[TowerTalk] Alliance HD73 Rotator calibrate and mast bolt size?

[Dick Green WC1M]

Sounds like the antenna has slipped on the mast, the mast has slipped in the
rotor jaws, or the lower rotor jaws have slipped on the pipe -- or any
combination of the three! If you expect winds like that in the future, you
might consider using bolts to pin the antenna to the mast, the mast to the
rotor and the rotor to the pipe. This will require some drilling. There's
probably a hole for this in the A3S boom-to-mast bracket. Can't recall
offhand, but I think there are holes for pinning in the HD-73 upper and
lower mast clamps.

You need to calibrate the controller before you have the antenna (or rotor)
moved back to the correct heading. In other words, you have to know where
the rotor "thinks" the antenna is pointing before moving the antenna to that
heading. The symptoms you describe indicate that the controller is still not
properly calibrated. I'm speculating here, but the symptoms also suggest
that the reason you can't calibrate the controller is that the coax loop has
reached the end of its travel! My guess is that this is happening when you
move the antenna to the west and could explain why the rotor slows down near
the end of travel. To see if this is the case, rotate the antenna to within
10 degrees or so of where it slows down at the west end then go outside and
see if the coax is stretched near its limit. If not, then rotate the antenna
all the way until it stops at the east end and see if the coax is stretched
near its limit.

If you find that the coax is the reason for the stop in travel, and it's
only happening at one end (probably the west side), then simply rotate the
antenna until it reaches the rotor's mechanical stop at the opposite end of
travel (probably the east end.) When you do this, make absolutely sure the
rotor is stopping because it's at a mechanical stop and not because it's
yanking on the coax. Then have your tower climber loosen the rotor clamps
and turn the mast due south. This should relieve the tension on the coax
when the rotor reaches the other end. Recalibrate the meter as detailed
below.

If the coax is not stretched to its limit at either end, then my theory is
wrong and the most likely explanation is that you have miscalibrated the
controller -- probably turning the meter adjustment screw too far from where
it should be. In that case, follow the meter calibration steps below.

METER CALIBRATION: (Do this only when you are sure the coax loop is not
limiting rotor travel!) 1.) Rotate the antenna until it reaches the end of
its travel on the west side. 2) Adjust the small screw below the center of
the meter to make the needle point due south on the west side. 3) Rotate the
antenna all the way to the east end. 4) Use the calibrate knob to set the
needle to due south. 5) Leave the rotor pointing due south and have your
antenna guy move the antenna due south by loosening the rotor clamps and
rotating the mast.

If none of the above helps, then there is another possibility. The HD-73
uses a simple friction braking system. In high winds, the brake can slip.
This is not a huge problem if the rotor doesn't turn too far -- it's just as
if you had moved the rotor with the controller. But I don't know what
happens if the rotor turns to one of the stops and high winds continue to
push the rotor against the stop. It's possible there would be enough
internal damage to cause the symptoms your are seeing.

Hope this helps.

73, Dick WC1M

> -----Original Message-----
> From: Gene Bigham [mailto:jbigham2 at kc.rr.com] 
> Sent: Wednesday, June 22, 2005 7:05 PM
> To: towertalk at contesting.com
> Subject: [TowerTalk] Alliance HD73 Rotator calibrate and mast 
> bolt size?
> 
> 
> The recent round of 80 to 90 MPH straight line winds in our 
> area has caused a misalignment of my rotator direction 
> indicator and the actual antenna position.
> 
> First, the indicator is centered on North and can go on the 
> meter to the (left) South of West and on the (right) South of East.
> 
> Right now playing with the calibrate knob and turning the 
> antenna, the azimuth indicator needle will travel to and show 
> South (of East) but the antenna and rotator stop at about the 
> 130 to 140 degree position and remain there, tracking of the 
> sweep of the indicator needle seems linear from North to the 
> stop point.  But the antenna will not advance past 130 or so 
> to due South 180 degrees.
> 
> On the other side of the indicator when I rotate back past 
> North toward South (of West) the indicator arrives at South 
> with a deceleration of the degrees traveled compared to the 
> indicator as the antenna moves past north to north west then 
> west, and finally ends up at south west say 210 to 220 and 
> stops shy of South.
> 
> I initially tried to use the calibrate button to adjust this 
> but the above results are the best I can get.
>   
> This is Alliance Model HD 73 and has been pretty bullet proof 
> until now.
> 
> The rotator initially torques on top of my Aluma tower top 
> section in heavy wind storms until my antenna guy put a 
> couple of self tapping large screws through the top plate and 
> against the lower bell housing of the rotator to limit the 
> rotation of the rotator on its mounting pipe.  This rotator 
> sits on top of the top plate using a lower pipe mount, the 
> bottom of the bell housing just sets on the top plate while 
> the pipe goes down into the tower and is secured to the tower 
> legs using U bolts to all three tower legs.
> 
> There are two options I am thinking about to correct the alignment.
> 
> First, place the indicator and rotator as far to the South 
> (of West) position and then loosening the mast clamp and 
> manually align the antenna to true south since the 
> correspondence of degrees measured to degrees turned is 
> different on this side of the rotation.
> 
> Or Second, place the indicator and rotator as far to the 
> South (of East) position and align the antenna to true south 
> loosening the mast clamp.
> 
> Which way am I safe to presume will correct full range of 
> rotation and more accurate correspondence to the measurement 
> scale?  I can get someone to turn the antenna in the rotator 
> to true South when the indicator is in either the South (of 
> East) or (West) position.
> 
> Anyone familiar enough with this rotator to assist?
> 
> The antenna is A3S so precise pointing is not absolutely 
> required, rather ballpark pointing.  At this point I cannot 
> cover the last 30 to 60 degrees across the south stops.
> 
> And if you know the bolt size on the bolt heads securing the 
> mast pipe I can send my painter friend up his ladder against 
> the tower, as climbing this small tower is impossible, with 
> the correct socket!  So he can loosen then move and tighten 
> the antenna into place.
> 
> If I am incorrect in this entire diatribe please let me know 
> your ideas.  I plan to attempt this move tomorrow evening.
>