Of course the gradient is real, and very measurable... even in clear
air. Even with no storm around there is a gradient that can be easily
measured and a current constantly flowing from the ground that can be
measured. I forget the exact values but the gradient is on the order of
.1 kv/m and current is couple pA/m^2. When a storm approaches this
gradient gets much larger 10-20kv/m(? off the top of my head) and causes
the corona effects seen on towers and buildings and heard in radios.
When a lightning leader approaches it increases even more until the air
breaks down and streamers form... a nearby lightning discharge of
course suddenly reduces the local gradient by neutralizing the pocket of
charge in the cloud that had formed, at least temporarily. It should be
noted that even snow clouds can develop quite a charge separation,
rarely enough to trigger lightning, but often enough to cause corona on
ground structures. Dust and blowing snow can also create a charge
gradient by the collisions with the ground and other particles (the same
mechanism that separates charge in a thunderstorm except there its
between colliding ice crystals moving up and down). Even the turbulent
flow of hot dust and gasses from volcanoes can cause enough charge build
up to cause lightning.
Enough speculation... do some reading:
http://ae.atmos.uah.edu/AE/abstracts/Latham64a.html
http://www.avalanche.org/~moonstone/issw%2094'/measurements%20of%20the%2
0electric%20field%20gradient%20in%20a%20blizzard.htm
http://www.spacegrant.montana.edu/Text/SandStorm.html
http://envsci.rutgers.edu/~veron/LightningNotes.pdf
go google if you want more, there are thousands of them out there along
similar veins.
David Robbins K1TTT
e-mail: mailto:k1ttt@arrl.net
web: http://www.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
> -----Original Message-----
> From: towertalk-bounces@contesting.com [mailto:towertalk-
> bounces@contesting.com] On Behalf Of David Jordan
> Sent: Tuesday, August 31, 2004 22:25
> To: jimjarvis@comcast.net
> Cc: towertalk@contesting.com
> Subject: Re: [TowerTalk] snow static, Quad v. Yagi
>
> Interesting...here is some real world experience that might prove
useful
> for this discussion.
>
> I was talking to a ham last night about this thread and he is also an
> avid gas model airplane flyer. He says when he was younger that he
used
> to use steel wires for control cables. Those wires were about 60-70ft
> long. When storms were approaching he noticed that flying the plane at
> four or five feet above the ground was no problem but when he took the
> plane up to 50-60ft to perform loops, etc., a charge would build up on
> the pair of wires and zapp the pilot operator's hand. SO, perhaps
this
> is another practical proof that the gradient is real and measurable
(?)!
>
> 73,
> dave
> wa3gin
>
> jimjarvis@comcast.net wrote:
> > Having just spent time explaining to a guy named Yagi that his name
was
> famous, I had two hours on trains to ponder the snow static thing.
> > Because the quad avoids the corona problems of the yagi and lpda at
high
> power and high altitudes, it is not unreasonable to think that that
same
> attribute of the closed loop would also reduce snow and rain induced
> static at lower power levels. Let me append a question mark to
> that...I'd be interested in thoughts.
> > I don't buy the "radome" effect notion, though. I'm not made of
> aluminum, but I can build up a lot of charge walking across a carpet
in
> New Mexico, and have an ESD event spanning close to an inch. (> 1
mile
> above sea level). Eventually, any charge buildup on the structure
due to
> moving snow or rain particles will have to be drained off.
> > When that happens, what's the current path? Down the conductors to
the
> spool holding the BeCu tapes? Is that grounded? IF it's grounded,
then
> it may bleed off continuously, as it would for plummer's delight
yagis,
> with grounded elements. Somebody might want to ask the Mertel's. I'm
> sure they'll tell you.
> > Which brings me to a corollary question...has anyone had first-hand
> comparison abilities between plummer's delight monobanders, and an
array
> with floating elements, like a kt34a, for example? I'd be interested
in
> the snow/rain static answer if so.
> > I've heard the differences in snow static on tall arrays...where the
> higher antenna has been much noisier than the lower ones. Pretty
sure
> that's true, although I'd like to see a theory as to why.
> > OK...so much for questions from Tokyo. Gotta get some bfst and go
to
> work.
> > 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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