Writing Procurement Specifications for a Telemetry Receiver

Abstract

Government and industrial telemetry users have the frequent requirement to procure telemetry receivers which will faithfully receive and demodulate physical and electrical phenomena occuring at the transmitting source. Such receiver output data accuracy requirements must be translated into meaningful receiver procurement specifications. Movement of the transmitting source, dynamic changes in the RF path through which the telemetry signal is transmitted, and the distorting effects of electrical circuitry in the receiver itself, all contribute to distortion of the baseband data. The parameters affecting baseband data quality must, therefore, be quantized in terms of telemetry receiver performance specifications. Where possible, the specifications should relate to input/ output parameters of the receiver; this may not be possible in all cases, however. The methodology for translation of telemetry signal data quality requirements into electrical specifications for a telemetry receiver is treated in this paper. Specification of RF and IF channel characteristics are covered, and AGC, AFC, and AM rejection circuitry requirements are analyzed in terms of received-signal amplitude and frequency dynamics. Overall distortion in the telemetry receiver is characterized for FDM signals by specifications whose reference is the noise-loading technique; for TDM signals distortion is characterized in terms of receiver transient response. FM demodulator specifications are treated, and specifications for allowable baseband distortion due to co-channel RF interference are introduced. Finally, the electrical performance requirements of the baseband channel are characterized.