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Re: [TowerTalk] Pl-259 Flash over voltage

To: "K8RI on TowerTalk" <>,<>
Subject: Re: [TowerTalk] Pl-259 Flash over voltage
From: Jim Lux <>
Date: Sat, 02 Dec 2006 06:29:30 -0800
List-post: <>
At 04:49 PM 12/1/2006, Jim Lux wrote:
>At 04:19 PM 12/1/2006, K8RI on TowerTalk wrote:
> >The talk about breakdown voltage which is basically air across the space
> >between the inner and outer conductors at the PL-259. Given LMR-400 has
> >roughly 34 pfd per foot (23.9) or 230 pfd per hundred feet that is not a lot
> >of capacity.
>Why would the capacitance for 100 ft not be 100*the C for 1
>foot?  Something is weird here.

Looking again, I think you have a typo.  24 pF/foot, 2400 pF for a 
hundred feet.

Other data of interest for this case.. They rate it at 2500VDC (It's 
air/foam dielectric.. gonna be a lot lower than solid PE RG-8 like 
cables)  If it were pure air, the actual breakdown (at sea level) is 
probably around 5 kV, given the dimensions, and it's probably a bit 
lower because of the foam. (things with voids have very low breakdown 

Resistance: about 3 ohms/1000 ft for inner and outer together (from 
that, one could calculate how much of the stored energy will be 
dissipated as heat as opposed to in the spark). That would be a lower 
bound.. It's actually a bit more complex since the current waveform 
is a pulse (so skin effect comes into play) and a travelling wave.



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