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There are a wide variety of modulation methods among the recently used telemetry systems. Characteristics and capabilities of some of these methods are briefly described. There is no generally accepted "best" method. Requirements for conservation of radio spectrum have a strong influence on the choice of modulation parameters. New Inter-Range Instrumentation Group (IRIG) modulation standards have been adopted. Some parameter variations within the new FM-FM standards are presented. The spectrum and data capacity of IRIG PCM-FM are discussed. Various forms of phase-shift keying (PSK) are described. Needs for increased data bandwidth have led to the development of single-sideband subcarriers, used as SSB-FM. Coded transmission with coherent demodulation can provide better carrier signal energy efficiency, but has been rarely used. Noncoherent orthogonal codes appear worthy of further exploitation, being almost as efficient as coherent orthogonal but simpler to produce and detect. Literature references are included for further study.