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Re: [RFI] Powerline Noise

To: rfi@contesting.com
Subject: Re: [RFI] Powerline Noise
From: Fred Stevens K2FRD <k2frd@mac.com>
Date: Sun, 4 Jun 2006 10:26:27 -0700
List-post: <mailto:rfi@contesting.com>
Kelly, I don't see anyone else jumping in to answer, so I'll give it a shot 
although somebody else may provide better information.

Powerline noise on VHF (diminishing as one goes lower in the HF bands) 
generally indicates a "leak" along a high voltage (high "tension"; anywhere 
from 4400kv to 115kv and higher) primary carrier line somewhere relatively 
nearby although it might be one to several miles away. I suspect that if you 
were to go up onto 2 meters, it would be even worse than on 6m. The RFI is 
usually caused by an arc somewhere along the line at a splice or, in your 
instance more likely at an insulator on a pole or tower. If it's at an 
insulator, especially on a metal tower, higher atmospheric humidity will 
enhance the degree of the shorted insulator. Beyond this, we're getting into 
meteorology in which humidity, temperature, and dew point become involved and 
the amount of atmospheric moisture available to create an insulator short 
varies widely with geographic location. Here in west central Arizona where the 
humidity is normally around 10%, we see high voltage RFI-creating insulator 
shorts very ra
 rely, but on the rare occasion when humidity goes up to, say, 50%, we see a 
lot more RFI; those insulators which are marginal will then short out enough to 
creat RFI. It'll vary from hour to hour as does the humidity and temperature.

How to track down a bad insulator on high tension lines? If one doesn't have a 
handheld directional antenna (like in foxhunting) and portable VHF gear, the 
next best thing might be to walk the line at night when the interference is 
acting up and look for an arc along the line. Some on this group might have 
better ideas and more sophisticated RFI-detection equipment, but I'm think more 
along the lines of those of us who are bothered by RFI only on occasion.

Hope this helps a little.

73 de Fred K2FRD

At 8:13 AM -0700 6/4/06, Kelly Johnson wrote:
>What does it usually mean if powerline noise slowly increases from S0
>to about S6 in the middle of the hot day and goes back to S0 an hour
>or two before sunset?  It seems to me that I remember hearing that
>certain types of causes tend to make it occur only when it is hot or
>only when it is dry/wet, etc.  The noise appears to be worst on 6
>meters and decreases as frequency is decreased.

-- 
73 de Fred Stevens K2FRD, VO2FS
http://homepage.mac.com/k2frd/K2FRD.html
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