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Date: 27 Jul 2011 23:24 GMT
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Subject: Re: LF: Lightning Story
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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" <ve2iq@magma.ca> 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
> 
> 
>