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

[EDWARDS, EDDIE J]

Alan, 

Sorry for my delayed post on this subject.  Some things previously mentioned on this group by the professional RFI investigators who have posted in the past but I wasn't sure if you were aware of in your post:

1. In older neighborhoods with older power lines, you should be able to find dozens and maybe over 100 RFI sources within a short distance to your station.  Not all of them are creating RFI being picked up at the location of you antenna(s).  And the utility is not required to fix all of them if they are not causing harmful interference to anyone.  

2. Best way to verify that a source in the field is your RFI source on your radio is to get a noise signature on a scope, save it on the scope, then go into the field and find a matching noise signature in the field.  One ham on the list has done this using his ears, but most of us with tinnitus need visual scope readings.  LOL

3. If you let multiple sources ramp up, you will be "pealing the onion" as you remove the loud sources first only to find less strong ones below that layer.  You may have found this to be the situation in your case.  

4. Back in the pre-cable, pre-streaming TV days, it was the utilities responsibility to find and repair RFI sources causing interference to TV or radios.  It is to their benefit to perform their work tasks in the most efficient way possible.  So it is to their benefit to have trained and well equipped RFI investigators.  Not all utilities will be this efficient as you have found.  Utility's budgets and internal politics can interfere with these tasks.  But the FCC's viewpoint is that it is the utilities responsibility to find and eliminate harmful interference from their equipment and only their equipment. The ham should only verify that it is from the utility's equipment and not his own or his neighbors'. 

5. Always continue to listen at higher and higher frequencies when searching for RFI sources on powerlines.  You should be able to confirm a source by finding it at 300Mhz or higher.  If you cannot hear it that high, keep moving down the line until it gets stronger or fades away.  And it is possible it is not from the utility equipment at all if it is not broadband noise.  


73, de ed -K0iL


-----Original Message-----
From: RFI <rfi-bounces+eedwards=oppd.com at contesting.com> On Behalf Of Alan Higbie
Sent: Thursday, September 23, 2021 11:21 AM
To: Rfi List <rfi at contesting.com>
Subject: [RFI] CASE HISTORY - Powerline - Multiple Sources (re-post w/o errata)

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
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