Steve, et al
I have thought of this 25G climbable mast, too. It is among the ideas I am
trying to remember for when I hit LOTTO.
The way I envisioned getting around the need to elevate the Rohn 25 way above
the pipe mast was to use the same technique used as that used in
preinstalling a mast when you first pour your base. By placing the mast in
the heart of the tower's first section and then and hauling it up through the
center of the tower and through a holi in the rotor plate once the tower
sections have all been stacked.
You are initially not installing the rotor and have the proturding mast only
protrude say a foot above the top of the top plate.
Then you would elevate the pipe to its final height, such that its bottom is
at the right height to fit into its home in the rotor clamping brackets.
A) Temporarily install the mast, say by resting it on a wooden 2X12 shelf
below the rotor plate, so that it is only partially extending above the
tower.
B) Bring up the "inverted" 25G and pass the short pipe through the "bottom"
(top?) bearing on the Rohn 25.
C) jack up the pipe so that it is passing through all the bearings in both
the larger tower and the 25G climbable mast, it is now at the correct height
to bring up and install the rotor into the tower.
D) With the weight of the antenna mast bearing on the rotor - which the
bigger rotors are designed for (!) - afix the pipe into the rotor.
E) Proceed vertically up, finally to your "pinning" location - where the pipe
actually attaches the to a shelf on the inverted Rohn 25, once bolted in the
invertage 25G top section IS the mast, and should be easily climbable.*
F) Absolutely mandatory is a K5RC/Productivity type of mast that has very
high tensil strength - this is not going to be a short length of pipe
sticking out of the top of your tower but a very massive mast system which
you will be belting into and leaning out on and the forces will be extremely
high on the point where the two thrust bearings bear on each other.
G) I would want to mount the rotor down 10 foot from the top of the bigger
tower at the mating point with the next section.
I've envisioned using a 10 foot straight section and a pointed 25AG section
for the top - these would be married to each other (female end to female end)
with three 10" rods whose OD is the same as the swaged end (prox 1") of the
#25....this type of installation may only be allowed in Hawaii, however.
This would net a mast almost 20 foot tall above the top of the fixed
tower....allowing (hopefully) enough seperation for 3 or possibly four yagis
to be mounted on it. Caution would have to be taken to try and weight balance
the antennas so that the were not all on one "side" of the Rohn 25 - some 7
inches off oc the center line of the rotating pipe.
One advantage of this is how it would often be nice to have an antenna
pointed in a different direction than your "running" direction in a
contest....be it Towards South America or the Pacific while beaming EU or
JA...or towards KP2 while beaming towards Mad River territory during SS. A
little Cushcraft A3S at the top of the tall mast on a lightweight rotor could
be beamed to the appropriate ("I want an SS mug, damnit") heading and
simultaneously driven (ala K5GA) while your heavy duty hardware was pointed
at your high population target footprint area.
* I am NOT an engineer - these are not proven methodologies, but - it sure
seems feasable - and as you stated, Steve - the necessary hdwe is almost all
already standard issue by Rohn.
73
Jim, K1ZX (still...but not much longer, I hope)
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