A satellite television system will expand the communications capabilities far beyond the horizon. TV viewers longer will be bound to the limitations imposed by conventional broadcast or local cable programming. With a satellite antenna a viewer 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 country.

The variety of programs that are presently available will astound the users. There are much channels of regularly scheduled programming and many channels that carry occasionally scheduled programs. Movie channels, sports channels, educational, news, spiritual, network, super stations, music, health, children and adult television programs are all beamed into user’s backyard.

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 are:

• 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, undersea cables, and earthbound microwave relay stations

:: 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.

:: Satellite TV System

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. There are two major freq bands allocated for satellite communication; C-Band and KU Band. Section 3 gives broader info about these bands. In order o understand covering areas of the satellites followings needed to be known;

Boresight Point: 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.

Effective Isitropic Radiated Power (EIRP): 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. 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.

Footprint: 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. See Appendix 5 for the footprint figures.

C Band: The uplink frequencies ranged from 5925 to 6425 MHz.  The downlink frequencies ranged from 3700 to 4200 MHz, providing 500 MHz of bandwidth in each direction. This freq reigion is overlaps with terrestrial microwave communication systems.. This stuation causes interference between C-Band and terrestrial microwave communication systems. Since these terrestrial systems existed prior to the development of satellite communication systems, the newer satellite systems must not interfere with the terrestrial systems. Therefore, the EIRP is limited to a level so that there is no interference from the satellite with the terrestrial system.  Also, the locations of the uplink earth-stations need to be restricted to prevent interference with terrestrial microwave communication systems.

Ku-band: The downlink frequencies are 11.7 to 12.7 GHz, and the uplink frequencies are 14.0 to 14.5 GHz. The Ku-band frequency region was selected in the 1970s for the exclusive use by satellite communication systems, thereby eliminating the problem of interference with terrestrial systems. The Ku-band frequency region allows increased EIRP levels from the satellite and significantly smaller earth-station antennas for the same gain and beamwidth as the C-band antennas.

Also, Ku-band uplinks can operate from any location and can be highly mobile.  These capabilities have made possible the use of live television coverage of both news and sports events. Small Ku-band uplink antennas can fit into suitcases and travel with new correspondents to any location on the earth.

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

:: 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.

The video format used on Ku-band is the same as is on C-band - about 32 MHz wide

KU Band transmits more power than C band systems. Where the C-band downlink power (EIRP), is 36 to 39 dBW, Ku-band satellites can be as powerful as 50 dBW. Some Ku-band satellites have spot beams that concentrate the power into small areas with 50 dBW levels, but the majority of the US will still have only 43 to 45 dBW.  See the figure in the Appendix  5 for the footprints.

Ku-band permits the use of smaller antennas than at C-band.  But this is only because the satellite EIRP at Ku-band is typically about 9.5 dB higher than at C-band, which exactly compensates the higher free space loss,

20 log(12 GHz/4 GHz) = 9.5 dB.

Thus, the power received by an earth station antenna is the same for antennas of equal gain.  However, since antenna gain is proportional to the square of the frequency, at Ku-band a much smaller antenna can be used to achieve the same gain.

Antenna gain is the next big difference between C-band and Ku-band systems. Under the same conditions a 6 foot C Band antenna will have 35 dBi gain and the size of antenna will have 44.5 dBi gain on Ku-band. Reader should be aware that 6 food Ku-band antenna is an assumption to give an idea about the gain. Ku-Ban antennas are much smaller than this size ( i.e 76 cm)

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. The transmitted power path loss for the Ku-band satellites is much higher than C Bad, because of the much higher frequency on Ku-band. The path loss for a C-band signal is -196.5 dB, while Ku-band loses -205.8 dB. So, under the severe weather conditions line heavy rain and snow path loss for Ku-band goes much higher than above given figure. Ku-band systems therefore have rain fade margins.

:: Noise Temperature

The 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