In my years of locating and having the local, very cooperative, power company
repair line noises, we have found that the vast majority of radiated line noise
is due to bad splices, connections and tie wires, not insulators. The
characteristic of a noisy connection is that it goes away during rain. The few
insulator problems seen were worsened during rain.
Also, the radiation comes from the power lines and as a result, the radiation
pattern changes depending upon the monitoring frequency. Power lines are nice
long wire radiators. In fact, when tuning across the entire spectrum while
listening to a power line noise, you can hear peaks and nulls in the pattern as
the pattern of the "long wire" antenna changes with frequency, especially in
the range of 10 to 50 MHz.
Identifying the location of the noise is sometimes difficult, particularly on
the low end of the HF spectrum where you can hear the noise level vary as a
function of wavelength as you drive along, especially with a AM car radio. I
use an Icom R-10 handheld receiver with a hand held 7 element yagi tuned to 440
MHz to locate the noises. At this frequency, the noise behaves like a point
source and easily identified due to the rapid attenuation as you move away from
----- Original Message -----
From: Jim Brown
Sent: Monday, July 19, 2004 9:39 AM
Subject: RE: [RFI] Power Line Noise in Indonesia
On Mon, 19 Jul 2004 12:43:08 -0000, David Robbins K1TTT wrote:
>Since you say that the noise is better when it rains there are two
>possible explanations. First, the insulator surfaces are cracked or
>have arc damage, in this case the rain is filling the gaps and causing
>steady current instead of arcing. These should be replaced. The
>is that the insulators are dirty. In this case the arcing is between
>gaps in the contamination, when it rains the gaps are bridged or the
>contamination is washed off for a while, once the surface dries the
>noise starts again. Power washing can remove contamination
>shutting off the line, but must be repeated regularly if you are in a
>marine or heavy industrial area that contaminates them quickly. I
>also seen some surface treatments that can help prevent surface
>contamination, but not sure how widely these are available.
While we're on this general topic -- one of my pro audio engineering
friends has pointed out corona discharge as a chronic problem in
coastal areas. Can someone address the mechanics of this problem
and arcing at insulators in general?
I am of the opinion that it is the vertical downlead (running down the
pole to earth) from protection devices that does most of the radiating
of noise that is coupled from protection devices to this "ground" lead.
Based on the height of a typical pole, this downlead is going to be a
most efficient as an antenna between roughly 5 MHz and 10 MHz.
Jim Brown K9YC
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