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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