298 Chapter 5
Concepts
Analog Modulation Concepts
FM Deviation Measurement Concepts
Purpose
FM Deviation measures the frequency deviation of the tuned input signal. The
demodulation signal’s frequency and distortion can also be measured.
Measurement Technique
Frequency deviation is the maximum frequency excursion from the average carrier
frequency. The FM on the IF is demodulated by a frequency discriminator. The
amplitude of the discriminator’s output is proportional to the frequency deviation.
The demodulated signal is filtered, audio detected, and displayed as Hz deviation.
FM de-emphasis equalization can be inserted ahead of the audio detectors, and the
demodulated FM signal always passes through the FM de-emphasis “network”.
PM Deviation Measurement Concepts
Purpose
PM Deviation measures the phase deviation of the tuned input signal.
Measurement Technique
Phase deviation is the maximum phase excursion from the average carrier phase.
Phase and frequency have the relationship that phase is the integral of the
frequency or frequency is the derivative of the phase. The PM on the IF is first
demodulated by a frequency discriminator. The amplitude of the discriminator’s
output is proportional to the frequency deviation. The demodulated signal is
filtered and passed through an integrator, which extracts the phase information.
The integrator’s output is detected and displayed as phase deviation in radians.
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