My first comment would be to forget about that skinny Rohn 25/45/55
stuff and get a "real" tower. My definition of "real" is one you can
climb on the inside.... That may be a bit much for your application but
seriously, I'd look for a used tower way before buying anything new. I
don't think I've met a ham around here that has ever bought a new tower,
but I would like to some day.
Just to say I did. I've always found used tower sections to be abundant
and inexpensive (cash wise) but possibly requiring a significant amount
of work to dismantle/haul etc. One of the most common towers you see
commercially up here in western Canada is the LeBlanc and Royale LR 20
series. I would suspect it would be very common all over Canada. All
welded angles, so no internal rust issues. Comes in heavy and light
sections, 100 feet of the heavy sections, with good guys (3 levels at
80%) would hold anything you are planning against anything your winds
gods could dish up. A couple of my towers use this LR20 so if you get
a chance you should stop by before you depart for the east. I don't
think you've been here when it hasn't been brutally cold and lots of
snow...
I'd also suggest that multiple towers (as in 2 or 3) with home brew
monobanders would reduce the need for expensive side mounted rotor
installs and/or compromise in directional ability. For likely less
money and more sweat, you could accomplish the same goal and maybe
pocket a few more db as well. As you mentioned SO2R as a goal,
separation between antennas/bands makes that goal a lot easier (read
cheaper) to achieve. Also the ability to point different bands in
different directions is a significant advantage.
73 Don
VE6JY
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of Gerald Boutin
Sent: April 6, 2007 6:12 PM
To: towertalk@contesting.com
Subject: [TowerTalk] Stacking Antennas and Windloads
Thanks for all of the responses to my "dilemma" that I am having to
endure in moving to the East Coast.
I have an additional question. (Won't be the last time I say that.)
I would like to put up a C31XR tribander with a Mag240N 2 element 40
meter yagi above it. The total tower windload is:
C31XR: 10.7 SF
Mag240N: 6.8 SF
16 ft Mast: 1.6 SF for 2 inch or 2.4 SF for 3 inch
Rotator: 1 SF (approx)
Total load: 20 to 21 SF
Still deciding on height, but the desire is for either 80/87 feet or
90/97 feet. In either case in a 100 MPH environment, this load exceeds
the capacity of 45G and 55G.
A light just lit up in my head. What if I rotate the 240N by 90 degrees?
Now the cross section in parallel with the tribander elements is that of
the boom rather than 6.8 SF. ie) Assume average 3 inch boom by 24 feet =
3/12*24*0.67 = 4 SF.
I don't know the actual boom diameter, so it may be slightly smaller.
Since I am right on the edge, the reduction in 2.8 SF is a big deal to
me. Is this really legit, or am I tempting the wind gods?
--
Gerald Boutin, VE6WA
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