Dear all,
I feel with Bill concerning the loss of his preamplifier, but in general
I would like to raise the question whether it makes really sense to
connect a preamplifier for an VLF loop directly at the loop. At VLF
noise is high, and even a cable 50 meters long should have a rather low
attenuation. Any protection for an amplifier should work better within
the shack.
HW?
73 Ha-Jo, DJ1ZB
"Bill de Carle" <[email protected]> schrieb:
> A couple of nights ago a thunderstorm came through here just after we
> had gone to bed. We thought the storm had passed but then there was
> a very loud bang. I heard the crackle and sizzle of electricity and
> the boom almost simultaneously. A few minutes later fire trucks came
> so I got up to investigate. Turns out the bolt hit a tall pine tree
> on my neighbour's property. What remained of the tree was on
> fire. Our telephone was not working but the mains power stayed
> on. I thought for sure the next morning I'd have to replace blown
> out parts. At the time of the lightning strike my antennas were
> disconnected (outdoors) from the house because we knew the storm was
> coming. I was concerned about a preamp for some VLF loops back in
> the woods and a newly-installed mini-whip (J-310 front end) on the
> garage roof. I measured the distance to where the lightning hit: 150
> M from the struck tree to the mini-whip and 200 M to the loop
> preamp. I checked the preamp first: it was dead. Burned IC (TL084,
> I could still detect the smell in the morning). When I tested the
> mini-whip I was amazed it still worked fine! The loop has protective
> diodes (1N4148) across the hi-Z ends and those diodes also survived
> the strike, which was unexpected. Starting at the base of the struck
> pine tree one notices a newly-made straight line trench in the ground
> (about 30 M long) heading towards the nearby river. Evidently the
> current was making its way to the water. I'm wondering why the
> mini-whip (closer to the strike) survived but the TL084 did not. The
> preamp drives a buried cable (about 50 M) to my radio shack. That
> cable (no DC path to ground at either end) runs in a direction
> parallel to the trench made by the lightning but displaced at least
> 100 M. Could enough voltage be induced to burn up a TL084?
>
> Bill VE2IQ
>
>
>
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