[TowerTalk] Star guys vs rotating tower ?
Jim Thomson
jim.thom at telus.net
Mon Oct 16 09:06:25 EDT 2017
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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