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[RFI] Noise .....

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Subject: [RFI] Noise .....
From: Roger P" <ve3zi@hotmail.com (Roger P)
Date: Wed, 28 Apr 1999 06:30:13 PDT

I would much appreciate some help in solving a noise problem which I 
have. Please excuse the length of the following, but I think that I 
need to explain the whole situation.

I live some 15km outside Sudbury Ontario in a rural area on the south 
side of a lake which is about 15km long by 1km wide. My house is one 
of about 15 permanent homes and 20 or so summer cottages along a 4km 
stretch of lakefront all of which are fed by a single phase overhead 
4kv line. There is an underwater hv feed from the north side of the 
lake which is also pretty rural. Most, but not all, properties have 
their own pole mounted transformer, and most of the cables to 
individual houses are triples, with a few 2 wire and neutral, and one 
or two (including mine) fed underground. About 1km to the east of me 
the power feed changes and all properties are fed from a totally 
separate line and direction.

The same poles carry telephone services, but there is no cable TV in 
the area.

For the past few months I have been plagued by what I thought was 
power line noise. This is intermittent on 160m (my main operating 
band), but fairly constant on 14 and 21 MHz. By comparison, when I 
first moved here a few years ago I wondered if my receiver was broken 
because 160m in the middle of the day was totally noise free.

I have two verticals for 160. Both are about 50m from the power line, 
but on opposite sides. I have a tribander about 25m, a 14-28Mhz trap 
vertical about 80m, and a 7MHz vertical about 30m from the line. I 
also have a number of beverages and EWEs. The former pass under the 

The characteristics of the noise on 160 is that there is a frequency 
range of between 10kHz and several hundred kHz which has impulse type 
power line noise. However, at the edges of the this frequency range 
there is some sort of switching signal which is a few kHz wide. 
Outside this range the noise level is zero. The noise ranges from S8 
to S9+ depending on the antenna I use but is loud on all of them. The 
bandwidth and centre frequency of the noise varies both by drifting 
and by sudden frequency jumps. Sometimes the noise is wideband so that 
it extends down into the broadcast band and up to several MHz. On 
increasingly rare occasions it is inaudible. When it first started 
I am of the opinion that it was much worse during the day but now it 
seems to make little difference. 

On the hf bands the noise is much worse on the tribander than on the 
trap vertical, and peaks when the beam is aimed at the 
transformer/pole on my property. It does not appear to be 
deterministic at all, but sounds like a typical ragged power line 
noise. It seems to be there most of the time, and is typically S7 on 
the beam. Of course, the pole is at a bearing of 45 degrees!

The noise is definitely (?) not coming from my house as it is still 
there with the main breaker out and listening on a battery receiver.

My first attempt at tracking was with a small broadcast receiver. I 
found I could only hear the noise at all if I was right next to a 
pole. I walked along a lot of the poles and hit them with a 
sledgehammer. Probably imprudent, but no change in the noise on any of 
them. I did find one point where a two wire and neutral (low voltage) 
section leading to a holiday cottage had the 240V wires twisted 
together where one had come loose and where a tree had fallen on 
another part of it. However, there was no audible noise there, no 
obvious fire or heat, and I'm of the opinion that a short would 
ultimately open the fuse on the input of the transformer.

My second was on 2m. Nothing heard at all anywhere.

I then made a large (1.5m sides) 160m loop, and started to listen with 
the following conclusions:

1. The noise is definitely being radiated by the power line. It is 
inaudible more than about 100m from the line.

2. The separate power line to the east (see above) is quite clean and 

3. I am totally unable to get a proper bearing on the noise. I get 
nulls, generally to the closest pole. The signal strength is fairly 
constant along the line. Sense (cardioid) bearings all point at the 
power line.

4. I would need to get several wavelengths from the line to take a 
bearing which may point at the noise source. Unfortunately, I would 
not be able to hear the noise at that distance no matter how large a 
loop I was to construct! Also, it is physically difficult to get there 
as it is virgin bush (or water).

5. I cannot imagine that the noise is being transferred along the 
underwater cable, so it is presumably being either generated within 
one of the 15 permanent homes or by the power or telephone line 
equipment. It 'cannot' be the holiday cottages as these were certainly 
unoccupied when the noise started.

6. The telephone line splits from the power line at one point and the 
noise gets progressively weaker as one moves along the line. There is 
a telephone switching (?) box where there is no noise, but there is a 
strong unmodulated carrier on 1925kHz audible. However, this carrier 
is not audible more than a few feet from the switching box.

I can think of no alternative but going cap in hand to all my 
neighbours and asking them very nicely if they would mind tripping 
their main breaker for a minute while I check for noise. I hate the 
idea of doing this, especially as if it is one of them I then have to 
ask them very nicely to trip individual circuits...


73 Roger


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