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[TowerTalk] STACKED TH7'S AND 2L40

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Subject: [TowerTalk] STACKED TH7'S AND 2L40
From: (rattmann)
Date: Mon, 24 Mar 1997 11:54:18 -0800 (PST)
Tom, N4KG wrote, partially:
>In a previous message, I recommended a 160 foot tower with
>2L40's at 160/80 ft and TH7's at 120/40 ft.

>Another suggestion with wider application would be the following:
>Put up 80 ft of Rohn 45, guyed at 40 and 80 ft. using Philystran or
>adequately insulated steel guys.
>Place TH7's (or other tribanders/5 banders) at 40 and 80 ft.
>Using a strong mast with at least 1/4 inch wall and 90,000 psi
>yield strength, put a 2 element "shorty forty" 10-12 ft above the
>top TH7. 

K6NA writes: 
 I can vouch for this (nearly) exact setup.  At 9Y4H we have 80 feet of Rohn
55, guyed at 40 and 80 feet.  A KT-34XA at 41 feet rotates on a homemade
sidemount (tight, because there is one element VERY close to the tower as it
wraps around!).  Another KT-34XA rotates at 81 feet, with a 2 EL
shorty-forty about 11 feet above it on a chrome-moly mast.  There is an
upper-lower-both switchbox mounted at 60 feet.

Tom didn't mention it but the 80-ft tower with all the top loading turns out
to be nearly resonant on 160.  I have about 15 or 18 radials laid out from
the base of the tower (the tower base is actually elevated 10 feet above
grade on a reinforced concrete garage roof), and the shunt-feed wire runs up
to an aluminum shorting bar bolted to the tower at the 40-ft guy level.  The
tower is fed with an omega match.

For 80m, at 76 feet I mounted a 34-foot fiberglass crossarm.  This supports
two coax-fed inverted vee dipoles facing more-or-less north (slightly
favoring Europe over the states), and fed as a parasitic wire beam (the
parasite has a half-wave line into the shack for manually switching its
tuning condition).  This is a poor-man's version of the wire beam I
described in Antenna Compendium 5.

For 80m, the crossarm at 76 feet (86 feet above grade) is probably a bit low
for most installations, but it happens that the tower is about 20 feet back
from the edge of a hill which slopes steeply down toward the north and
seawater about 250 feet below. This wire beam works well, as does the 160
shunt-feed described.  Many of you on this reflector have heard the low-band
signal from Trinidad. 

Thanks to Tom for reminding us on the reflector how to build a competitive
station with a single 80-foot tower!

73, Glenn K6NA

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