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[TowerTalk] precipitation static & folded verticals

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Subject: [TowerTalk] precipitation static & folded verticals
From: W8JI@contesting.com (Tom Rauch)
Date: Mon, 22 Jan 2001 22:33:24 -0500
Hi Ed,
 
This was mainly about precipitation static, but your comments 
appear to be about noise in general including precipitation static.     
 

Remember what causes precipitation static. It is a corona 
discharge either from the antenna itself or something around the 
antenna. 

> So, are you saying the top loading contributes significantly to the
> capture area of the antenna to invalidate the test results? If so, I
> will withdraw my comments about the test.

As for precipitation static, how do you know the voltage gradient 
around each antenna was the same? 

Look at the structure. Was it physically bigger or smaller? Spread 
out or pointed? The more spread-out and blunter, the higher the 
voltage you can apply before corona starts. 

Was one nearer something else than the other? 
 
> But, before I do, can you (Yuri) explain to me why the electrically
> longer (folded and top loaded) structure was inherently quieter than
> the naturally resonant monopole structure when they are both resonant
> at the same frequency?

Now as for other noises, Yuri answered part of that. The pattern is 
almost certainly different. 

I'd like to add the following. Where does your noise come from?

If it comes from skywave and both antennas have the same 
pattern, the LOWEST efficiency antenna will deliver the lowest 
noise.

If noise is groundwave, how do you know the noise field is exactly 
the same at each antenna?

I can walk 1/4 wl measuring groundwave noise sources, and see a 
big difference in level.

Measuring base impedance is not always a good way to tell the 
antennas aren't affecting each other's patterns. For example, a 
tower 400-500 ft from my main 160 meter vertical affects the FS in 
that direction by almost 6 dB, yet I can't measure a bit of mutual 
impedance change at the feedpoint as I tune that tower.

My quietest antennas are all verticals. They are not "dc grounded", 
they are simple series-fed verticals with 100k leak resistors across 
the feedpoint. They are, for the most part, quieter than my 
Beverages because they are more directional than my Beverages. 
They would be no more quiet if they were shunt-fed, and they are 
not noisier by not being shunt-fed. If they were loops, and had the 
same pattern, they would have the same S/N ratio.

The only exception would be if they were in inclement weather, and 
had corona discharge problems. In that case the antennas with the 
lowest voltage gradient would be the quietest, because they would 
have the least corona.


73, Tom W8JI
w8ji@contesting.com

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