ABSTRACT

This chapter discusses frequency modulation (FM) and Phase modulation (PM) systems for transmitting analog data and phase shift keying and frequency shift keying systems for transmitting digital data and looks at the trade-offs involved in choosing a modulation system. It provides the basics of analog and digital transmission techniques that are commonly used in command and telemetry systems. The chapter draws on typical modulator and demodulator hardware configurations for the different formats and explains how the radio frequency spectrum is divided in a general sense by International Telecommunications Union region and usage. Telemetry systems are dominated by digital transmission techniques. The value-added signal processing available to digital communications networks is also available in telemetry systems. One characteristic of FM and PM modulation systems is that the carrier has a constant transmission envelope because the amplitude remains constant while frequencies or phases are manipulated. Higher modulation orders are more often considered since more bits per symbol can be transmitted.