Daron,
You have done all the right things, so far. Since your antenna is very
likely to suffer a direct strike at some point in time, you may want to
plan for the "worst-case scenario." Heavy-Duty is the name of the game.
First and foremost, make certain that the tower itself has the best
possible connection to Mother Earth. If one of your antennas is going
to take a strike, the stroke current should see a straight, direct,
low-impedance path to a good ground. That means that your antenna
clamps should have good metal-to-metal contact between the antenna
sleeve and the tower member, with some sort of zinc-based contact
enhancement compound smeared around the contact areas. If the tower
grounding system is not good, the stroke current will take alternate
paths through the equipment building- and that means major damage.
Next, your equipment cabinet needs to act like a Faraday Cage, so that
everything inside is protected from voltage differentials. Your
feedline should enter this cabinet through a very robust surge arrestor
that is solidly bonded to the cabinet sheet metal. I prefer
Huber+Suhner gas tube arrestors, but the best Polyphaser arrestors are
okay. The top of the cabinet should be bonded to any overhead trays
with #4 copper wire, and the bottom of the cabinet should be bonded to
any metal conduits penetrating the slab at floor level, again with #4
copper wire. Do not depend on the equipment grounding conductor
bringing 120 VAC to the cabinet, to perform lightning surge grounding
duties as well. Of course, the 120 VAC power supply should be protected
with a full-wave surge arrestor before it enters the cabinet, and again
before the power is distributed within the cabinet.
Finally, any telephone autopatch or alarm lines should be fully
protected both before and after they enter the cabinet, which entry
should be through metal conduit grounded at both ends.
Does all of this effort seem excessive? To some people, yes. However,
it is grounding and protection techniques like these that have kept my
UHF repeater on the air after at least four direct strikes in as many
years, when most of the other radios at the same site were seriously
damaged or destroyed. Choose wisely....
73, Eric Lemmon WB6FLY
"Daron J. Wilson" wrote:
>
> Installing VHF and UHF antennas on some towers in locations where the
> whip may extend above the highest point of the tower, essentially
> becoming the lightning rod makes me wonder if I'm doing all I can.
>
> Currently my plan is a good DC grounded antenna, grounding kit bonding
> the heliax to the tower just below the antenna and again where it leaves
> the tower headed into the building. Grounding kit bonded to the
> grounding bus bar on the exterior of the building where it enters,
> polyphaser lightning arrestor inside the building grounded to the inside
> bus bar. Am I missing anything obvious? The polyphaser seems rather
> small, but they must be able to do the job. Just trying to do all I can
> to protect the equipment.
>
> Thanks in advance
>
> Daron J. Wilson, RCDD ) )
> Telecom Manager ( (
> LH Morris Electric, Inc. ) )
> (541) 265-8067 office _|****| mmm!
> (541) 265-7652 fax ( | | coffee!
> (541) 270-5886 cellular \| |
> [EMAIL PROTECTED] |____|
>
>
>
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>
>
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