In a message dated 12/22/02 2:53:14 PM Pacific Standard Time,
geoffrey@jeremy.mv.com writes:
> I remember all the various materials, diameters, wall size being published
> somewhere.
> Ive looked all thru my 94 Antenna Manual and no luck.
>
> Did I just miss it or where could I find that info?
Good question. The best info I've seen on this is in Dr. Dave Leeson's
(W6NL, ex-W6QHS) book "Physical Design of Yagi Antennas". It's out-of-print
but you might be able to find a copy.
Here's a little recap that's from my practical standpoint. There are many
grades of steel and also finishes (drawn-over-mandrill [DOM], seamless,
welded, etc.) so I'm not going to get involved with those specs.
The specification that you need is 'yield strength'. This is what the
bending-moment forces are compared to. In short:
STEEL PIPE: i.e. conduit, water pipe, etc. NOT rated for strength (they carry
water) but a Schedule 40 or 80 might be in the 35,000 psi yield strength
range. Only suitable for low windspeed or small antenna arrays (i.e. VHF
stuff).
ALUMINUM 6061-T6: Yield strength 35,000 psi. Basically the same as steel pipe
above.
CARBON ALLOY TUBING: This is the desired material. The most common available
is SAE 1026 or 1027. Its yield is around 65,000 psi. Suitable for most ham
applications; i.e. 2L 40M yagi ten-feet up the mast.
CHROMOLY 4130: This is investment grade piece of steel and typically runs in
the neighborhood of 115,000 psi yield.
Most ham mast related hardware (thrust bearings, rotators, etc.) are
designed around a 2" mast. What you vary is the wall thickness. For BIG
antennas, moving up to a 3" mast will get you more mast surface area for the
antenna boom-to-mast bracket to bite into.
I sell a little software program that calculates antenna mast loads and
gives you the mast specs you need. It's called the Mast, Antenna, and Rotator
Calculator (MARC) program and it's ten bucks at <A
HREF="http://www.championradio.com";>www.championradio.com</A>.
I will be handling masts shortly and they'll be on the website. There'll
be an announcement when it's ready. In the meantime, drop me a line if you've
got any questions.
Cheers,
Steve K7LXC
Champion Radio Products
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