Imagine there is communication satellite on geostationary orbite. It transmits signal in a defocused beam, "illuminating" whole Earth hemisphere it's floating over. For example, signal is amplitude-modulated with 10GHz carrier frequency.

What if satellite transmitter power is very, very low, like 25mW, is it possible to receive this signal on Earth with temporal resolution high enough for high-speed data transfers by just using sufficiently large or huge satellite antenna dish; or will noise get amplified too and this approach will be fruitless?

What if two identical satellites are transferring signals of their own, and floating close enough (say, 1° away) to each other to be visible at once from surface, is this possible to receive separate signals from both satellites, or interfence will cause total mess? Are there ways to overcome this?


1 Answer 1


In general a larger antenna gives a larger signal at the input of the receiver. Since the receiver is not noise-free the signal to noise ratio is increased, resulting in better reception. The antenna itself is not noise-free (unless strongly cooled down) but this is usually of minor importance.

Actually amplitude modulation is not so much used, rather a form of pulse modulation is common. Clever techniques, involving phase-locking methodes, are used to obtain better reception. Often the signal is very narrow band and one has to worry about Doppler shifts. The above techniques can cope with this.

As to your last question, if the satellites emit at different frequencies there should be no problem. It is not practible or even impossible to construct antennas with sufficient directional properties to distinguish the signals of the satellites.


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