In a message dated 97-03-05 19:50:45 EST, you write:
Hi, Dave --
If you're still in Gwinnet County, it is a 75 MPH wind zone. Add a fudge
factor if you're on a hilltop or otherwise exposed spot.
> hygain 204ba above that a cushcraft 402cd 2ele. 40 beam....first tower
Assuming ten feet of mast above the tower and the 402CD mounted at 9
feet, the bending moment is 18,727 in.lbs. You need a mast with 46,000 psi
yield strength and 0.188 wall. This installation exerts 2294 ft/lbs of
Effective Moment on your rotator.
> force 12 duo-band 10/15 (4 ele on each band) above that a 4 ele 17m beam
> above that a 30m rotatable dipole...second tower
Assuming 15 feet of mast above the tower and 7 foot spacing between
antennas, you have 17,446 in.lbs. of bending moment. You'll need a mast with
40,000 psi yield strength and 0.188 wall. This configuration exerts a force
of 1320 ft/lbs of Effective Moment on your rotator.
Feel free to spend the big bucks on the chromoly mast but it really
isn't necessary. Contact your local steel supplier for specifics and prices.
These calculations were done with TOWER TECH's new MARC program - the
Mast, Antenna and Rotator Calculator. This program will be available soon
from TOWER TECH.
73, Steve K7LXC
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