In a message dated 97-04-10 00:54:04 EDT, kt6ra@netfeed.com (Ray Antasek)
writes:
> I just got on Tower Talk a couple days ago. Hopefully I'm not asking about
> something that was just discussed. I would like to know what options I
> would have for mast material. I want to go with 2" O.D., 20' long. I'm
> guessing 20' is as long as I would safely want to go. I have heard of one
> called Chrome-molly. A friend suggested using 6061-T6 aluminum tubing
with
> a 3/8" wall. What else should I be aware of? Any info on price range and
> strength would be helpful. I'm looking at putting a Force 12 C-4XL at the
> top of the mast.
>
Masts are typically non-controversial but everyone has to go through
the learning curve. An excellent discussion and technical data is contained
in Dave Leeson, W6QHS's book "Physical Design of Yagi Antennas". I also have
a reprint of Stan Griffiths, W7NI's landmark article from the NCJ. An SASE
to TOWER TECH will get you a copy.
You need to know the wind speed for your county per the TIA-222; send
it to me and I'll look it up. With that information, you can calculate the
bending moment on the mast.
A far simpler solution is to get a copy of the new MARC program. It is
a Mast, Antenna and Rotator Calculator. It'll calculate the bending moment
of any scenario, recommend a mast with wall thickness and will even give you
rotators with appropriate capacity. Armed with the mast information, you can
call your local tubing supplier. It's $9.95 + s/h from TOWER TECH.
BTW, the suggested chromoly mast is about as good as it gets and the
aluminum mast is generally unacceptable.
The mast, like all other tower and antenna components, is something that
should be properly engineered for safe and reliable service.
73, Steve K7LXC
TOWER TECH -- professional tower supplies for amateurs
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