[RFI] Power line noise

Jimk8mr at aol.com Jimk8mr at aol.com
Mon Feb 8 11:51:54 PST 2010

My experience is that line noise does not drop off quickly at the lower  
frequencies. I wonder if you are just hitting some resonant hot spot where the 
 HF noise peaks because of the RFradiating properties of the power line.  
You really do need to move your search up in frequency.  I find  that six 
meters is a prime band for power line noise. Good for finding noise,  not so 
good for operating there.
I like to do line noise chasing from my bicycle. (Yes, I know it's a  bit 
too cold and white in Boston right now :>)  ).  I have an ICOM  IC-R10, with 
a 2M 5/8 wave mounted on the metal rack in the rear. I program a  frequency 
for each ham band, 160M through 432MHz, with AM detection.  Then  I can 
easily switch between bands. I find that on 10 or 6 meters, I hear noise  
several hundred yards away. Maybe a hundred yards away on 2 meters, and pretty  
much just from one pole on 432. 
I also carry a 5L 432 yagi that I can hook up when I find a suspicious  
pole. Aiming that, I can with confidence pick out a bad pole.  Most, but  not 
all, problems can be heard at 432.
I also use my FT-7800 in the car, again with an AM detected frequency on 2  
meters and 432. I have some noise problems from the car on 2M, but a  
driveby of a noise source on 2 meters usually shows up +/- 3 poles or so. On 432  
it's +/- one pole.
I also have a W1TRC ultrasonic noise detector, which adds a whole extra  
level of detection confidence.  But that's another story.
73  -  Jim  K8MR
In a message dated 2/8/2010 2:26:12 P.M. Eastern Standard Time,  
w6yn at juno.com writes:

Using a  higher frequency is helpful in pinpointing the problem. This noise 
is very  wide spectrum.
I use 33cm am equipment for this purpose as HF signals  travel well along 
power lines.

The possibility of a ground wire on  the  transformer pole will make the 
RFI appear louder when sampled at  ground level near the pole.

Transformers are rarely the cause of RFI.  An internal arcing may not be 
detected with an ultrasound  detector.
Transformers are often suspected because it's "the biggest thing  up there."

Any loose connection in close field proximity to the HV  circuits can cause 
sparking between the metal parts.
Wooden construction  may shrink over time and just tightening the hardware 
can solve this  problem.

Sometimes striking the affected pole (Watch your head! Junk  may fall.) 
with a large hammer or mallet can change or even temporarily stop  the noise.

Good Luck!

73,  Don,   W6YN

---------- Original Message ----------
From: Ash Thornton  <thorntonash at comcast.net>
To: rfi at contesting.com
Subject: [RFI]  Power line noise
Date: Mon, 8 Feb 2010 13:36:08 -0500


I  found the posting from Corn country interesting.

I have a situation  that also seems to appear with the cold weather,  
appears to be  limited to a stretch of poles that dead end near my  
QTH. I found it  with a loop cut for 7Mhz and a K3. Several other hams  
in the local  neighborhood have the same noise problem I am seeing,  
160-40. I see  S9 +20-30 noise under several poles and then drops off  
rapidly as I  move along the line.

NStar the utility her near Boston has been  checking this problem for  
several weeks. They use a ultra sound  detector which has shown  
nothing. Several of there grounds are  suspect and they will add  
additional grounds. A question, anyone  know how to recognize a pole  
transformer failing?The noise seemed to  peak on an AM radio just  
under one of them. NStar is coming back  tomorrow to look again before  
they send out a maintenance crew for  the grounds. I am getting a  
little worried because if it is not a  ground problem they are saying  
nothing they can do as they see no  arcing.

Any  ideas?



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