Jim,
I have a 140' rotating tower.
We get regular high winds here in Amarillo. The last big wind storm was
back in June when we had 80mph straight line winds. Both my
towers/antennas survived nicely, but my fence on the north side was
blown over and it had steel posts.
My rotating tower will twist in the wind. If the winds are high enough
it will end up moving the prop pitch rotor in one direction or the
other. If I have a wind event that moves the tower I'll walk out with
my iphone, bring up the compass app and take the new reading. Then I go
back to the shack and enter the new heading in my Green Heron rotor
controller.
I think it's a good thing that the tower rotates within the rings when
it gets windy as it takes the stress off of the system. Since the prop
pitch doesn't have mechanical stops it's very easy to re-calibrate.
My 2nd tower is 80' of 45g. It's on a pier pin for the same reasons,
wind. The tower can at least twist a bit to relieve the stress on the
tower. It has a normal set of guys vs star guys. I want the tower to
twist freely if needed.
The only problem I have on the 45g tower is the Orion rotor. The stock
mast clamp is terrible. I have to climb the tower several times a year
to re-position the antenna stack. One of these day's I'll order a K7NV
or Champion after market mast clamp. Then again, it may not be a bad
thing for the antenna system to slip a bit vs tearing something up like
the rotor itself.
Rich - N5ZC
On 10/16/2017 8:06 AM, Jim Thomson wrote:
Ok, heres something I dont get. Star guy setups.... with 6 guy wires. The
idea is to reduce tower twist. I can readily see that vs a standard 3 guy
wire ...per level setup.
Then we have folks with a rotating tower assy, whose guy wires essentially
allow for unlimited tower twist. The only thing I can see limiting the
twist is either the rotor at the bottom of the rotating tower,
and / or the bearings at each rotating guy ring assy. The folks with
rotating towers typ load em up with yagis from top to bottom. All yagis are
mounted to the same tower face, so you now have a TQ offset from
boom to exact center of tower... which just makes any TQ issues worse.
It appears that a rotating tower assy is one giant, 100-200 ft tall
driveshaft. How much twist do you rotating tower owners see in a 40-75 mph
windstorm ? (and tower sitting there, not being rotated at the time).
Ok, what if no wind at all, nice sunny day, and you rotate tower say 300 degs.
Do you see any twist when rotor initially engaged ? IE: base of tower is
turning, but very top of tower has not started to rotate..yet.
What am I missing here ? Rotating towers vs star guys is from one extreme
to the other. One would think with a 100 ft rotating tower...and esp with a
200 ft rotating tower, it would twist like a pretzel ?
When I worked for the telco, the odd site would have star guys, if a guyed
tower was used, and large diameter microwave dishes used. Same deal, 6 guy
wires used, with star guy assy just below the dish.
In some cases, a square tower was used, with 8 guys, 2 for each of the 4 x
faces...and 4 x guy anchors on the ground, 90 deg apart. I can understand
the telco application, the dishes had their side built up, and
they have an extremely narrow main lobe. With the sides of the dish built up,
there is no side lobes. For amateur HF, its not an issue. But tower twist
is an issue. Or is it a non issue ? Obviously 65G will twist less than
25 G. For this discussion, lets use 45 or 55G as tower used in a typ
rotating setup.
Jim VE7RF
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