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How a Satellite TV Antenna Works
Practically all broadcast systems use antennas to transmit and receive radio signals. These antennas are based on single metal pole to which the carrier signal is sent through a cable. First letís talk about how this most simple type of antenna works:
A Pole antenna basically consists of one metal pole that transmits it signals around it as if it was the center of a sphere. In all directions the transmitted signal has the same power. The length of the antenna is determined by the frequency of the transmitted signal.
Radio waves, like light waves, always travel at the same speed, which is about 186.000 miles (300.000 km) per second. One wave length is determined by the frequency of the signal by the following formula:
Wavelength = speed of light / frequency
This results in higher frequencies having shorter wavelengths. A pole antenna doesnít have to have the length of a complete antenna but can also have a length of about Ĺ , 1/8, or 1/16 of the wave length. This is done mostly for practical purposes (shorter antennas). Wave lengths for pole antennas can go as high as 1 to 2 Giga Hertz. A cell phone for instance works at frequencies of 950 Mega Hertz which is almost 1 Giga Hertz.
Satellite TV or Parabolic Antenna
A satellite TV Antenna or parabolic antenna works on the same principle. The frequencies used by satellite transmissions are of much higher frequencies; 2 Giga Hertz or higher. Wavelengths get so short at these frequencies that it is not possible anymore to transmit using a pole antenna and transmit in all directions. The power needed would be very high because high frequencies are subject to much more resistance from the atmosphere.
Bundling all the transmitted power into a beam improves the power transmitted in one direction by a huge factor. Depending on the distance between the transmitter and the receiver the amplification compared to a normal pole antenna can be as high as 40 to 50 dB (which is as much as 10.000 to 100.000 times amplification).
In reality the beam is not completely straight, but gets wider over the distance. The angle is small, but in case of an antenna on a satellite that transmits all over the USA the angle is actually a little bigger so that the whole USA is covered.
The antenna at your roof or in your garden is pointed at the satellite and receives the signal and does the same thing; it bundles the radio waves into a point, thus amplifying the radio signal with 40 to 50 dB. (see illustration below).
Amplification in the whole path is extremely big. The transmitting antenna amplifies, the receiving antenna amplifies, the transmitter it self amplifies, and the receiver itself also amplifies the signal. A total amplification of over 120 dB (over 1.000.000.000.000 times) is necessary because the atmosphere and also the long distance just decrease the signal power a lot.
By Gary Davis
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