DIGITAL DECODING IN RANGE SAFETY RECEIVERS

Abstract

Command Destruct Receivers are used on all launch vehicles for the purpose of initiating flight termination. The up-link command signal is a UHF carrier frequency modulated with Inter-Range Instrumentation Group (IRIG) audio tones. Typically three commands are used to control and terminate the flight: ARM, DESTRUCT, and OPTIONAL command. The combination and sequence of specified IRIG tones determines the command to be issued. The decoder portion of the command destruct receiver determines the presence and sequence of IRIG tones. Through the use of a microprocessor and digital signalprocessing-technology, Cincinnati Electronics has designed and developed a digital decoder which detects four IRIG tones simultaneously. The digital decoder provides stabilities and repeatabilities unattainable with analog decoders. Reliability and reproducibility are also superior when using the digital approach through the elimination of select and variable components. This improved performance of the decoder is a result of crystal controlled digital filtering and a constant false-alarm rate provided by the microprocessor. The digital filtering is achieved through Finite Impulse Response digital filters. There are a number of additional features provided by the digital decoder. Self-testing of portions of the receiver and correcting for temperature drift can be performed by the decoder. The digital decoder can have its command sequences reprogrammed in the field allowing separate control and termination of each vehicle in a multiple vehicle launch. Also, acceptance test data, date of manufacture, total time unit has been powered up, and other data can be stored inside the Command Destruct Receiver and recalled when needed.