91.5Hz Tone Generator
Some notes on the generator
- Perhaps a disclaimer note should be inserted by EMDRC with suitable words to the effect that its application is at the user’s risk.
- The schematic provided gives a way to generate a low frequency tone.
- The output could be, say, inserted after the microphone preamplifier via a high value resistor, perhaps >20k. The generator output would be adjusted to just access the repeater.
- The schematic shows an AF transformer for isolation purposes. A direct output without the transformer may be more convenient. The 220n capacitor on the transformer primary was found by experiment to clean up the output waveform a bit more. The stepdown transformer turns ratio is not critical.
- For accuracy, the frequency or waveform period needs to be measured. The 10 turn tuning potentiometer makes adjustments easier than a skeleton preset!
- Not tried, but two 741 ICs could be used instead of the LM358.
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