[TowerTalk] 14' Extra Worth It for 80m Dipole?

[Jim Thomson]

Date: Sat, 6 Nov 2010 20:42:57 -0700 (PDT)
From: Edward Sylvester <navydude1962 at yahoo.com>
Subject: [TowerTalk] 14' Extra Worth It for 80m Dipole?
To: TowerTalk at contesting.com
Message-ID: <101321.51969.qm at 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