Since my last two postings regarding my findings with various power
lines, and the noise they generate, I received a number of positive
responses. With this in mind, I will continue with my findings.
1) Equipped with a 20M and 80M mobile setup, I went to do some noise
comparisions with single phase 25KV, 3 phase 25KV, 3 phase 138KV, and 5
phase 350KV and 500KV high tension lines.
2) Assuming that there are no *major* faults in the line, the best line
to live near is the single phase 25KV, by a leap, jump and a landslide
over the rest. Noise levels directly underneath the lines seldom lifted
the S meter at all, with just a audible difference in noise, primrarily
on 80M. I did however, find some bad ones, which were approx 12dB
noisier, about 2 s-units. The *bad* ones were the very old lines,
looking like they were dated back to the 50's, and probably did not see
much maintenance. Even transformers were not *overly* bad, again with
some exceptions. The new ones were as quiet as a church mouse. Even if
these single phase lines *were* noisey, they are the easiest to fix,
since you would be only dealing with one phase.
3)Next up three phase 25KV. The three phase lines were significantly
noisier than the single phase in *all* cases. I checked about 40
instances, all of them proved this point: three phase equals about 3
times the noise plus a bit. Some of these lines were tolerably quiet,
getting better at a distance of about 200'. I noticed that these lines
got hideously noisey when they were *spaghetti* strung, like what you
see around and industrial area. Noise levels were up to 40dB stronger
than the single phase lines at their worst, when around the multiple
connection 3 phase lines. Distances you need to be from these varied a
little, but in most cases, about 800' was the absolute minumum you would
ever want to be from these DX killers, as the s meter dropped to nil,
but the noise floor was still there, and that is on a mobile whip, so
expect a little more noise from a full size antenna.
4)Next: 3 phase 138KV. These lines seem to be utilized by cities and the
immediate vicinity for some reason. I consulted with an ex-power company
worker, and he stated that most of these lines were for industrial, and
ring feeds. The voltages on these lines are relatively high, and is not
consistent with the type of poles and insulators they are on. Sure, they
stop the voltage from getting to the pole, but as far as noise
goes...look out. I don't know if it is standard, so I won't mention it
here, but there was a way I was told I could tell if it was a 138KV
line. Otherwise, it would be tough to tell. I did not find any 138KV
line that was clean. They were all brutally noisey. These are the same
ones that I live across from. For anyone who might be thinking about
setting up a competitive station-listen very, very carefully; Do NOT
get close to these lines. After numerous tests, I found that I needed to
be about 1 mile away before it got rid of the noise on 80M, and
proabably farther for 160M. I did find one line that was quieter than
the other 138's, but it was still hell as far as noise goes. I am
convinced that these voltages should be on METAL poles.
5) 350KV and 500KV high tension grid lines (ski lift style!). These were
lines that until now, I had not compared with the others. I have been
told numerous times that the lines on METAL poles were better than those
on wood poles. They were very, very right. I was astonished at how
little noise these things give off compared with other medium voltage
lines. I'm sure there are exceptions, but in the 8 times I drove
*directly underneath* them, I only found 2 times, where the noise on 20M
came up over S-4. On 80M, understandably, the noise right underneath
them was about 5 over s-9, decreasing VERY rapidly as you get away from
them. If found that 300' was about all I needed to get rid of most of
the noise. Considering the voltages on these lines, that's not too
shabby! I was worried that these lines 3 miles from my new QTH would be
a problem until I drove under and away from them. If these lines are
maintained, they are quiet. Due to safety, I wouldn't buy a house closer
than 1 mile anyway, as I've heard the horror stories about people
getting cancer. Might not be true, but I'm not going to let my family
be the guinea pig.
Summary:
If you are considering buying a piece of land, before you even
CONSIDER paying for it, check the noise level. Even if you think that it
should not be noisey, do it anyway; you'll sleep better at night. Get
the hell away from any 138KV 3 phasers- big problems. You have to be
careful when doing noise checks with a mobile setup. You must realize
that average signal strength readins will be lower on your 8 foot loaded
whip on your vehicle. Don't think that just because it says you have an
s-4 noise, that your full size dipole will read the same- it won't
(expect higher noise on the full size). Compare one KNOWN noisey
location to another. If a friend has a noisey area, go over with your
mobile, and on a particular freq, check the S-meter, then you can
COMPARE with those you take at your proposed site.
If I had known this when I was looking at this house, I wouln't be in it
today. Luckily this was just a rental, and I'm not stuck with it for 25
yrs. Others may not be so lucky, so double, and triple check if you want
peice and quiet on the HF bands.
Cheers,
Shawn
VE6PV
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