[RFI] Difficult power line RFI find.

[Dave Cole]

Hi Don,
Thanks for sharing!  It was good to see you using the FLAG...  I may 
build one after seeing the nice null...  I like the choke you have on 
the handle!!  :)

73, and thanks,
Dave (NK7Z)
https://www.nk7z.net
ARRL Volunteer Examiner
ARRL Technical Specialist, RFI
ARRL Asst. Director, NW Division, Technical Resources

On 3/9/21 4:27 PM, Don Kirk wrote:
> Just thought I should share something that was a first for me when tracking
> down power line RFI and man it was frustrating, and I have tracked down a
> lot of powerline RFI.
> 
> I noticed some weak RFI at Dans (KB9AX) on 160 meters earlier this year but
> did not have time to track it down.  Dan also complained about the RFI and
> he mentioned this week that it was not strong but had become very
> consistent.  It definitely looked and sounded like powerline noise (120 Hz
> spikes observed on audio scope and SDR receiver, etc.)  Today I decided to
> follow up on this RFI and using both my portable flag as well as a tuned
> loop the direction indicated the noise was North from Dans QTH.  I did some
> tracking and both antennas kept pointing perpendicular to some power lines
> a long distance North from Dans that were running East/West along a major
> road and I was standing a good distance from the lines out in farm fields.
> No matter where I walked my antennas kept indicating the signal was coming
> from the lines with my antennas always  pointing perpendicular to the lines
> for peak signal even when I was hundreds of feet away from the lines (like
> 500 feet or more away from the lines).  Dans 4 square receive antenna
> system (DX Engineering 4 square receive array) indicated the signal was
> about equal when pointing NE and NW which pretty much agreed with the North
> direction my portable flag and tuned loop indicated and the East/West power
> lines are 0.75 miles North of his receive array.  I started to get the
> feeling that the ground wave signal from the pole generating the signal was
> weaker than the signal propagating down the line in our direction, and
> therefore I could not detect the RFI directly from the faulty pole with my
> ground based antennas.
> 
> We therefore looked for another frequency where the powerline RFI might be
> heard from Dans, and using his horizontal HF beam (4 element beam up at 112
> feet) we found the signal up on 24.9 MHz and it was strongest when pointing
> NNE.  Again my portable flag and tuned loop used on 24.9 MHz indicated the
> signal was coming from the North (antennas perpendicular to the power
> lines) when standing at Dans house very far from these lines (0.75 miles
> from the lines).  I then decided traditional direction finding was not
> going to work.  I then used my tuned loop adjusted for 24.9 MHz and with
> receiver gain backed way down I drove the East/West lines with my small
> tuned loop sticking out the window until I could hear the signal on 24.9
> MHz.  I then got out of my car and used my portable 4 element beam on 135
> MHz and quickly found the faulty pole but the faulty pole was different
> than all other poles I have located in the past from an RFI level
> standpoint.  I normally have to use 20 to 30 dB of attenuation with my 135
> MHz receiver and 4 element portable beam to isolate a faulty pole, but I
> actually was able to isolate the pole from nearby poles using no
> attenuation at all but 10 dB of attenuation was ideal.  This pole was
> definitely generating RFI and I could even see low level of RFI coming from
> it up on 437 MHz with a portable 4 element beam with SDR receiver, but it
> was generating the weakest amount of RFI than I have ever encountered with
> a power pole and I believe this is what caused traditional radio direction
> finding to be useless (propagated signal along the lines was stronger than
> the ground wave signal when viewed from Dans house).  The faulty pole
> turned out to be located 0.84 miles from Dan at a heading of 44 degrees
> which really is not very far compared with other faulty poles we have
> encountered at his QTH and some have been double that distance while
> generating much stronger RFI.  When close to the pole (few hundred feet
> away as an example) my traditional HF direction finding techniques using
> both my portable flag as well as tuned loop worked great and pointed
> directly at the faulty pole which I was happy to see but this sure had me
> scratching my head as I spent many hours tracking down this faulty pole.
> 
> I just wanted to share this experience as it was definitely frustrating,
> but I'm glad I didn't give up.  I suspect others may unknowingly run into a
> similar situation but hopefully it will be few and far between.
> 
> P.S. I had my easiest powerline RFI find just a few days ago at Kens (KJ9B)
> and the utility company responded today and said the problem was a bad
> insulator.  You can see my youtube video of this find at
> https://youtu.be/X_5h-gSc6Ns
> 
> 73,
> Don (wd8dsb)
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