[TowerTalk] Vertical antennas and lightning

[K1TTT]

Unfortunately in this case the 'bleeding' when there is a charged cloud over
head is putting charge ONTO the antenna from the ground to equalize it with
the rest of the charge being attracted to the base of the cloud.  So it make
it MORE likely to start the upward streamer that completes the path.


David Robbins K1TTT
e-mail: mailto:k1ttt at arrl.net
web: http://www.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
 

> -----Original Message-----
> From: Bill Aycock [mailto:billaycock at centurytel.net]
> Sent: Sunday, August 01, 2010 17:36
> To: David Gilbert; towertalk at contesting.com
> Subject: Re: [TowerTalk] Vertical antennas and lightning
> 
> 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
> >
> >
> >
> > 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
> >>>
> > _______________________________________________
> >
> >
> >
> > _______________________________________________
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> > http://lists.contesting.com/mailman/listinfo/towertalk
> >
> >
> 
> 
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