This brings up an interesting question, Jim. The gas
tube ground blocks I mentioned are basically the same
thing with a gas tube used in addition or in place of
the air-gap. Since the aggregate RF voltage swing on
a cable drop is pretty low, I wonder how much additional
protection is really afforded by the gas tube? IOW, how
do the breakdown and clamping voltages compare
between a simple air-gap and the gas tube.
At 40 volts/mil or whatever air gives, it may be a
manufucturing issue to get the breakdown voltage on
the ground blocks down to the level of a gas tube
(CATV ground blocks are really low-cost devices).
73 de Mike, W4EF..........
----- Original Message -----
From: "Jim Lux" <jimlux@earthlink.net>
To: "Pete Smith" <n4zr@contesting.com>; <towertalk@contesting.com>
Sent: Thursday, July 10, 2003 9:43 AM
Subject: Re: [TowerTalk] lightning suppression on cable
> Didn't the cable company provide an appropriate lightning/overvoltage
> protection device? One would be required for the installation if it was
> done according the NEC. It will look like a little aluminum block with a
> F connector on each side and a lug on the side that connects to the
> uninterrupted wire to the ground rod/UFER/etc.
>
> And, it would probably be on the cable company side of the "line of
> demarcation", so it's on their nickle.
>
> As a practical matter, these things are basically a coaxial feedthrough
> with a suitably chosen gap that will breakdown at the right
> voltage. They're inherently a fairly broadband device (DC -> 2 GHz).
>
> You can also get them at, e.g. Radio Shack, for Satellite TV installations
> (since they have to send DC and control signals up the coax, and 1GHz back
> down from the LNB)
>
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