RadioBanter - View Single Post

June 13th 06, 04:29 PM posted to rec.radio.amateur.antenna

wrote:
Cecil Moore wrote:
When I lived in the Arizona, clear-sky wind-driven charged
dust particles transferred lots of energy to my bare-wire
G5RV. It caused arcing whether the outside braid was grounded
or not. It only happened when the wind was blowing and
the humidity was very low.

But that effect is common no matter where we live. As I've said several
times, a high dipole here for 160m charges enough to knock you on your
rear on a calm sunny day if the coaxial line is well insulated from
ground.

During the "H Field Antennas" thread, you said the following:
************************************************** *************
Reg Edwards wrote:
Precipitation static, eg., from highly charged raindrops and fine snow
or fine sand, impinging on the antenna wire, just causes an increase
in receiver white noise level. It can be reduced but not removed by
using a very thickly insulated antenna wire, like the inner conductor
of a coaxial cable complete with its polyethylene jacket.
----
Reg.

W8JI replied:
I've never seen a case of precitation static occuring that way.

In every single case I've seen, whether on tall buildings, tall towers,
or antenna hear earth, it has always been corona discharges from the
antenna or objects near the antenna. ... 73 Tom

************************************************** **************

I have only noticed the charged particle arcing in Arizona when
the wind was blowing and that is what I am reporting.

It is not wise to have a large high antenna that was well-insulated
from ground, since the accumulated charge can suddenly discharge
through a series capacitor and damage equipment.

Where does the accumulated charge come from if not from charged
particles? If the antenna is link coupled, the charge equalizes
between the two dipole elements and, in my experience, doesn't
arc.

Do you agree that a charged particle will transfer energy
to the bare wire in a dipole when it touches it? If not,
why not?

Of course it will IF it is at a different potential than the wire.

If the antenna were link coupled, do you agree that the
above transferred energy will try to equalize between the
two dipole elements? If not, why not?

Of course it will.

Do you agree that the equalizing of the charges between
elements would cause a current to flow through the link?
If not, why not?

Of course it will.

Seems we are in agreement that charged particle RF noise can
therefore be picked up by a receiver as Reg says above. It is
only logical that it will be worse when the wind blows causing
more charged particles to encounter the antenna wire. And,
as shown below, it is only logical that a folded dipole would
transfer less of that noise to the link than a non-folded dipole.

I disagree with your contention that the link, if the noise comes from
each particle hitting the antenna, will reduce noise. That's the part
that makes no sense.

In my experience, it eliminated the arcing. Thus it eliminated
the *AURAL* arcing noise that my ears were hearing. Why does that
make no sense? I was very clear that my receiver was off and
disconnected at the time and that I made no RF noise measurements.
A short, or 4:1 voltage balun, or choke, or link across the
connector eliminated the *AURAL* arcing noise.

Maybe you can explain why the link (or folded element) would reduce
that noise.

Seems you confused my statements about aural noise with RF
noise. I have previously said I didn't measure the RF noise.

In any case, please see the pictures below to understand why
a folded element redirects the charge equalization process
away from the link.

The process of equalizing the charge on the non-folded dipole
elements causes RF noise across the link which is picked up by
the S-meter on the receiver. I observed that many times in AZ
and wish I had made some measurements. The S-meter reports a
higher level of charged particle noise during high wind
conditions and dry-air snowstorms.

Please explain what it is about the following that you don't
understand.

1. The equalizing of the element charges on a link coupled
dipole will cause a current to flow through the link resulting
in higher RF noise readings on the S-meter during high wind
conditions when more charged particles are encountering the
antenna wire.

2. Turning the dipole into a folded dipole (or loop) gives a
preferred localized path for the equalization of the charge.
Not nearly as much RF noise current flows through the remote
link.

Maybe a picture would help. Here's a non-folded dipole with a
charge hitting it. In order to equalize charge with the other
element, part of the charge must flow down the transmission
line, through the link, and back up the transmission line to
the other dipole element. Virtually all of the pulsed charge
equalization process goes through the link.

---------CH----+ +---------------
| |
/ /
| |
link

************************************************** **************

+--------------------------------+
+--------CH----+ +---------------+
| |
/ /
| |
link

Here's a folded dipole with a charge hitting it in the same
relative place. What is the most efficient preferred path for
equalizing the charge with the other element? Not down the
transmission line and through the link but simply straight
through the antenna wire. Hint: Charge would rather take
the 50 foot path of least resistance than a 200 foot path
of most resistance.

Eureka! The folded dipole is less noisy during high wind
conditions than is the non-folded dipole because most of
the charge equalization takes place locally through the
antenna wire and not remotely through the link.

BTW, thanks for forcing me to think this through in detail.
--
73, Cecil http://www.qsl.net/w5dxp