[RFI] Line noise vs Frequency

[EDWARDS, EDDIE J]

Pete, 

Ed Hare's description of the metal cross-arm on a pole structure is exactly what our RFI investigator and line troubleshooter found on a pole on the Salvation Army campus in Omaha.  The RFI tech could not believe it was getting stronger on higher and higher frequencies so he initially thought it was coming from off-campus somewhere else, but we found it was coming from and very strong on every point on the pole that had the metal arm when using ultrasound.  

When one of our very experience line tech Troubleshooters came out to assist, he looked at the pole with a metal arm and went to his truck and pulled out a notebook.  He showed us a manufacturer notification on the metal arms warning about possible sparking/arcing on the metal arms.  He had found one like that before that had arced for so long it charred up the pole so bad the entire pole had to be replaced.  Apparently there was not a nearby ham to pick up on that one before it cooked the pole.  

The one we found wasn't charred much so the troubleshooter had a line tech replace the arm with a non-metal cross arm.  Problem solved.  Salvation Army ham station was happy.  

Start searching for the source keeping in mind if might be some sort of large metal component on a power pole.  But focus on location first of course.  

73, de ed -K0iL
Omaha, NE

-----Original Message-----
From: RFI On Behalf Of Hare, Ed, W1RFI
I have heard reports of noise that is stronger on higher frequencies, though.  This seems to occur when the radiating conductors are smaller than long power lines.  If there were induced currents in the metal crossarms of a structure, for example, and a gap where sparking could take place, the resultant noise would broadly peak on the resontant frequency of those crossarms.