Chris - thanks
Yes it was very odd and one of those "what?" times in my professional and ham career when you really want to check and recheck.
The cable was short circuited DC wise at the antennae end via the (working) Balun at the time it was unscrewed from the coax - I checked this afterwards in case it wasnt. I checked the TX/RX side too - nothing there.
So the time the coax had to charge was only the time from disconnection to "touching" which was appx 5 mins. And remember the coax cable was defacto sitting on the "ground" for 80m.
Now - what that charge was is something that Ive been sleeping on. How about a curved ball and seismic activity beneath where I was staying caused by rock movement and the piezo affect caused a field to be generated etc? - ok outlandish, but I was sitting at a base of an active and smouldering volcano and daily tremors were felt....Hmm perhaps not so outlandish after all...but I did check again and again after the fact and no charge was present again until we shoved it all back up in the air again a few hours later.
However, logically (probably wrongly too given my luck) the amount of "c" in pfs for 80m of RG213 aint that large and nothing like capable under normal circumstances to give such a wallop. Yes it could charge to many Kv I suppose before it reached it breakdown Voltage - and it is a few, but wallop and (White) flash and bang was audible and visible in daylight about 50 metres away (!) but what mechanism would cause the inner to get a gradient again the outer,,,,?
As I said before, apart for the Whiz Bangs in the deserts of whereever you really wouldnt think a cable could do that - but it did.
I learnt a lesson - never, ever presume because a cable is open circuit that its safe - even one that could normally not have a Pd across it, or is sitting on the ground.
I seem to remember SIDE - Switch Off, Isolate, Dump and Earth.
Chaps - any more suggestions or solutions or was this an enigma?
73 Laurence
> From: [email protected]
> To: [email protected]
> Date: Thu, 16 Apr 2009 10:07:17 +0100
> Subject: LF: RE: Arcs and sparks - user beware
>
> Dear Laurence,
>
> Thanks for your post.
> > (Its got a bit of MF in it honest)
> Whether it has or not, it could save one of our lives some day!
>
> A friend who worked for the London Electricity Board years ago told me a similar story about working on 3-phase underground cables. You disconnect both ends, then before you touch them you short each phase to earth. Rarely will you have happened to disconnect at the zero-volts part of the cycle, so apparently you get some satisfying bangs.
>
> But that may not completely explain your recent experience. One would guess that (a) you turned off the Tx before unplugging the aerial and (b) the Tx has a DC path across the aerial socket (e.g a transfo secondary). So did some other process charge up your cable?
>
> Your experience might suggest that, for those who fiddle with their aerials frequently, it might be worth permanently fitting a resistor (100k, say) across the two halves; or two, one from each pole to earth.
>
>
> 73,
> Chris G4OKW
>
>
>
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