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Transmission

The satellites typcially transmit at only a few watts power and at a frequency of 430 MHz. UOSAT 2 is an early satellite which transmitted using audio frequency shift keying. It added an audible tone of 1200 Hz (i.e. an analogue sound wave) to the carrier wave. Then it shifted this sound wave up and down to represent the 1s and 0s of the digital code. Anyone picking up the signal from UOSAT 2 would be able to hear this tone as is warbled up and down. In fact you might even hear the same thing from your own modem attached to your computer at home. Modern satellites use such a high frequency (10000Hz) that all you hear is a hiss.

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