossible to teach someone how to find satellites without hands on participation. They have different footprints, beacon frequencies and transponder characteristics. At times two or more satellites may look alike which may make it more difficult to identify the correct spacecraft. Even the same satellite may have different types of carriers at different times of day. Learning to identify them and even memorizing the patterns will prove useful under deadlines.
Some technicians use digital cameras to take screen shots of each satellite they identify to compare when needed, many others draw charts, grids and even draw traces of the actual image off the spectrum monitor. If you chose to do any of the above, make sure to update your drawings regularly.
Even after finding a certain satellite, it is advisable that you call the satellite access center and try to talk them into allowing you to “pop” a test carrier for few seconds on the transponder you will be using. That way, they can, without a shadow of a doubt confirm that you are looking at the right spacecraft.
There are numerous sites on the Internet that will give you any satellite look angle from anywhere in the world. All you have to do is enter the Longitude, Latitude of your site and the desired satellite. Example: http://www.satellite-calculations.com/
You can get the Longitude and Latitude of any
location off the Internet or you can invest in a hand held GPS unit like the “e-Trex”, Garmin Vista (for hikers) that can, amongst many other things such as saving way points, pointing out restaurant locations, highways and city maps, display the Longitude and Latitude of any site around the globe. http://www.garmin.com/
PEAK AND POLARIZE THE DISH
After visiting the satellite look angles web site above and entering Longitude: 121.5 West and Latitude: 38.55 North for Sacramento, California, amongst other information the program yielded, were the look angles. Satellite “X” at 74 degrees can be found at 24 degrees elevation and 119 degrees Azimuth (the program takes into account the magnetic deviation of the site and calculates the output accordingly). So, the look angles should be, theoretically, “SPOT ON”.
Now, all I that needs to be done is to use a compass to find 119 degrees azimuth then aim the antenna in the same direction. Once the antenna is there, move the elevation up to 24 degrees, scan the sky back and forth a few times and with any luck, you should find the satellite. This is normally a bit difficult the first time but with practice it becomes a second nature.
After you find the satellite, if your controller peaks and polarizes automatically, you may skip this section otherwise, read below.
Once you find the satellite, you need to optimize the transmission path. Place the dish controller in the “SLOW” mode, find a nice stable carrier then peak your Azimuth and Elevation angles for optimum signal levels. When done, center the same carrier you peaked on, switch to the opposite polarity and inspect for any remnants of that carrier. If you are polarized properly, there should be none visible.
If you see any of the carrier bleeding through the other side (pole), use the POL switches CCW and CW on your controller to null out (flatten the noise bleeding through).
Summary:
The purpose of using a stable carrier to peak the Azimuth and Elevation angles is to, obviously obtain the maximum signal levels.
The purpose for nulling that same carrier completely on the opposite polarity is to minimize spraying the opposite pole with the same frequency you will be transmitting and possibly interfering or washing another customer off the spacecraft.
The overall purpose of peaking and polarizing is to optimize your transmit and return signal levels, otherwise, the majority of your amplifier power will be lost into space during transmission and your return carrier level will not be strong enough for the client’s or your receiver to lock up on.
POWER HOOK UP
With the satellite in site, it may be time to hook up to shore power. Turn everything off including your generator and find the electrician.
Some of the latest satellite platforms offer “Dual band”, “Multi path” uplink capability in Analog, Standard Definition and/or High Definition, simultaneously.
Every broadcast platform needs electricity to run, it either uses it’s own onboard generator(s) or draws shore power from the venue, the power they draw varies accordingly. Make sure you know what your platform power requirements are.
Typically, most platforms require a single-phase connection with two hot wires and one ground at 240 Volts with a 50 amps breaker. It connects to the venue using pre-fabricated 50’ to 150’ cables, usually with bare ends affectionately known as “pig tails” or cam lock connectors. Traditionally, the electrician on site is responsible for hooking the bare ends or cam locks to their system (or on site venue generator) before allowing you to connect your truck. Most platforms use the majority of their electricity for the transmitters and the air conditioners (needed to keep all the equipment cool in the summer and winter).
The operator must always confirm that correct voltages are drawn to a platform. That’s accomplished by using a high voltage test-meter which most platforms carry in their tool kits. Always and without exceptions test the leads the electrician hands you on site for proper voltages prior to hooking it up to the truck. After confirming the voltages, ask the electrician (actually, watch him do it) to shut the breaker off so you could connect the wires to your distribution panel. Even if the electrician assures you that your cable has the correct voltage(s), you must still use your meter to confirm his information.
EVERYONE MAKES MISTAKES. IT’S BETTER TO OFFEND THE ELECTRICIAN THAN DIE.
To perform the testing, connect your meter between the two hot wires (usually Black and Red) and measure the voltage(s), they should read between 208 to 240 depending on what the electrician has available. Measure each hot wire (black or red) separately against the ground wire to insure the same voltage exists on both. If your truck requires a fourth White wire (neutral), measure the electricity between the Neutral and Green (ground) wire… There should be none – Zero electricity. The only electricity you should read should be between the two hot wires and between each hot wire to ground.
Again, no electricity should be present between the Green (ground) and the White (neutral) wires (if White is required).
If your platform requires 220 to 240 volts to run and you are handed 208 volts, use your tap transformer to boost the voltage up to the required level. Most if not all platforms will have at the very least a tap transformer and/or a regulating transformer installed onboard to compensate for voltage differences. Learn how to read the voltages and tap them up or down on your transformers.
Example, if the venue has 208 volts at 100 amps, the tap transformer onboard the truck can be switched to 208 (usually before hooking up the cables to the truck) to boost the power up to the required voltage (220--240 volts). Take the time to learn your truck’s power system and distribution panel, particularly the location and the current position of your tap transformer (usually they are installed behind the racks or in one of the storage compartments) plus all the selections it offers for shore power hookups.
Turn the main breaker(s) “ON” (to power the truck and equipment) only after you are certain all voltages and grounding has been validated.
ELECTRIC HOOKUP WARNING
READ AND ALWAYS FOLLOW
NEVER, NEVER, NEVER CONNECT OR DISCONNET THE TRUCK TO SHORE (ON SITE VENUE) POWER WITH *LIVE* CABLES. MAKE SURE THE BREAKER THE CABLES ARE ATTACHED TO IS *OFF* FIRST.
Apply power to all racks and systems only after confirming all hookups and configurations are correct.
SERIOUS INJURY OR LOSS OF LIFE MAY OCCUR.
EXITERS AND ENCODERS
There’s no need to learn everything about exciters and encoders at this stage. But, it is important to learn what they do and how they are utilized in the SNG platform.
For now, remember this:
Exciters are used to transmit analog carriers. Digital video encoders are used to transmit digital carriers.
Even if the exciter came in one enclosure, internally, it is made up of two basic stages. The first stage processes the audio and video signals, the second stage places the signals on an IF (Intermediate Frequency) carrier, usually 70MHz.
By the same token, even if the encoder came in one enclosure, internally, it is made up of two basic stages also. The first stage takes analog or SD (Serial Digital) audio and video, digitize and compress the signal, then sends it on an ASI (Asynchronous Serial Interface) stream to the second stage (modulator) which places it onto an IF carrier, usually 70 MHz.
Although most transmissions are moving towards digital, some clients still request and feel more comfortable with analog transmissions. On the long run, to save bandwidth and transmitter power on the satellite and within the SNG platform, the majority of transmissions will most likely move to and stay in the digital mode.
If your assignment is analog, adjust and equalize the audio and video levels via the DA’s then send them to your exciter. At this time, you should also program your upconverter with the proper frequency. For additional information on analog exciters see Appendix Z.
If your assignment is digital, you will need to program your encoder and IRD (Integrated Receiver Decoder) with the proper symbol or data and FEC rates. See Appendix AA on encoder basics and IRD’s. If you are not an SNG technician and are reading this text for general knowledge, continue reading.
SATELLITE CONFIRMATION.
You should now turn your amplifiers on and give them a few minutes to warm up. Instead of waiting until the actual transmit window to put up a carrier, and find out that there may be a problem somewhere in the system, we will now perform a quick “pop” up, or “access” test on the satellite. This test is being done solely to confirm that we are indeed looking at the correct spacecraft.
For this test we will use a digital encoder. Program your modulator, encoder, codec (whichever you have in the truck) with symbol, data and FEC rates then enter the satellite frequency on your upconverter.
Remember, the sole purpose of this “test” transmission is to identify the spacecraft. No video or audio will be transmitted or is needed at this time, in fact, keep your modulator or codec in “CW” (Clear Wave) mode.
When your amps warm up, place them in “High Voltage” mode, make sure you are switched into the load then apply drive to confirm that your codec, upconverters and amplifiers are working properly. Apply enough power so the amps are showing about 5-10 watts.
Contact the satellite provider and explain that you are at a new site and are supposed to be transmitting on satellite “X” transponder “Y” at time “Z” but you want to make sure that you are actually looking at the correct spacecraft. Sometimes, if they’re really busy, they will deny you the test access. If that happens, you will have to wait and hope you are on the right spacecraft when your window opens.
Often however, they will allow you to access for the test. Just in case they happen to be in a good mood or slow that day, make sure to pre-tune your IRD so you could decode your signal if they allow you to stay up for a few minutes and even modulate.
Once that’s done, cool your amps down and turn them off (usually 5-10 minutes). Contact your on-site producer or telephone the assignment desk and inform them that you have found, identified, test accessed and locked on your return off satellite X. The news will undoubtedly make them very happy.
CABLING THE SITE
At this point, you should start cabling your truck to the actual live camera or production facility position.
Various types of multi bundles aka “Siamese” cables (bundles with one or two video and 3 to 6 audio cables) have traditionally been used for analog audio and video signals. These cables served well until the introduction of SD (Standard Definition) and HD (High Definition) transmissions. Uncompressed SD streams run at 270 Mb/s, HD streams run at 1.485 Gb/s (Giga), such specs superseded the traditional cables and demanded a higher-grade method of transfer. For short runs with embedded audio, Belden 1694F for example serves the purpose but for runs beyond 300 feet, a fiber links is advisable.
Cables are often snaked through rose bushes and flown over busy boulevards with no regard to the commodity they carry. The fact is that a cable with faulty connectors (wrong impedance, short or missing center pins) could handicap a link. Take the time to evaluate and mark your cables properly, long cable runs could attenuate a digital signal and throws it off the “digital cliff”.
Perform a loop test at the I/O panel prior to stretching your cable to the designated location (live camera, production trailer etc…). Hook one end of the cable into an input and the other into an output then send color bars through it. Watch for video art effects on your waveform monitor. This step could save you lots of time and most importantly a stressful headache.
For redundancy, always test and run two cables to live events. If one fails you won’t have to run like a chicken with it’s head cut off to replace the faulty cable. After stretching the cable, confirm immediately that you are receiving proper levels. If not, pursue and fix the problem immediately.
If you’re transmitting in analog, route the audio and video signals to the waveform monitor and adjust all the levels on the corresponding DA’s.
A properly equalized video signal will have the Chroma and gain at 100 units above the zero line (as in the picture on the next page - left) and Sync will be 40 units below the zero line. Color burst will occupy 40 units, 20 above and 20 below the lines.
Sync and Burst at 40 units
100 units of Chroma over 40 units of Sync
If you’re transmitting a digital signal, the production platform will send you an SD (Serial Digital) stream, most likely uncompressed. The stream could have audio imbedded on it or separate on additional audio cables. Furthermore, the audio could be in analog or AES/EBU (digital) format, clarify and confirm all of that prior to plugging the cables into the truck.
For this example let’s assume that you are getting digital video and audio separately from the production source. Plug the cables into the proper ports on the I/O panel then route the video to the digital waveform monitor. Instead of equalizing Chroma, sync and gain like you would for analog, you will need to examine the eye pattern.
As shown in the picture above, the eye pattern displays jitter, noise and timing faults. The best way to see how these three parameters change with video quality is to compare a good vs a bad video signal. Use color bars from the truck first to establish what a good signal looks like then switch to a bad video source (color bars over a very long cable without going through a DA), you will be able to immediately spot the difference in quality. The lines will vibrate and oscillate (jitter increases), their width or girth (noise level) will increase (gets wider) and the overall pattern will shrink down from the level it’s at to below +.8 volts (timing).
All the above parameters could be adjusted via the digital re-clocking DA.
The “gamut” is another way to gauge your video signal. It displays color information within the signal and as displayed, most of the color congregates close to the letter they represent. Deviating from that represents a bad video signal.
As shown in the lower left quad (drawing below), most digital SNG trucks will have digital audio passing through the waveform monitor after the DA’s in order to at the very least adjust the volume.
Something to always ponder when you have digital video and audio being ingested separately into the truck. There always exists a chance that they may not be synched up together (lip sync problems). You or the production venue may need to adjust the delay/timing on the audio (via the encoder) so the two sources are synched up.
It is near impossible to simplify waveform equalization but enough information has been covered to allow you to manipulate and adjust to needed parameters. You will need to study waveform adjustments further on your own.
In summary: You should use the proper cable for the proper assignment. Confirm the cable is working by performing a test loop prior to stretching it from the truck and lastly, make sure the levels being received at the truck are equalized properly.
Analog video signals could degrade greatly (after a long cable run – without a DA) but never actually go away. Digital signals on the other hand will reach a certain attenuation point and drop off completely (never make it to the other end of the cable).
Make sure the camera or the production trailer is sending you audio and video then test all your cables for continuity and proper levels.
DO NOT WASTE TIME.
Do not rest until you identify and confirm all signals are proper and valid as soon as possible.
AUDIO BASICS
IF YOU’RE NOT A SATELLITE TECHNICIAN OR WANT TO BECOME ONE, SKIP THIS SECTION.
There are three “main” types of audio that can be ingested into the uplink platform. Analog, AES/EBU (Digital) and Embedded. Each type of audio has sub-parameters that could be manipulated for a desired service.
For example; Up to 4 analog audio channels can be ingested into the MPEG-2 encoder (or analog exciter). Those channels can be manipulated so they are transmitted in two stereo pairs or in mono (each channel on it’s own). Each exciter / encoder may have different options depending on model and software installed on the units. Scroll through your equipment to find out what options are available for you.
All analog exciters will accept up to 4 analog audio channels. MPEG-2 encoders on the other hand, come from the factory with the ability to handle up to 4 audio channels but unlike analog exciters, additional cards can be added so the encoder could handle up to 8 audio channels in analog or up to 16 AES/EBU (digital) or embedded channels.
It’s not simple to cover all audio standards and parameters that could be processed or have to be dealt with during a transmission. There are numerous books on the subject but most are un-readable due to heavy use of technical jargon. To keep things simple, I’ll provide basic explanations plus links and or book titles to whom ever is interested in pursuing the subject further.
ANALOG AUDIO
Analog audio is the simplest to ingest. Some of the parameters to be aware of is injection levels and pre-emphasis. Injection levels on analog exciters mean that the audio sub-carriers should be 18 to 21 dB’s below the main (video) carrier. Pre-emphasis deals with noise on audio carrier. Visit this web site for an explanation on pre-emphasis and what it does for analog broadcast audio.
http://etvcookbook.org/audio/ntsc.html
AES/EBU (DIGITAL) AUDIO
The AES/EBU (Audio Engineering Society / European Broadcasting Union) digital audio format is used for carrying audio between various devices. This audio format is also known as AES3. Unlike analog audio, AES/EBU audio does not need digitization after entering the encoder. For a more “technical”, in depth explanation visit this web site:
http://en.wikipedia.org/wiki/AES/EBU
EMBEDDED AUDIO
http://www.embedded.com/columns/technicalinsights/201202515?cid=RSSfeed_embedded_news&_requestid=259506
DOLBY DIGITAL OR AC-3 AUDIO
http://en.wikipedia.org/wiki/Dolby_Digital
Since audio uses smaller amounts of data, it is digitized faster than the video, if certain settings are omitted on the encoder, lip synching problems could occur. Learn your encoder’ settings and study how you could manipulate audio delays to match the incoming video.
TEST LOOPS
After confirming the signal integrity, the next step is to perform a test loop within the truck with the actual signal (audio and video) running all the way through the encoder and the RF chain.
Some trucks will have a sample port on the amplifiers that could be downconverted to L-band from C or KU then decoded via an IRD to analyze the integrity of the signal.
Other trucks will only have the ability to sample the 70MHz IF carrier out of the encoder and decode that by upconverting it to L-Band then sending it to an IRD.
The RF test method is a better way to perform a test loop simply because it allows the technician to sample and validate the signal flow all the way through the amplifiers prior to leaving the truck therefore discovering any faults or problems if any.
At this point it doesn’t matter which way your truck performs a test loop, one should be performed and we’ll go over both.
Before we go further, you must take the time to program and confirm (again) all the correct parameters have been entered on the Codec and the upconverter. Then, program your second (back up chain) with the same parameter. You should have both your primary and back up chains ready for this test with audio and video from the venue running through both.
THE RF METHOD
This is done by taking an RF sample from the on air amplifier or a cross guide coupler installed within the waveguide run while the amp is running with drive and power on (use about 20 watts) into a load or into space – off satellite. The signal is downconverted to L-band then it is sent to an IRD. If your truck is designed and set up to do that, it will have some kind of a panel with all the connections and switching already installed. Stop reading, familiarize yourself with that panel and perform a test loop at this point.
THE IF METHOD
Most Codecs will have an “IF MONITOR” port in addition to the main IF output port that usually goes to the upconverter. That port is sent to an IF to L-band upconverter then to an IRD.
If your truck is designed to use IF for test loops, it will have a panel with all the necessary ports to accomplish that. Stop reading, familiarize yourself with that panel and perform a test loop now.
In summary, test loops are very important because they provide signal integrity information and equipment operational status. You don’t want to wait until the actual feed time to find out that your codec, for some reason is not happy with the video coming from the field.
After performing the test loop with your main (primary) chain (codec, upconverter and amplifier), switch to the back up (secondary) chain and perform the same test. Do not omit this step you may need it if you encounter an on-air failure with your primary set up.
If the tests are satisfactory and you still have a long time before going on the air, cool and power down your amplifiers. You are ready for the transmission.
Now would be a good time to visit the bathroom and/or find something to eat, once the transmission starts you won’t be able to leave your post in the truck.
TRANMISSION TIME
You should by now have carried out all the steps necessary to make the actual transmission effortless and are ready to transmit the actual event.
Turn the amplifiers “ON” at least ½ hour prior to the transmission window then go over all the rates and settings one last time.
Send drive to the amplifiers and place them into their perspective loads at around 10 watts each.
Most DVR’s (Digital Video Recorder) have 4 video and one audio inputs if your truck has one route your two incoming and two received signals into it, you should record the signals throughout the event. If a problem arises, you can use the information to trace it.
Contact the satellite access center at least 5 minutes prior to the window and access the satellite.
After accessing, set up your redundant path and place it into the load with about 5-10 watts of power. If a failure occurs you don’t want too much power going through the RF/waveguide switch, it may cause high reflective power to bounce back to the amp and possibly damage it.
A better way to run a redundant uplink (if you have the ability) is to place your RF system (both amplifiers) into a phase combiner. Run both amplifiers to the satellite with equal amounts of power, if one fails, the second amplifier will take over, all you need to do is a slight adjustment to the power level but at least you won’t come off the satellite. Phase combining should always be used for important live events where failure is not an option and a satellite signal drop is detrimental.
On most live events, the client will book the satellite window with at least ½ to 1 hour of test time prior to the actual event. So, after placing the redundant (back up) system in place start the DVR recording then call the client’s downlink site immediately to perform a “check in” so signal reception and integrity could be confirmed.
The downlink site will walk you through various requests that may include having you send your own (truck) color bars to compare to the venue’s color bars. If they know what they’re doing, they will also ask to see your redundant path so they can set levels to it in case you encounter a failure and switch to it.
After accessing, you should always acquire the following reading from the downlink site and your own site then write them down on a piece of paper, they will come in handy during troubleshooting and searching for problems.
C/N = Carrier to Noise level (in dB’s) when in CW
S/N = Signal to Noise level (in dB’s) after saturation
Eb/No = Error bits in Noise bits (in dB’s)
BER = the amount of “Bit Error Rate” in a transmitted stream shows as errors per million bits. For example: 1 in 10-
(1 in 10 to the minus 7 means 1 error bit in every ten million bits -- 10 followed by 6 zeros.
Some downlink sites monitor “EVM” and “MER” also, ask them for the readings if they do.
EVM = Error Vector Magnitude is the ratio of RMS – Root Mean Square – It displays the error magnitude to maximum symbol magnitude – it is measured in percent and a good signal yields below 18%)
MER = Modulation Error Ratio (Transmitted symbol vector versus received symbol vector)
Don’t forget to also write down your amplifier output power readings.
Only when the “check in” is done that you can relax, sit back and watch the event.
Keep a watchful eye on the spectrum and waveform monitors. NEVER LEAVE THE PLATFORM DURING A TRANSMISSION except for quick bathroom runs or emergencies.
DIGITAL SIGNAL SATURATION
A digital transmission link like an MPEG-2 signal does not have to saturate a transponder, all that is needed is a required "Signal to Noise" level on the satellite which is usually between 15 to 18 dB's for an SCPC (Single Channel Per Carrier) uplink.
The extra power will not contribute to the signal strength, instead it may interfere with other carriers and usually shows up as " noise floor shoulders" on either side of the digital carrier causing additional distortion in some cases.
Always cooperate with the satellite access centers to resolve any power or carrier balancing issues. A good “Signal to Noise” carrier produces a required “Eb/No” (Energy bits per Noise bits) on the receive end. The higher the received “Eb/No” the better the quality of the signal will be.
An 8448000 Mb/s data rate (equals to 6111319 Symbol rate) with 3/4 FEC coding signal requires a minimum of about 6 dB's of “Eb/No” on the receive end. Every link should allow extra power (3 dB’s more power) on top of the minimum required “Eb/No” to compensate for rain, transmit and receive dish pointing errors, waveguide and cable losses, atmospheric signal dissipation and electronic threshold such as a high noise LNB or IRD.
Some IRD's utilize an Eb/No count while others display BER readings. Since the Eb/No is a measurement of the overall received signal performance, you need it to be as high as possible. Since BER measures the average bit errors in a stream, you want it to be the lowest possible.
In summary we should remember that a good digital signal should yield a high “Eb/No” and/or a Low “BER” at the receive site.
CONDITIONAL ACCESS
At the beginning, every manufacturer developed a proprietary conditional access or digital signal scrambling system, but due to market pressures everyone is now moving towards “BISS” (Basic Interoperable Scrambling System) standard.
Although a digitally compressed signal is sort of scrambled, anyone with an IRD and the correct settings can decode it. So, for more protection it is possible to scramble a digitally compressed video signal and allow only certain IRD's or clients to receive it.
Tiernan’s original proprietary scrambling system for example allows their encoders to be programmed via a computer with the IRD identification numbers. Only the programmed IRD's will be capable of receiving and decoding a scrambled Tiernan signal. The BISS method allows the operator to enter a code up to 7 digits long, the code is then given to the receive sites to be entered on the IRD’s, no computer hookup or complicated programming is needed.
HD TRANSMISSIONS
By now you probably have a very good grasp on analog and SD transmissions so let’s bring in HD (High Definition) links.
Unlike analog and SD the High Definition format is in a class on it’s own. In addition to Symbol/Data, FEC and sampling rates, HD offers different frame aspect ratios, resolution and frame rate scanning methods plus various modulation schemes. On top of all that, with current technology (DVB-S – MPEG-2) HD requires a much higher bandwidth.
A standard full transponder NTSC or PAL analog carriers occupy anywhere from 17 MHz (half transponder) up to 72 MHz. The actual NTSC color information signal is only 4.5 or 5.5 MHz.
A standard, uncompressed SD signal could occupy up to 270 Mb/s. Clearly, such a signal cannot be transmitted on a satellite transponder without compression. There would only be enough bandwidth on the satellite to handle a little less than 2 uncompressed SD carriers.
A standard, uncompressed HD signal on the other hand could occupy up to 1.485 Gb/s. At that rate, one uncompressed HD signal would need three satellites (each satellite has 500 MHz of bandwidth). Even when HD is compressed at the rate of 36:1 (1.485 divided by 36) the data rate remaining (with the proper FEC), 41 Mb/s is still large enough to occupy a full 36 MHz transponder. A lower data rate (higher compression of 40:1) will yield a lower resolution.
Let’s take an HD transmission being sent in 1080i at 41 Mb/s. That would mean the transmission might have the following parameters to be entered on the encoder.
41 Mb/s with QPSK modulation (40.963725 to be exact)
27 Ms/s (26.670000 Mega Symbols per second to be exact)
DVB-S (Digital Video Broadcasting Standard 1)
5/6 FEC
16:9 Aspect ratio
1080i format --- “i” = Interlaced scanning
1080 = Vertical lines by 1920 Horizontal lines of resolution
59.94 frame rate (drop frame)
4:2:2 sampling
Frame rate of 15 GOP (Group of Pictures)
As you can see, HD requires a few additional parameters that an SD transmissions does not need.
Additionally, all the parameters above could be altered or changed on the HD encoders depending on the results sought after by the client.
If we change the QPSK modulation to 8PSK (8 Phase Shift Keying), we could then raise the data rate value up to 60 Mb/s with 5/6 FEC. That decreases our compression ratio down to 24:1 but still allows us to occupy 36MHz of bandwidth.
If we change to DVB-S2, we could use 16APSK (Amplitude Phase Shift Keying) and be able to increase our data rate much higher but still transmit on a 36MHz transponder.
HD offers a multitude of options that cannot possible be covered in this text. Learning your encoder’s capabilities and parameters is important.
HD AUDIO
The same goes for HD audio, HD encoders offer analog, AES/EBU or embedded audio that could be in Dolby E 5.1 or AC-3. Again, the type of audio the encoder ingests depends on the client’s needs and application.
APPENDIX Z
ANALOG VIDEO EXCITERS
Analog exciters ingest one video and up to four audio inputs, process them then places the signals on an IF carrier to be sent to an upconverter. Traditionally, audio sub-carriers have been placed on 5.76 MHz, 6.2 MHz, 6.8 MHz and 7.4 MHz.
7.1 MHz is usually used for an ATIS signal (Automatic Transmit Identification System). The ATIS is a Morse code signal that beeps the uplink phone number with the main video and audio carriers. It is there primarily for the benefit of the satellite service providers to contact the uplink in case of emergency.
Some of the analog exciter’s processing functions are:
IF (INTERMEDIATE FREQUENCY) ON/OFF
Must be on to transmit.
IF DRIVE LEVEL
This is the actual signal drive output that drives the upconverter and amplifier to achieve a high power output (300 – 400 watts).
CLEAR WAVE (CW) OR MODULATED (TRAFFIC) SETTINGS
Allows placing the modulator in CW mode to access the satellite then into Modulate mode when instructed to do so after reaching the required power (saturation) settings on the satellite.
VIDEO AND AUDIO CARRIER LEVEL ADJUSTMENTS
Allows the adjustment of the actual video and audio sub-carriers to meet required specifications for analog transmissions. Usually, the audio sub-carrier levels are set about 18 dB’s below the video sub-carrier.
MAIN CARRIER DEVIATION ADJUSTMENT
Allows adjusting the actual bandwidth (width) of the entire analog carrier (including the audio sub-carriers) being transmitted to meet satellite bandwidth requirements. Uses 36 MHz, 27 MHz or half transponder 17 MHz settings.
AUDIO DEVIATION ADJUSTMENTS
Adjusts audio deviation settings from 25 KHz up to 200 KHz. This is the actual bandwidth (width) of the audio sub-carriers.
ENERGY DISPERSAL ON/OFF
When turned on, this function helps disperse excess signal harmonics to prevent them from interfering with adjacent satellites that are using similar frequencies.
VIDEO EMPHASIS
This function selects the video standard being used such as NTSC (for USA), PAL (for Europe), Flat (if no emphasis is needed) and MAC (if the signal is being transmitted and encrypted in B-MAC).
AUDIO EMPHASIS
Allows 50 or 75 microseconds plus J17 or FLAT emphasis to the audio carriers. Pre-emphasis and de-emphasis are used in the transmit and receive chains to help improve high frequencies. For a better description of what pre-emphasis does and how it does it exactly, visit the link below.
http://www.batlabs.com/predemp.html
APPENDIX AA
MPEG-2 BASICS
MPEG is an acronym for "Moving Picture Experts Group", the unit was formed by the I.S.O. "International Standards Organization" to help develop and deploy digital transmission standards
An MPEG encoder with a built in modulator and an IRD (Integrated Receiver Decoder) is called a “Codec”, this is an acronym for “Co” der and “dec” oder.
MPEG-1 was developed first, it compresses audio and video into a maximum of about 1.5 Mb/s (Megabits per second). Clearly, that does not reproduce a sufficient quality product for commercial television broadcasting.
When MPEG-2 was developed, it allowed broadcasters more flexibility by introducing higher profiles and levels which translates to better sampling capabilities and higher resolutions which produces better pictures on the receive end. Since MPEG-2 is a subset of MPEG-1, MPEG-2 IRDs are manufactured to often be able to decode MPEG-1 streams also.
THE IRD
The “IRD” (Integrated Receiver Decoder) requires a minimum of five basic parameters whether you are sampling your own or decoding a satellite signal. IRD’s by different manufacturers may have additional needed settings, but the following five parameters will most likely be always similar and sufficient to cause a signal lock.
The five parameters are: The “Data” or “Symbol” rate, the “FEC” code rate, the actual “RF” frequency of the satellite transponder and the “IRD’s” built in “LO” frequency. The fifth parameter is turning the “DC” power “ON” or “OFF” to energize an LNB or the 70 MHz “IF” to “L-band” upconverter being used for a test loop.
ASYMMETRICAL ?
The way data is transmitted in one-direction from one encoder to one or more receivers forms an “Asymmetrical” link. It simply means that the encoders, although manufactured by different firms (Tandberg, Tiernan etc…) they have to comply with pre-set MPEG-2 data stream outputs regardless of how the internal electronics achieve that. Basically, each manufacturer is free to build the encoder in whichever way they like as long as it’s output complies with the MPEG group specifications for DVB (Digital Video broadcasts).
At the receive sites the IRDs have to also be DVB compliant in order to receive the signal and decode the streams. This infrastructure allows manufacturers to fabricate “dumb” IRDs, all they need to be able to do is follow instructions from the encoders to paste together the necessary video images. The nature of satellite broadcasting creates a need for much more IRDs than encoders to deliver events therefore encoders are smarter, more complicated and more expensive.
COMPRESSION
Compression has been around for a while; it was even being used in analog color transmissions. Without compression it would be difficult to move a digitized signal on an RF link economically from one site to another, simply because digitally uncompressed signals take up lots of bandwidth.
There are two types of compression: "Loss less" compression, which is what computers use to save data. And, "Lossy" compression, which is what MPEG-2 encoders utilize. "Lossy” compression is a process where all duplicate information is discarded.
Let’s assume you have a live shot beaming in from the field with a reporter standing in front of the police department. There are 30 frames per second in the NTSC system, each frame is looked at by the encoder, digitized, compressed then sent out to the satellite.
Since the reporter is standing in front of the police station and is not moving much, most likely, only the reporter’s facial expressions move but not much changes in the back ground. The encoder learns that fact by comparing successive frames from the camera then it actually stops encoding and digitizing the frames, it only encodes and digitizes the movements within the frame which is not as demanding as the whole frame.
In effect, it sends information to the receiver telling it to change the mouth movements but not to change the background because it’s still the same.
The encoder sends new information only when the entire frame changes, otherwise it repeats the instructions to the receivers until the event ends. This process results in what is called GOP’s (Group of Pictures) and is a basic description of Lossy compression.
Let’s assume you have a 9 MHz satellite segment you want to use. Since an SD signal occupies up to 270 Megabit stream, a 30:1 ratio produces approximately a 9 Megabit stream we got that by dividing 270 by 9. If you had a 6 MHz segment to use we would then have a compression ratio of
45:1. Obviously a 45 to 1 ratio is higher than 30 to 1, if the event being transmitted have lots of action and motion on it such as automobile racing or a basketball game, it is more than likely that the higher compression ration will encounter more error bits and produce unwanted art-effects on the final program output. We see here how important it is to use a proper compression ratio with a proper satellite bandwidth to deliver various programs.
In summary, by using digital transmissions, we save on satellite bandwidth resources in space and on transmitter power resources on the ground. The minor limitations digital transmissions present could easily be overcome with proper planning.
For more details on Lossy compression and the method frames are grouped, read Appendix FF.
SERIAL DIGITAL VIDEO
A digitized, uncompressed serial digital video signal could occupy a large bandwidth (up to 270 Mb/s). Satellite bandwidth resources are limited, so compression is utilized to allow the transmission of multiple digital carriers.
The first generation SD (Standard Definition) MPEG-2 encoders required many parameters the new ones only need four. Often the encoder parameters are supplied by the customer, if not, they can be calculated by the uplink engineer.
The first parameter is the data or symbol rate, if you enter one of them, the encoder will automatically calculate the other. A standard Data rate being used for a 9 MHz bandwidth slot is 8448000 which yields a symbol rate of 6111319, this rate is best utilized by using a ¾ FEC code.
Appendix GG contains more details on the difference between Symbol and Data rates.
The second parameter is the FEC (Forward Error Correction) code. This code is needed to help the receiver retrieve enough data off the stream to reconstitute a legible picture. Typically, the FEC is calculated when the Data and symbol rates are being devised. If you are interested in playing around with bandwidth and Data/Symbol figures, send an email to: emaalouf@pacsat.com with the words Data/symbol spreadsheet in the subject line. I will send you my homemade Data/symbol/FEC calculator. Read Appendix HH for more details on FEC codes and their meanings.
The third parameter to set is the sampling rate, 4:2:0 or 4:2:2. Often, for most quick news shots, 4:2:0 is used because it delivers sufficient details/resolution on a small amount of bandwidth. For sporting events with lots of moving action and wider bandwidth (18 MHz for example), 4:2:2 is a better option to use. It’s not easy to describe the difference between them in a short paragraph, all you have to remember to program the encoder is if the data rate or bandwidth being used is between 4 to 15 Megabits, use 4:2:0 sampling. If the data rate is above 15 Megabits, use 4:2:2. And, yes, a better, slightly lengthy explanation is available in Appendix II.
The forth parameter is the modulation scheme being used which will often be QPSK (Quadrature Phase Shift Keying). Since newer Codecs come with 8PSK (Eight Phase Shift Keying) modulation also you need to make sure the correct option is selected. For a better explanation on QPSK and 8PSK see Appendix JJ.
APPENDIX FF
MPEG-2 GOP’s
GOP's are the results of MPEG-2 Lossy compression. GOP’s are the end product of inter-frame and intra-frame compression states. Most GOP structures within the encoder, for most transmissions are set to IBBP with the frame lengths at 12 or 15. The reason these rates are used is because they offer the most quality video pictures for a reasonable or acceptable delay at the receive site(s).
Longer frame groups may introduce a lower quality video return at the receive site and shorter frame groups may introduce higher compression and encoding algorithms at the encoder resulting in longer delays at the receiver.
Longer delays could cause problems on live talk back programs. A "LIVE" reporter on site will not be able to respond to an IFB question in timely manner because it will take longer to digitize and compress the generated video signal on site and transmit it than it took for the IFB audio to be heard in his ear.
To understand what IBBP means, we have to break down what each letter stands for within the GOP frames structure.
"I" = Intra-coded frames. This is an originally digitized and compressed frame - Specially coded "anchor" frame, the beginning of a GOP structure.
"B" = Bidirectional frames. These frames relay the difference in information changes from the "I" and/or the "P" frames.
"P" = Predictive frames. These frames are sent after a few repetitions of identical frames (like color bars), the encoder stops encoding the video and sends "P" frames only which are in reality information only “data” frames directing the receiver to repeat the last frame it displayed with no changes. A 12 GOP frame structure leaving the encoder would look like this to the receiver.
APPENDIX GG
Data/symbol rates
Like just about any form of digital transmission, the receiver has to know the rate at which the transmitter is sending information. In the computer world, we call this the bit rate. For example, PCs can transmit from their serial ports at up to 115,200 bits per second. Lets get something straight before going forward with this explanation. A bit aka “Data” rate and a baud aka “Symbol” rate are not the same. The bit rate specifies how many bits per second are carried across the channel (phone line, serial cable or satellite transponder), however, the baud rate describes the rate that data is sent within the channel.
Let’s take a modem that transmits at 50 bps (Baud/Symbol rate) by using two tones. One tone could signal a 1 needed to be sent and the other would signal a 0.
Now imagine that you wanted to double the transfer rate across the channel. By using four tones instead of two, you could signal two sets of bits at the same time by switching various combinations of the four tones. The baud rate is still 50 baud (i.e. the tone pairs change 50 times per second), however, the bit (Data) rate is now 100 bps. The combination of the sets of tones is called a "symbol" because too many people are confused by the term baud.
APPENDIX HH
FEC codes
Every step of an uplink transmission, from the camera, cable, playback deck, DA's, encoders, upconverters, amplifiers, dish misalignment, terrestrial interference and particularly satellite transmit/receive components can and do introduce additional noise to a transmitted signal.
MPEG-2 encoded transmissions travel "Asymmetrically" that means; only the encoder sends information (one way) to one or multiple receivers. Since the receiver cannot send a signal back to the encoder saying for example: "I didn't get that last piece of information, please re-transmit it" an error correction scheme had to be implemented.
FEC (Forward Error Correction) allows the encoder to insert error correction information along with the actual data stream so the information could be used to re-constitute/re-generate a frame or a part of a frame in case errors occur.
There are two forms of Forward Error Correction. The first is "Viterbi coding" and is quoted as a fraction.
Let’s take ¾ FEC as an example. The fraction represents the amount of bits entering the encoding engine versus the amount coming out onto the stream. So, 3/4 means that 3 bits entered and 4 came out. The four represent the three original bits plus one correction bit.
One draw back of the "Viterbi" error correction code is that it introduces bursty cluster of errors when it is unable to correct a strain of errors on the stream so a second error correction scheme is implemented to smooth out the bursts.
The Reed-Solomon code corrects by assigning “parity bits” to the overall packets generated by the original encoding algorithm. MPEG packet bit length are 188/204, the Reed-Solomon code raises the value to 192/208, the extra bits are used by the IRD to correct any remaining errors resulting form the Viterbi code.
Additionally, the FEC scheme also uses interleaving of the data stream to prevent noise bursts from interrupting the flow of data in much the same way that CDs use it to prevent scratches from causing dropouts.
Consider the following example:
We’re coming to you live from Tokyo
If interleaved, it might look like:
Kuwcovi emgtyemo ronol eify ot
Should an error occur and say wipe out the 'eify' part of the message, the de-interleaved message will now read
We’r* com*ng to you live *rom Tok*o
As a result, only single characters are missing from the message (shown here as an astrix), rather than an entire word in the case of non-interleaved data.
As a final step, the QPSK symbols are scrambled (not the same as scrambled video) to ensure that long “same” symbol runs which could cause a change in the phase of the carrier do not occur.
Since the QPSK demodulator obtains its signal clocking directly from the signal itself, a large number of phase changes is necessary to re-generate the clock which is accomplished by scrambling the symbols.
APPENDIX II
4:2:0 vs 4:2:2
When MPEG-2 encoders process video (color and picture information), they sample the analog picture (from the field camera for example) at certain resolution, both as horizontal and vertical pixels, but they do it separately as color (chrominance/hue) and brightness (luminance).
Since the human eye notices "luminance / brightness" changes in the picture much more than "chrominance / color / hue" information, the DVB standard specifies that the "luminance" be sampled more times than "chrominance" so a valid, broadcast quality reproduction can be achieved.
So, a 4:2:0 sample mode on the encoder designates that the "luminance" be sampled 4 times and the "chrominance" or color differences between Red, Blue and Green (the three main TV colors) be sampled 2 then 1 time each... I know what you're saying now... Where did the 1 come from? I thought it was 4:2:0... Not 4:2:1?? Well in their infinite wisdom, the MPEG engineers working on the standard designated a 0 to a single sample because in math, a Zero is an actual number... In math, 0 (zero) does not mean the absence of a number it simply represents a position of a number.... We can go on discussing this but just take my word for it... 4:2:0 is actually 4:2:1, otherwise, why would they go to 4:2:2 from 4:2:0?
Basically, in 4:2:0 encoding, the resolution of the color information is one quarter of the resolution of the video information. 4:2:0 quickly proved inefficient for production work so a better quality than DVB system was developed and offered 4:2:2 sampling which increased the color information and in turn increased the quality of the re-produced pictures. This system doubles the amount of vertical color information being transmitted.
Another format exists that is in very common use today but not used much in SNG, called HHR - Half Horizontal Resolution, this part of the MPEG-2/DVB standard transmits only half of the normal 720 pixel horizontal resolution while maintaining normal vertical resolution of 480 pixels (although, since it's 4:2:0 format, the color information is only encoded at 240 pixels vertically and 176 pixels horizontally.
A lot of the smaller DBS (like the ethnic packages on IA5 etc) use HHR format since it dramatically reduces the bandwidth needed for channels - of course at the expense of picture quality (VHS quality). Special logic in the (home version) video decoder chip within the set top box re-expands the picture to its normal horizontal size by interpolation prior to display.
The diagram on the next page shows the ratios of 4:2:0, 4:2:2 and HHR resolutions.
Here's a good book on MPEG-2: Digital Video: An Introduction to MPEG-2 by Barry Haskell, Atul Puri and Arun N. Netravali - ISBN 0-412-08411-2.
APPENDIX JJ
Digital modulation schemes
When satellite transponders are used to transmit MPEG-2 signals, some form of Phase Shift Keying in this case QPSK (Q=Quadrature or 4) is used to modulate the digital information onto an RF carrier.
Rather than using the amplitude or frequency of the carrier to convey the information, QPSK modulates the phase of the carrier signal. Depending on the data being modulated, the carrier is forced into one of four different phase states, known as a symbol. The great advantage of this method is that each symbol contains two data bits, thus doubling the potential amount of data that is transmitted over conventional amplitude or frequency modulation (AM or FM) techniques.
The diagrams below illustrate a typical implementation of QPSK:
Figure 1 shows that each possible pair of data bits is represented by a different phase angle and figure 2 shows an example of a QPSK waveform.
This is a simplified way of expressing digital modulation using QPSK, other forms of modulation include 8PSK, 16QAM, 32QAM, 64QAM (up to 256QAM) and 16APSK with the upcoming DVB-S2 standard are available and in use on various transmission mediums.
FEC (Forward Error Correction) contributes to the actual data/symbol rates being used.
APPENDIX HH
WHAT ARE PIDs?
MPEG-2 transmits its data in packets of 188 bytes each. A package identifier (or PID) is inserted at the top of each packet that tells the receiver what to do with the packet.
If the MPEG-2 data stream is a part of an MCPC transmission, the receiver searches for the packet of the channel selected on its menu and passes those packets on to the Decoder portion of the receiver then simply discard all other PIDs.
Typically, four types of PIDs are used by satellite receivers.
The VPID is the PID for the video stream, the APID is used for the audio stream. Occasionally, a PCR PID (Program Clock Reference) is used to synchronize the video and audio packets by utilizing a Presentation Time Stamp (PTS), however, most of the time, this data is embedded into the video stream and is handled automatically via the receiver.
The forth PID, System Information (SIPID) is used for data such as the program guide, information about other frequencies that make up the total package etc... The SIPID is usually assigned a number between 0000 and 0014 (hex).
The "V" and "A" PIDs are what the receiver identifies first and displays to confirm reception of a certain program.
APPENDIX II
WHAT IS DVB?
DVB stands for Digital Video Broadcast and is a standard based upon MPEG-2 video and audio. DVB covers how MPEG-2 signals are transmitted via satellite, cable and terrestrial broadcast channels along with how such items as system information and the program guide are transmitted along with the scrambling system used to protect the signal.
With the exception of the United States of America, Mexico, Canada, South Korea and Taiwan, DVB has been adopted by just about every country in the world for digital TV & radio.
DVB-S, is the current satellite format of DVB - DVB-S2 is destined to replace it within 1-2 years.
DVB-C is the specification for DVB/MPEG-2 over cable.
DVB-T is DVB/MPEG-2 over terrestrial transmitters such as your local TV station.
DVB-H is the specifications for DVB/MPEG-2 / 4 over handheld devices such as mobile phones.
QAM
Quadrature Amplitude Modulation (QAM) is the cable version of QPSK.
Using many different symbol phases (the initial standard for the US is 64 different phases - 64QAM), a given 6MHz of cable bandwidth will be able to carry the same amount of data as a single 30MHz transponder.
A 125 channel cable system @ 6MHz per channel = 750MHz bandwidth. With 64QAM modulation the cable company will be able to carry up to 625 (Standard Definition) video and audio programs (assuming compression levels where five video services are sent on a single RF channel).
VSB
Vestigial Sideband modulation (otherwise known as VSB-8) is the technique that will be used in the US for terrestrial ATSC transmission (TV station over the air broadcasts). VSB-8 uses AM transmissions with phase information within one of two sidebands. The other sideband is almost totally suppressed except for a pilot carrier inserted to help receivers initially acquire the signal.
No need to delve further into VSB, it is not used in satellite transmissions (as of yet anyways). It is worth mentioning because most of the newer MPEG encoders will have that function and you need to understand where it would be implemented.
THE MPEG-2 TRANSPORT STREAM
MPEG-2 transmissions are either transmitted as SCPC or MCPC feeds. However, at an individual channel level, both techniques use the same method for building a data stream containing the video, audio and timing information. We will concentrate on MCPC because once this is understood SCPC becomes obvious. This combination of compressed video and audio is called the PES or Packet Elementary Stream and is built as follows:
The time field isn't the actual time that the encoding was done, but timing information to allow the audio and video to stay synchronized together. This part of the PES is called the PCR (Program Clock Reference) and may be sent either as part of the video stream or as a separate stream.
Multiple PES streams get multiplexed together into a faster stream and the System Information or SI stream gets added, resulting in the final MPEG-2/DVB multiplex that gets uplinked to a transponder on the satellite:
The SI is responsible for telling the receiver all kinds of useful information about the data stream, so that the receiver can write the appropriate data into its program guide. The first part of the SI is called the Program Association Table or PAT. The PAT is always transmitted on PID 0000 and contains a list of Program Map Tables or PMTs that are part of the data stream. For example:
PAT (PID 0000) = 0100, 0200, 0300, 0400
PMT 1 (PID 0100) = Video PID 0101, Audio PID 0102, Audio PID 0103, PCR 01FF
PMT 2 (PID 0200) = Video PID 0201, Audio PID 0202, PCR 01FF
PMT 3 (PID 0300) = Video PID 0301, Audio PID 0302, PCR 02FF
PMT 4 (PID 0400) = Video PID 0401, Audio PID 0402, PCR 0401
Given this information, the receiver knows that the DVB transport on the current frequency contains four programs. The first channel contains two audio services and all of them except for the fourth program contain separate timing information - the fourth has the PCR timing embedded into its video stream.
The reason that the PCR might be transmitted separately from the video stream is in the case of multiplexed channels which were encoded with a common clock reference. In this case, it would be redundant to send the PCR again, since the receiver would always use the same clock reference for all the signals within the multiplex.
Obviously, the PMT contains other information, such as pointers to the name of the channel in the SDT table and things like information about data services that might be multiplexed in as part of the PES. But in addition to the PAT and PMT, there are a few more interesting ones. The Network Information Table (NIT) on PID 0010 contains a list of associated transponders that make up the package along with their SR and FEC values, which can be different.
There are few other PIDs that make a DVB receiver work the way it does. The optional BAT or Bouquet Association Table tells the receiver about programs of the same type (such as sporting events, movies, news etc.) that are part of a "Sports" package on a DBS bird for example. The EIT or Event Information Table on PID 0012 contains a list of the programs (or events) that when interpreted by the receiver's firmware, make the program guide. The EIT allows for up to two weeks worth of programming to be sent ahead of time.
And finally, if you wondered how MPEG-2/DVB receivers know what the time is, the TDT (Time and Date Table) tells the receiver what the date and time is in Universal Time - the IRD contains the UTC offset, so that you see local time on the screen.
ENCRYPTION
Many types of encryption algorithms exist. The ones being used in satellite transmissions these days are usually B-MAC for analog and BISS for digital.
In B-MAC (Multiple Analog Component) type “B” each line of video information is delayed by several microseconds, creating B-MAC's characteristic diamond-hatched pattern. Only those terminals equipped with decoders that are addressed by a packet of data contained in the vertical blanking interval of the B-MAC signal can descramble the video. B-MAC's horizontal blanking interval contains up to six digitally-encrypted audio channels and one utility data channel.
B-MAC is a setting that used to come standard on most analog exciters, now days a B-MAC encoder will have to be placed in line to scramble the signal.
At the onset of MPEG-2, most encoder manufacturers developed and incorporated their own proprietary encryption techniques. Tiernan had PGCA which required inputting all identification codes of every IRD intent on receiving the programming into the encoder prior to the transmission.
Tandberg (NDS back then) developed the “SNG key” which is a 7 digit number that was programmed into the encoder which had to be entered on every IRD at the receive end to decode the programming.
Regardless of which system was being used, the encoders and IRD’s had to be by the same manufacturer… I smell a monopoly here… Don’t you?
Eventually the EBU helped develop BISS encryption (Basic Interoperable Scrambling System). BISS provides three levels of encryption complexity and allows any encoder to be decoded by any IRD regardless of the manufacturer as long as both have the needed “BISS” software/hardware on board.
GOOD PRACTICE
Digital signals require precise settings. They don’t tolerate imperfections and will not put up with unusual input levels.
Digital transmissions are difficult to troubleshoot when they fail. Due to inherent characteristics, they don’t fade or show “Sparklies” like analog signals, they just drop off completely. Locating the precise cause could be challenging, time consuming and will require numerous inquiries into many variables.
Below are a few suggestions to follow if digital problems are encountered.
VIDEO AND AUDIO CABLES
Always draw good video and audio levels from the production venue. If you are ingesting an analog signal, run the video signal thru a “Frame Synchronizer” (when possible). A Frame Synchronizer will help maintain and/or re-constitute the integrity of the video.
Inspect and confirm that the video and audio cable runs from the source to you are free and clear of EMF (Electro Magnetic Field) interference. EMF could induce hum and unwanted effects into audio and video cables when they run close to it – An example of an EMF source is a high voltage wire (truck’s power cable).
Basically, in addition to maintaining a proper well grounded single power source for your equipment, pay special attention to high voltage cables crossing or coiled over your video and audio runs.
DIGITAL EQUIPMENT INITIALIZATION
Always run a complete software factory initialization on the encoder and IRD before entering any new settings. Confirm that all the settings on the IRD match the settings on the encoder, check transmit and receive frequencies, Data and/or Symbol rates, FEC coding, video data rate too low or too high (too high uses up too many bits, too low produces lower video resolutions on the receive end). Check audio settings not to be too low or too high, extreme variations could yield amongst other effects a tinny sound on the receive end.
Replace Codecs, upconverters and transmitters if necessary to test a path that keeps exhibiting problems. Some Codecs or IRD's could have faulty chips, small error buffers or software faults. These units may experience problems under certain circumstances and never display a fault indicator (light) on the front panel.
BNC AND F CONNECTORS
Inspect and test all in rack (internal) cables that run into and out of the encoder, modulator and onto the RF chain. Confirm that the 70 MHz IF (Intermediate Frequency) cable from the codec (modulator module) to the upconverter is of proper length and impedance (usually 75 Ohm). Check for old or non-broadcast cables in the system.
SMA AND N CONNECTORS
Confirm that the RF cable run between the upconverter and the HPA is free of kinks and the SMA or N connectors are mounted and screwed on tight. Inspect all SMA, N, L or T shaped connectors and splitters within the path, they all go bad and cause signal degradation or loss.
UPCONVERTERS
Confirm that your upconverters are digital capable. If a non-digital grade upconverter is being used, it may function OK for low data rate carriers but will introduce unstable, spurious effects on high data rate signals. The unstable carriers will suffer from constant timing corruptions that will effect the overall signal and cause intermittent or permanent loss of lock at the receive site.
Watch out for wide band transmitters, they may harbor inherent intermodulated products that could under some circumstances or frequencies cause undetected high bit errors right at the transmission port (amplifier output). An IF sample loop will never detect such errors, a cross guide coupler within the waveguide is needed to sample the RF stage and look for problems.
WAVEGUIDE
Inspect all waveguide runs for hot spots. Look at the input and output flanges for flattened rubber washers, moisture build up, kinks, unusual twisting, loose screws and rust. DO NOT perform any waveguide repairs or dish inspections while transmitting.
SPECTRUM AND WAVEFORM MONITORS
Keep your spectrum monitor tuned to the satellite receive frequency, if your signal drops you’ll be able to see it immediately. A waveform monitor will prove useful in detecting ground loops and unusual effects in the ingested signals use it to confirm your incoming video quality and levels.
DISH
Inspect the dish surface and feed horn aperture clearance at least once a month. Prior to setting up and deploying the antenna, always confirm that the path in front of it is clear of obstacles such as trees, buildings and people standing directly in front of it. Re-peak and re-polarize when in doubt to correct for dish pointing errors, inspect your deviation and polarization often.
TRANSMISSION PATH
Watch for other carriers bleeding into or sitting too close to your signal on the satellite. Digital carriers that are stronger in amplitude could cause interference to lower signals.
Even though geostationary satellites move within a designated orbital box, as it ages, the movements will eventually take the satellite farther away from the center of the box. To compensate, the satellite access center intervenes by firing the satellite thrusters and guiding it back into its correct orbit. If you are directly under the satellite while its orbit is expanding and contracting, you could experience a brief "Doppler" (abrupt signal timing change) effect that could corrupt the digital signal timing and cause temporary problems.
THE RECEIVE SITE
Confirm that the LNB, LNC or LNA being used is rated for low noise and is digitally stable.
Pay special attention to lengthy cable runs between the receive dish and the IRD. Long cables will cause signal attenuation that could lead to data corruption and a noticeable Eb/No drop. If possible, use good grade cable with heavy shielding like an RG6 or RG11.
TERRESTRIAL INTERFERENCE
Other factors that could cause disruptions are TI's (Terrestrial Interference) from microwave and local cellular towers, sun spots and various television or military facilities in the area of the transmit and receive sites.
MCPC VIA IF COMBINING.
This can only be done with encoders that have 70 MHz offset capability.
In order to perform IF combining, the two signals must be on the same polarity and within 40 MHz of each other. If signal one is at 14250 and signal two is at 14260. Set the IF on Codec 1 to 70 MHz and Codec two to 80 MHz.
A digitally stable upconverter is needed, the analog modulator is not used for digital transmissions.
To receive a good signal, a digital grade LNB is recommended.
Use the drive on the Codecs’ modulator to manipulate the power output levels on the satellite.
70 MHz TEST LOOP
USEFUL TERMS
ASI: Asynchronous Serial Interface. The final stage of a digital signal before it is fed to a modulator.
Bit rate: The number of bits of data sent over a set time.
BPS: Bits per second
DVB: Digital Video Broadcasting - A standard providing specifications for transmitting and receiving digital video broadcasts.
FIFO. First in first out, a type of data buffer within the MPEG encoder.
GOP: Group of pictures, a product of lossy compression representing video frames.
IRD: Integrated Receiver decoder
LNB. LNC. LNA. Low Noise Block, Low Noise Converter, Low Noise Amplifier. Usually mounted on the antenna’s feed horn to provide a return signal to an analog or a digital receiver.
LO: Local Oscillator
MCPC: Multiple Channel Per Carrier
PID: Packet Identifier, data used within a packet to identify it.
QPSK: Quadrature Phase Shift Keying. A form of digital modulation implemented with MPEG-2.
SCPC: Single Channel Per Carrier
Symbol: An identifiable electrical state linked to a signal element within a set period of time. The Symbol rate is also referred to as the Baud rate.
UNCOMPRESSED VIDEO DATA RATES
HDTV = 1485 Mbps
SD video 10-bit CCIR 601 = 270 Mbps
SD video 8-bit CCIR 601 = 216 Mbps
SD video 8-bit 601 (active only) = 167 Mbps
Digital Betacam (R) ~90 Mbps
MPEG PARAMETERS
MPEG-2 4:2:2 P@ML 10-50 Mbps
MPEG-2 4:2:0 MP@ML 2-15 Mbps
MPEG-1 constrain. Parameters between 0.5-1.8 Mbps
MPEG-4 H.261 videoconferencing 64 Kbps - 1.5 Mbps
MPEG-4 H.263 videoconferencing 4 Kbps - 0.5 Mbps
PICTURE SIZE / RESOLUTION
CCIR 601 525/30/2:1 720 x 486
CCIR 601 625/25/2:1 720 x 576
MPEG-2 422P@ML 30fps 720 x 512
MPEG-2 422P@ML 25fps 720 x 608
MPEG-2 30fps (quasi-std) 704 x 480
MPEG-2 25fps (quasi-std) 704 x 576
SIF (30fps, 25fps) 352 x 240,288
CIF (always 30fps) 352 x 240
HHR, 2/3-HR, 3/4-HR 352,480,528 x 480,576
SIF (30fps, 25fps) 176 x 128,144
QCIF (always 30fps) 176 x 144
SAMPLE DATA, SYMBOL AND FEC RATES.
8448000 Data rate with 3/4 FEC yields 6111319 symbol rate – 9 MHz bandwidth
8134380 Data rate with 2/3 FEC yields 6620000 symbol rate- 9 MHz bandwidth
7148000 Data rate with 3/4 FEC yields 5170894 symbol rate – 7 MHz bandwidth
SYMBOL RATE CALCULATOR
Here’s a formula to calculate the symbol rate if the client provides the data rate only.
This applies to most of the SNG work done in the field. This formula assumes that external MPEG framing is set to 188 byte frames (default SNG).
8448000 X 1 X 204/188 X 4/3 X ½ = 6.111319 symbol rate
8448000 = Data rate (supplied by the client)
1=MPEG external framing (default factor for QPSK)
204/188=Reed Solomon rate (RS)
4/3=FEC rate inverted from 4/3 for use with this formula.
1/2=Modulation index for QPSK (use 1/3 for 8PSK and 1/4 for 16QAM)
BANDWIDTH CALCULATOR
Symbol rate (6.111319)X1.38=8.43362022 MHz or about 8.5 MHz used on the satellite leaving ¼ MHz on either side as guard bands.
IRD AND LOCAL (LO) FREQUENCY SETTINGS
If your satellite frequency is between:
10950 and 12050 IRD LO frequency to be used is 10000 MHz
If your satellite frequency is between:
11700 and 12800 IRD LO frequency to be used is 10750 MHz
If your satellite frequency is between:
12250 and 13350 IRD LO frequency to be used is 11300
If your signal is in C-band then your IRD Local Oscillator frequency will usually be: 5150 MHz
DOMESTIC (USA) FREQUENCY CONVERSIONS
Take any uplink frequency in KU band and subtract 2300 MHz, you will have the downlink frequency.
Example: 14250 – 2300 = 11950 MHz
Take any downlink frequency in KU and subtract 10750 MHz, you will have the L-band equivalent frequency.
Example: 11950 – 10750 = 1200 MHz
Take any uplink frequency in C band and subtract 2225 MHz, you will have the downlink frequency.
Example: 6150 – 2225 = 3900 MHz
Take the C-band LO frequency and subtract any downlink frequency from it, you will have the L-band equivalent frequency.
Example: 5150 – 3900 = 1250 MHz
This works on all satellites domestic and global as long as you know the LO and the conversion factors to use.
MINIMUM Eb/No AND VITERBI RATES
Viterbi rate Minimum Eb/No (dB’s)
1/2 4.5
2/3 5.0
3/4 5.5
5/6 6.0
7/8 6.4
Use this table as a benchmark; actual results will vary depending on link conditions.
STANDARD RATES TO USE FOR EVENTS
Resolution Bit rate range Suggested use
704 ppl above 7 Mbps sports
544 ppl 4 to 7 Mbps movies & shows
352 ppl 2 to 4 Mbps talking heads
SIF 1 to 2 Mbps multimedia
ppl = pixels per line
Parts of this text were collected, compiled and edited from articles found on the World Wide Web. Academic credit was granted when the author was posted.
This manual and all its contents are the property of Eddie Maalouf. Use, sharing and/or reproductions are encouraged as long as credit is given/posted.
Eddie Maalouf – Director of Engineering – PACSAT – 916/446-7890
emaalouf@pacsat.com
www.pacsat.com
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