[TowerTalk] Vertical antennas and lightning

[David Gilbert]

That doesn't pass my perception of the physics involved.

How does bleeding static from the clouds not initiate an ionized path 
itself?  It seems to me that's like sticking a pin in a balloon to let 
out enough air so that it won't pop.

Dave   AB7E


On 8/1/2010 10:36 AM, Bill Aycock wrote:
> David--
> This argument has always had holes, as far as I am concerned. It is  not the
> strike energy that "Bleeding" will handle, but the static charge that helps
> create an ionized path, that the strike can follow.  Diminishing that path
> HAS to help.
> Additionally, I know this is not absolute; I merely want to improve the odds
> a little.  Other protection is also needed.
> Comment?
> Bill--W4BSG
>
> ----- Original Message -----
> From: "David Gilbert"<xdavid at cis-broadband.com>
> To:<towertalk at contesting.com>
> Sent: Sunday, August 01, 2010 11:35 AM
> Subject: Re: [TowerTalk] Vertical antennas and lightning
>
>
>    
>> Look at it this way ... the magnitude of arcing you get across the end
>> of the coax if you don't have the antenna DC-shorted to ground is rather
>> tiny.  My experience over the years (when I had a dipole or vertical
>> that was not DC-shorted to ground) was that I'd get a spark across the
>> end of a PL-259 (roughly half inch spacing) every few seconds.  Add up
>> the energy from all those little arcs over maybe a ten or fifteen minute
>> period and compare it to the energy from a single lightning strike.
>> Then consider the likelihood that the portion of the cloud system that
>> generated the lightning strike wasn't even near your QTH ten or fifteen
>> minutes ago.
>>
>> It's like trying to drop the level of a flowing river by removing water
>> with a teacup.
>>
>> DC-shorting an antenna to ground is important to protect both equipment
>> and people from static buildup.  I once drew a really thick (lots of
>> current) 2 inch long bright blue arc to my left hand from the shack end
>> of the coax coming from an unterminated 80m dipole (my right hand was on
>> the floor) ... that calculates out to about 300,000 volts and the biceps
>> of both arms were sore for three days.  Imagine what the energy that is
>> capable of generating those half inch arcs might do to a receiver front
>> end or the contacts of a small relay.
>>
>> But grounding the antenna isn't going to even come close to bleeding off
>> enough charge from the clouds overhead to prevent a lightning strike.
>>
>> 73,
>> Dave   AB7E
>>