> Using
> http://www.sengpielaudio.com/calculator-air.htm I get about 6dB loss
> per 100 feet. So assuming an additional drop in the noise of -12 db
> (-20 db total under background ambience) would still mask
> communications, we get 150' + 200' or 350 feet on both sides of the
> cables at 11 K hz.
Rob,
Yes, but they will shoot you down in flames of you don't include all
the variables. In addition you have the DB drop due to distance, which
is not quite inverse squared at 6dB per double the distance. At 30KHx
sengpiel gives -28dB at 100 feet plus distance loss, so the high
frequency response of audio mics is academic.
Electromagnetic radiation is more important. This comes from corona
discharges especially in wet an icy weather. Electric companies will
quote warm and dry figures. In effect, the whole line is a giant radio
antenna which loses a percentage of the power it transmits (in
gigawatts).
What effect does the alternaiing magnetic field have on birds which
use the Earth's magnetic field for navigation, like pigeons? I don't
know and I don't think anyone knows as the research hasn't been done.
> condenser capsules mostly can
deliver dozens of khz. so you probably better use a microphone built
for measurement purposes.
Or a bat detector as in my earlier message. Here's one, the songmeter:
http://www.batecho.eu/html/frame18.html:
> As for determining "public necessity" for the double circuit 345Kv
> line, our studies suggest so far that the high capacity project is
> not needed.
The usual argument is that they are needed to "average out"
intermittent wind power, which is my anti campaign. This is adding
insult to injury after the turbines have chopped up large numbers of
bats and birds. Wind power is a highly visible "greenwash" with very
little overall benefit, but that's another campaign. I've always
maintained that nuclear energy is the answer. Don't try that one now.
:-) Of course the real solution is to stop extracting oil and gas but
I'm not putting any money on that one either.
David
David Brinicombe
North Devon, UK
Cogito cogito ergo cogito sum - Ambrose Bierce
|