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Old June 8th 06, 12:08 AM posted to rec.radio.amateur.antenna
 
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Default H FIELD ANTENNAS?

J. Mc Laughlin wrote:

P-noise is not found on an antenna imbedded in a clump of trees when an
antenna out in the open (many wavelengths from the first antenna) has
P-noise. The follow-on is that since most sites are urban or suburban, few
radio amateurs will experience P-noise.


That does not disagree with anything I said. A lower antenna surrounded
by taller objects is not subject to the same high voltage gradient as
an antenna out in a flat clear field.

P-noise is observed when there is no rain nor thunderstorms, but plenty
of wind. This is suggestive of moving charge discharging into the antenna.


So how does it get there? How does it build up? Where is the spark arc
or sizzle?

Of course, one could define this action as being "corona." Of course, if
one places enough charge on a piece of metal eventually there will be
"corona." Many antennas have a conductive path to earth that makes such an
accumulation of charge unlikely.


The fact is grounded or ungrounded antennas all behave the very same
way. Ask anyone who has yagis on towers. It is a potential difference
between earth and the atmosphere around the antenna. It isn't the
antenna charging up so much differently than earth. It is the
difference in potential between the antenna and the space around the
antenna.

Remember those old tall mast wooden sailing ships soaked with sal****er
and the fire off the yardarms at night?

Your #6 is interesting. Unfortunately, there is so much radiation from
what else is on a tall building that it is difficult to sort out where
excess noise is coming from. An antenna inside of a slightly conductive
radome that is placed a long distance from anything that could radiate might
be different.


You can walk right up to the noise source, and even see the corona at
night. It's very easy to take a FSM with audio monitor or AM receiver
with S meter and walk the roof for strongest noise, and it will
generally take you right to the tallest sharpest object (grounded or
not) on the roof.

The last place you want to be is the tallest antenna on the building.
Get high winds or inclement weather and you will be destined for
noise....grounded antenna or not.

We serviced dozens of repeaters and a few STL or Remote links in the
70's, it was a pattern that repeated.

I have a suggestion. Go to a forum where there are many people with
antennas at various heights, like a contesting reflector. Ask people
who have similar or identical antennas at various heights on a single
tall tower what they observe during high winds, nasty weather, or rain.
The very same wind and the very same moisture is impacting all of the
antennas, but without fail they will tell you the lower antennas are
always much better and the taller antennas are the first to go.

If the P-staic is actually coming from the particles or moisture in air
striking the antenna, and if the same basic sample of weather is at all
the antennas, why are the upper antennas affected more?

If it is the conductor charging, why do plumber's delight antennas or
folded elements with grounded centers have the same noise as insulated
elements?

If it is moisture or particles striking the antenna causing the
problem, why is an insulated antenna with a single sharp protrusion
just as noisey as a bare antenna? Why doesn't the noise follow the
pattern of the particle rate, and why does it occur (as you even seemed
to say) when there is no actual precipitation?

Since I've always had towers taller than 100 feet, and since I've
worked on VHF and UHF systems that had to stay up during storms, I've
spent a lot of time looking at this. I've not found anything that
points to the antenna charging differently than earth or being struck
by charged particles.

73 Tom