CALL_ALERT

Published:2009/7/4 20:10:00 Author:May | From:SeekIC

Developed to trigger relay when signal arrives at squelch tube in GE Progress Line 2-meter FM receiver. Relay is held energized about 2 s, determined by C1-R1, then deenergized for at least 25 s. Used for flashing red spotlight in room that is too noisy for hearing bell or buzzer. Circuit is easily adapted for any other FM receiver having squelch stage. Control circuit responds to small change in voltage at cathode of squelch tube. With no carrier present, tube conducts and places positive voltage at face of Q1, making it conduct and turn off Q2.When carrier arrives, Q1, restores bias to Q2, turning on relay. Connection to push-to-talk switch keeps lamp from flashing during transmission.-L. Waggoner, The WA0QPM Call Alert, CQ, May 1971, p 48-49



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