Published:2009/7/3 3:00:00 Author:May | From:SeekIC
Relay is energized when carrier is present in FM receiver, to activate transmitter for repeater applications or turn on tape recorders, alarms, or other devices.Will work with either solid-state or tube-type receivers. Inverting (minus) input of opamp is connected directly to collector of audio preamp transistor or any other point having voltage change between signal and nosignal. If voltage change is in wrong direction, reverse leads to opamp input. Use 1K pot to set reference voltage so relay trips reliably on incoming signal.Relay can be reed-type drawing less than 75 mA.-S. Uhrig, The 5 Minute C0R, 73 Magazine, Dec. 1976, p 152-153.
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