That is 3/16" through the material, or with an air gap of 3/16"? the
problem is not the 1/4" if it were inside the fiberglass. But if the 1/4"
is between the ground and hot parts of the vertical and is along the surface
of the fiberglass rod it's a different story.
David Robbins K1TTT
e-mail: mailto:k1ttt@arrl.net
web: http://www.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
> -----Original Message-----
> From: john@kk9a.com [mailto:john@kk9a.com]
> Sent: Saturday, October 10, 2009 00:17
> To: TOWERTALK@contesting.com
> Cc: n8de@thepoint.net; David Robbins K1TTT
> Subject: Re: [TowerTalk] Insulators
>
> I have used PVC pipe (which probably has a 3/16" wall) to insulate
> verticals
> from their mounting plate and ran a KW with no arcing problems.
>
> John KK9A
>
> To: <towertalk@contesting.com>
> Subject: Re: [TowerTalk] Insulators
> From: "K1TTT"
> Date: Fri, 09 Oct 2009 22:35:53 +0000
>
>
> Only 1/4" exposed? Not much of a gap for an antenna feedpoint unless you
> operate barefoot or qrp all the time. granted, the dc sparkover voltage
> of
> a 1/4" gap is on the order of 5kv or so in dry air... and 1500w at 50ohms
> is
> only 275v or so if I punched that through the calculator right. but you
> are talking the conduction along a rather large surface area that will be
> wet, contaminated with metallic salts that run down the vertical, and may
> be
> porous if you don't keep it well sealed. Take a good look at how power
> line
> insulators are designed, the actual gap between the hot and ground metal
> pieces may only be 1/2-1" for 20-40kv of line voltage straight through the
> insulating material... but trace the surface distance between them and
> you
> get anywhere from 4" to maybe 24" for that same voltage. The extra
> surface
> area along the glass, porcelain, hard plastic, or silicone rubber surface
> is
> to make it able to handle that contaminated rain water.. and in most
> insulator designs there is a method used to keep at least part of the
> surface dry. This approach is also seen in commercially available
> insulators for verticals, there is always at least several inches of
> insulating material between the conductors.
>
>
> David Robbins K1TTT
> e-mail: mailto:k1ttt@arrl.net
> web: http://www.k1ttt.net
> AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
>
>
> > -----Original Message-----
> > From: n8de@thepoint.net
> > Sent: Friday, October 09, 2009 21:36
> > To: jimlux
> > Cc: towertalk@contesting.com
> > Subject: Re: [TowerTalk] Insulators
> >
> > Have already cut the rod with a hacksaw with a new blade .. no
> > degradation of performance from first cut to last.
> >
> > I tested the first 6+" length by stressing it with the lower tower
> > section and the tower base. Very strong stuff.
> >
> > I agree that some kind of lacquer needs to be put on the insulator to
> > protect it from the 'weather demons' even though less than 1/4" is
> > exposed to the elements.
> >
> > I'll let you know next Summer how it's holding up.
> >
> > Don
> > N8DE
>
> _______________________________________________
>
>
>
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