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
_______________________________________________
RFI mailing list
RFI@contesting.com
http://lists.contesting.com/mailman/listinfo/rfi
|