Hi Eric,
> I'm looking for specific information which compares the level of
> precipitation static on folded vs unfolded antennas (preferably
> verticals). Is anyone aware of published literature which, for
> example, reports of measurements of measured precip static levels on a
> normal vertical, compared to a folded vertical on the same site during
> the same time?
You won't find any data on this, because there isn't any reason to
take the data in the first place.
Precipitation static is caused by corona discharges from the
antenna or from other structures near the antenna. Corona is a
function of voltage gradient between the antenna and charged
clouds or "stuff" floating in the air.
Folding the antenna won't change that. The effect is no different
than shunting the antenna to ground with a large inductor. There
will be no change in static levels, unless something in the feed-
system is arcing from charge buildup.
Reducing antenna height, making the antenna "smoother"
(especially at the top), adding other taller structures around the
antenna, and perhaps covering the antenna with a dielectric at
points where corona is forming will often help.
> Alternatively, has anyone installed a folded vertical and a normal
> vertical and been able to make SIMULTANEOUS comparisons
> between precip static levels?
I have. I have also charged a mist from a hose and sprayed an
antenna to see if the noise was from charged droplets hitting the
antenna. The only noise sources I could find were corona based
noises, and nothing other than what I mentioned above made any
difference.
I had to do the test because of an emergency communications
system on a tall building that would go down from receiver noise
when weather was bad. The solution was to put a backup system
on a much lower roof, and switch to it when weather was bad.
The taller structure shielded the lower roof from the charge gradient
during inclement weather. Folded antennas, "dc" grounded
antennas, etc were absolutely no different than anything else in
solving the problem, since everything on the roof was discharging
and making noise.
73, Tom W8JI
w8ji@contesting.com
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