[time-nuts] Lightning arrestors for GPSDO antenna

[George Dubovsky]

If anyone is interested, I have a few NOS Zap-Tech 30-105 (now called CX-TF
apparently) surge suppressors available. These are basically a single shunt
gas tube (the coaxial center conductor runs through the center of a custom
gas tube), and they were sold as GPS in-line suppressors. I use them at the
far end of the rf spectrum: all of my receive-only wire antennas
(Beverages) for 1.8-7 MHz have one on each feedline where they enter the
house. These antennas are up to 800' long, and I know for a fact they pick
up surges from every passing storm and, so far, the elephants have stayed
away... ;-)

These units have TNC female adapters on both ends, but if the TNCs are
screwed off (they are loc-tite'd on), there are F-female connectors
underneath. $20 will get one mailed in the US.

73,

geo - n4ua

On Fri, Oct 17, 2014 at 1:23 AM, ed breya <eb at telight.com> wrote:

> Of all device types, I think gas tubes are the best for this sort of
> application - very low C, and high surge current rating. I'm picturing the
> kind that are used in power supplies and such for limiting line transients
> - about 1 cm dia and length with axial leads. I don't know what kind are
> used in "lightning arrestors," if they are the same or scaled up in size.
>
> Whether you make it able to take a direct hit depends on how big of a hit,
> your budget, and the environment of the antenna and lines. If it's the
> tallest thing in a huge field in a lightning-prone area, then it could be a
> big issue, but I don't think most people have that situation.
>
> You may want to look at the US National Electrical Code (NEC) for ideas -
> I believe that subject is covered there. The main thing there would be
> safety against injuries and fire, even if the equipment is destroyed.
>
> I think what you would want is kind of a pi network - the lowest impedance
> path to ground at the antenna zone that can be practically realized, then a
> high common-mode impedance (or even fusible) line to carry the signal to
> the building, then another low impedance path to ground at the building.
> This means that in my opinion, you should not put the feedline in metal
> conduit unless it's essential for protection - or underground, which should
> improve the grounding. You want the antenna zone to absorb the brunt of any
> discharge, then use the higher line Zcm to hopefully give some degree of
> isolation from there to the building.
>
> Ed
>
>
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