[TowerTalk] Vertical antennas and lightning

[David Gilbert]

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



On 8/1/2010 8:40 AM, Bill Aycock wrote:
> Gene--
> In your message to Dan, you say:
>   "you'll be draining off the static electricity (DC charge) to
> ground, hopefully thus minimizing the likelihood of a strike to begin with."
> I have always believed this to be true, but whenever I even hint at it,
> someone on this reflector jumps on me. Do you have a reference for me?
> Thanks--Bill--W4BSG
>
>
>    

> --------------------------------------------------
> From: "Gene Smar"<ersmar at verizon.net>
> Sent: Friday, July 30, 2010 5:40 PM
> To: "Dan Schaaf"<dan-schaaf at att.net>; "Tower and HF antenna construction
> topics."<towertalk at contesting.com>
> Subject: Re: [TowerTalk] Vertical antennas and lightning
>    
>> Dan:
>>
>>      If the inductor is the correct value (high enough XL at the vertical's
>> lowest frequency of operation so as not to upset the feedpoint impedance
>> appreciably) you can permanently connect it to the feedpoint.  In that
>> configuration you'll be draining off the static electricity (DC charge) to
>> ground, hopefully thus minimizing the likelihood of a strike to begin
>> with.
>>
>>      I'd recommend XL>  10 X 50 Ohm = 500 Ohms at the lowest frequency.
>>
>> 73 de
>> Gene Smar  AD3F
>>