A peak inside a PolyPhaser 095-0927T-A unit....
http://users.burlingtontelecom.net/~n1...@burlingtontelecom.net/images/gps_surge.jpg
Mike
On 10/17/2014 2:18 AM, John C. Westmoreland, P.E. wrote:
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 <e...@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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--
73,
Mike, N1JEZ
"A closed mouth gathers no feet"
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