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[RFI] PLN case SOLVED

To: RFI List <rfi@contesting.com>
Subject: [RFI] PLN case SOLVED
From: "Chris L. Parker" <parker601@earthlink.net>
Reply-to: "Chris L. Parker" <parker601@earthlink.net>
Date: Sun, 17 Jan 2016 16:17:15 -0800 (GMT-08:00)
List-post: <rfi@contesting.com">mailto:rfi@contesting.com>
Hello Group,

Thought it may be helpful to share a powerline noise (PLN) case that’s been 
dogging me for 3 years. It manifested itself as a very low level (almost at the 
noise floor) non-stop 120 Hz rasp that made weak signal listening on my Yaesu 
fatiguing and aggravating. The noise blanker had no effect.

Using a 440MHz beam and homemade ultrasonic pinpointer I finally identified the 
source as a guy wire rubbing against a secondary (120VAC) ground cable.  I will 
try my best to describe the situation.  2 blocks from my home is a 16kV pole.  
At the top, the 16kV passes through two cutout fuses and into a pole pig 
transformer.  Since the 16kV wires are from one side only, the tension on the 
pole is balanced with a diagonal guy wire anchored into concrete at ground 
level.  About midway up the guy wire is a “Johnny Ball” insulator (porcelain 
strain relief).  About halfway up the pole extending horizontally are the 
120VAC secondary wires and ground from the pole pig. (2 insulated black wires 
loosely wrapped around a bare supporting cable which also serves as ground.)  
The local utility had the foresight to position a 3 ft. long plastic insulating 
tube around the 120 VAC secondary wires and bare support cable to keep the guy 
wire (above the Johnny Ball insulator) from rubbing against them.  (The guy 
wire and secondary wires are in the same “plane” so to speak.)  Over time, this 
insulating tube slid away, and residual 16kV, tracking through the old wooden 
pole, and down the guy wire (above the Johnny Ball) was shorting out against 
the 120VAC bare support cable.  The RFI was particularly bad when the wind 
blew, as the guy wire would slide back and forth against the bare support 
cable.  To make matters worse, the top half of the guy wire (above the Johnny 
Ball) made a great antenna.  The fix was easy.  A utility worker just slid the 
plastic insulating tube back into position, and secured it with a couple of 
large plastic tie wraps (instead of the previous electrical tape).  The 
difference in listening to the radio is like night and day.  I can hear 
stations almost at the noise floor I haven’t heard in 3 years.  I hope this 
case description helps someone.  Keep persevering!


73,

Chris

AF6PX
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