Frequency Modulation (FM) (FM)

A modulation method in which the instantaneous frequency of a carrier varies in accordance with the information signal.

Marine VHF radiotelephony uses frequency modulation with channel spacing and deviation defined by the applicable standards. FM can reject amplitude noise effectively but still requires adequate signal strength and compatible receiver settings.

It does not describe digital selective calling, which sends encoded digital information using a specified modulation. Users must select the correct channel, mode and bandwidth.