Hi Mike,
> As Tom points out, DC grounding doesn't make much
> difference except in the case of electrostatic discharge.
The choke, or a dc ground path, helps only in the case where it
actually modifies the "arcing". If it prevents some component in the
system from arcing, it will reduce noise.
It will not shunt noise to ground and while not shunting signal to
ground, since any noise your receiver hears is at the frequency the
receiver is tuned to.
> This can manifest itself in the form of rain or snow
> static. I recently saw an anecdotal account from Mike, N7MH
> up at the Stanford Radio Club, W6YX. Seems that all their
> KLM monobanders were wiped out by rain static in the ARRL
> CW contest while their Mosley PRO-67 stayed quite.
> I suspect, but I am not sure that this has something to
> do with the fact the KLM antennas use insulated elements
> whereas the Mosley elements are grounded to the boom.
I don't believe that is true Mike. I'd bet money the Mosley was
mounted lower than the other antennas, and had less corona
coming off the elements and off the structure the antenna was
mounted on.
The "rain and snow static" we hear is primarily caused by the large
voltage gradient between earth and sky, and corona discharges
from various points in the system. Even dc grounded antennas are
subject to this noise.
Anything that reduces the voltage gradient between the antenna
and space around the antenna will reduce corona. Multiple "blunt"
elements in a close area, lower height, a broad smooth area
exposed to the charge gradient will all reduce corona noises.
Another problem is impedance matching between the high
impedance corona discharge and the system it is affecting. Quad
antennas are quieter under conditions where corona exists
because the high impedance ends of the elements are folded in,
and not at the highest point or outer edge in the structure like a
yagi. The tiny high impedance "arc" from the tips of a yagi are right
at the point where the system has its highest impedance, and
noise energy transfer is maximized.
As a matter of fact, the quad was popularized because it's first
widely known use was at a radio station (HCJB) that installed one
to minimize corona discharge from the antenna! That corona
change had nothing to do with the antennas "closed dc loop"
design. They got rid of dipole elements because the corona was
actually damaging the antennas by eating away at the element tips.
73, Tom W8JI
w8ji@contesting.com
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