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Re: [RFI] Powerline Noise

To: "Fred Stevens K2FRD" <k2frd@mac.com>
Subject: Re: [RFI] Powerline Noise
From: "Kelly Johnson" <n6kj.kelly@gmail.com>
Date: Sun, 4 Jun 2006 12:07:41 -0700
List-post: <mailto:rfi@contesting.com>
Thanks for the advice.  You probably hit it on the head.  I have high
tension lines only a few hundred feet away.  The towers are about 300
or 400 feet away.  I figured it was probably coming from there, but
thought I would get other opinions.  I have an FT-817 that I use for
RFI finding, but don't yet have a portable, directional VHF/UHF
antenna.  It should be easy to walk the high tension lines since they
run parallel to a set of railroad tracks.  I'll give it a try without
the directional antenna, but if that proves unfruitful I'll have to
finally break down and buy a VHF/UHF DFing antenna.  Thanks again.


On 6/4/06, Fred Stevens K2FRD <k2frd@mac.com> wrote:
> 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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