[Wswss] How far can noise carry via power lines?

[KJ6KO]

Hello to all
  Sorry to bombard all the groups with this, but this is someting I havn't seen before and am just looking for help/advice.  

Including some broadcast guys in this also.

  I have been working with the Bishop Amateur Radio club on finding an interference issue that is a bit odd..Here are the symptoms and what we found so far.....

.. Broadband VHF (140-170) noise, about an 18db degredation in receiver sensitivity.  

.. No "obvious" source.   Traced it a while back to a small low power FM station building next toor...coming out of the building, not the antennas.

.. This last trip, we found it seems to be coming from all the buildings on the hilltop!  The broadcasters shut down ALL their transmitters, and noise was still present coming from the building, around -100dbm 20' from the building...or now, ANY of the buildings on the mountaintop.

..  Getting closer to any of the buildings really doesn't seem to get much stronger, pretty much about -100dbm 20' from any of the buildings, always pointing at the building, with the exception of the building that houses So Cal Edison's MW systems, it is much stronger inside (the only one we could really get inside of) , about -80 when very close to the XFER panel, but they have a LOT of power in the building and a generator.  Everything was VERY well grounded in that building also!  You can never find that one device the should really "light up" when you get close to it!

.. We went further to the main power meter panel and small building, that houses the step down XFRMR, that is 150' away from any of the TX buildings, and it has the same noise level coming from that building!  No transmitters on site!

.. We "listened" to the noise, and it is not just white noise, it has some "component" in it that sounds 60Hz.

.. After determining that it is most likely NOT an RF issue, we began a search along the power system.  We found an extreemly noisy pole about 1/3mi away with an obviously broken insulator on it just a couple poles from the "mini sub station" that converts 60KV down to ?? for the underground run to the site.

So my question to you all is,
  Has anyone seen this or something similar before, where noise from a bad power line will travel 1/3mi through an underground power feed to a site and pollute every power panel in every building on a mountaintop and cause the noise floor to raise??
  To me, it seems possible, but sort of "unlikely"?

  This is not an extreemly big site from an RF point of view, 4 low power FM stations (<5KW) one digital UHF TV station (<5KW) a cell site, local PD/Fire etc.  Mt Wilson, it is NOT!

  Looking for any ideas, experiences or comments!  It is difficult to trace as you need a good BPF on your instrument to keep all the other broadcast etc from overloading your front end, but we had a pretty good one.

The club is purchasing a DCI 2M filter for future noise hunts and to put on the repeater full time, but we should have found something that lit up the analyzer with noise, but never did!

Thanks and 73 de Greg


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