Design and analysis of ground stations for Pacsat applications

Abstract

Engineering problems involving the development of cheap, easy-to-use, and effective packet communications terminals for connectivity to low-earth-orbit satellites (PACSATs) are addressed.

Two prototype terminals were developed: a base station for maximum duration connectivity to the satellite, and a smaller station for portability and low cost. Commercially available systems for related amateur radio uses were integrated for these prototypes. The prototypes illustrated areas for further development before widespread use of PACSATs can be realized.

To better understand some of the issues for PACSATs, two analyses were developed. The first analysis approach characterizes PACSAT orbits so that tradeoffs are readily identified and quantified. Results from an analysis of one PACSAT orbit indicate conflicting needs for the two terminal types.

The second analysis approach addresses issues involving the use of an increasingly popular method for transmitting 9600 baud FSK which combines the spectral efficiency of premodulation pulse shaping with the simplicity of using FM discriminators for demodulation. The spectrum of the transmitted signal is studied and the performance of the demodulator is compared to that of an appropriate coherent receiver. Doppler shifts on the channel is particularly important for PACSAT communications. An analysis approach that addresses the mistuning problem is presented. Results of this analysis identify changes that would better suit the needs of PACSAT terminals.