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06 Feb 2018

Noise From My Receiver

I built an FM receiver for NOAA Weather Radio awhile back. It works pretty well but there's an annoying howl out of the speaker when I turn up the volume about half way or so and up to maximum. The receiver is housed in an aluminum enclosure. The noise seems to go away, almost, when I remove the metal cover and returns when I put it back on. I have a theory, but I'm not sure, as to what's causing the problem.
The receiver is PLL synthesized using a discrete transistor VCO that undoubtedly generates excessive RF in the enclosure. I think the RF is riding into the circuitry on the power supply lines and causing this strange problem that I used to think was a audio problem. It would explain why the noise pretty much goes away when the cover is removed and returns when the cover replaced. The RF is more concentrated in the enclosure when the cover is on...right?
If it's RF interference, would something as simple as placing EMI filters on the power supply lines to critical circuitry solve the problem?
Does anyone out there have experience with this problem?

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