Topband: Exciting noise sources

[N7DF]

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.

 
Larry N7DF

 WHEN YOU ARE FACING THE LIGHT THE SHADOWS FALL BEHIND YOU