[time-nuts] Lightning arrestors for GPSDO antenna

John C. Westmoreland, P.E. john at westmorelandengineering.com
Fri Oct 17 02:18:29 EDT 2014


Hello Dave,

I think we had a similar question recently - and I have been told the
PolyPhaser products are gas tubes - I haven't opened one up yet.
TESSCO sells these online - you can find them here:
https://www.tessco.com/products/displayProducts.do?groupId=90143&subgroupId=91046

Regards,
John W.


On Thu, Oct 16, 2014 at 10:23 PM, 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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