[TowerTalk] snow static, Quad v. Yagi

[Jim Lux]

On static bleed paths...
The charging current should be quite low, since the antenna is physically
fairly small.  The cases reported in the literature of continuous sparks are
from things like miles of telegraph wires strung across the prarie.
On an antenna with no DC path to ground (say there's a transformer balun)
then there's no path for the charge to ground, so it will just build up
until it sparks into air.
On an antenna with a DC path (like a dipole fed with coax), one arm of the
antenna is directly connected to ground at some point (presumably the shield
of the coax is grounded somewhere, if only though the chassis of the radio
and the third pin ground).  the other arm is probably dc connected through
the input impedance of the radio.

One could make a good case for always having some DC path, with reasonably
high impedance, from every conductor to ground.  It could be a fairly high
impedance (several tens of K) since the current is low (microamps, probably)
so the DC voltage won't be all that high. It would also prevent your static
discharge path from becoming a lightning discharge path.

Jim raises an interesting point about parasitic elements on a Yagi which are
ungrounded. Clearly, they could accumulate charge from blowing particles
(dust, rain, snow, etc.) , and periodically discharge with a breakdown, and
the resulting impulse is almost guaranteed to have a fair amount of power
"in-band" since it's coupled to a nice resonator.
----- Original Message -----
From: <jimjarvis at comcast.net>
To: <towertalk at contesting.com>
Sent: Tuesday, August 31, 2004 2:48 PM
Subject: [TowerTalk] snow static, Quad v. Yagi


> 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 at contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk