All About Satellite Television - Main application of Sat. comm.
Why does satellite television beat every other kind ?
Having a satellite television system will expand your communications capabilities far beyond the horizon. No longer will you be bound to the limitations imposed by conventional broadcast or local cable programming.
With a satellite antenna you will gain access to the entire North American, Canadian, Mexican and Brazilian Geostationary Satellite System, making it possible to enjoy television programs from every part of the countrys.
The variety of programs that are presently available will astound you. There are much channels of regularly scheduled programming and much channels that carry occasionally scheduled programs.
Movie channels, sports channels, educational, news, spiritual, network, superstations, music, health, childrens and adult television programs are all beamed into your backyard. You are entitled to use these signals and a satellite TV system lets you do just that.
There are several satellite TV programming guides available. Find a satellite TV dealer, he should have one or more for your inspection. Satellite TV is truly a wonderland of entertainment, and thousands of households all over the world are enjoying its benefits.
What is the geostationary satellite system ?
The geostationary satellite system is a group of relay satellites that orbit the Earth in a seemingly fixed position in the sky. They receive television signals uplinked from Earth and then they retransmit them to areas as large as an entire continent at once.
It has long been known that objects that circle the Earth at a great distance (high orbit) will travel at a speed slower than the rotation of the Earth. The best example of this is the moon, which circles our planet at a distance of about 220,000 miles. The distance at which a satellite will become geosynchronous is 22,279 statute miles above the equator in a orbit path (also called the Clarke Satellite Belt). Satellites in such an orbit appear to remain fixed in relation to a specific point on Earth, but traveling at almost 7,000 miles per hour in the same direction the Earth turns. With an accurate and properly adjusted polar mount, the antenna can be aimed at any satellite in the Clarke Satellite Belt. Most antennas have provisions to move the reflector either by hand or with a motor drive system.
A permanently mounted antenna would receive one satellite and would miss the programming on all other visible satellites. Satellites are considered visible to a antenna if they are above the horizon at the receiving antenna's location.
Do the satellites ever wear out ?
Yes. As the satellites get older their solar batteries will fade. While some satellites have an optimum life expectancy of 10 years, they often begin to loose power after only a few months. The satellites transmit at 5 to 8 watts of power and they spread their signal out over a huge area. The signals received on Earth are extremely weak and they must be greatly amplified before they are usable. Even if everything works as planned and the satellites perform for their expected service life, they will eventually run out of station keeping fuel. When this happens, the satellite is moved out of orbit so a new one can replace it.
Which are the advantages of satellite communications ?
In a relatively short period of time, satellite communications grew from a simple but successful experiment into a complex series of networks comprising a multi-billion-dollar industry. Phone companies use satellites to carry thousands of long-distance calls, businesses use them for data communications, and all phases of the television industry employ satellites to relay their programming from point-to-point. Satellites, have solved a number of problems inherent in other forms of communications. The major advantages to use a satellite system is :
- Satellites are reliable. Their transmissions are virtually unaffected by changes in the weather, time of day or sun activity. - Satellite picture quality is superior, since the satellite system uses only one repeater. - The frequencies used by satellites allow bandwidths of sufficient capacity to transmit TV signals that won't fade periodically, such as HF radio signals will do. - Satellites are by far the lowest cost means of medium to long-distance communications, as compared with landline wires, underseas cables, and earthbound microwave relay stations.
How satellites work ?
Satellites operate in the microwave frequency range. This allows them the bandwidths necessary to handle several television channels and thousands of voice and data transmissions simultaneously. Most commercial satellites communications operate in the 4 and 6 gigaherts (GHz) frequency range, also called the C-Band. A few birds use the 12 and 14 GHz range known as the KU Band. The Ku Band is used mostly by contries other than the USA, with the exception of some data transmission by SBS (Satellite Business Systems).
At present, virtually all domestic satellite television transmission take place in the 4 and 6 GHz range. Specifically, the uplink signals beamed up to the satellite from the ground station are between 5.9 and 6.4 GHz. The satellite converts these signals to between 3.7 and 4.2 GHz and sends them downlink to Earth.
The satellite uses a series of repeaters (transponders) which downconvert the signals from the 6 to the 4 GHz range. This allows a two-way communications, where the incoming and outgoing signals don't interfere with each other. This way, an effective relay is established.
The satellite receiving antenna is a fairly wide-beam antenna that covers the necessary frequency range with reasonable efficiency. It is a directional antenna, which processes received signals with a broadband (5.9 to 6.4 GHz) front end.
The satellite transmitting antennas are highly directional, high-gain, narrow-beam antennas which are focused on a narrow area, like the lower half of the United States, for example.
Since both of the satellite's antennas are directional, they both have a pattern. The center of this pattern, where maximum gain occurs, is called the boresight point. The pattern of the transmitting becomes particularly important when attempting to determine the strength of a satellite signal reaching the Earth. As the transmissions leave the satellite, they form a beam that covers a specific area of the Earth. The energy levels of this beam are called Effective Isitropic Radiated Power (EIRP), and they are distributed in a pattern where the signal is stronger in the center than at the edges. This pattern is referred to as a "footprint" and is shown on a map with contour lines that connect equal levels of EIRP together. This is called a footprint map and looks similar to a meterological survey map, where isobars connect equal levels of atmospheric pressure.
The levels of EIRP are expressed in "decibels above one watt" (dBW), and they tend to fall away from the center of the footprint pattern in decending values. A typical footprint map, for example, might show a boresight point strength of 35 dBW with concentric lines indicating 34 dBW, 33, 32, and so on, towards the outer fringes. These values do not take into account the pathloss incurred between the satellite and the receiving antenna, but they are the most important indicators of available signal strength.
What is Microwave band ?
As you may have noticed, both the uplink and downlink frequency bands are 500 MHz wide. This permits twelve TV channels of 36 MHz each, with 4 MHz guard bands between them. The rest of the band is used for ground-to-satellite command signals, and a couple of beacons to help ground control measure the exact position of the bird at any given moment.
Generally, a satellite can be expected to relay one TV channel per transponder, for a total of twelve within its assigned frequency range. Several satellites, however, double the numbers of TV channels they can handle through a technique known as "opposite-sense polarization". What this does is to use the same 36 MHz-wide frequency for two separate channels by processing one with a horizontal polarization and the other with a vertical polarity. This "frequency re-use" has proven highly effective and will probably become standard.
What is TVRO ?
The abbreviation TVRO stands for Television Receive Only and refers to home satellite reception. Satellite TV systems pick up signals from satellites that are in an orbit that exactly matches the speed that the Earth spins. This special orbit is around the equator of the Earth and is called the Clarke Belt. Satellites that are properly positioned in the Clarke Belt will appear to be stationary when viewed from the Earth. What this means for the satellite television viewer is that while the viewer watches TV, the satellite dish does not have to move in order to keep up with the satellite.
Satellite television in the USA is divided into two major types. The first major type is TVRO. TVRO satellite systems have a large dish which is moveable. The moveable dish enables a TVRO system to view programs on the many different satellites that are positioned in the Clarke Belt. There are different names that are used for TVRO satellite systems. Some of these names are BUD, Big Dish, C-Band, and Full View. Just remember that if the dish is large (usually 6 - 12 feet across) and it moves, it is a TVRO satellite system.
The second major type of satellite TV is DBS. DBS systems have a small dish (18 inches to 3 feet across) that does not move. In the US there are currently 3 types of DBS satellite systems. Each DBS system requires it's own special receiving equipment and has it's own programming line up. The 3 types of DBS systems are DSS, DISH Network, and Primestar. The receiving equipment for the DSS system is currently being manufactured by 11 companies and the DISH Network receiving hardware is being made by 2 companies. All Primestar equipment is made by Primestar only.
The first satellite television systems for the consumer were TVRO (TeleVision Receive Only) satellite systems. TVRO started sprouting up all over the U.S. in the late 1970s and early 1980s. TVRO satellite systems are characterized by big dishes that are usually 6-12 feet across. TVRO systems receive television signals from C-Band satellites. A C-Band satellite has 24 channels (transponders) on each satellite. There are over 20 C-Band satellites that may be received in the continental United States. A TVRO satellite system must have a movable dish in order to access the signals from so many satellites. Even though most of the press and most of the advertising that you now see involves the small dish DBS systems, TVRO is still alive and well.
Other words are often used to describe a TVRO system. Some of these words are Big Dish TV, Full view, C Band Satellite TV, and BUD (Big Ugly Dish).
The biggest variety of programming in satellite television is available through TVRO. Cable TV programming is available to the TVRO owner, along with programming that is usually not available to cable TV subscribers. There are two types of TVRO satellite channels.
The first type of TVRO satellite channels are called scrambled or subscription services. In order to view these scrambled channels you will need two things. Number one is a piece of electronic hardware called a descrambler. In most modern satellite receivers the descrambler lives inside the receiver and is sold as part of the receiver. The descrambler has a metal plate over it and can be removed by simply sliding it out. Be sure that you unplug the receiver from the wall socket before you remove or replace the descrambler from its slot in the receiver. The second thing you will need to view scrambled channels is to buy a subscription to the channels of your choice. A subscription is just a phone call away. There are many companies that handle satellite TV subscriptions. Each company will have a variety of program packages designed for your viewing preferences. You can find out about the programming companies from one of the satellite TV magazines or from the advertisements that may appear when you go to a satellite channel that is blanked out because you don't have a subscription. When you call the programming company the picture will usually pop on the screen while you are talking. It's easy!
In addition to scrambled satellite TV channels, TVRO has a big variety of free channels available. The variety of channels includes news, educational, foreign language programming, music, old movies, and many other unusual programs. These free channels are called in the clear or unscrambled channels. Some of these free channels are regularly scheduled programs, such as The Learning Channel, other free channels are known as feeds. Feeds can be scheduled or unscheduled programs. Feeds are used by networks or other programming providers to beam shows, events, or news to their affiliates. When these programs are beamed unscrambled, TVRO viewers can pick them up. For instance, if a game is being played in Atlanta Georgia and a TV station in L.A. is carrying that game, a TVRO system can pick the game up, provided the signal is not scrambled. There is a huge wealth of programs, available to the TVRO owner, that are broadcast unscrambled. News feeds are a favorite of mine. News feeds may be used by network or other program providers to beam reports out in the field to their central location. Some news feeds are used by their program providers live, others are fed to their central location where they are edited for a later program. Unedited news feeds can be very interesting.
If you enjoy radio you can tune in MANY radio stations from all over North America. The variety of music available for free with a TVRO system is truly amazing.
The TVRO owner can upgrade a regular C band TVRO system in order to add the capability of picking up Ku band signals. From Ku band satellites, the TVRO system can pick up additional free feeds and free programming. There are also scrambled signals on Ku band, but most of what the TVRO system can view on Ku band is free. People that are into sports and news feeds are some of Ku band's biggest fans.
Ku band satellite signals are at a higher frequency than C-band. Most modern satellite receivers have the ability to receive Ku band signals. The only upgrade that is required is in the modification of some of the outside electronics at the dish. The upgrade involves the feed and LNB, which are above the center of the dish, usually under a plastic cover.
The abbreviation TVRO stands for Television Receive Only and refers to home satellite reception. The basic equipament for TVRO systems is composed of at least four components; the antenna, the feedhorn, the Low Noise Block (LNB) and the receiver.
What is DBS System ?
DBS stands for Direct Broadcast Satellite. DBS is broadcast by medium and high powered satellites operating in the microwave Ku band. These high powered, high frequency satellites make it possible for the signals to be picked up on a small dish. Digital compression makes it possible to have many channels on a single satellite. The current DBS systems that are operating in the U.S. are DSS, DISH Network, and Primestar. The DSS and DISH Network systems both have 18 inch satellite dishes. Primestar has a 3 foot satellite dish. One of the big advantages of DBS systems is that the small dish does not have to move.
All current DBS systems in the U.S. have nothing but scrambled channels and require descrambling with their own special receivers. For example a DSS system can't pick up Primestar, DISH Network, or TVRO signals. A Primestar system can't pick up DSS, DISH Network, or TVRO signals. The consumers can only receive programs for their system.
How does the antenna work ?
The parabolic shape of the antenna collects the very weak microwave signals transmitted from the satellites and reflects them toward the central area of the feedhorn (attached to the LNB). The overall performance of an antenna system is referred to as G/T (merit factor), which measures the gain over the noise temperature. The gain is expressed in decibels, and the noise is expressed in degrees Kelvin. The higher the G/T, the better the antenna performance.
The feedhorn is the device on a satellite antenna that collects the concentrated signal from the dish and feeds it to the rest of the eletronics in the reception system. With the prime focus feed antenna, the feedpoint is suspended above the dish as the focal point of the dish. This type of arrangement offers good G/T figures and excellent performance.
When sizing antennas, the general rule is "the bigger, the better", but there are a number of variables to consider. The homeowner should find that a three meter antenna will give him perfect picture quality, provided that his LNB and receiver perform well. This is the trade-off. You can get away with a smaller antenna if you are willing to invest in LNB with extremely good noise figures. It should be noted, however, that all antennas less than eight feet in diameter will probably experience some interference.
How important is surface accuracy ?
Very important. The parabolic reflector has to start with an accurate shape and this shape must remain dimensionally stable if it is to perform well. Small changes in the surface or the suport structure of the reflector will cause major changes in the way the microwave signals are amplified and focused at the opening of the feedhorn. A dimensionally inaccurate reflector will change the phasing of the reflected microwaves and instead of amplifying them, it will diminish their strength. When the reflected signals reconvene at the focal point, they must arrive in phase or they begin to cancel each other out.
The antenna capture noise ?
Yes. Antena temperature is how much of terrestial noise is detected by it. An antenna detect more noise when your elevation reduce.
What is feedhorn ?
Is the device on a satellite antenna that transfer signals from the antenna to the rest of the equipament in the reception system. The efficiency of the feedhorn system is a very important part of the overall performance of your system. A tuned feed exactly matches the focal length over diameter (f/D) requirements of the antenna to which it is tuned.
Keep in mind, satellite signals are extremely weak when they finally reach Earth that they are easily overpowered by all sorts of (TI) terrestrial interference.
The Earth itself generates more than enough microwave energy to overpower the hottest satellite signal. Add to this, the tremendous amount of microwave broadcasting done by local telephone companies and noise from adjacent satellites, you begin to understand why having a full-size antenna and a tuned feed system is critical if you expect excellent performance.
Each stock feedhorn is designed and engineered to have an ideal focal length over diameter (f/D) ratio where optimum performance is achieved. When a manufacturer applies a feed system to an antenna and the ideal f/D conditions aren't present, neither the feedhorn nor the antenna can perform to its maximum potential. The most respected feed manufacturer of feedhorn is Chaparral Communications. The only way to fully and properly illuminate the reflector surface is with a tuned feed. Any other compromise will mean a loss of performance.What is Low Noise Block (LNB) ?
The LNB is probably the single most important part of the reception system with regard to picture quality. Somes LNBs are rated by gain, but most are rated by noise temperature, expressed in K degree. A highly effective LNB for use with a home earth station might have a rating of 25 K degree, provided there were no special reception problems to contend with. LNB noise temperature, antenna elevation and antenna gain (primarily determined by antenna size) are the main determinants of overall system performance. This is where the G/T rating comes in. The G/T can be improved either by increasing the gain of the antenna (making it larger or by reducing the noise temperature). The LNB also performs the operation of "downconvert" the 3.7 to 4.2 GHz downlink frequency to an intermediate frequency, normally 950 to 1450 MHz.
The Receiver
Though the antenna and LNB are the chief determinants of the G/T, the receiver is responsible for the audio and video specifications (video bandwidth, response, gain, etc.). It is an extremely important component, and its quality must be carefully selected.
The first operation that the receiver performs is to select the particular transponder (channel) signal that is to be received. The LNB has amplified the entire 3.7 to 4.2 GHz range, and the receiver must select from this the 36 MHz that represents the desired channel. The second operation the receiver performs is to "downconvert" the 950 to 1450 MHz signal to an intermediate frequency, normally 70 MHz. This may be accomplished in one step (single conversion) or in two (dual conversion). The third receiver function is to demodulate the audio and video from the intermediate frequency. It does this in two stages. In the first stage, the baseband, wich includes the audio and video signals and sometimes additional subcarriers, is demodulated from the main carrier. In the second stage, the audio and the subcarriers are separated from the video signal. The audio and video are then processed (filtered, clamped, de-emphasized) and fed to the monitor or TV through a one-channel modulator.
The Modulator and Monitor
The final stage of satellite television reception, of course, is to get a picture. You can use a standard television set, or you may want to spend the extra money for a high quality color monitor. When you are using a standard TV set, you will need a modulator to feed the signal from the receiver into the appropriate channel. Satellite reception would normally be assigned to an unused channel on a TV set.
C and Ku band - Compatibility and Performance
First, what is Ku-band and what does it stand for ? If you have a satellite system now, most likely it is a C-band system. The designators "C" or "Ku" describe a general frequency band. C-band describes a 3.7 to 4.2 GHz frequency band, while Ku-band describes an 11.7 to 12.2 GHz band. Actually, the designators C and Ku describe a much larger band of frequencies, but we are only interested in a small portion of the total band. Using C or Ku is just a shortcut to describe the frequency band of interest.
Typically, each frequency band is set aside for a certain purpose by international agreement. Some bands are used for point-to-point microwave systems, mobile telephone systems, police frequencies, or satellite broadcast bands. There are other satellite communication bands lower in frequency than our C-band system and higher than the Ku-band systems.
Actually, there are approximately 15 C-band satellites, 17 Ku-band and 13 hybrid C and Ku band satellites in west longitude. A hybrid satellite is one that has both C-band and Ku-band transponders available for use on the same satellite. Before you rush out and buy a Ku-band satellite reception system, you should know the systems.
The first requirement for C and Ku band compatibility is that the receiver must use the same IF for both downconversion systems. The next major difference between C and Ku band is the transponder bandwidth and spacing. C-band uses 40 MHz wide transponders spaced either 20 or 40 MHz apart, center-to-center, depending on whether you are dealing with a 12 or 24 transponder satellite. Ku-band transponders can be almost any width, and spaced just about any distance apart. Some transponders on Ku-band are as narrow as 43 MHz or as wide as 108 MHz, though most are 54 to 72 MHz in width.
Transponder spacing also varies from 61 MHz apart to 80 MHz apart. How do you expect your C-band receiver to handle these varying transponder bandwidths and spacing ? Not very well. To make things a little easier, the video format used on Ku-band is the same as is found on C-band about 32 MHz wide. Thus, if you can get your receiver to tune into the proper transponder, the video and audio will be the same as those found on C-band.
Let's suppose that you now own a Ku-band compatible receiver and you have somehow obtained a Ku-band LNB. What should you do for a feedhorn and antenna, and is your current antenna usable on Ku-band ? The feedhorn is no problem. Much manufacturers offer dual and single band feed systems.
The antenna is a totally different proposition. Obviously, it would be very convenient if your current antenna could be cajoled into working on 12 GHz. I am going out on a limb here to say that most antennas currently in use on C-band will work a little bit on Ku-band. The question is, how much is enough ? A 12 foot mesh antenna provide a good picture on Ku-band though the mesh antennas have low efficiency (25%) on Ku-band. A 6 foot spun antenna too works as well as, or better than that a 12 foot mesh antenna. Solid antennas with multiple sections will really need to be aligned very accurately to operate on Ku-band that mesh antennas.
The feedhorn focal point adjustment of the antenna becomes even more critical on Ku-band, so fine tuning the feedhorn system is a must if you are going to squeeze the last drop of performance out of your antenna system.
Unless you are going to use a separate antenna for each band, tha subject is whether to offset the C or Ku band feed system on a common antenna. All manufactures have gone with centering the C-band feed and offsetting the Ku-band feedhorn.
Considering the difference in wavelength between 4 GHz and 12 GHz, I prefer to either center the Ku-band feed and offset the C-band feed or split the difference. The wavelength at 4 GHz is 3 inches and at 12 GHz is 1 inch. You can see that if you moved the C-band feed six inches to one side of the focal point, you would be only two wavelengths off boresite, while moving the Ku-band feed six inches means you have moved the feed six wavelengths off boresite.
The first major difference at the performance is that the Ku-band satellite can have much more powerful transmissions. Where the C-band downlink power, or EIRP, is 36 to 39 dBW, Ku-band satellites can be as powerful as 50 dBW. The reality is that there are very few satellites on Ku-band that have that much power over the entire country. It is true that some Ku-band satellites have spot beams that concentrate the power into small areas with 50 dBW levels, but the majority of the country will still have only 43 to 45 dBW. This is nothing to sneeze at, but not the high power level that some folks like to talk about.
Antenna gain is the next big difference between C-band and Ku-band systems. If we hold everything constant except frequency, a 6 foot antenna will have 35 dBi gain on C-band and 44.5 dBi gain on Ku-band. Will most six foot C-band antennas have the same percentage of performance on Ku-band as on C-band? Probably not, but depending on the accuracy of the parabolic curve, the performance could be quite acceptable on Ku-band.
The Ku-band satellites are located on the same arc as the C-band satellites, so the distances from earth to the satellites are essentially the same. But because the frequency is so much higher on Ku-band than it is on C-band, the transmitted power path loss for the Ku-band satellites is much higher. The path loss for a C-band signal is -196.5 dB, while Ku-band loses -205.8 dB. So, while we start off with more satellite power, we lose most of it in traveling to the surface of the earth. If we are in the middle of a snowstorn or rain squall, the path loss for Ku-band can go even higher. C-band does not tend to be bothered to any great extent by weather conditions. Therefore, a Ku-band system must have some rain fade margins if we want it to continue to operate in rainy weather.
The last difference is the noise temperature of the LNBs used in Ku-band. The typical C-band LNB noise temperature is 25 degrees Kelvin, while typical Ku-band LNBs have a noise temperature of 65 degrees Kelvin. When this difference in noise temperature is used in G/T calculations, it comes out to a -4.1 dB performance loss on Ku-band.
Installing your Satellite Dish
The location of the dish itself is another decision that has to be made. You can select a site yourself. Print from the TrackingSat software the report with all data relating to Azimuth and Elevation of the dish for the selected satellite. Take your compass and by using the angles from the report, verify if the site is free of terrestrial interference. In other words, there must be no obstructions between the dish site and the satellites in the sky. Trees, telephone lines, clotheslines, electrical wires, radio and television towers, etc. are all possible sources of interference. Once you determines that the location is suitable, you will have to decide on a permanent or portable installation. Unless you fell you will be relocating in the near future or you are living on rental property, a permanent installation in concrete is the better way to go.
Once you have the dish mounted with the LNB attached at feedhorn and all cables (LNB and Polarotor) connected, I recommend that you place the receiver and a portable TV set near the dish for that you see a picture while make the adjusts. The next pass is turn on your equipment (read the receiver documentation first of all).
Set your receiver for the channel that is most likely to have video (consult a satellite TV guide for this or set in a high channel number with video signal). The satellite dish must be aligned with the azimuth magnetic value from TrackingSat report (use the magnetic compass for this) and fix the dish in this position for the time being.
The dish mount has an adjustment for controlling the elevation. Then move this adjustment until the dish is pointing up at the same elevation value showed in TrackingSat report (use a inclinometer for this). The picture may not be completely clear yet.
Make very slight adjustment in azimuth and in elevation until you have got the best picture. Keep this up until no more adjustments are necessary. Your dish should now be aligned and and with a good picture in screen. Look the quality picture in others channels and if necessary repeat the adjustments. Good luck and enjoy of TrackingSat.
