[600MRG] RFI identified

[Brian Pease]

Let us know if it works and where you bought it.

I have an active loop and VPA 200 ft away, but they are too close to 
power lines. A beverage starts 400 back and is clean except for wind 
farm inverters ~1 mile away on 630m, which appears to be direct 
radiation from the towers.


On 1/4/2025 7:29 AM, Paul N1BUG FN55mf wrote:
> Hi Tom,
>
> Thanks for sharing your knowledge and experience.
>
> I am going to try a commercial filter. I spent some time looking and
> found very few in stock anywhere that offer more than a couple dB at 137
> kHz which is also affected and of interest. I ended up ordering one that
> claims 39 dB common mode, 70 dB differential mode at 150 kHz (in a 50
> ohm circuit), 42/70 at 500 kHz. I will give that a try.
>
> The LF/MF receive antenna is about 200 feet from the refrigerator but
> there is electrical wiring in a detached shed about 120 feet from the
> antenna. I wish I had the space to move all antennas further away.
>
> Paul, N1BUG
>
>
>
> On 1/3/2025 9:41 PM, Tom W8JI wrote:
>> 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
>>
>
> ______________________________________________________________
> 600MRG mailing list
> Home: http://mailman.qth.net/mailman/listinfo/600mrg
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:600MRG at mailman.qth.net
>
> This list hosted by: https://www.qsl.net
> Please help support this email list: https://www.qsl.net/donate.html