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[TowerTalk] Emoto rotators

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Subject: [TowerTalk] Emoto rotators
From: (Dave Hawes)
Date: Wed, 16 Apr 1997 02:23:48 -0400
On 15 Apr 97, Marcel Gervais wrote:

> Has anyone on this list ever used the EMOTO 1300MSAX antenna rotator.  If
> so how well does it preform and what good or bad do you have to say about
> it.

We use an Emoto 1300MSAX on the 3 element full size 40 meter beam at 
N3RS.  This antenna is a brute, with a 48 foot boom and weighing in 
at about 500 pounds.  The 1300 has been turning it reliably for 3-4 
years now.

We did have an early failure.  The Emoto design uses something akin 
to a universal joint to allow a few degress of vertical misalignment 
between the mast and the rotator.  It's hard to explain, but the top 
of the actual rotator has a circular plate bolted to it, with three 
vertical posts welded to it along a diameter; one in the center and 
one near each edge of the plate.  The mast clamp is attached to 
another plate which has two holes to mate with the two outer posts on 
the lower plate.  The lower central post supports the upper plate, 
while the outer posts engage the upper plate (through the holes) and 
provide the rotating torque to the mast clamp.  The fact that the 
upper assembly rests on the lower central post, and the outer posts 
are a somewhat loose fit in the holes in the upper plate provides the 
desired capability to accommodate a bit of misalignment.

Completely confused?  Nevermind.  The failure was that the torque of 
the big 40 broke off one of the two drive posts.  In our opinion, the 
plate it was welded to was too thin, so we had a shop make up a new 
plate using the next size up material.  I believe we went from 1/8 
inch to 3/16 inch material.  Fixed.

K1EA uses an Emote 1300 MSAX to turn his full size 40 meter beam as
well.  He has had trouble keeping the rotator firmly bolted to the
rotator shelf in his Rohn 45.  The bottom bolts keep falling out! 
This may be a beam vibration transmission issue, since he has the
mast (3 inch aluminum, I believe) directly in the rotator.  At N3RS
we use an intermediate thrust bearing, which would tend to couple
any mast vibration into the tower before it could affect the

73 - Dave N3RD

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