This reminds of something that I observed about 18 years
ago when I was going to school at Ohio State in Columbus.
Steve, N8SM (now sk) and I were at the radio club on a cold
windy winter afternoon. The radio club at Ohio State had a
600 foot long wire hanging about 90' feet in the air which
was offset fed with open wire line. The pstat that afternoon
was so intense that Steve was drawing 4" long arcs off the
feedline to ground where it came into shack. It was pretty
amazing.
BTW, I agree that the noise we so loathe is likely due to
discharge rather than charging. In the aircraft world, static
dischargers are commonly used to reduce precipitation
static caused by charge buildup on the aircraft fuselage.
These are lossy carbon loaded rods that come to a sharp
point, the idea being to promote continuous low-level bleed
off a charge from the fuselage rather than large abrupt
discharges which can be more disruptive to avionics. If
noise were primarily due to charging impacts, dischargers
would not be effective. In fact, here is an article that I found
while "googling" on the subject. Looks like this guy did
some reasonably well controlled tests on Yagis with and
without dischargers attached:
http://www.repeater-builder.com/rbtip/buster.html
This technique does seem to be at odds with low noise
characteristics that some have observed with quad antennas.
Perhaps there are two ways to combat precipitation static.
One method is to sharpen everything to a point in order to
increase coronal discharge so that it is at a steady low-level
(as with the static dischargers). Alternatively it seems that
blunting everything so much that discharge seldom occurs
(as with the quad) works at the other extreme.
73 de Mike, W4EF..................................
----- Original Message -----
From: "Jim Lux" <jimlux@earthlink.net>
> There's a fairly complete literature on electrostatic charging by dust,
etc.
> Vollrath is one author to look for (he made a Van deGraaff type apparatus
> using blowing dust as the charge carrier, rather than a belt). There are
> also reports in the literature of 3 foot sparks from the tops of sand
dunes
> at White Sands National Monument apparently from windblown dust charging.
> And, of course, there is an enormous amount of literature when one starts
> looking at electrostatic dust precipitators.
> ----- Original Message -----
> From: <jimjarvis@comcast.net>
> To: <towertalk@contesting.com>
> Sent: Tuesday, August 31, 2004 2:57 PM
> Subject: [TowerTalk] upper yagi noise--a reason?
>
>
> > I have a theory....
> > w8ji wrote:
> > Snow would have an entirely different noise than heavy rain
> > drops, and dust in wind would be an almost perfectly smooth
> > white-noise hiss. It would all tie directly in to the
> > particles per second hitting the antenna if it was charge
> > movement between the antenna and the media striking the
> > antenna. If I had 60 large drops per second hitting the
> > antenna it would be a strong 60 Hz pulse. If I had 5000
> > gentle snowflakes, it would be a 5000Hz low level pulse.
> >
> > The frequency would NOT change unless the contact rate
> > changed since the pulse rate would very clearly be synced to
> > the rate of the media contacting the antenna. Only the
> > intensity (level) would change as charge gradient varied.
> > -0-
> > Yesterday, I observed what a 40 story building did in the backwash of
> tropical storm Chuba, typhoon # 16, as it blew across Tokyo yesterday.
On
> the 21st floor, the building creaked like a sailboat, with about a 4
second
> resonance period. First the window wall, then the hallway door
frame..back
> and forth...
> > When I went out, it was blowing a good 35-40kts on the ground. At up
at
> the tops of the buildings?
> > The answer is, airflow is less affected by friction with objects, trees,
> etc. up high, than it is down low. The upper antenna sees more wind,
> intercepts more particles of snow, rain, sand, etc. and thus builds more
> charge.
> > I remember taking down a 100' rohn 25 at 2000' in the poconos, some
years
> ago. At 50', it felt breezy. At 100', my tag line blew out horizontal
and
> stayed there. I had to add 10 lbs to the bucket, to keep it where the
> ground crew could reach it.
> > So that's my theory...it builds on Tom's physics discussion, and makes
> intuitive sense.
> > n2ea
> > _______________________________________________
> >
> > See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
> Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with
any
> questions and ask for Sherman, W2FLA.
> >
> > _______________________________________________
> > TowerTalk mailing list
> > TowerTalk@contesting.com
> > http://lists.contesting.com/mailman/listinfo/towertalk
>
> _______________________________________________
>
> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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