Re: [amsat-bb] Dish aiming

["John Boudreau" <john@xxxxxxxxxxx>]

I am currently writing software and designing a position feedback system for automatic pointing.  The solution I am using to get around the AZ accuracy problem is to use two inputs for azimuth, one for 0-180 and the second for 181-359.  Assuming I will be using 0-5V analog inputs, I'll use a 0-10V signal from the AZ indicator and put a 5V zener diode on the first input to limit the input to 5V max.  Then 7 diodes in series on the second input to 'convert' 5-10V into 0-5V.  This will give better than 1 degree accuracy.  In addition I'm putting manual slew controls into the software to allow some ability to 'fine tune' the aiming if necessary.
73
John - VE8EV

-----Original Message-----
From: Roy Welch <rdwelch@swbell.net>
To: David Guimont <dguimon1@san.rr.com>
Cc: Richard@g3rwl.demon.co.uk <Richard@g3rwl.demon.co.uk>; amsat-bb@AMSAT.Org <amsat-bb@AMSAT.Org>
Date: Friday, March 03, 2000 7:08 AM
Subject: Re: [amsat-bb] Dish aiming


 >Assuming that the rotor controller interface uses an 8 bit A/D converter
 >that divides the AZ 360 degrees into 0-254 segments, then the AZ accuracy
 >can be about +/- 1.4 (360/254) degrees regardless of the control box to
 >rotor accuracy.  The EL accuracy from the same arrangement would be 180/254
 >or 0.7 degrees.  Then on top of that the accuracy in actual pointing would
 >depend on the linearity of the resistance of the rotor position
 >potentiometer, gear lash, etc.
 >
 >David Guimont wrote:
 >> 
 >> >
 >> >Seems like lots of folks have high hopes for the microwave parts of P3D.
 >> >BUT ... are the average rotators/elevators sufficiently accurate to use
 >> >with the narrow beamwidth of dishes etc ?
 >> Hello Richard,
 >> 
 >> No problem on the rotors, Richard.....
 >> 
 >> I think the problem MAY be with the accuracy of the program that directs
 >> the rotors...the many programming gurus we have on here can comment on that
 >> statement.
 >> 
 >> I've done some experimenting....Very easy to bias the EL with a positive
 >> forward weight with the antenna.....Accuracy is about 1/2 degree....And
 >> with a little work it is easy to bias the AZ with a pulley and a
 >> weight.....Same error then on the AZ.
 >> 
 >> Remaining, of course, is the antenna alignment, but I'm hoping that can be
 >> done with some experimenting, and minor re-alignment.  We have a mico-guru
 >> here in town, and am hoping I can get him to educate me....There was a time
 >> when I could barely breathe "up" on 435, but feel pretty comfortable there
 >> now....Live and learn I guess...
 >> 
 >>         73 de Dave, wb6llo@amsat.org
 >> 
 >>                             Disagree; I learn.
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 >
 >-- 
 >73, Roy
 >
 >Internet: w0sl@amsat.org
 >Home Page: http://home.swbell.net/rdwelch
 >----
 >Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
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 >


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