[TowerTalk] Shunt Feeding Crank Up Towers

[James C. Hall, MD]

Hi Tom:

I have a UST 72' crankup with similar top-loading. I have coax arms on mine
as well. What I did is bolt a 3 foot section of 1" square aluminum channel
stock in the groove of the coax arm so that it points out opposite to the
coax arm. I dropped a wire attached to the standoff and attached it, via a
turnbuckle, to a 2 x 4 bolted just above the tower mounting bolts and
extending under the drop wire. You can make a cage if you want to improve
band coverage, but I found this unnecessary. BTW, I attached the cross arm
to the next-to-top section of tower. I purchased a Russian-made vacuum
variable capacitor (500pf, 15kV rating, I believe) and made a simple mount
with squares of plywood with circles cut out so that I could slide these
around the capacitor and hold them, along with the attached wires with hose
clamps. I have the whole thing mounted horizontally in a Rubbermaid box. I
have a SO-239 bulkhead connector (a longer barrel connector) attached to the
box with a bit of copper flashing for outside ground connection and a simple
bolt with wing nut on the other side of the capacitor for feeding the shunt
wire. A section of coax goes from the antenna switch to the SO-239 bulkhead
connector and a ground wire connects to one of the 2 x 4 attachment nuts.

That's it. Take your antenna analyzer and tune the capacitor to your
favorite section (I set mine to 1840 khz), and you're good to go. I did not
need as much capacitance as I thought, and I didn't need another capacitor
to omega match it - it worked fine with gamma matching. At times, it also
receives better than the beverage. 

I have some pictures I would be happy to send you if you desire.

73, Jamie
WB4YDL



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-----Original Message-----
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com] On Behalf Of Tom Lutz
Sent: Saturday, April 02, 2005 7:57 AM
To: towertalk at contesting.com
Subject: [TowerTalk] Shunt Feeding Crank Up Towers

Does anyone have experience they can share with loading a crank up tower on
160?  In particular I have a 72 foot US Tower crank up with 6 el 20, 2 el
40, and a ratable 80 dipole on it.  Details would be appreciated.

Thanks, Tom, W0ZR

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