Open Wire Lines and Lightning

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From: Doug (doug@sunrise.alpinet.net)
Date: Sat Apr 19 1997 - 13:59:22 EDT


Hi Qrp'ers....lots of info posted on this subject. So, I thought I'd
put my experiences in the pot in case some would find it helpful.

I live in an active lightning area...the high plains. I use a large
inverted vee antenna for my main station radiator...400 ft in length.
The feed is 2.5in open wire from the poletop down to the side of the
house, where I've mounted one of the baluns made for open wire feeds.
That balun has a grounded (to the case) center tap for static reduction
and of course lightning protection. I have it bonded back to the ground
network using #2 copper and crimp on lugs...no solder joints.

This arrangement does away with the "gap" requirements, provides a good
path to ground for noise and static and hopefully will help dissapate
the energy from a nearby strike. It'd be very diffucult to handle a
direct hit...which I hope never happens.

Several hams I grew up with used a pair of old spark plugs mounted in
a grounded steel plate for spark gaps, but the plugs have sufficient
resistance that they are a hi impedence for heavy surges, and therefore
of little use in a near hit situation.

Since most of lightning's energy is of VHF in nature, it pays to ground
with that in mind, ie use copper straps instead of braid or fine wire,
as those tend to be as conductive as a length of rope for high frequency
surges. In addition, if you do have a good arrestor in your system, use
as heavy a conductor as is available to you for your ground tie, as the
device WILL use that path to dissapate energy...assuming the conductor
will take the current flow.

At one site I maintain we took a hit last July, burning off #6 and #4
copper ground ties like they were cut with a hot knife, forcing the rest
of the strike to look for ground via the A/C power wiring. The result
was complete destruction of the wiring in the conduit and welding of all
the conduit joints, blowing all the outlets out of the boxes and
blasting the meter base off the wall....impressive to say the least.
No piece of electronic gear in the site escaped damage of some sort,
with the most damage occuring to a $10k base station that had just been
delivered to the site and wasnt hooked to any antenna or power mains...
figure that one out!

Poly Phaser Corp. sells rolls of copper strap, lots of different kits
for proper grounding of coax, towers and transmission lines. They also
sell coaxial protection devices that DO work well and provide a low
impedence path to ground for static. Reading their literature is an
education in lightning protection procedures.....I recommend it.

A few years back I attended to a seminar put on by Andrew Corporation,
the antenna and coax folks. The Postulate they offered for those of us
working in the communications racket and hoping to provide a modicum
of protection at remote sites was; "Bond and ground until you run out of
money, then do a little more and it MIGHT be enough"....Sheesshhh!

Happy Grounding....

73

Doug, K7YD


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