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In the days of round aircraft engines
and wire HF/MF antennas, you could depend on a 2-3" arc from either wire against
A/C ground while flying through heavy weather...
Expensive VanDegraf
generator...
On the flip side, you could light your
cig from the antenna terminal of the ART-13 when on a lower
frequency...
Just hold a pencil lead near RF
terminal, key the TX, and VOILA, cigarette lighter!!!
But that is all gone
now...
Dave @ /17
qrpp 505.750 CW beacon
----- Original Message -----
Sent: Thursday, April 16, 2009 7:51
AM
Subject: LF: Re: Arcs and sparks - user
beware too
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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