[TowerTalk] Comments on tower design (long)

Dick Green WC1M wc1m at msn.com
Fri Nov 18 13:52:05 EST 2005

Thanks again to all who steered me to the right pages in the Rohn catalog.
As mentioned, I have lots of questions and would like to get feedback from
the group on my proposed design:

I'm asking the town for permission to put up a 100' tower with up to 15' of
mast above the top. There's no specific height limit, but they advised that
I stick pretty close to what is described on my permit application so no one
can come back later and complain. I've inserted a caveat that antennas and
antenna placement may change over time. I could probably extend the height
of the tower later, but would have to get a new building permit. It's more
likely that guy placement and increased visibility of the tower to my
neighbors would preclude making it any higher. There won't be a problem if
the tower and mast end up lower than the application heights.

Right now the plan is to have a 3-stack of 4-element SteppIR yagis, a 40-2CD
and a Force 12 EF-610 6-el 10m yagi (I already own one SteppIR, a 40-2CD and
an EF-610.) HFTA says 90'/60'/30' is the best placement for the SteppIRs for
20m-10m, but various constraints may lead to 95'/65'/35' (see below.) The
40-2CD would be at 100' or 105' and the 6-el 10m would be at 105' or 110'. 

It's likely this will be the only big tower I can put up here, so it needs
maximum flexibility for SO2R contesting. In general that means being able to
work two different bands in different directions simultaneously. For
example, running EU on 40m in the late afternoon while S&Ping JA on 20m.
Flexibility also means being able to work multiple directions on the same
band. For example, power dividing on 15m between a beam pointing NW and
another beam pointing South. Since I've been limited to single-antenna
towers here, my station switching is designed to be able to quickly switch
between antennas on different towers or to power divide between them. In
addition to adding a much-needed stack for the high bands, the SteppIRs will
add the ability dynamically configure monobanders on the same or different
bands. The SteppIRs can also switch directions 180 degrees or to a
bidirectional configuration in a few seconds. I'll configure the StackMatch
so the middle SteppIR can be pulled out of the stack and routed to the
second radio.

I'll continue to use part of my current setup in conjunction with the new
tower. I have a 72' U.S. Tower rotating tubular crankup that will probably
have a C3E or 3-el SteppIR, plus two 50' AB-577s with small rotatable yagis
(currently one has a C3E and one has a 5-el 15m monobander.) I also have a
40m 4-square, wire antennas supported by trees for 80 and 160, and a 540' NE

There will be a lot of flexibility when I add the new tower, but my sense is
that I should design it so the top and middle SteppIR can rotate
independently of the 40-2CD (the bottom SteppIR will be fixed NE.) I'm
thinking about putting the top two SteppIRs on TIC rings and putting the
40-2CD and 6-el 10m on the mast. Since the TIC rings have to be above the
guys, I'll either have to make the tower 90' or guy it in the middle of the
top section. The first option would put the SteppIRs at 90'/60'/30', the
40-2CD at 100' (10 feet up the mast) and the EF610 at 105' (top of the
mast.) The second option would put the SteppIRs at 95'/65'/35', the 40-2CD
at 105' (5 feet up the mast) and the EF-610 at 110' (top of the mast.) I
like having less mast above the top of the tower, but my non-engineer
opinion is that the bending moment is the same in either case. Is that
correct? Are there any advantages/disadvantages between the two alternative?

Life would be easier if I put the top SteppIR on the mast with the 40-2CD
and EF-610. Then I'd have a 90' tower guyed at 90'/60'/30', the top SteppIR
on the mast right above the top of the tower, the 40-2CD 10 feet above that
and the EF-610 at the top. Life would be easier still if I fixed both bottom
SteppIRs NE, but I can see a lot of value in putting the middle SteppIR on a
TIC ring. 

I'm aware that guy clearance is a critical consideration when using TIC
rings. A local friend barely had enough clearance from the top guys when he
installed a TIC ring on a TH-7 in the middle of his tower, and he had to put
the ring lower on the tower than originally planned. My rough calculations
show I'll have enough clearance for the SteppIR's 24' turning radius, but I
still need to figure out how much the guys will sag. How do I do that?

I'd like to plan this project to allow for antenna upgrades down the road.
Specifically, I may want to replace the 40-2CD with a 2-el Cal-AV or a 3-el
yagi. These would add substantially more windload at the top. From what I've
seen on other ham towers, my sense is that Rohn 45 would be adequate for the
initial configuration, but if I want to put a much bigger 40m beam at the
top I should go with Rohn 55 (and probably star guys.) Comments?

Finally, I'm planning on a pier-pin base. I've read some TT threads on this
subject which suggest that the 55G tapered base is preferable to the flat
base plate in that leveling the concrete base is less critical. Lots of
dealers sell the flat base plate, but I haven't seen anyone selling the
tapered base. Is this not available anymore? Is it worth pursuing this

Would much appreciate any insights on this plan. This is my first guyed
tower project and I want to get it right.

73, Dick WC1M 

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