[TowerTalk] Star guys vs rotating tower ?

[Richard Thorne]

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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