# Transmitters

### Comparison of modulation methods

AM is not now commonly used; operation is in Class C but efficiency is low due to the audio power required.

FM is widely used for hand-held and mobile operation at VHF and UHF. It gives good coverage over a relatively small area (greater when used via a repeater) but has little use at HF.

SSB is the most effective system from the point of view of bandwidth and power efficiency, and is less adversely affected by disturbances inherent in ionospheric propagation.

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