SQUELCHABLE_AMPLIFIER

Published:2009/6/30 2:05:00 Author:May | From:SeekIC

Circuit designed for portable FM scanners and two-way walkietalkie radios can be tumed off by noise or by control signal to minimize battery drain. When squelched, LM388 opamp-transistor-diode anay draws only 0.8 mA from 7.5-V supply.Diodes rectify noise from Iimiter or discriminator of receiver, producing direct current that tums on Q1 and thereby clamps opamp off. Voltage gain is 20 to 200, depending on value used for R1. Power output without squelch is about 0.5 W for 8-ohm loudspeaker.- Audio Hand-book. National Semiconductor, Santa Clara, CA, 1977, p 4.37-4-41.



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