[RFI] Home RFI Hunting

Dave Van Wallaghen dave at w8fgu.com
Thu Sep 13 13:36:01 EDT 2018


Hi all,

I believe this is my first post to this list, but I've been lurking here 
for a number of years.

After reading through Jim's, K9YC excellent RFI-Ham paper numerous times, I 
decided to track down some RFI sources in my home. I listen around 40m 
quite often and there were a number of SMPS signatures and birdies that I 
found annoying. So, using the breaker by breaker method, I was able to 
track down a few sources fairly quickly and eliminate them with a number of 
turns of the power cord through #31 cores. Worked beautifully just like Jim 
outlined.

I then set my sights on a pretty horrible buzzing noise that I always heard 
in the AM broadcast band mostly on the lower end. With my K3 and P3 I found 
the noise was quite wide starting around 380 kHz to around 660 kHz. I 
decided to move my setup upstairs and run off a battery while switching off 
breakers to track the noise. This is where I found out that if I floated 
the rig and antenna, the noise did not show up at all. But if I grounded 
the rig to my AC ground system the noise was horrendous. So far, I've 
tracked this noise to my LCD TV in the living room and my cable modem in 
the basement. The TV is the largest offender and has the widest signature.

I wound the power cable and HDMI cable several turns (13 or so) around a 
couple of #31 cores and it did reduce the noise on the upper freq range 
from 660 kHz down to 580 kHz or so. But what remains is still S9 + 10 at 
the peaks in the remaining range.

10 - 12 years ago, I had my neighbor, who is an electrician, run a couple 
of new circuits in the house. A 15 amp circuit to my living room for just 
my AV equipment and a 20 amp circuit to my shack just for my rigs and 
supporting equipment. Thinking there might be a wiring problem, I began 
opening things up to inspect. For these two circuits he ran a multi-wire 
run (with a few more wires for future expansion) from my panel in garage, 
through metal conduit to a junction box feeding into my basement (about a 
20 foot run). At the junction box, these two circuits run together for 
about 30 feet where they split off to the living room and my shack. While 
he ran separate hots and neutrals for each circuit back to panel, he 
combined the ground wires at the junction box and tied a single ground wire 
back to the panel.

So, my questions are: as the largest portion of this noise comes from my TV 
plugged into the AV circuit, would running separate grounds for my AV and 
shack circuits back to the panel help alleviate some of the noise that I 
find on my shack circuit ground? Or do you think most of it is being 
physically coupled? I would have tried this myself, but while certainly 
doable, it will be a little work to make it happen.

I also read on the Polamar website about using #75 mix Clamp On cores for 
use on frequency ranges down to 200 kHz. Is this something applicable to my 
problem?

I thank you all in advance. I have learned a lot from this list over the 
years and I have learned a lot in the past few weeks as I've begun to clean 
things up in my own back yard. This problem is a little over my head though 
and I didn't want to crawl down any more rat holes until I get further 
direction. Compared to some of the situations I've read here, I didn't 
think my noise was much of an issue until I turned off my breaker panel. I 
had no idea how many noise generators I had in my own home!

Thanks again & 73,
Dave W8FGU






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