On Sun, 18 Jan 2004 20:28:16 GMT, "Brian"
wrote:

Since I have replaced my feed line with grounded coax I have noticed that
from 30 meters on up is almost completely free of noise. However 120
through 41 meters is still pretty noisy.Could this be due to the impedance
mismatch? I am hoping this will be reconciled when I implement the matching
transformer between antenna and coax. I'm not sure if I used that in the
correct context but I guess you get my meaning.

Not likely. As a practical matter, man made noise is a lot more
trouble on the longer wavelengths. Machinery just tends to produce it
there. The corollary is that in generally the higher frequency, the
more of a problem a good RF ground is. What is a good ground at 60Hz
can be terrible at 1Mzh, and what is good at 1Mhz isn't necessarily
good at 100Mhz.

For example suppose the lumped constant equivalent of your ground lead
is 1 µ H . at 1 Mhz that is 3.77 ohms, so relative to a 75 ohm feed,
that is a pretty good ground. At 100Mhz however it will be 377 ohms,
and relative to a 75 ohm feed, that isn't a ground at all!!! In
addition, the skin depth changes as the square root of frequency, so
at higher frequencies, the surface condition of the conductor becomes
a larger and large issue, further complicating grounding issues.