Amplitude modulation is one way to carry information on a carrier, such as a
radio signal. Another way is FM (Frequency Modulation). While FM offers greater
clarity for audio, and the higher frequencies that FM use offer a wider
bandwidth, allowing for more information to be transmitted, one application
where FM and digital are not suitable are Aviation communication, which to this
day still use AM analogue. This is because weaker signals can be heard over
stronger, closer ones with AM, allowing for emergency transmissions to have
more chance of being heard over other traffic. Also, AM uses a narrower
bandwidth than FM, allowing more users in a smaller space. This is important for
the lower frequencies of Radio, where space is at a premium (ie shortwave
bands).
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