Topband: Re: [TowerTalk] precipitation static & folded verticals

[Tom Rauch]

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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