[600MRG] RFI identified

[Tom W8JI]

Having had to clean up multiple SMPS for commercial applications and fix 
RFI around here from multiple things, my view is the following.

The enclosure and wiring of the refrigerator is far too small and 
confined to be much of a radiator. The refrigerator is also a poor 
"counterpoise" for injecting a whole lot of common mode out the cord, 
although very close that could be an issue.

Usually the problem will be differential mode excitation of power cord 
wires. The wires then act like two or three wire leaky transmission line 
and carry or distribute that noise as it gradually radiates.

Almost every SMPS I have cleaned up has been from making every conductor 
leave at the same noise potential. The bulk of the filtering is with 
bypass capacitors that hold the exiting leads all at the same noise 
potential. This is usually much more effective than series chokes, 
although individual chokes in each line (which could be beads) can 
"help" the capacitors make everything the same potential.

The problem on 630M is having low enough capacitive reactance to hold 
the exiting conductors all near the same potential for 630M noise 
without having enough current through capacitors to nip you or cause 
other problems on 60 Hz, even though that is about an 8000:1 difference. 
Any capacitor also should be VDE/UL/CSA rated for line bypass.

With a three wire cord I would bypass the hot to neutral, then the 
neutral to safety ground. This is the safest way.

I think the suggestion of a good commercial line filter is a good one, 
they usually tie all the conductors together for differential noise. 
Otherwise use a few bypass capacitors and see what happens.

73 Tom



>> On 1/3/2025 11:47 AM, Paul N1BUG FN55mf wrote:
>>>
>>> Early this morning I found it the culprit. It is my refrigerator!
>>> Perhaps a line filter will help, although my luck is rarely that good.
>>>
>>> I'm still chasing one, possibly two serious RFI sources affecting 2200m
>>> but won't go into that here.
>>>
>>> 73,
>>> Paul N1BUG

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