Thanks to all who provided comments on this topic. They were all great
and helpful. I've decided to pass on this QTH for the reasons advised
and some cursory measurements I made with a mobile rig. Here are some
comments which may be helpful to others:
The owner provided a professional field intensity study, that the FCC
had paid for, and it showed the 10 to 300Mhz fields were lower than 50%
of the maximum permitted continuous exposure levels. Good news, but not
conclusive.
The noise levels on a Alinco DX-70 with pre-amp on, 12' whip, & LDG
tuner were excessive on 20m, eg S5-6; marginal S3-4 on 15m and fairly
quiet on 10m. There were a few W3, 8, 9, 0 signals at S7-9 on 20. 40m
seemed noisier than normal daytime. The noise was broadband and sounded
very similar to what I've looked at where I have a HP 8586B spectrum
analyzer, probably switching power supplies with 60Hz subharmonics and
other digital circuit hash. I couldn't hear any birdies or spurs from
the transmitters on site. The power lines on the mountain are all on
poles, including those to the high power commercial transmitters.
I then drove to another (very good) site about 15 miles away, The 20m
noise was S1 or so, occasional light static crashes, and there were
numerous Europeans on the band at S1-3, Q5 (at 3pm PDT). That was the
clincher, if you can't hear em you can't work em. All utilities at this
site are underground, although there is a VERY large HV transmission
switching center about 2000' away. I've been very nervous about noise
there, but this and prior noise measurements were very good. My current
CA QTH has pole power distribution (18kv?) which sometimes is S4-5 with
the beam aimed at the pole pig, 200' away. I can't hear anything from
the HV (300kv?) transmission lines 3000' away with the beam pointed
right at them.
Summarizing my conclusions/generalizations -
1. Switching power supplies and digital circuits are the biggest man
made noise problem on HF
2. Underground utilities win big for noise reduction
3. HV transmission systems are now so well monitored/maintained that
they don't (unless seaside?) contribute much noise (I watch the copter
wash the transmission tower insulators several times a year)
4. VHF/UHF ham work is usually "above the hash" and resonators/cavities
can eliminate front end overload.
5. Locate where the number of noise producers is fewest
6. Low noise is more important than highest QTH elevation.
7. You can buy antenna gain and pattern easier than fixing multiple
external noise sources
b.t.w. for those curious, the mountain top site is 2 acres for sale on
top (1500' asl) of Cougar Mt, east of Seattle. You can see into Canada
from it (100 miles) and it is the preferred antenna location for
coverage of the FM radio metro Seattle market. At some point in the
past the owner let some hams on site with a spectrum analyzer to check
it out. Anybody know who this was or the results?
73's,
Grant KZ1W
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