Hi Jerry,
I, personally, have never used the MARC program but I think it was based on the
article I wrote years ago tht got published in the NCJ about "Mast Strength".
Anyway, the article described how to manually calculate the strength for a given
set of hardware to see if it was strong enough for the given wind conditions.
You could run two sets of calculations. The first one for the 0.250" wall
60,000 psi mast and the second set for the 0.188" wall 120,000 psi mast. The
results would tell you if either, or both, (or neither!) mast would work in your
installation. The original article has been recently republished in one of the
League's new books on antennas and towers. If I remember right, the new book is
called something like "Antenna Classics" . . .
When I wrote the original article (about 1977), I included a section on
determining the wind area of your antenna using the accepted methods of that
time. In the last decade or so, those methods have been upgraded but,
unfortunately, the ARRL did not tell me they were planning to publish my
original article in their book. The result is that the antenna wind load
calculation portion of the ARRL book article is now obsolete. The good news is
that the rest of the article is still valid and you can use it to answer your
questions about mast strength.
Stan
w7ni@easystreet.com
J. Kincade wrote:
> If a calculation says you need say a 60,000 PSI mast with a .250" wall, then
> as an example would a 120,000 PSI mast with a .188 wall be an acceptable
> substitute? I haven't found a way to answer this using MARC. Actually, I
> wish MARC was an Excel spreadsheet, so a guy could do "what-ifs" to his
> heart's content. How 'bout it, Steve?? :-)
>
> Tks, Jerry W5KP
List Sponsored by AN Wireless: AN Wireless handles Rohn tower systems,
Trylon Titan towers, coax, hardline and more. Also check out our self
supporting towers up to 96 feet for under $1500!! http://www.anwireless.com
-----
FAQ on WWW: http://www.contesting.com/FAQ/towertalk
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
|