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Re: [TowerTalk] Polyphaser power ratings vs frequency

To: Mark n2qt <>
Subject: Re: [TowerTalk] Polyphaser power ratings vs frequency
From: jimlux <>
Date: Wed, 07 Jul 2010 17:48:48 -0700
List-post: <">>
Mark n2qt wrote:
> Why is the transmit power rating of polyphaser lightning protectors derated 
> at higher
> frequencies?   Does the ionizing voltage of the gas tubes decrease with 
> frequency?
> Mark n2qt
> (this refers to the typical polyphaser design that has series, dc blocking 
> capacitor and a
> gas tube shunted to ground)

It could be the power rating has nothing to do with the gas tube 
breakdown, but, rather, it related to thermal limits from IR losses.  As 
frequency goes up, the skin depth gets shallower, so the losses get 
higher (roughly in proportion to sqrt(f))

The breakdown voltage of the tube probably doesn't vary much with 
frequency (unless there's some sort of weird package parasitics).  That 
is, the breakdown voltage of a gas doesn't depend very strongly on 
frequency, once you're above a certain point (which is low).

In a vacuum, there's multipaction, and that *is* frequency dependent.

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