I've seen evidence if this also. Some years ago, one
of the locals had a 205BA/40-2CD stack at 80-90 feet.
On top of the mast was a Super Stationmaster for 2M
(think these are 20 some feet long). Therefore, tower
had a long, pointy top. After two or three direct hits
that blew the Stationmasters to bits (and did other
damage), the newest 2M Stationmaster was side-mounted
down the tower. It was probably 30 feet lower but
still worked well. The tower was never hit again. Or
if it was hit, there was no damage noted. Coincidence?
Hmmmm...
73, Stew K3ND
--- Tom Champlin <w0hh@msn.com> wrote:
> No one can predict what lightning will do,
> regardless of whatever protective
> mechanism is used, or regardless of the theoretical
> prowess of the designer.
> I have observed many hams who have a yagi above
> their tower, but do not have
> the 20 foot 2 meter shaft above the yagi who have
> never had any lightning
> problems. I also know hams who did have this big
> lightning rod above their
> yagi who lost the whole station. After personally
> inspecting such an
> installation that had just been hit, I decided to
> never have anything above
> the yagi except maybe 5' of mast for the truss. In
> 13 years, I have never
> had a hit. I do use heavy solid copper radials and 3
> ground rods under the
> tower to help dissipate a strike should one occur. I
> also use the Polyphasor
> coax lightning arrestor which may be of some value.
>
> 73, Tom W0HH
>
>
> ----- Original Message -----
> From: "Tower (K8RI)" <tower@rogerhalstead.com>
> To: "Jim Lux" <jimlux@earthlink.net>;
> <TOWERTALK@contesting.com>
> Sent: Sunday, March 21, 2004 9:48 PM
> Subject: Re: [TowerTalk] Static, Lightening, and
> protection
>
>
> > I'm gonna stick with it just as I wrote it. <:-))
> >
> >
> > >
> > > ----- Original Message -----
> > > From: "Tower (K8RI)" <tower@rogerhalstead.com>
> > > >
> > > > First, Lightening is a discharge of static
> electricity, just like the
> > > spark
> > > > from your finger to the door knob after
> walking across a carpet. They
> > are
> > > > pretty much developed by the same kind of
> process which is friction
> > > removing
> > > > electrons from atoms.
> > > Not exactly.. shuffling your feet across the
> carpet is a somewhat
> > different
> > > charging mechanism than, say, rain drops and ice
> crystals being carried
> > > by
> > > up and down drafts.
> >
> > Not really, Electrons are stripped by friction.
> >
> > >The exact mechanism for thunderstorm
> electrification is
> > > the subject of a fair amount of research (made
> more difficult by the
> > > fact
> > > that thunderstorms tend to kill probes inserted
> into them).
> >
> > True, but it's not the basics, but the actual
> mechanics for which we still
> > search.
> > Such as the amount of energy given off when hail
> stones are formed and the
> > amount of energy
> > They contribute versus the water and wind. One
> theory holds that only with
> > hil forming is there enough energy to produce
> thunderstorms.
> >
> > >
> > > >
> > > > The lightening strike occurs when a low enough
> resistance path is
> > > > established between two points be they cloud
> to ground or between two
> > > > clouds.
> > >
> > > Resistance has very little to do with spark/arc
> breakdown in air. It's
> > > a
> >
> > It has every thing to do with it. Just not in the
> way most people think in
> > terms of resistance.
> >
> > > (not very well understood, in the details)
> ionization phenomena, with
> > > cascading leaders proceeding in short jumps,
> with charge moving through
> > the
> > > leaders to the head end of the leader.
> >
> > How they proceeded is one thing, but the ionized
> air is a relatively low
> > resistance compared to the sourrounding air.
> > >
> > >
> > > >
> > > > It can be, and has been shown using a Tesla
> coil, and Vandegraff
> > generator
> > > > that some pretty hefty sparks can be
> developed.
> > > And, as well conventional capacitors... A Tesla
> coil has a v, ery
> > different
> > > spark propagation mechanism than lightning or a
> DC single shot spark
> > > (like
> > a
> > > Van deGraaff generator, or, more commonly in
> impulse research, something
> > > like a Marx generator). However, like
> lightning, these are all
> > > characterized by extremely non uniform fields,
> at least at some point in
> > the
> > > process. (Tesla coils can make quite long sparks
> with relatively low
> > > voltages because they are repetitive impulses
> and have high peak power
> > > in
> > > the impulses)
> >
> > True, but lightening strikes consist of a number
> of relatively short
> > pulses
> > with high currents and very high, or steep rise
> and fall times.
> >
> > >
> > >
> > > Add a couple Lenhide Jars
> > > > (sp?) and they and give you a poke you won't
> soon forget. It has also
> > been
> > > > shown that a single *sharp* protrusion added
> to the static ball on top
> > can
> > > > completely eliminate the *big* spark. A
> coronal discharge will
> > > > develop
> > > > around the sharp point bleeding off the
> energy.
> > >
> > > Yes, indeed, having sharp corners will create
> corona, which will bleed
> > > off
> > > charge, but that's a small scale effect. On a
> Van deGraaff generator,
> > where
> > > you're basically charging a capacitor of a few
> tens of pF with a current
> > of
> > > microamps, a corona current of a microamp is
> significant. When you're
> > > looking at transferring 10's of Coulombs at
> kiloAmps, as in lightning,
> > it's
> > > another story entirely. Corona is the bane of
> HV engineers everywhere
> >
> > Except the build up is not abrupt. It may take
> tens of seconds or even
> > more
> > than a minute for the charge differential to
> build. If the build up can
> > be
> > spread out, or partially drained it should have a
> positive effect. With
> > the
> > sharp points the charge should start bleeding
> immediately while still low.
> > That is not to say the lightening strike could be
> prevented. Maybe so
> > and
> > maybe not.
> >
> > > (except those making ionizers<grin>) for a bunch
> of reasons: Where
> > > there's
> > > corona, there's ozone and nitrogen oxides and
> other reactive/corrosive
> > > species, which tends to degrade insulation;
> Corona is often a precursor
> > > to
> >
> > You should see the top of my tower. I have to
> replace the connectors
> > every
>
=== message truncated ===
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