[RFI] Finally located my RFI

[Jim Brown]

On 6/19/2024 6:08 PM, David Eckhardt wrote:
> Dave, install ferrites on BOTH the input AND output.

I think you mean on both the mains power side and the control lines. 
Strongly agree. BUT -- it's going to take more than single-turn clamps 
that peak around 140 MHz to make much of dent between 17 and 29 MHz.

Couple of thoughts. First, dedicated twisted pair for the current 
carrying conductors.

Second, look for anything that would divide some of the return current 
with a random ground path, like building structure. The logic -- when 
forward and return current can form a transmission line, their fields 
cancel as long as they're equal, (and are confined to the narrow region 
between the conductors that make up the line), AND the transmission line 
is a much lower impedance than the wider random path, so all the current 
goes to it. But if their is no transmission line, the return current in 
that random path creates a large magnetic field, and also radiates as an 
antenna.

Henry Ott got me to see this light years ago, and I got the same 
analysis with an EMC engineer I encountered when he showed up as a 
friend of the client at a church in Dayton for which I was designing a 
sound system. The first thing he said after I'd outlined the issue was 
"twisted pair."

73, Jim K9YC