In a message dated 8/7/2008 9:02:46 A.M. Pacific Daylight Time,
towertalk-request@contesting.com writes:
Vis-a-vis the Champion Radio Products MARC (Mast, Antenna and Rotator
Calculator) Program:
> 1) What is the meaning of the "wind speed" parameter. The dialog box
says
"maximum wind speed expected". In my county, basic wind speed is 70 mph
fastest mile, 85 mph 3-second gust. So I figured the max instantaneous is
probably higher. So I figured 90 or 100 would be a good number. But it
really depends on what the meaning of this number is in the MARC tool
(fastest mile, 3-second gust, other). Can you define?
We used the formulas and specs from Dave Leeson's (W6NL, ex-W6QHS) book
"Physical Design of Yagi Antennas." Maybe there's more of an explanation
there.
The over-riding spec is your county windspeed rating from the TIA-222
windspeed chart (available from _http://www.championradio.com/windspeed.php_
(http://www.championradio.com/windspeed.php) ). There are several ways of
arriving
at a figure.
> 2) Also, when the calculated total is 12,290 in-lb, the lightest
suggested
mast type shown in the list is a 40,000 in-lb yield strength. It's seems
like it's only displaying mast types that are at least 3X higher than the
calculated total. Maybe you could shed some light on that too?
No, that's because tubing has that as a minimum rating. As opposed to pipe
which doesn't; it's around 35 kpsi and we don't include pipe as a generally
suitable mast material.
If your design yield strength is 13 kpsi, then anything will work. That's
why I suggested Schedule 40 or 80 water pipe or conduit. You're over-thinking
this whole thing. If you want to spend the bigger bucks for a pedigreed piece
of steel, knock yourself out. But IMO it ain't necessary.
Cheers,
Steve K7LXC
_www.championradio.com_ (http://www.championradio.com)
and
TOWER TECH
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