Topband: Exciting noise sources

[donovanf at starpower.net]

Hi Larry,

Congratulations on finding that neutral arc! I've never had any difficulty isolating neutral arcs to an individual pole by using a 400 MHz receiver, but your experience may be different than mine.

Arcs from the neutral conductor often produce intense RFI at long distances because even though the neutral conductor is typically only a few volts above ground potential, significant power can be dissipated in an arc to a grounded conductor.  

30 years ago at my previous QTH an S9+++ line noise popped up on Friday night in an ARRL 160 contest.  I hunted for the RFI and it turned out to be an neutral conductor that was rubbing against a grounded guy wire about a mile away.  A few tugs on the ground wire and the problem cleared itself for the rest of the night.

Sure enough, the line noise returned on Saturday night.  This time gentle tugs on the guy wire did not correct the RFI.  After a few very powerful tugs there was a big arc at the top of the pole and the high voltage fuse opened up.   Oops...  I thought I would be QRT for a few hours, but fortunately the the fuse affected only cemetery adjacent to the pole.  

On Sunday morning many unhappy people were waiting for the power company to restore power so they could conduct a planned burial service in the chapel!   But the contest was a big success....

73
Frank
W3LPL 



---- Original message ----
>Date: Sat, 26 Mar 2011 09:08:59 -0700 (PDT)
>From: N7DF <n7df at yahoo.com>  
>Subject: Topband: Exciting noise sources  
>To: 160 reflector <topband at contesting.com>
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>Yeaterday K0HGW and myself spent the day with a line crew from the Otero County Electric Cooperative trying to find two noise sources which have plagued them for several months and occasioned numerous complaints.  In the first case we were able to locate a power pole with our direction finding equipment that seemed to be the location of the noise and they began to work on the hardware from their bucket truck.  We use an MFJ noise meter coupled to an external speaker to let them listen as they tighten hardware, drive in staples and adjust wires. There were definite changes in the noise as they worked but the situation didn't really improve.  They even took the wire (14KV) off the top insulator and cleaned the insulator and replacede thhe twist wire holding it but, while there was some improvement,  that didn't solve the problem. By shaking the hot wire they could get the noise to change, though.  In the meantime we identified another nearby pole
> that showed noise so they moved to it with the bucket truck and repeated the entire sequence of tightening hardware,etc.  Once again there was.some improvement but, after servicing the pole the original problem was still there.  We began checking every pole in the area and found significant noise on each pole that could be affected by jarring the pole and poking on hardware with a fiberglass rod.  As we moved down the line the overall noise level varied and could be changed slightly by manipulating hardware.  Finally, at one pole about a half mile from the first one they worked on, they pulled on a neutral wire with their pole and the noise completely went away.  The wire had been just barely touching the head of an eyebolt holding a transformer.  Not only did the noise at that pole disappear but all the other noise sources in the area disappeared.       When we went to the other noise source (about 5 miles away) the same proceedure was
> followed and we located the primary noise source in the same way.  It was also a neutral wire touching a bolt.  When it was moved noise sources that we had picked up at other poles up to a half mile away also disappeared.  This was not the first time we have found that loose hardware and staples can be excited by a distant noise source into emitting noise on their own but, once the primary noise source is eliminated, they no longer create problems.  Although we know that this problem recurrs we have not found a realiable way of detecting the primary source other than pole by pole testing and hardware tightening.  The reason is that the primary source is no stronger on our detection equipment than any other source, and is often less intense that the sorces excited by its radiation down the line.  We have developed a good enough relationship with the local power conpany that they frequently call on us to help them find noise sources that they
> receive complaints about.
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> 
>Larry N7DF
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> WHEN YOU ARE FACING THE LIGHT THE SHADOWS FALL BEHIND YOU
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>UR RST IS ... ... ..9 QSB QSB - hw? BK