[RFI] Powerline Noise

Kelly Johnson n6kj.kelly at gmail.com
Sun Jun 4 15:07:41 EDT 2006

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 at 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 
>  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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