Good Morning Rick
Good luck with the permitting process. It sounds like this tower is totally
enclosed. If this is the case will the rotator sit on a flat plate on the top
If so this will be the weak point in the design. As far as how to hang the
cables I can't help you there. At about 35' tall you may get away with just a
cable strain relief to support each cable. You would have to check the specs.
The feed lines will have to exit the tower somewhere unless you bring the
conduit up inside the tower base, so the holes may be necessary.
You can run your LV and RF cables in 1 conduit, but it will be much better to
use 2 separate conduits. The access door at the bottom should be as large as
possible. What really concerns me is the design of the rotator mounting. If you
do it like your description then the only thing holding the rotator, mast, and
antennas are the mounting bolts for the rotator. This type of tower should have
climbing pegs or steps built onto it. For under 100' runs LMR 400 should be
up to 6 meters maybe more. If you run the cabling inside the tower you might
consider 2 water proof boxes for cable entrance and exit points mounted on the
exterior of the tower. Of course this is JMHO. I am not an engineer. Good Luck.
73 DE K4XZ Joe Patrick
God Made Man
Sam Colt Made Them Equal
From: Rick Kiessig <firstname.lastname@example.org>
Sent: Fri, June 8, 2012 2:20:44 AM
Subject: [TowerTalk] Tower advice
After a multi-year battle with the city, I am finally in the process of
drawing up plans for a tower that have a decent chance of being approved.
The tower height will be about 9m above immediate ground level (but I'm near
the top of a 100m-high hill, so I have some hope of getting a decent
signal). The tower will be octagonal galvanized steel, 290mm diameter at the
base, 140mm at the top, in 4 sections. I'm planning to use a PST-61 rotator
with either an Ultrabeam UB50 or a SteppIR UB-18 (the rotator is
intentionally oversized, since I'm hoping to increase the size of both the
tower and the antenna in a few years when the city's rules are changed to
reflect a recent court decision in favor of hams). The tower was not
originally designed for use as an antenna mast, but the manufacturer is
willing to do a little customization to make it work, such as adding a plate
at the top of the tower with bolt holes to match the mounting plate on the
Would it be OK to run RF and control cabling on the inside of the tower
without supports for strain relief other than one at the top? (coax will
probably be LMR-400 UF in conduit, not direct burial; the total length is
pretty short (roughly 20m) so the expense and hassle of using LMR-600 or
Heliax may not be worth it).
The manufacturer has suggested three 20mm grommeted exit holes close to the
top of the tower, one for each of the three cables that will be needed
(slightly below the mounting plate for the rotator). Sound OK?
The tower will have an access plate at the base, which I can use to tie the
coax shield to a ground rod that would be present in that space. The base of
the tower would also be tied to ground rods. Is there anything else I should
allow for in or near the base?
I was thinking of running one conduit for the RF coax and a separate one for
the antenna and rotator control cables. Is that overkill?
This design would not have a thrust bearing or an interior shelf for the
rotator. The rotator would need to carry the full load of the antenna (5.8 x
6.6m, 44kg, 10.1 sq ft wind load). Am I asking for trouble, even with the
What's a reasonable maximum length for the mast, going from the rotator to
the antenna? I'm thinking of using 50mm galvanized water pipe. A longer mast
would mean a slightly shorter tower and a little more flexibility with total
height (very tightly restricted here), but would also present a larger load
on the rotator, right?
73, Rick ZL2HAM
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