With FM, the carrier frequency is modulated by the audio signal, with the transmitter power remaining constant. FM typically produces better quality signals than AM when the received signal is strong, but worse quality under poor reception conditions. It is rarely used on HF frequencies, with the exception of CB operators in certain countries, amateur radio operators using the FM in the 10 meter band and land mobile radio users operating on a small number of channelized frequencies in the 25 to 30 MHz range.
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