-=> On 11-21-96  03:04, Harvey Harbicht said to Alex Draper,<=-
-=>"About Antenna installations...,"<=-
 
Hi, Harvey and Alex;
 
 >   I've heard stories about lightning coming down the coax even when
 >   the coax were disconnected from the radio.  A large sparks would
 >   leave the connector to say a grounded wall outlet.  Could this be
 >   true or just an old CB/Ham radio myth?  Take care.
 >                                                    Alex...
[snip]
 
 HH> Back to your question. If your coax is laying very close to a ground
 HH> like an electrical outlet, theoretically yes. It just might go through
 HH> there. Maybe. It'd be rare though because that really isn't a very
 HH> good path. It's happened to guys already though. In fact I use to
 HH> disconnect my SWL antenna, hang the end near the center screw of an
 HH> outlet and and watch it spark during high winds (static charge
 HH> build-up). The end would go tick. ..tick.....tick...... That was before
 HH> I grounded the antenna outside. 
 HH> True story:  A friend of mine took a direct strike to his tower. His
 HH> coax carried the current for a couple seconds before it vaporized
 HH> (20,000+ amps of currect there). In that couple seconds though, it
 HH> worked it's way though his radios. POP POP POP POP! Needless to say all
 HH> the smoke leaked out and they didn't work any more. That's why you
 HH> disconnect all coaxes and lay them *FAR* away from a ground.
 
Nope.  Far from the radios!   :-}
 
 HH> Note: There are people who say to disconnect them and GROUND them.
 HH> That has a good point to it. Grounding the coax will allow any static
 HH> charges that build up to drain off.  BUT......it will also turn your
 HH> antenna into a lightning rod of sorts since it's now a grounded object.
 HH> I myself do NOT ground the loose coaxes.
 
I am in favor of grounding antennas during thunder storms, (and it is
REQUIRED by the National Electric Code!).  In the event of a direct hit,
there is less chance of lightning coming in on the coax and finding a path
through something else in your house.  As you mentioned, it also
discharges static, which could give you a very nasty "surprise."
 
BTW, the shield of ANY coax that goes outside should ALWAYS be grounded!
 
Here ara a copule of tricks you can use if your tower is a few feet away
from the house:
 
1: Bury the coax.  (It will last longer if it is protected against
chemicals, especially acids, which are present in the soil).  You can
run it through electrical conduit to protect it.  (Be sure to seal the
open end(s) so moisture won't get in!)
 
2: Lightning does NOT like to go around sharp corners, or, (especially),
around coils!  Coil the buried part of the coax inside a (watertight)
metal box, and connect the box to a nearby ground rod.  This will
encourage lightning to jump off the coax and go to ground instead of
inside your house.  This would also be a good place for a coaxial
lightning arrestor.
 
3: If your antenna does not have D.C. continuity, (such as a 1/4 wave
ground plane or a Discone), connect a resistor from the center conductor
to the shield of the coax.  This can be anywhere along the coax, but would
probably be easiest it installed right on the antenna.  The value isn't
critical, but I would suggest around 1,000 ohms at 1/2 or 1 watt.  This is
too high a value to effect the radio signals, but will give a path for
static to drain off.  If your antenna has D.C. continuity, such as a base-
loaded 5/8 wavelength, a resistor is useless.
 
You can also get coaxial lightning arresters which connect between two
sections of coax.  You can get them with "F" connectors for 72 ohm coax
anywhere that sells TV antenna (or cable) supplies, such as Radio Shack.
There are also heavier duty arrestors for 50 ohm coax available from
Ham radio suppliers.  Some coaxial lightning arrestors have a built-in
bleeder resistor.
 
 HH> The simple fact is that *NOTHING* will save you from
 HH> a direct lightning strike. *NOTHING*! All you can do is set up the
 HH> best system you can and pray.  :)
 
AMEN!  But the better prepared we are, the less chance there is of having
major damage, (including the house burning down), from a lightning strike!
 
Catch you later... Happy Scanning & Hamming!
   Ivy
 
 
 
... What's a mischievious Amateur Operator?  A Deviled Ham!
 
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