In the modeling for high band beams I have done with induced current on
guy wires, the following combination methods seem to get the most bang
for the buck, varying by what one has to pay for stuff, whether you have
insider/free access. Note that it's the 1/2 wavelength plus metallic
right under the antenna that does the most damage. All metallic right at
tower is insulated at the tower.
Philly for first 33 feet, then unbroken metallic. 45 feet is somewhat
better for 40 meters.
21 ft fiberglass insulator, then 11 foot metallic, then regular
insulator, then unbroken metallic.
three 11 foot metallic sections with insulators, then unbroken metallic.
21 ft fiberglass insulator, then unbroken metallic.
two 11 foot metallic sections with insulators.
First option is a lot of value out of 100' of Philly.
Last two options not much help on 40 meters.
The ARRL published figures for non-resonant sections are ineffective on
metallic guys directly under an antenna, because the current is
unequally induced across it's length, and the current does not
distribute according to the classic halfwave sinusoidal form. The 27
foot length directly under the antenna is PARTICULARLY ineffective on 10
and 15. The only metallic length worthwhile directly under a beam is 3/8
wl, 1/3 wl or less at the highest frequency in use.
73
-----------------
Guy Olinger
Apex, NC, USA
----- Original Message -----
From: "Pete Smith" <n4zr@contesting.com>
To: <towertalk@contesting.com>
Sent: Thursday, June 07, 2001 8:24 AM
Subject: Re: [TowerTalk] Rohn fiber insulators
> At 06:53 AM 6/7/01 -0500, J. Kincade wrote:
> >Still, to follow the "non-conducting materials for the first 1/2
wavelength
> >at the lowest freq" (this rule makes perfect sense to me), one would
need
> >three of these end-to-end on each guy, and at $50 a pop x 2 guys,
we're
> >talking $900 minimum + fittings. Again makes 6 70' lengths of 6700-lb
> >Phillystran look pretty attractive at about $530 + fittings, doesn't
it?
>
> Sure does, which is why I now am using all-Philly top guys, and moved
the
> fiberglass insulators down to my middle guy station. And I got 3
> previously-owned 100-foot lengths of 6700 lb. Philly for $75, with
potted
> ends, which made that look even better.
>
> I would never use more than one of these per guy, and then only if the
> nearby antenna was for 20 meters and above. Not 1/2 wavelength, but
at
> roughly 45 degrees from the antenna elements no interaction was
discernible.
>
> 73, Pete N4ZR
> No, no ... that's WEST Virginia
>
>
>
>
>
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