455_kHz_FREQUENCY_MODULATED

Published:2009/7/21 21:03:00 Author:Jessie | From:SeekIC

Can be used to align IF amplifier and quadrature detector of FM receivers. Unit is stable and provides ample deviation for amateur receivers. Uses 8038 function generator and 741 opamp connected as audio oscillator to provide about 1000-Hz modulating voltage. Includes deviation control R1, output level control R2, and carrier frequency control R3. Adjust 500-ohm pot between pins 4 and 5 of 8038 for clean sine-wave output on CRO. Adjust R3 to give 455 kHz as measured by meter or frequency counter. To check audio oscillator, connect AC voltmeter or CRO across R1, which should have clean 1000Hz sine wave of several hundred millivolts. Transformer in power supply can be two separate 12.6-V units with primaries in parallel and secondaries in series.-J. C. Chapel, Build This FM Signal Generator, 73Magazine, Jan. 1978, p 154-155.



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