[Laser] Stepper motor control of laser communication unit

[WA2BPE]

I think you really hit the nail on the head with reference to the raster scan.
Knowing exactly where to point is always a problem but one can get close thus
rastering to peak becomes a necessity.  Doing this with steppers takes a lot of
pain out of the operation but one must still do the calculations to determine
the step size at distance - one step could hop right over the target.  Of
course, it still is a problem if the signal is so weak that it must be
deciphered via DSP or other averaging techniques.

Tom - WA2BPE

Kerry Banke wrote:

> Actually we use  the micrometers to move one  end of a 12" bar hinged at
> the other end. If I did the calculations right  the StepperMike moves our
> laser beam  about 1" per step at 10,000 feet.  There are  three reasons
> that come to mind for trying the stepper approach.  Just placing my hands
> on the manual micrometers puts tension on the mechanics no matter how
> careful I am.   I found that working on a target 4 miles out with a 12"
> spot is a problem when you try to let go of the micrometers as things move
> slightly. This maybe not a problem if one is hauling around a very heavy
> base & mechanism but that's not what we do. We use the same tripods used
> for our microwave hilltopping.   I also have found that we end up
> nearly  always  doing a manual raster scan to find the target as our scope
> and laser are never perfectly aligned after transporting & setting up.  The
> cross hairs on my 24X rifle scope are wider than the laser beam at 4
> miles.  The final reason is that since we stumbled across these
> StepperMikes, the opportunity to learn  seemed  to good to pass up. These
> units may also be useful as we move up beyond 47 GHz.
>   - Kerry N6IZW -
>
> At 07:15 PM 10/21/2004, you wrote:
>
> >Kerry,
> >
> >The stepper motor approach works pretty good.
> >I use a pair of "BIG" compumotor drives that were used for disk drive servo
> >writing. I put a pair of mirrors (x,y) and used them for pointing the beam.
> >
> >The 1/10000 of a turn (0.6mR)is still a bit course.
> >Typical beam divergence is about 2mR (0.1 degrees). 360 degrees = 2*PI
> >radians.
> >If you run thru a 10:1 beam expander, divergence will drop by 10 to 0.2mR.
> >So you might want to use some mechanical leverage to reduce movement.
> >
> >I ran my 1/50000 steppers into a leadscrew system that stepped it down to
> >10uR.
> >
> >Jim
> >N9JIM/6
> >
> >-
>
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