The RFI Chase – Getting 20 Meters Back

For quite a while now I have been putting up with heavy RFI on 20 Meters in my shack and I have been really thinking it’s a neighborhood problem more than an in-home one. It looked like this on my waterfall:

Flex Smart SDR 20 Meter Band View

I was getting ready to call the power company and ask them to come fix the transformer outside my house. I based this on the fact that as I turned the antenna in a different direction, the closer I got to pointing at the transformer, the stronger the RFI became. Here is my chart.

Home made polar coordinate chart showing peak signal strength, along with a second measurement

So, step 1 was to identify the problem and a likely suspect. After reading a bunch of articles on RFI chasing, I wanted to 100% eliminate the chance that it could be something in the house, because if you look at the path between the Antenna and the Transformer, it goes over the house.

Antenna to Transformer

On to step 2 then, eliminate the house. So on Friday I set up one of my radios on battery, tuned to the peak of the signal and one by one turned off every breaker in the house and wouldn’t you know it went away!

So, one by one, I powered the breakers back up, starting with areas where I have a lot of electronics, including my shack, which is in that line. I needed to leave 30 seconds between each power up so all the devices would get to normal “radiating” state. The shack was clear, but when I got to the Living Room – there it was.

Step 3 was figure out what the offending device was. I had experience in the past with an ethernet switch causing interference. So I disconnected that and powered up the rest of the media center. All quiet. Here’s what happened to the waterfall when the switch was plugged in.

Waterfall showing RFI appearance when ethernet switch was powered on.

Gotcha! Because that switch was in heavy use, I wasn’t able to replace it immediately, but today was the day. I bought a smaller switch that was powered over POE instead of a brick and here’s what the waterfall looked like when that old switch was disconnected for the last time.

Waterfall of 20 Meters (top) when ethernet switch was disconnected for the final time.

So, a couple of lessons for me:
1) Troubleshooting using the directional antenna was a time saver because I knew where to focus my energy.
2) Don’t assume it’s outside the house when there are other potential issues in the path.
3) The scientific method of change one thing only and then go on REALLY shined in this test.

This didn’t solve it all. There is more noise to be chased, but the largest offender is no more, and that opens up a great deal more of 20 meters for me, which makes me happy.

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