Are you using any commercial equipment, like a standard dish drive assembly, or is it from scratch. If it is from scratch, you may do better with stepper motors. If you have an older PC, probably it may be easier to use a 2 channel parallel port stepper motor driver. You can buy or make this. Suggest google for circuits. As I said, I am not sure how the DC motor ones work, possibly optical encoders. Do you mean you want the dish to find as well as memorize position. Or just memorize when you have found them.