Using a linear potentiometer

As one of a number of alternatives to the AS5040/AS5045, the shackunit accommodates use of a potentiometer at the antenna. This offers accuracy within a few degrees, depending on its linearity/quality. The actual Analogue/Digital conversion in the shack unit is able to decode one part in 1024 but most potentiometers are not this accurate. Simply connect a linear potentiometer to the DB9 (pins 4 and 5 with the wiper to pin 8) and set the menu item of the shack unit to 10 bit for the appropriate port (menu items 25,26). Many internal rotator sensors are wired as rheostats so would require an additional connection IF you want to use an existing pot and the A/D mode. I recommend the use of the AS5040 solution rather than pots, however for those with broad antennas or existing rotators this could be a workable solution.

I found that putting a 10uF from the wiper to the earth connection seems to smooth things out a bit and it helps a lot to set averaging on too (that's menu item 27 in Ver 7.02 and 28 in Ver 8.00). A potentiometer of 4K7 linear would work satisfactorily. Too high a value may result in increased error as the load impedance of the A/D input to the 18F4620 becomes significant.

The AZ/EL unit is not required for potentiometer use.

An AS5040, an AS5045, or an MA2/3 series from US-digital can all be used to generate a DC voltage either by integrating the PWM output (MA2/3-P) or by choosing a device that outputs a DC voltage (MA2-A).