In a message dated 97-06-12 03:09:08 EDT, jhumet@mhv.net (Joe Humet) writes:
> I know this subject has been beat to death before, but, I need
> some help. I will be installing some new antennas at the U.S. Military
> Academy in West Point NY this summer and i'm not sure what we should be
> using for mast.
Yes, this is one of the most recurrent topics but if YOU don't know the
answers, it'll be news to you.
First of all, Putnam County (I think that's where you are), is a 75 MPH
wind zone but it's within 100 miles of hurricane oceanline plus, like you
say, there is a pretty good venturi effect from the river. So I would
probably use a higher wind speed for construction and reliability purposes.
After all, it has to be MIL SPEC, right?
> We will be putting up a th7dxx and a 40-2 on the same
> mast. The winds are a killer since they come stright down the Hudson
> River and the tower is on one of the highest buildings there.
> I would hope to use a 2" mast for this setup.
> My question is "What should we use for the mast" and
> "Where to get it" and "How much should it cost"?
According to my MARC (Mast, Antenna and Rotator Calculator) Program, with
an 8 foot spacing between the antennas at 90 MPH you'll have almost 25,000
in.lbs. of bending moment. You'll need a steel mast of 46,000 psi yield
strength and 0.250 inch wall. Look in the yellow pages for a steel tubing
supplier.
The MARC Program is available from TOWER TECH for $9.95 (+ $2.55 s/h).
It'll also recommend an appropriate rotator.
TOWERTALK HEADS-UP: Speaking of masts, rumour has it that Rohn will be
introducing a 20 foot galvanized 2 inch mast with 1/4 inch wall and 90K psi
yield strength in the $225-250.00 range. This should make it easy for anyone
to get a really good mast from their local Rohn dealer at a good price. It'll
be suitable for just about any mast application and much cheaper than the
$400.00 4130 masts that are available.
73, Steve K7LXC
TOWER TECH -- professional tower supplies for amateurs
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