Yes. W3LPL alerted us to this at least 4 years ago, identifying
switch-mode power supplies (SMPS) and antenna rotators as common culprits.
EVERY active ham should go on a search out and destroy mission for
switch mode power supplies, replacing them with linear supplies. My
junkbox contains a LOT of vintage linear wall warts and line lunps. When
finding an SMPS built into a product like a TV or refrigerator, wind
ferrite chokes tuned to the noise frequencies on every cable attached to
the product. Frank advised bonding around rotators, and many of us have
been doing that.
None of this, of course, helps with the noise generators in neighboring
homes and businesses.
73, Jim K9YC
On 12/22/2021 10:41 AM, Don Kirk wrote:
A month ago I had never dealt with stubs or PIM (passive intermodulation
distortion) and only had limited experience working with active IMD in
regards to overdriving mixers, nevertheless I now know much more about
these subjects than I did a month ago.
The biggest thing we discovered is that the Raspy sound everyone talks
about when listening to their transmitter up on the harmonic band most of
the time is probably the result of mixing with 60 hertz, and the only way
we were able to figure this out was to use my cheap laptop based SDR
receiver zoomed in on the RF spectrum display while using the minimum RBW
(resolution bandwidth) available which in my case was 7.6 Hz.
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