FREQUENCY MODULATION - INDIRECT METHOD

Transmitters and Receivers Glossary

Transmitters and Receivers — Frequency Modulation - Indirect Method

Information on Frequency Modulation - Indirect Method

Improved frequency stability can be provided by the indirect method of frequency modulation (FM), which is able to use a crystal LO. In this technique a phase modulated (PM) signal is produced and modified to be an FM signal. The phase deviation of an FM signal is proportional to the amplitude of the modulating signal and inversely proportional to the modulating frequency. The phase deviation of a PM signal is proportional to the modulating-signal voltage only. These relationships mean that if the modulating signal is integrated before it is used to phase-modulate a carrier, an FM waveform is obtained.

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