[RFI] Request For Comment (2nd Post)

[Jim Brown]

On 10/27/2020 4:28 PM, Karin Johnson wrote:
> I received a reply from Don Kirk, WD8DSB and Dave Eckhardt W0LEV.
> First off a big thank you for both replies.  I do have a commercial
> Power line filter, which I did not mention in the Power Point documents
> because I wasn't trying to propose solutions just yet.

Power line filters are rarely a solution to EMC issues when the problem 
equipment fails to follow proper bonding practices for wiring leaving 
it. Noise is often radiated as a common mode signal on that wiring, and 
what we call common mode is not what the EMC world calls common mode. 
What we call common mode, and what radiates, is the algebraic SUM of the 
noise current on all the conductors in a cable.

Line filters operate on the common mode current between phase and 
neutral, and on differential current between phase and ground and 
neutral and ground. The noise current is often on the green wire, 
because it is improperly terminated.

These filters are only effective when their case has a very short bond 
to the equipment chassis; otherwise, current on the green wire goes 
right past the filter and radiates. The best solution for this problem 
is a common mode choke formed by winding multiple turns of the cable 
around a Fair-Rite #31 clamp-on or toroid, with the turns wound in a 
disciplined manner, with no crossovers.

There's a lot of tutorial content on my website about chasing noise, 
including k9yc.com/RFI-Ham.pdf and k9yc.com/KillingReceiveNoise.pdf

k9yc.com/2018Cookbook.pdf is the result of nearly two years in my lab 
developing transmitting chokes for legal limit operation on the HF 
bands. Its recommendations can be used as a starting point for wiring of 
similar dimensions. http://k9yc.com/ChokesVHF.pdf includes 
recommendations for VHF and low UHF bands.

73, Jim K9YC