What you can really do with 1W
RFI Hunters VIII – Resolution!!!

RF Hunters VII – We close in!

Through the search phase of this quest, the RFI was clearly radiating from the power lines. Therefore, I called up the local utility company and filed a trouble ticket for RF interference from the power lines.

The utility company opened a trouble ticket and told me I would get a call back. Sure enough, well within the period they had advised, I got a call back from one of their RFI specialists and we made an appointment to meet.

Happily, the day of the appointment was dry AND the RFI was present! I had nightmares the previous night that they would show up and the RFI would be gone – fortunately Murphy was on vacation this time!

After a discussion (and demonstration) about the RFI, we headed up the road to where I had identified the suspect pole. We confirmed the suspect pole by using a receiver and my small tuned loop antenna that I had built for close in work.

The small loop is a re-purposed AM antenna from a long discarded stereo system. It's about 4" square with multiple turns of insulated wire – on my LC bridge, the coil has an inductance of about 9 micro-Henry. I resonated the loop to 160m using a combination of fixed and variable capacitors then used the same transformer coupling to the parallel tuned loop that I described in my second RFI Hunters post.

The smaller loop is less sensitive as an antenna than the 8-foot diameter loop but it is perfect for close in work as it does not swamp the receiver with as much signal yet retains the deep null when the loop is perpendicular to the noise source.

Using the loop, we quickly confirmed the right pole. We did this by holding the coil a fixed distance from the neutral/grounding drop on each pole and looking at the signal strength indication on the receiver. The suspect pole was the hottest by far!

Borrowing my small loop, the RFI specialist headed on to the property… he was gone about 20 minutes but came back with a big smile! With the aid of the small loop, he had quickly located the source of the RFI…

It turned out to be a variable speed pool pump with an electronic controller.

The utility folks had already contacted the owner of the property and told them about the problem – they told me that the RFI was radiating from everything in the house as the RFI coupled back into the house wiring. Fortunately, the small loop had made short work in finding the actual source in the pool house.

It was a great moment! We had successfully located the source of the RFI and started action to get it resolved!

Best of all, part of my guesswork had been right – the source was an AC motor!



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