[RFI] Tower/Antenna Reradiation

Jim Brown jim at audiosystemsgroup.com
Wed Dec 22 15:16:37 EST 2021


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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