[RFI] Power line noise question for the experts

Ed K0iL eddieedwards at tconl.com
Wed Dec 26 17:01:58 EST 2012


Paul, 

What brand/model of ultrasonic unit are you using?  

If it's one of them DIY "kit" units, you might want to use a more sensitive
unit if you want to confirm your findings.  Or possible just have the
utility confirm your findings with their equipment, assuming they are using
better equipment.

73, de ed -K0iL

-----Original Message-----
From: RFI [mailto:rfi-bounces at contesting.com] On Behalf Of N1BUG
Sent: Wednesday, December 26, 2012 3:27 PM
To: RFI at contesting.com
Subject: [RFI] Power line noise question for the experts

I have successfully located multiple sources of power line noise and the
power company has kindly fixed them. At this point 90% of the noise has been
eliminated but what remains is still quite bothersome. I am having
considerable difficulty getting positive identification of the remaining
source pole(s).

The noise is present from at least 1 to 60 MHz on the home station receiver
(no equipment for higher frequencies). Looking at it with a scope there
appear to be two intermittent sources of noise, one each on two different
phases. The pulse count on each is highly variable, usually just one or two
pulses per positive and negative peak on calm day, rapidly varying from none
to many on a windy day.

At 135 MHz (3 element yagi) I cannot resolve the source pole. Noise is
strong and nearly constant along a stretch of 7 poles but drops quickly
beyond either end of that area never to be heard again (I have checked the
line 2 miles in both directions from there).

At 445 MHz (7 element yagi) I cannot detect it at all.

Given that the noise is quite strong at 135 MHz but not detectable at 445
MHz, is it likely some frequency in between might help in resolving the
source pole(s)?

The poles have a 13 kV distribution line with a 46 kV transmission line
overbuild. I have reasons to believe all remaining noise is from the 46 kV.

On windy days I have been able to hear ultrasonics from two 46 kV insulators
on one pole about in the middle of the 7 pole stretch. 
The highly variable ultrasonics partially correlated with variable noise
from the station receiver (listening to both at the same time). The
correlation left something to be desired and I was having great difficulty
holding the dish steady in the wind. On calm days I cannot hear ultrasonics
from the suspect insulators. I would like more/stronger evidence this is the
source before asking the power company to look at this pole for the third
time.

Any tips or suggestions?

Paul N1BUG


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