> Many people have described observing this anecdotally, like W0UN with his
50
> to 100-mile view in Colorado, lighting strikes would cease when they
neared
> his antenna farm and pick up again a couple miles on the other side.
>
The strikes may decrease, but I doubt it's due to the grounded towers.
Strikes ocurr due to a potential difference between the cloud (source) and
ground. As a storm moves localized and moving areas of charge form on the
ground as well as in the clouds(NWS). A grounded tower only serves to move
opposing portions of the charged area closer together. OTOH the charged
area my be to one side of the tower at a distance greater than the height of
the tower. In this case the ground feeder will probably initiate from the
nearby ground instead of the tower. Strikes are preceeded by what are
called leaders, or feeders. These leaders extend both from the cloud(s)
downward and from the earth upward as well as between clouds. *Generally*,
but not always, the downward strike comes after an initiating upward
current.
The theory behind lightning rods and static balls is they help bleed off the
charge faster than it can accumulate much like the corona discharge from a
Vandagraph generator. It's basically a high voltage corona with little
current. It takes time for the charge to build high enough for a strike to
occurr. This takes a fine point, or a lot of fine/sharp points. Still, in
many storms the charge builds far faster than the lightening rod(s) or
static balls can bleed off.
It is not the job of the rod or ball to protect the structure during a hit,
but hopefully to prevent the hit from happening, or lowering the charge so
the strike is not as strong as it could have been.
> Many of us have also observed the tic-tic-tic of static discharge coming
in
> on a coax.
Everything is relative. Looking at it from the lightning's perspective that
spark is the antenna *charging* to the localized, higher potential
difference of the ground.
>
> I doubt these things "prevent" a lightning strike, but I personally do
> believe they help discharge the atmosphere near the antenna farm, which
> helps prevent some strikes. This effect may be much more pronounced with
a
> multi-tower station than with just one tower.
I don't think any one knows for sure, but logically all those high points
could help bleed off charge, ... or they could just pose as a generalized
ground at a higher altitude. After all, it is generally the taller objects
that *tend* to get hit. Look at the repeated hits the Empire State Building
takes.
>
> On a dry winter day when you're walking on the carpet at the office and
then
> touch the metal drinking fountain you get a sudden static discharge,
Ever see snow static cause arcs across a PL-259? I've never had a mag that
put out that much juice. IF it's cold and really blowing you can get an arc
every 5 seconds or even less and that is one potent strike. They are a real
good reason for not disconnecting the cable and letting it lay on the floor.
The choke from center conductor to ground at the coax connector on most rigs
prevent the snow static from building to much of anything.
When static starts to build here, I can hear the popping of the flash overs
at the center insulators on some antennas. One reason I now have normally
grounded relays and the antennas are at DC ground.
Like Tom I never, or rarely ever, disconnect a rig during a storm. I do
quit operating at times though. <:-))
> analogous to a lightning strike (though micro). Touch something metal
every
Kinda, sorta, almost, similar...<:-)) The dynamics and as you say, scale,
are different but there are similiarities.
> few steps and the charge cannot build up to such a size. You are
> discharging the buildup before it gets so big.
Which is what lightning rods and static balls are supposed to do.
Roger Halstead (K8RI, EN73 & ARRL Life Member)
N833R, World's Oldest Debonair (S# CD-2)
www.rogerhalstead.com
>
> 73 - Rich, KE3Q
<Snip>
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Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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