Andy and Doc,
Having been the recipient of a direct hit last summer, I can not emphasize
enough the importance of proper grounding techniques and NO unprotected
lines into the shack.
Doc, I think ground shorting coax switches are fine ... as auxiliary
devices only. I have one in my shack, and it is acceptable for protecting
against 2 things: ESD (static discharge) that I might cause by touching
the center contact of a coax cable or connector, and the other is induced
lightning. We call that NEAR STRIKE LIGHTNING in the aerospace biz. It
is the field induced by a direct discharge at some specified distance,
which in most cases is 10 meters. However, I can testify to the fact that
it's pretty nasty at 20 meters or more if the main lightning strike is a
"big" one.
In short: per numerous articles that have been written in QST and other
places, use proper protective devices on EVERY conductor that goes
into/out of the shack or dwelling. That includes all coax cables, rotator
lines, power lines, phone and CATV lines, etc. The correct location for
the protectors is at the entry point of the building, preferably on the
outside, so that lightning energy stays out there. Since it is difficult
to protect open wire feeders, I do not advocate their use into the shack -
use an external balun and tuner so that only coax enters the shack. All
towers, support masts, and antenna systems should be thoroughly DC
grounded, and the grounds tied together at a common point - such as at the
bulkhead panel where the lines enter the building.
NO, this is not cheap, and it is not easy to do if not pre-planned when
the house and/or shack were built. However, as someone who was using his
radio to conduct emergency communications at the time of the lightning hit
(yeah - mic in hand and talking into it), and who can say that he, the
radio, and everything in the house not only survived the hit, but kept on
working afterwards, every dollar spent and every minute spent on the
grounding system and the protectors was totally worth it. One coax
lightning protector was destroyed, several runs of coax were damaged
(jackets turned to carbon and voltage punch-thru of the center
dielectric), and one antenna was converted to toast (a high quality
2m/70cm duobander with a beautiful fiberglass radome over the working
elements). Further, a rotator and two remote antenna selector relays
(tower-mounted) were damaged. In one case, relay contacts were welded
together.
I consider myself lucky. I put in the "brick outhouse" grounding system
starting in 2000 when the house was built and over the next few years as
towers were added. In the 38 years of hamming prior to that, I had
squeaked on by with minimal grounding and protection, due to either cost
or difficulty of construction issues. Had I taken a hit back then like I
did last summer, I would have been a crispy critter and my house converted
to charcoal.
Go ahead and use that switch - but NOT as your main means of lightning
protection. Believe me, that's one function it is not designed to provide
- irrespective of vendor claims.
73, Dale
WA9ENA
"Andy" <ingraham.ma.ultranet@rcn.com>
Sent by: rfi-bounces@contesting.com
03/12/2009 09:14 PM
Please respond to
Andy <ingraham.ma.ultranet@rcn.com>
To
"RFI List" <rfi@contesting.com>, <tvi-rfi-emi@mailman.qth.net>
cc
Subject
Re: [RFI] Is a Ground-Shortening Switch Better?
> Is a ground-shortening coax-antenna switch preferred
> for lightning/static reasons?
>
> Any down side?
Forgetting to throw it before the storm comes!
The best place for a switch (or physical disconnect) is before the
feedline
enters your shack, with the shortest possible connection to ground. Which
makes it inconvenient to toggle. Putting the switch inside the shack adds
risk.
For discharging static before it builds up to dangerous levels, a switch
inside probably works. But for anything approaching a direct hit (keeping
in mind that nothing can save you from an actual direct hit), putting the
switch inside brings the energy from the lightning into your house, which
could ruin your day.
Andy
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