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any radio experts on here?

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welshman:
 when doing silly things with a transformer, i noticed a different of output frequency. any ideas what is going on here?

rossw:

--- Quote from: welshman on August 01, 2021, 10:27:32 am --- when doing silly things with a transformer, i noticed a different of output frequency. any ideas what is going on here?

--- End quote ---

What are you measuring it with? A DMM or simple frequency meter will be reading either the highest or lowest frequency (depending on its sampling technique), or strongest (highest amplitude), or some mix of the above.

How are you generating the different frequencies? Are they phase-locked? Are they sinusoidal?

Run two or more frequencies into a transformer and you've just made a basic mixer. Depending on the inputs, you should get the sum and the difference. So put 150Hz and 200Hz in, and you will get 150 and 200 out, but in addition you'll get 350 (the sum) and 50 (the difference). You'll likely also then get at decreasing amplitudes, the sums and differences between the the new outputs too, so   350+/-50, and those products.
You have 3 lots of input, so you'll be seeing sum/diff of a+/-b, a+/-c and b+/-c, and all the resulting mixing products.

You are showing that you have an open-connection on one of your secondary windings, so you are purely measuring a voltage, there is no practical power coming out (because the source impedance is virtually infinite). Thus, apart from the mixing occurring in the transformer, you are also adding capacitive coupling between primary (primaries) and secondaries.

Add the non-linear transfer characteristics of the transformer as a function of frequency, and you could have anything on the output!

If you have (access to) a decent DSO, have a look at the output in the frequency domain (as opposed to time domain usually used). I think you'll suddenly see all these spikes in a graphical form that'll be obvious.

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