I've recently completed erection of 110 ft of Rohn 55G on a rotating tower
base. Total height is about 114 ft when the height of the base rotor section
is included. There are three guy rings with Phillystran guys. On the
stationary portion of the bottom guy ring, which is located at about 34 ft
above the concrete foundation, I welded a 2 ft long 3/4" pipe horizontally
to use as a support for tinkering with the possibility of trying to shunt
feed the tower. From this support a matching wire is dropped to grade. So
it's 34 ft long and about 2.5 ft out from the tower. But remember the
geometry of the space between the tower and the matching wire will change as
the tower rotates. I really can't go any higher than the first ring given a
matching wire will get caught in the Yagis mounted above it.
Before any antennas were mounted I got this arrangement to dip nicely by
trial and error on 160m using a single series Gamma capacitor.
Now the antennas are mounted: Force 12 Delta 230/240 at 112.5 ft above
ground and a stack of 4 el SteppIRs at 103.1, 69.6 and 36.1 ft above ground.
None of the elements on these antennas are electrically connected to the
booms. The booms are attached to the face of the tower using an angle iron
cradle arrangement, so there is not an additional TIC or similar rotor on
any of these. All the SteppIR elements are retracted. Now I cannot get the
antenna to dip on 160 m (again using trial and error.. I don't have a grid
dip meter).
I've heard that the bottom Yagi in a stack basically determines the capacity
and essentially "hides" the Yagis above it. Would this be true even in the
case in this situation where the bottom three antennas (with all the
elements retracted) are essentially just booms? Anybody ever get something
like this work? Thoughts, ideas, next steps?
BTW, I can get the tower to dip on 80 m with all the antennas mounted on it.
And, yes, there are potential issues of conductivity across the bearings
both at the rings and at the base.
Larry Burke K5RK
Brazoria County Texas
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