Satellite ranging is one of the necessary techniques for satellite orbit determination. Although several techniques exist, phase tracking is one of the most commonly used techniques. A satellite ranging system should be capable of reliable operation at low signal levels, a common condition in satellite communications. In the present work software-based digital phase tracking loops are investigated. A specially designed digital signal processor card is built for this purpose. The design allows the DSPcard and a host PC/AT to operate in synchronism to implement a real-time software-based digital phase tracking loop. Several loops were realized digitally including the classical type-II phase-locked loop. Additionally, loops of types three and four were also realized. Loop parameters were optimized for satellite ranging using several optimization methods. In this respect two new digital loops are proposed. The first is an adaptive digital PLL. It makes use of the special characteristics of the satellite trajectory to adapt loop parameters during a satellite pass.