[TowerTalk] Where to put the arrestors

[Gene Smar]

Martin:

     I have a similar tower installation, with the tower fifty feet from the
ground-floor shack, and three ninety degree turns and one forty-five in the
conduit run.  My two cents follows.

     I'd recommend four inch conduit minimun for your installation.  I used
three inch PVC and it's a tight fit with the few cables I have in it
already.  I'd also recommend you break up the conduit at the house end with
a steel box at ground level.  That is, don't turn up the coax at ground
level, run the twelve feet to the shack , then install a box for grounding.
The downcomer lead from this box to an earth ground rod will be too long
(inductive) to provide adequate protection.

     In my installation I have the Polyphaser lightning suppressors at the
base of the tower, where the coax enters a steel box where I keep the
antenna switch.  I have the coax shields grounded at the top of the tower
and at the bottom, just before the coax turns to go into the box.  I also
have a single-point ground bar in another box at the other end of the
conduit run, just outside the shack.  All coax shields are connected to this
bar through bulkhead feedthrough fittings.  My control wires are connected
to a Polyphaser DC line lightning arrestor at this point, too.

     My thinking on this design was that I have a much better earth ground
connection at the tower (three round rods to 135 feet of #2 wire radially
from the tower with eight more ground rods along the way) than at the house
(one ground rod at the end of a single ground radial.)  I wanted to shunt
any lightning energy from the Polyphaser coax protectors to ground at the
tower, where this better ground exists, rather than closer to the house.

     Many will argue (and have in the past) that this approach exposes the
buried coax segment between the tower and the shack to a scenario wherein
lightning energy can be coupled onto the coax center conductor (the main
reason for the Polyphasers).  I disagree.  At worst any lightning energy in
the ground, from a nearby strike let's say, will be coupled to the shield,
not the center conductor.  This energy will be captured at the shack-end SPG
panel and shunted to ground outside the shack.  Plus, with my and your coax
in PVC conduits,  the likelihood of such energy coupling to the coax is
reduced, IMHO, vs a direct-buried coax run.

     I learned a lot at the time of my project from N3RR's web pages.  Check
out http://www.users.interport.net/n/3/n3rr/lightningprotection/index.htm
for detailed info.  You can, of course, install arrestors at BOTH ends of
the conduit system, budget permitting, but I consider that unnecessary
(belts-and-suspenders kind of approach.)

73 de
Gene Smar  AD3F


----- Original Message ----- 
From: "Martin Sole" <msole at loxinfo.co.th>
To: <towertalk at contesting.com>
Sent: Monday, May 31, 2004 1:09 AM
Subject: [TowerTalk] Where to put the arrestors


> Hi,
>
> The hole for the tower is being dug. A trench will also be dug and layed
> with suitable coduit. This will run from the tower to the radio room
> entrance, about 70 feet from the tower and includes a 90 degree turn. I
will
> probably run 3 or 4 feeders all 1/2" heliax type together with rotator and
> ancillary switching cables. Feeders will be buried from the tower to the
> house but will rise up about 12 feet to enter the upstairs radio room. The
> question is where would be the best place to put my protection devices, if
> any, at the grounded copper entrance panel fitted to the house or in a
> grounded steel box at the base of the tower?
>
> 73's
> Martin, HS0ZED
>
>
> _______________________________________________
>
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>
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