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R: More Kansas City Tracker Questions

----- Original Message -----
From: Joe Leikhim <jleikhim@nettally.com>
To: <amsat-bb@AMSAT.Org>
Sent: Wednesday, December 04, 2002 5:21 AM
Subject: [amsat-bb] More Kansas City Tracker Questions

> I have a KCT-T I would like to use to control a 10' dish antenna. What I
> have in mind is to use a potentiometer with a weighted pendulum to sense
> the elevation angle (0 to +90 degrees). Another pot will sense the
> rotation of the dish by direct mechanical connection. Finding a suitable
> 360 degree rotation pot for the latter seems to be a problem. However 3
> turn and 10 turn pots exist.
> What drawbacks if any will I have if I use a 3 turn or 10 turn pot?
> Since I am using a 10 foot dish for the S-band downlink the pointing
> error (and pot resolution) will be critical.
> Is a carbon pot OK or should I be looking for wirewound?
> What value is recommended?
> Is there any drawback to using an externally regulated supply for the
> reference voltage?
> By the way, I have been using the "ultimate charger" site for reference
> but would appreciate links to other sites or suggestions about the
> mechanics of AZ/EL positioning of a 10 ft dish. If there are surplus or
> commercial sources for positioners I would like to hear about them as
> well.
> --
> Joe Leikhim K4SAT
> Jleikhim@nettally.com
> "Jazz is not dead.  It just smells funny." -F.Z.


For indication of elevation i use a 2" selsyng motor with a weighted
pendulum and for azimuth indication of rotation i use another 2" selsyng
motor by direct mechanical connection to mast.

Two receiving selsyng motors in the shack are indicating  the AZ/EL angular
position in two compass with 20 cm diameter and the resolution of the
pointers  is better than 0,5 degrees and this is OK for my 1.2 meters dish
at 2401 MHz for AO40

The AZ and EL  AC motors are driven CW-CCW and UP-DOWN respectively
by manual operation about every 15 minutes.

It would be possible to use the receiving selsyng signals in to a  close
loop servo mechanism to automatically command traking with a PC but
unfortunately the weighted pendulum signal is the limiting factor because
the weighted pendulum oscillates and swing everytime you rotate for 
azimuth and because of any very soft wind !

In conclusion the weighted pendulum is not recommended for automatic
tracking systems.

73" de i8CVS Domenico

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