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Old 26th May 2022, 7:27 pm   #55
Radio Wrangler
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Join Date: Mar 2012
Location: Fife, Scotland, UK.
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Default Re: 6-gang FM stereo tuner heads

Oscillators are interesting beasties. Their power demands are not linear and not resistive. Start/stop phenomena can cause hysteresis and they can exhibit a negative resistance function. In other words, unless you've been careful with their HT feed decoupling, the little beggers can superimpose a low frequency relaxation oscillation on top of their RF oscillation. If you can trigger your scope on the LF component, you'll see the RF component turning on and off. This has long been known about and has the name 'Squegging'. It works the same way as the old neon bulb + capacitor + resistor oscillator, only with the RF oscillator playing the part of the neon.

There are some other possibilities, but this is the one to check first.

David
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