[RFI] DFing intermittent connection

[AA5CT]

"Materials too far apart in the Galvanic Series."

This means no steel against Aluminum (or brass in my experience).

There used to be a nice little chart/diagram in the old DB Products catalog
(land mobile and cellular antennas) covering this subject.

And Galvanized (Zinc) steel is okay against Aluminum. With time though, the Zinc 
can wear away.

My experience with a full duplex low band (50 MHz) system showed that an
antenna with a plain steel (even cleaned so it shined) mounting bracket with 
aluminum radials bolted to it and a brass assembly holding the active element 
and RF connector produced prodigious amounts of "white noise" when excited
with 50 Watts of RF. 

The 'solution' was a 6m Ringo that was "quiet", generated NO white noise
owing to its all aluminum construction, no differing materials. The antenna was
bolted to a Galvanized steel mast.

de AA5CT Jim

-------------------------------------------






On Wednesday, August 11, 2021, 1:35:42 PM GMT-5, Jim Brown <jim at audiosystemsgroup.com> wrote: 





On 8/11/2021 11:26 AM, Steve London wrote:
> It's nice to
> have a name for this: PIM (passive intermod).

W3LPL was the first to alert me to this mechanism as a cause of 
harmonics, with rotators as a common place on towers where it occurs. 
The fix is to bond around it. He also observed that it commonly occurs 
in an SMPS, which could be anywhere. The fix is to search and destroy. :)

73, Jim K9YC

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