[Towertalk] yagi spacings

[n4kg@juno.com]

I like to have ~1/3 of the mast INSIDE the tower
to minimize the bending moment applied to the
upper portion of the tower.

Some people cut diagonals to place a rotor inside R25.
Another good position is to put the rotor plate at the 
very TOP of the next section down, and cut one of the
Horizontal Steps at the bottom of the Top section.  This
provides enough clearance to insert / remove the rotor
without weakening the tower since there is another
horizontal step only inches below at the top of the 
lower section (along with the rotor plate).  Yes, it
does take some extra mast but it is SAFER than
placing the rotor near the top when you use a long mast.

You may want to consider using a crane or boom truck
to insert your mast.  The most scary thing I ever did on
a tower was insert a 24 ft mast in the top of a 130 ft 
tower using a standard 12 ft Rohn GIN pole.  I do NOT 
recommend that approach.  A sturdy (thick wall) 20 ft 
tube (preferably aluminum) securely attached to the 
outside of the tower with a pulley at the top is another
viable method for knowledgable tower riggers.  You need
to really understand all the forces involved and the
capabilities of your materials.  This is a DANGEROUS
process. The SAFEST approach is a crane or boom truck.

Tom  N4KG


On Mon, 14 Oct 2002 (PDT) steve sala <stetrekve@yahoo.com> writes:
> I am going to put the following three yagis up on my
> Rohn 25 using a M2 2800 rotator.  My 24 foot mast
> (2&#34;OD)is too heavy (98 lb)at that length so I want
> to cut it off and use only that which is necessary to
> mount the three Yagis.  Are my spacings adequate for
> non interaction?  Can I go closer or further apart?
> 
> top of mast = Comet GP9 2/440 fm vertical
> 
> 1 foot down from top of mast = M2 2M5WL 17 element,
> 33' boom 2 meter yagi with support rope.
> 
> 5 foot down from top of mast = M2 6M7JHV 7 element,31'
> boom 6 meter yagi with support rope
> 
> 13 feet down from top of mast = Force 12 5BA 5 band
> Yagi with support rope. That will be no more than 1
> foot from top of tower.
> 
> This makes only 14-15' above the tower and whatever it
> takes to the rotator, which I hear will only fit in
> the top most part of Rohn 25? 
> Steve K7AWB
> 
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