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Date: Wed, 27 Jul 2011 23:32:36 +0200
From: =?ISO-8859-1?Q?Stefan_Sch=E4fer?= <Stefan.Schaefer@iup.uni-heidelberg.de>
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Subject: Re: LF: Lightning Story
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Hi Bill,

Really an exciting story ;-)

I think once the TL084 got damaged it acts like a rather low impedant 
part and will carry several mA or A, thus it smells after a long time 
;-) It's a questing of the dissipated power and energy. The E field 
probe was protected against overvoltages and as Roelof says, it is 
rather immune to short impulses and protects itselfe a bit by becoming 
conductive. The 1N4148 would have protected the amp input even if the 
distance to the strike would be 1m i bet :-)

73, Stefan/DK7FC


Am 27.07.2011 19:24, schrieb Bill de Carle:
> 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
>