Telemetry Simulation Using Direct Digital Synthesis Techniques

Abstract

Direct digital synthesis technology has been employed in the development of a telemetry data simulator constructed for the Western Space and Missile Center (WSMC). The telemetry simulator, known as TDVS II, is briefly described to provide background; however, the principal subject is related to the development of programmable synthesizer modules employed in the TDVS II system. The programmable synthesizer modules (or PSMs) utilize direct digital synthesizer (DDS) technology to generate a variety of common telemetry signals for simulation output. The internal behavior of DDS devices has been thoroughly examined in the literature for nearly 20 years. The author is aware of significant work in this area by every major aerospace contractor, as well as a broad range of activity by semiconductor developers, and in the universities. The purpose here is to expand awareness of the subject and its basic concepts in support of applications for the telemetry industry. During the TDVS II application development period, new DDS devices have appeared and several advances in device technology (in terms of both speed and technique) have been effected. Many fundamental communications technologies will move into greater capacity and offer new capabilities over the next few years as a direct result of DDS technology. Among these are: cellular telephony, high-definition television and video delivery systems in general, data communications down to the general business facsimile and home modem level, and other communications systems of various types to include telemetry systems. A recent literature search of the topic, limited only to documents available in English, indicates that some 25 articles and dissertations of significance have appeared since 1985, with over 30% of these appearing in international forums (including Germany, Japan, Great Britain, Portugal, Finland...). Product advertisements can readily be found in various publications on test instruments, amateur radio, etc., which indicate that international knowledge and product application of the technology is becoming increasingly widespread.