[RFI] RFI LG Refrig Corcom filter and #31 core

[Jim Brown]

On 9/29/2021 5:04 PM, Don Kirk wrote:
> Hi Jim,
> 
> Looking at your published plots, it looks like there would not be much 
> difference on 10 meters between #43 and #31 material for the common mode 
> choke.  Do you agree?

No. I would stick with #31, and use the recommendations in the 2018 
Cookbook for TX chokes for comparable size cable as a starting point. If 
the problem is only on 10M, I'd try 4 turns through a clamp-on, paying 
careful attention to avoid crossovers. If the noise goes much lower, 
probably one more turn.


 > The case of the commercial filters were not mounted directly to the case
 > of the fridge, but the ground wire from the fridge power cord was
 > connected to the case of the commercial line filter, and the case of the
 > commercial filter then had a wire connected to it going out toward the
 > wall outlet ground via the power cord, so the ground wire from the
 > fridge was a continuous connection to the commercial filter case and
 > then from the commercial filter case to toward outlet ground.  All power
 > cords used were 3 wire (line, neutral, and ground).

What you did might be sufficient for LF, but we're talking 30MHz. That 
filter needs a VERY short bond to the chassis of the fridge that runs 
tightly with the AC cable from the fridge. If that's not done right, 
that wiring can radiate, because it forms a loop. When run tightly 
together, the conductors form a transmission line, and/or act as a 
single wire.

Think of it this way -- done correctly, the Corcom (or Delta) bypasses 
phase and neutral to the chassis, like a feed-through cap, so the RF 
can't exit the box via the line cord. As one of my best my EE profs said 
it years ago for emphasis, "zero length leads."

On 9/29/2021 4:09 PM, Gary Johnson wrote:
 > For best results, the Corcom filter should be bonded directly to the 
chassis of the offending equipment. That may mean cutting the cord very 
short, which we did on the UPS. Then the CM choke is placed on the cord 
right nearby. If these filters were in a nice external box with 
connectors on it, the long untreated power cord might still be enough of 
an antenna to radiate plenty of RFI.

Agreed.

73, Jim K9YC