[RFI] CASE HISTORY - Powerline - Multiple Sources (re-post w/o errata)

[Alan Higbie]

Amongst the usual residential area microprocessor RFI trash,  I have also
endured powerline RFI at my station for years. I only operate on 160 to 6
meters. Sometimes it gets worse - sometimes it subsides somewhat.  Wind,
moisture, and frequency dependent.

I have kept an RFI log for at least the past 3 years.

Despite my best efforts, finding the location of the source has been
difficult.  I didn't want to squander any goodwill with the power company
by having them come out before I had actually located the offending
pole(s).

I had always assumed I had one RFI source.

I have been using the National Radio HFDF loop with a Tecsun PL660
receiver. And, also I use an SDR (and the Tecsun) with a WD8DSB portable
flag. Also an FT817 on 440 MHz with 7 element yagi.

Eventually, I noted very strong RFI that appeared to be coming from an area
of a chain-link fence that runs below and parallel to the powerline.  I was
perplexed.

Using my station's SteppIR I finally figured out that on 21 MHz the RFI
peaked in one direction (240 deg.) and on 28 MHz the RFI peaked in another
(105 deg.).

So, that indicated at least 2 separate sources.  There is a power
pole (with a transformer) along each of those headings.

But, I still wondered if this distinction was a result of re-radiation or
induced RFI.

Eventually, I was awakened in the middle of the night by high winds.  So I
came into the station, flipped on the receiver to note how the suspected
sources were acting.  At one point, the 21 MHz predominant source sputtered
off and the other (28 MHz) kept going. Then I knew for sure I had 2
separate sources!

The next day I emailed our utility RFI guy.  I sent pole numbers, photos of
the hardware on the poles, an aerial map showing my beam headings to
their poles.  I asked him to come out. Within a few days he and another
engineer (who is a ham!) showed up with a troubleshooter-lineman and bucket
truck.

I demonstrated the DF steps I had gone through (station receiver, beam
headings, how the RFI drops dramatically when the SteppIR is put into the
180 reverse mode).

We DF'ed again outside with the Tecsun and the VHF gear.  We walked to the
1st pole (21 MHz source) and the lineman went up.  He inspected and
reported seeing significant deterioration on top of the transformer and
also track marks from arcing. As he poked around with the fiberglass hot
stick - the RFI sputtered and he eventually got it to stop (at least
temporarily).

The utility guys had a Radar Engineers M 331 - but didn't use it today -
relying on my 440 MHz set-up instead.

We repeated the process on the next pole down the line and then the next.

During the visit, there was much discussion about the age of the
poles/hardware.  The subdivision dates to the late 1940's - so the
equipment might be 75 years old.  There has been at least one lightning
strike to one of the poles within the past 2 years.

Well, after these sources were calmed down - listened some more - and still
had RFI coming from close to the same beam heading as one source we had
located.  I went hunting with the VHF gear.  I was able to confirm that the
next pole down the line was also generating significant RFI (which I was
still hearing on HF).  We had figured this was re-radiated or induced RFI -
- but it now turns out to be an independent source all on its own.  I have
supplemented my trouble ticket request and am told they will confirm
it, etc.

Note: After the two sources on the poles were quieted down - the chain-link
fence RFI also went quiet.

The good news: The utility advised yesterday that it will "replace 3 of
those poles and associated equipment" within the next 2 to 5 months.

The bad news: Yesterday I saw my neighbor getting an estimate for a solar
system.

73, Alan K0AV
Colorado Springs