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Electrically charged volcanic ash in a 'cloud' above the
antenna? Have observed some pretty impressive flashovers
with thunderstorms passing overhead.
Charged ash particles descending on the antenna? Snow,
rain and wind static can make a pretty impressive showing...although not
like the passing thunderstorm.
Jay
----- Original Message -----
Sent: Thursday, April 16, 2009 7:19
AM
Subject: LF: Arcs and sparks - user
beware too
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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