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

[Art McBride]

Greg,
I have had some experience with VHF wide band noise. It can travel for miles
on the power lines. Generally caused by rusty hardware on the guy lines.
Iron Oxide acts like a rectifier, the guys are in the near field of the 60
Cycle line providing excitation to the "rectifiers". In damp weather it goes
away. Hiting the pole with a sledge will also temporally stop the noise. 
Arcing insulators usally cause noise on the lower frequencies.
MOV's that have been stressed by lightning will also cause this problem. A
all mode 2 M receiver does a good job of receiving noise in the AM mode.
Almost undetectable in FM mode without a weak signal on frequency.
Good Luck,
Art,
KC6UQH

-----Original Message-----
From: KJ6KO [mailto:kj6ko at innercite.com] 
Sent: Thursday, September 12, 2013 3:31 PM
To: Wswss at mailman.qth.net; 'SBMS'; nc9rs at yahoogroups.com; WA6JQV at aol.com;
Bob Olson; skipp025 at yahoo.com; Tom, N6MVT; Dave Fortenberry; Knox La Rue
Subject: [Sbms] How far can noise carry via power lines?

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


__________ Information from ESET NOD32 Antivirus, version of virus signature
database 8793 (20130912) __________

The message was checked by ESET NOD32 Antivirus.

http://www.eset.com

_______________________________________________
Sbms mailing list
Sbms at lists.altadena.net
http://lists.altadena.net/mailman/listinfo/sbms