Tuning meter for use with a pulse count FM demodulation circuit

Demodulators – Amplitude modulation demodulator – Having specific distortion – noise or other interference...

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325349, 325455, 329106, 329111, H04B 116

Patent

active

041807774

ABSTRACT:
A tuning meter circuit for use with a pulse count FM demodulator of an FM receiver. The circuitry comprises a limiter circuit for amplitude limiting a frequency modulated input signal to produce a train of pulses the width of which varies in accordance with the frequency modulation of the input signal; a pulse shaping circuit for generating a trigger pulse for each of the pulses of the pulse train; a monostable multivibrator responsive to each trigger pulse for generating a train of pulses of substantially constant width, the number of which per unit time interval varies in accordance with the frequency modulation of the input signal; a low pass filter responsive to the last mentioned pulse train to produce a low frequency signal and thereby demodulate the frequency modulated signal; a difference amplifier also responsive to the last-mentioned pulse train, the difference amplifier having a threshold level at which it changes state; a tuning meter responsive to the direct current component of the output of the difference amplifier; the duty cycle of the monostable multivibrator and the threshold level of the difference amplifier being so related that the tuning indicator indicates the FM receiver is tuned correctly when a signal of exact intermediate frequency is applied to the limiter circuit; and where the monostable multivibrator includes means for varying the duty cycle thereof to compensate for undesired variations in the FM demodulator.

REFERENCES:
patent: 3366894 (1968-01-01), Newcomb
patent: 3471392 (1969-10-01), Axford
patent: 3878430 (1975-01-01), Boltz, Jr.
patent: 3886463 (1975-05-01), Caprio

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