Using The Bessel Null Method To Verify FM Deviation Measurements

By Dave Engelder, Agilent Technologies, Inc.

Frequency modulation (FM) has been used in various radio frequency (RF) transmitters and receivers for decades. While more complex forms of modulation have been developed, analog FM is still in widespread use for walkie-talkies, police/fire/military radios, FM broadcast radio, telemetry, and other systems. Consequently, RF and microwave test equipment -- signal generators (sig gen), signal analyzers, and modulation analyzers -- often provide features to generate or measure FM.

FM modulates the RF carrier frequency. The frequency deviation (f_DEV) -- the peak frequency change, above and below the unmodulated carrier frequency – is a critical parameter of FM.