Topband: Finding powerline noise

[Pete Smith]

At 11:21 PM 12/9/02 -0600, Ford Peterson wrote:
>It occurs to me that hardware and insulator maintenance are the only real
>fixes to power line noise.  Finding the source of the noise is a real
>problem, especially when there are many points of noise sources in the
>neighborhood.  What about this...
>
>The leakage is between the wires and the hardware on the pole, right?  Well,
>there is a source and sink to every circuit, right?  It seems to me that the
>noise should be inducing currents flowing in the wood of the pole, sinking
>it to ground, right?  So there is a current flowing in the pole, right?
>
>Can a person wrap the pole with a few turns of wire and simply measure any
>induced currents?  A good pole = zero current, a leaky pole=some current
>flowing.  Possibly use a field strength meter as a detector?
>
>This seems too easy.  What am I missing.


Based on my experience over the last several years, I think this is 
mistaken.  My worst noise sources are the old-style insulators on slack 
spans, stretches of high-voltage feeder that hang loosely (hence the name) 
across roads or in other situations where the wires can't be pulled taut by 
guying the poles.  There, the sparking occurs as the wires move in the 
wind, between metal-to-metal joints in the insulator assemblies.  No 
current induced in the poles.

Similarly, in one case we found a lighning arrestor where the sparking was 
occurring between the bracket of the lightning arrestor and a mounting lag 
screw that had worked loose in the pole.  Neither item was connected to the 
HV feeder, but they were in the close-in field, and apparently the field 
gradient was enough to cause sparking between them.

I have had quite good luck using my car AM radio to locate a source 
generally, closing in with a portable AM shortwave radio, and then going 
the final step with an aircraft-band receiver.  I just built up a Moxon 
rectangle from the March 2001 QST RFI article to go with the aircraft-band 
receiver.  It seems to be quite directive and have a deep, narrow null off 
the back, and I expect to be able to single out the source pole with it 
even more easily.


73, Pete N4ZR
Sometimes a tower is just a tower