[Wswss] [NC9RS] How far can noise carry via power lines?

[Jim Brown]

Some fundamental principles.  

Most noise gets into our equipment as radiated RF. Current through a conductor causes radiation. When you have noise issues, always ask what are the antennas, what's putting noise on those antennas, and HOW it's putting noise onto those antennas. 

One of the most common noise coupling mechanisms is "The Pin One Problem" -- failure to bond cable shields to the chassis of equipment, first discovered by engineers working in pro audio. The same error often happens with ground conductors in power wiring. There are several tutorials on RFI and the Pin One Problem on my website.   http://k9yc.com/publish.htm

Noise that originates inside buildings is generated by switching power supplies, or by digital circuitry.  Strength of the noise is inversely proportional to the rise time, and faster rise times makes higher order harmonics stronger.  Circuit layout, equipment design, improper termination of cables, all contribute to the spectral distribution of the noise. Gaps in shielding (for example, the gap between mating enclosure parts that are painted form a slot radiator) allow direct radiation from gear.  Circuit design that cause current to flow in large loops rather than transmission lines cause lots of radiation. Again, a circuit layout problem. 

In general, VHF and UHF don't travel very far on power lines -- experienced power line noise chasers look for noise with an AM RX in the 100-200 MHz range (and even higher) to localize the source.  Nearly all noise GENERATED on power lines is DC-to daylignt arcing, mostly at a broken insulator, but also at broken hardware.If I'm not mistaken, arcing can occur in a transformer. 

Lower frequency components of the arcing will radiate from power lines, and the strength will vary with peaks and nulls of antenna current on those lines.  From your description, there's a good chance that the source is that noisy pole. Those with lots of experience in getting power noise problems solved say that using words like "sparking" and "arcing" can get the power company's attention.  But it might also a multi-source problem.  

I've seen MF/HF noise on the grounding conductor running down a wood pole. That means the wire is carrying that noise current, so it will radiate.  I've also seen massive HF noise radiated by CAT5/6/7 cables feeding UHF links for internet systems. 

If this trash is causing serious QRM to licensed services, especially commercial services, I'd be inclined to get the FCC involved. 

73, Jim K9YC

________________________________
From: KJ6KO <kj6ko at innercite.com>
To: Wswss at mailman.qth.net; 'SBMS' <sbms at ham-radio.com>; nc9rs at yahoogroups.com; WA6JQV at aol.com; Bob Olson <w6bo at w6bo.com>; skipp025 at yahoo.com; "Tom, N6MVT" <N6MVT at carlaradio.net>; Dave Fortenberry <jammerdave at gmail.com>; Knox La Rue <k6nox at yahoo.com> 
Sent: Thursday, September 12, 2013 3:31 PM
Subject: [NC9RS] 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

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