[time-nuts] Lightning arrestors for GPSDO antenna
n4ua.va at gmail.com
Fri Oct 17 06:49:53 EDT 2014
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
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.
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.
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