Date: Sat, 6 Nov 2010 20:42:57 -0700 (PDT)
From: Edward Sylvester <navydude1962@yahoo.com>
Subject: [TowerTalk] 14' Extra Worth It for 80m Dipole?
To: TowerTalk@contesting.com
Message-ID: <101321.51969.qm@web120514.mail.ne1.yahoo.com>
Content-Type: text/plain; charset=iso-8859-1
I have multiple antennas on a Hygain 70' Crank up Tower and a 10' Mast.? The
80m Rotary Dipole sits on top at 76'.? Have this yearning to raise the the 80m
r. dipole so that it sits at 90' with the tower fully extended.? The net gain
in height would be 14'.
?
Is this effort worth it?? Will I gain much?? Is this just plain crazy?
?
Thanks for your input.
?
73,
Ed NI6S
## sure, it will be well worth it....BUT.... you require a 20' mast out the
top of the tower to pull this off. And this assumes the dipole has it's own
overhead truss riser [which put's the truss riser at 92-93'.]
## How many other yagi's are on the same tower? What is the tower rated for?
I'd suggest you use the free ARRL mast software before you destroy the top
of the tower. How low into the tower is the
rotor plate? Do you have an intermediate thrust bearing?
http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=17127 scroll down a bit...then
down load the free software. Make damn sure you enter
the info correctly. The mast length they want is ONLY the portion that
sticks above the top of the tower. You also need to know the exact OD/ID/wall
thickness of the mast..and also the YIELD STRENGTH
[ not tensile strength]. Now if the 80m rotary dipole is inline with any
booms below it..... you have to run the calcs..twice. Once for the 80m
dipole broadside to the wind..which will also include the
boom area of any yagi's below it.......and a 2nd time, with els of all yagi's
broadside to the wind [ 80m dipole area is then almost zero]. Also beware,
the surface area the software wants to see for each ant/boom
is PROJECTED AREA of a cylinder [ length x width]... and NOT effective area.
F-12 rates their ants in effective area. To change to projected area, you
have to take the F-12 numbers..and multiply
by 1.5. F-12 only gives you the total area of the el's. You will have to
calculate the boom area's by hand. What type and how long is the 80m rotary
dipole ?
later....... Jim VE7RF
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