RF MODULATOR

Posted on Feb 5, 2014

First section of free-running 7413 Schmitt-trigger oscillator runs at one-third of desired TV-channel carrier frequency (about 20 MHz for channel3) and drives buffer section whose output is square wave at oscillator fundamental. Q1 modulates RF output by varying effective supply voltage to IC. Since standard video is 1 V P-P, modulation depth is a

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bout 20% with 5-V supply. Capacitive connection is made to TV set, using short lengths of 300-ohm line after removing regular antenna leads from set used as experimental display terminal for microprocessor. R1 determines frequency of oscillation; ad just for best reception. -W, Banks, The Waterloo RF Modulator, BYTE, Jan. 1978, p94.

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