Low Frequency CTCSS PL Sub-Tone Audio Oscillator

Hello there and welcome,

The lf555afosc1.pdf file download is the diagram (with notations) of Sub-Tone (CTCSS or "PL") Oscillator, made with the famous 555 timer IC set up for astable-multivibrator operation. The values shown place the tone range near the center of the standard CTCSS Sub-Tone Range. You can build this circuit very small, about postage stamp size. Connection is made to the "high side" of your transmitters deviation pot (not at the mic input).
The comparator operation of the 555 provides a measure of stability against voltage fluctuations. You can adjust the tone range with slight value changes in the .1uf capacitor. This circuit also makes a nice DC Clock Pulse Generator by taking the output as noted. The file is in Adobe PDF format, but you can right click your mouse and save the gif file picture (shown just above) from this description page.


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