In a message dated 6/7/01 9:20:40 PM Pacific Daylight Time,
SPELUNK.SUENO@prodigy.net writes:
<< Kurt:
With my planned antenna arrays, I won't have appreciable mast torque
caused by off-center mounting of the boom on the mast. I'll have a small
V/UHF vertical at the top, a D40 rotatable dipole (same length on either
side of the boom bracket) below that, and the Bencher Skyhawk (purportedly
torque balanced by the element and boom compensator pieces.) If and when I
install the 2M Yagi (KLM 144-148-13LBA), it will be mounted at the center of
its boom; there's not enough element aluminum to worry about finding the
balance center of the boom.)
I think what you're cautioning us about is the case where we have large
HF Yagi arrays in which the balance point (and mounting point) of the array
is not the center of the boom. In these cases, wind blowing broadside to
the boom will want to turn the longer side of the boom away from the wind,
creating torque on the mast/rotator/tower.
Dick's papers on aerodynamic balancing discuss how to compensate for
such imbalances, e.g., fixing a weight onto the boom so the balance point is
shifted to the center of the boom, or entending the shorter side of the boom
with a piece of aluminum tubing sleeved onto the main boom, or installing
compensators.
BOTTOM LINE: You have to do some "cypherin' " before you put up an
antenna/tower system. Apparently, there's more to ham radio than Ohm's Law.
GL es V=IR de
Gene Smar AD3F
>>
All these factors are certainly important. However there are ways to avoid
all this concern and calculations for mechanical and wind unbalance that can
occur. Use a Prop Pitch Motor, it's far cheaper and trouble free if properly
converted and installed. In over 55 years of spinning many beams, the size
of the beam and any wind unbalance and other factors have never ever been
given the slightest consideration. The beam was balanced mechanically and
that's it--end of story. I use friction aluminum bearings I make and no
other "Band Aids." I've never had a rotator problem except water got in a PP
once and rusted some bearings. I overhauled the bearings and improved the
rain protection. All this time I apply power the beams turns each and every
time at 2-6 rpm depending on the size of the beam. No other commercial
rotator user can make that statement. I use other rotators all speeded up
(even the small TV rotators) and just never overload them. A fast spinning
TV antenna is a joy to see. My rotator budget has been a little over $200
for PP motors and I just paid an all time high of $50 for a medium PP motor.
It was a mechanical joy converting one again after 55 years. I have
purchased 4 of the typical $120 rotators at flee markets for a total of $120.
The 3 Big Fears of John Q Ham are:
1. There's a big wind and he worries about all the TT Band Aids not holding
up
2. He's running over power and thinks the FCC may be checking power levels
3. His gal friend tells him she missed her period
If you have all 3 on the same night--it's almost unbearable. (Old K7GCO
Axiom)
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