[RFI] Rheem AC RFI

[Jim Brown]

On 9/5/2020 3:38 PM, Karin Johnson wrote:
> Now with the new so called “state of the art” system the noise sources
> 
> Are much different.  Eventually I will get this solved.  Just takes a bit
> 
> Of time.  Especially since I know where the source is.
> 

Hi Karin,

The problem with these products is typically NOT the lack of filtering, 
but the failure to treat current paths carrying RF current as 
transmission lines, combined with bonding return conductors to grounds, 
which tends to divide return current between a proper return (the 
transmission line) and the ground path. Example -- decoupling caps 
accomplish that division.

If a transmission line is the only path, forward and return fields 
cancel; when the return divides, cancellation is not only incomplete, 
but the return path is both a large magnetic loop AND and antenna. In 
other words, it's a circuit layout problem, NOT a filtering problem.

There are discussions of this in several tutorials on my web page, one 
written for hams, others for pro audio system designers. Scroll down for 
the pro audio tutorials. I'm retired from designing large audio systems 
for public spaces, and still Vice-Chair of the AES Standards Committee 
WG on EMC. In that world, we run into sources like motors for public 
elevators in performing arts centers. A colleague, also an EMC 
specialist, encountered this at NJPAC.

Also -- the vast majority of RFI is radiated common mode, often on the 
ground conductor (green wire). If the RFI current driving the motors can 
be isolated to a transmission line, a common mode choke tuned to the 
operating frequency is the weapon of choice, and Fair-Rite #31 mix is 
the only good choice for HF. See the "chasing RX noise" app note on my 
website for more specific recommendations.

k9yc.com/publish.htm

73, Jim K9YC