[NLRS] Elevation rotators for small stuff

[Dr. Gerald N. Johnson]

On 9/11/2013 8:40 PM, tosca005 at umn.edu wrote:
>
>
> Another approach altogether came to mind. I am reminded of a toy (game)
> that I loved as a child, called "Space Tilt". It apparently was also
> sold under the name of "Labyrinth".
>
> http://boardgamegeek.com/boardgame/6546/labyrinth
>
> The basic idea is that you have three nested square frames. The
> outermost one is fixed in place, e.g. attached in some way to the roof
> rack of your rover vehicle. There is a swivel between the outer frame
> and the middle frame, at the front and back, which allows the middle
> frame to tilt left and right (relative to the vehicle). Thee innermost
> frame has swivels between itself and the middle frame, so that it can
> tilt front and back. The innermost frame has a platform on its top that
> can hold a conventional antenna rotator.
>
> Simple gearing at two of the swivels, say front side and left side, to
> electric motors would execute the tilting Up/Down in the front-to-back
> plane and the left-to-right plane. A three-axis magnetometer could
> measure the tilt and an Arduino could make the tilt measurements and
> control the motors to get it all level. A second unit on the rotator
> mast (or linked to it rigidly in some manner) would allow an absolute
> magnetic compass bearing instead of relying on the vehicle-relative
> bearing indication of the rotator controller. Or you could install your
> antenna(s) pointing North and always park the vehicle with its front
> pointing North so the rotator controller matched the actual
> direction(just kidding).
>
> https://www.sparkfun.com/products/10530
> https://www.sparkfun.com/products/9815
>
> If I wasn't so busy with preparing for the next two contests, I'd build
> a scaled-down mock-up, maybe out of balsa wood, just for grins to demo
> the idea. If I was building it for real, I'd likely use square aluminum
> tubing and/or square aluminum U channels for the frames, and fabricate
> some sort of aluminum sheet metal mounts for the electric motors.
>
> As I mentioned, if I was building this project, I'd use a conventional
> azimuth rotator (most likely my Yaesu G-450A rotator) for pointing.
> Since I have one already, I would consider using a Yaesu G-500 elevation
> rotator so that instead of the limited tilt of the platform (reserved
> for just getting the platform level in spite of the terrain on which you
> park the vehicle), I would have the ability to turn the dish to the
> vertical position (dome or birdbath) for driving, and then horizontal
> with full elevation control for operation. That would involve a
> cross-boom, and it would make sense to put two dishes, one on either
> side of the vertical mast. For the 10G contest, the most sensible would
> be 10G and 24G. For SBMS or a VHF or UHF contest, 10G and 5.7G (since I
> don't own any 24G equipment and have no plans to go there anytime soon).

The conventional rotors made for antennas with 30 to 50 degrees 
beanwidth work OK for stow and rough aiming of a dish with 3 db 
beamwidth of 5 degrees or less (18" DSS) but are poor for refining the 
aiming. The conventional rotors work poorly for a single 5WL yagi at 2m 
with 15 degree beamwidth. You really need two speed rotors, 1 RPM or 
faster for rough aiming and stowage and removal from stowage and much 
slower for fine aiming. Characteristics of a servo motor system proposed 
a few years ago by N5AC for roving with 1 meter dishes for 10G.

Magnetic might work some places, but not on either shore of Lake 
Superior because of the many iron ore deposits that tend to be 
magnetized driving any magnetic compass batty. And even batty if a 
passing car has big woofers with big magnets, so say nothing of the 
speakers in the rover vehicle affecting the magnetic compass. Magnetic 
compasses in aircraft include compensators to cancel the radio speaker 
influences as well as fields from magnetized engine parts and structures 
magnetized form DC welding but the aircraft compasses are mounted 
ridgedly so they don't need compensation every day, but I have seen them 
30 degrees in error in some directions in a new aircraft.
>
> Even better would be if there was an inexpensive source for radomes that
> could enclose the dishes all the electronics! But I don't know of any
> such sources.

Ordinary plastic storage bins or garbage cans might be a possibility. 
Trouble is their microwave transmission loss isn't known. Perhaps 
installed inverted for traveling, popped off for dry weather operation.
>
> Anyway, just more food for thought.
>
> John
> W0JT
> ______________________________________________________________
>