Synthesisers for low data-rate satellite receivers

Because of the small antenna gain and associated low carrier-to-noise density, VSAT terminals operate at a low data-rate (typically no higher than 64 kbit/s, and often considerably less). Phase noise is a significant parameter in low data-rate receivers such as VSAT terminals. Both thermal noise and phase noise from downconversion synthesisers affect demodulators employing a carrier recovery loop (CRL), giving degradation of BER performance. Each places conflicting demands upon loop bandwidth of the CRL. Single loop synthesisers are simple and attractive as downconverter local oscillators, but their phase noise can be excessively large for data receivers. It is possible to predict levels of phase noise from given configurations as a function of the logic technology employed. Synthesiser phase-frequency detectors may be critical design components. Some low cost synthesiser designs may prove inadequate in this respect to meet receiver BER requirements