[TowerTalk] Polyphaser power ratings vs frequency

[Roger (K8RI)]

On 7/7/2010 8:48 PM, jimlux wrote:
> 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))
>    
Gas Tube?  All the Polyphasers I have use a solid state device, but no 
gas discharge tubes.

73

Roger (K8RI)
>
> 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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