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?