Re: [amsat-bb] Adapting convention rotors for Fodtrack?

[Jesse Morris <w4mvb@xxxxxxxx>]

Hi Rich,

It is very easy to interface FODtrack with standard rotators.  I use it
here with an old TR-44 for azimuth and one of the "Orbit 360" TV rotors
by Gemini which showed up two or three years ago.  The TR-44 has a
standard 500 ohm pot in it wired as a two terminal rheostat.  If you send
10 ma of constant current through it will generate 0 to 5V for a complete
revolution.  The Gemini rotator has a three lead pot of about  875 ohms
in it and I think it also has about a 1K resistor in series with the
center lead but since the input to FODTrack is a very high impedance and
I use a very high impedance Digital panel meter for a readout the extra
resistor does not seem to affect the operation.  I plan to open up my
spare one day and take that resistor out.

FODTrack wants to see a 5V change for 180 degrees of travel in elevation
so you need to supply the elevation pot with 10V.  I put a zeroing 
circuit in mine by placing a small divider between the ground lead of the
pot and a minus voltage but in actual operation the zeroing circuit is
more unstable than the rotor circuit so when I get around to it I'm going
to take it out.

If you send me your address I will send you a copy of the schematics I
use.  Good luck.

73's de Jess - W4MVB
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