Electronics > RF, Microwave, Ham Radio

strange static or microphonic radio squeal


I'm hearing an interesting phenomenon with tonight's low humidity, that seems to involve microphonics, when tuning my simple preselector, it must involve static electricity-

I've read that direct conversion style (softrock, etc) receivers can have microphonic issues, but Ive never experienced it quite like just now.

So, I've been fooling around with preselectors and the current configuration basically only uses a single toroid and a single variable cap, the input and output and a parallel circuit involving the cap are all windings around the same toroid. the input and output both have 2 turns through the T50-2 toroid and the winding that is going to the cap has around ten turns. So i am tuning around trying to find the peak using the regular band noise to see where it resonates best when it starts making this very strange squealing sound, listening to it I realized that it must be static discharge.. I dont think its where the RF peak is, its somewhere else.

Also, the radio was behaving as it would when there is DC getting in there with the noise floor going way up and way down, semi randomly.

The radio is a softrock and looking at it closely and probing around with a toothpick, I can tell that the board is also exhibiting some kind of microphonic activity, but only when the the preselector is tuned in a certain way does it elicit this behavior.

See attached screenshot - it was taken while both the microphonics and the weird squealing were occurring.  If you look closely, you can see some strange fuzzy/moire activity superimposed onto the "center discontinuity".. that seems to be caused by the static discharge or whatever it is. (the antenna does have a DC path to ground)

Anyway, I thought it was interesting.  It must be in part because of the winter dryness.


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