Squelch circuit with variable squelch tail and variable hysteresis

The period of time that the squelch circuit maintains a radio receiver's audio amplifier active after the signal strength of a received carrier fades below a threshold level is inversely proportional to the strength of the received carrier immediately before the fade. This threshold level is al...

Full description

Saved in:
Bibliographic Details
Main Author KEHLER, JR.; WALTER H
Format Patent
LanguageEnglish
Published 05.02.1991
Subjects
BASIC ELECTRONIC CIRCUITRY
CONTROL OF AMPLIFICATION
ELECTRIC COMMUNICATION TECHNIQUE
ELECTRICITY
TRANSMISSION
Online AccessGet full text

Cover

More Information
Summary:The period of time that the squelch circuit maintains a radio receiver's audio amplifier active after the signal strength of a received carrier fades below a threshold level is inversely proportional to the strength of the received carrier immediately before the fade. This threshold level is also variable. If, immediately before the fade, the received signal strength exceeds a predetermined trigger level (Vtrg) the threshold level is raised. A buffer amplifier (102) charges a capacitor (C) to a voltage which is proportional to the strength of a received carrier. If the carrier fades below a threshold (Vth2 or Vth3, the buffer is disabled and the capacitor slowly discharges through a resistor (R). When the voltage at the capacitor crosses a reference voltage (Vref1) the output of a comparator (104) switches, thereby deactivating the receiver's audio amplifier. If the voltage at the buffer output is within a specified range, a feedback control circuit (112) switches a variable hysteresis feedback circuit (110) such that the negative-going threshold of the comparator (106) is switched from one threshold level (Vth2) to another (Vth3).
Bibliography:Application Number: US19880141853