[RFI] RFI detective story - with successful outcome and 30 dBm reduction of noise floor

[Gary Smith]

Outstanding service form your local P & L.

Gary...wa6fgi


On 2/28/2018 9:23 AM, Alan Higbie wrote:
> In October 2017 I started to observe some spitting type broadband RFI noise
> spikes. Within a week or so noticed that when outside temperature cooled in
> evening the noise spikes would become constant.  Then noticed high winds
> would cause more spikes in noise level.  Eventually the RFI became
> constant.
>
>
> This noise caused my normal noise floor (on P3 scope) of about -120 dBm to
> increase by 30 dBm to -90 dBm.  The noise responded well to the NB on K3 -
> but using the NB during contests also resulted in IM products and made
> communications difficult.
>
>
> *These are steps taken*:
>
>
> 1. Cut power at the panel of our house - K3 on battery power.  No change.
> So coming from outside.  Had neighbors cut their power too. Eliminated them
> as source.
>
>
> 2. Used National RF Vector Gun w/ loop - to DF the source.  Best used to
> null off ends of loop. Initially hooked loop to Tecsun PL 660 set on 20
> meters; then connect DF loop to KX2, then eventually set the P3 to run
> ALONE as SDR receiver on 14.020 MHz (see page 25 of P3 Manual) (also
> Instructions found at: http://www.g3tct.co.uk/P3.html ).  Connected the DF
> loop to I.F. Input of the P3.  Ran on battery and carried around.
>
>
> 3. The P3 connected to the DF loop tuned to 14.020 showed noise signal
> level only about 12 dB down from the strength shown on P3 when connected to
> 2 el. 40 mtr. yagi.
>
> But using that portable set up allowed for making sure I was tracking same
> noise signal that was bothering me in the shack.
>
>
> 4.  Before getting zero'ed in on the offending pole(s) - - it dawned on me
> to try pinpointing noise source by carefully peaking the beam.  The P3
> (with SVGA) may be configured to display signal strength in 1 dB increments
> (spaced about 1 inch vertically) !!  And, I now have a digital readout on
> my rotator indicator (Green Heron).  I spent about 20 minutes slowly going
> back and forth. Finally determined that noise source peaked at 65 degrees
> from my antenna.
>
>
> 5. Then, walked with P3 and National RF Vector Gun DF loop roughly along
> the 65 degree line away from my house.  Eventually the signal got stronger
> and stronger.  This was 1/3 mile away.
>
>
> 6. Then borrowed a friend's FT 817.  With that set for 220 MHz AM and a 7
> element yagi (Arrow 220-7) - located which pole I thought it was.  But
> wasn't completely sure - because the QRN/RFI signal was so strong - thought
> it was one of two poles close to each other.  I should have inserted step
> attenuator between beam and FT-817.
>
>
> 7. Having narrowed it down to two poles, I emailed the Colorado Springs
> Electric Utility.   Mentioned that my FCC licensed station was now
> essentially off the air because of RFI from the arcing and the utility's
> power leak.  And mentioned that this was coming from 1/4 mile away.  I sent
> along photos of the poles - with close ups showing pole numbers.  I also
> sent a map and aerial photo (from Google Maps) showing my house, the 65
> degree beam heading, distance, location of poles, handwritten pole numbers,
> etc.
>
>
> I went to the area at night - using binoculars - I looked for visible
> arcing - but couldn't see any.
>
>
> 8.  A utility engineer emailed back - and he suggested we meet at the site.
> But I suggested we first meet at my house.  He brought a lineman. I showed
> them my shack and especially how the noise looked on the P3 scope - and
> demonstrated what it should look like by flipping the SteppIR 180 degrees.
> They could SEE my problem.
>
>
> 9. The engineer brought along the utility's Radar Engineers RFI locator
> M330 !! (Yes, I told him I was happy to see they had followed my suggestion
> of 12 years earlier - about buying one)  He also brought along a Radar
> Engineers  MODEL 250 Parabolic Pinpointer Ultrasonic Locator.  (another
> suggestion)  Note: This felt like I had dropped a hint about what I wanted
> from Santa !!
>
>
> 10.  Triangulating around the immediate area - using that nifty gear - the
> engineer  confirmed which pole supported the noise source.
>
>
> 11. The pole in question carried 7200 volt lines at lower level and 34,500
> volt lines above that.
>
>
> 12. On the first day - the lineman went up and wiggled and tightened stuff
> on the 7200 lines  But that made no difference.  Being by himself - with a
> bucket truck which couldn't reach the upper wires - they suspended the
> operation for the day.
>
>
> 13.  A week or so later - the engineer came back with a larger bucket truck
> / a crew of two lineman - and a foreman.
>
>
> 14. They couldn't quite zero in on exact source on the pole.  But they
> started by de-energizing the 34,500 lines.  They sent me home to check my
> noise in the shack.  Still the same.  None the less they tightened and
> replaced hardware on those lines
>
>
> 15. The linemen came back down lower to the 7200 volt lines.  They wiggled,
> tightened and disconnected stuff - until eventually they made the noise
> stop on engineer’s RFI locator.  The source of this noise was a lightning
> arrester which was failing.
>
>
> 16. They *replaced lightning arrestor* and the noise was gone on their RFI
> locator - - but to be sure, they had me drive home to check noise level in
> my shack - and yes, the particular noise had been eliminated
>
>
> 17. The replacement of the defective lightning arrestor reduced my noise
> floor by 30 dBm (from approx. -90 dBm back down to -120 dBm.)
>
>
> 73, Alan K0AV
>
> Colorado Springs
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