RSS 1.0International Telemetering Conference Proceedings, Volume 09 (1973)
ABOUT THE COLLECTION
The International Telemetering Conference/USA (ITC/USA) is dedicated to the promotion and stimulation of technical growth in telemetering and its allied arts and sciences. It is the premier annual forum and technical exhibition providing telemetry specific short courses, technical papers from professionals and students, and exhibits of the industry’s leading companies. ITC/USA is sponsored by the International Foundation for Telemetering (IFT), a non-profit corporation dedicated to serving the technical and professional interests of the telemetering community.
This collection contains the proceedings of the ninth International Telemetering Conference, October 9-11, 1973. The conference, sponsored by the International Foundation for Telemetering, was held at the Sheraton Inn Northeast in Washington, D.C.
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International Telemetering Conference Proceedings, Volume 09 (1973)International Foundation for Telemetering, 1973-10
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CROSSPLAY COMPATIBILITY OF WIDE-BAND TAPE RECORDER/REPRODUCERSThis paper describes the procedure and results of a series of tests on a cross section of tape recorders to determine the effects of record bias and record signal level on the quality of data recorded in the Pre-D (predetection) mode. FM (frequency modulation) and PCM (pulse code modulation) formats were used in the study. The tests were performed on tape recorders at five test sites to determine the effects of crossplay under typical operating conditions. The results are summarized and possible methods of improving crossplay data quality are suggested.
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A HIGH CAPACITY, HIGH DATA RATE INSTRUMENTATION TAPE RECORDER SYSTEMA 240-megabit/second, serial bit stream recording system using a longitudinal (fixed-head) magnetic recording technique called HDMR (High Density Multitrack Recording) has been developed. This system provides maximum bits per square inch of tape at reliable in-track packing densities. Unique “unitized” fabrication techniques have been used to construct single stack magnetic heads (record/play on the same head) at track densities of over 100 tracks per inch. Commercially available tape is accommodated by the use of error detection and correction. HDMR technology, applied to the implementation of a typical ground instrumentation recording system, allows key performance parameters of: 240 Mb/s serial data input, 108 in/s tape speed, a 142-track head, a bit error rate of 1 x 10^-6 and 240 Mb/s serial data output.
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CRYSTAL-CONTROLLED HIGH-G TRANSMITTERContinuous telemetering during and after a 10,000 to 16,000g shock pulse experienced by the telemeter is a requirement that is frequently not met. In most cases a free-running oscillator is used in the transmitter while a very wide band receiver is used to acquire and provide leeway for the drifting and shifting RF signals.
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APPENDIX A: TWELFTH ANNUAL REPORT OF THE TELEMETERING STANDARDS COORDINATION COMMITTEEThe Telemetering Standards Coordination Committee (TSCC) was formed in 1960 and has been in continuous operation since that time. It is now sponsored by the ISA and the ITC and its membership is drawn from a wide cross-section of the telemetering community. Thus the views of Government, industry, user and manufacturer are brought out when any standard is reviewed by the committee. In accordance with its charter the TSCC is charged with the following tasks: establishing what standards, methods, and procedures are in existence and published; examining the technical adequacy of existing and proposed documents; exploring the need for new standards, methods, and procedures and promulgating the derivation of new documents. The TSCC does not issue standards, but rather acts as a review, coordinating, and fact-finding body, endorsing specific standards, methods, and procedures, and making recommendations to the appropriate document originating groups, to telemetry users and manufacturers, and the Government agencies. For further information on the origination of the TSCC and its original Charter and Bylaws, please see the 1962 Proceedings of the National Telemetering Conference. An annual report has been published each year since that time. Years 1963 through 1967 may be found in the NTC Proceedings of that year and, starting 1968 and all following years, may be found in the Proceedings of the International Telemetering Conference.
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A REVIEW OF MULTIPLE AMPLITUDE-PHASE DIGITAL SIGNALSThis paper reviews the data rate, error rate, and signal-to-noise ratio relationship for various uncoded M-ary digital amplitude modulation (AM), phase modulation (PM), and combined AM-PM systems. These signal systems have the common virtue that expanding the number of possible signals to be transmitted increases the data rate but not the bandwidth. The increased data rate generally requires an increased signal-to-noise ratio to maintain constant error probability performance. Thus, these systems use power to conserve bandwidth. A general treatment of the error rate of M-ary digital AM-PM permits development of a simple yet accurate expression which approximates the increase in average signal-to-noise ratio (over that of binary phase shift keying) required for constant error performance. This equation provides insight into why arrays differ in their signal-to-noise ratio requirements.
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PERFORMANCE OF A 350-Mb/s ADAPTIVE EQUALIZERThis paper applies baseband adaptive equalization techniques to rf multipath and transmitter/receiver distortions. Included are test results comparing 350-Mb/s adaptive equalized and unequalized receivers. These comparisons are made with distortion typically encountered in a high data-rate line-of-sight microwave system such as demodulator quadrature errors, demodulator phase offset errors, and moderate rf multipath distortion. The design and construction techniques are also illustrated.
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AN ULTRAHIGH RATE DIGITAL TAPE RECORDER FOR SPACECRAFT APPLICATIONSSpaceborne digital recorders must satisfy the conflicting requirements of maximum data storage of high rate data (particularly for high resolution sensor data) and a long life with high reliability (meaning rugged design and moderate head-to-tape speeds). The multitrack longitudinal (fixed head) recorder can successfully resolve this conflict and satisfy both requirements. The evolutionary machine described herein was originally designed to store and reproduce 30 min of 39.9-Mb/s sensor data, for mission lives on the order of 1 year; newer designs have surpassed these parameters by significant amounts.
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A NEW ERA IN WORLDWIDE TACTICAL COMMUNICATIONSThe Fleet Satellite Communication System (FLEETSATCOM) now under development will provide the first U. S. military satellites designed from the start as operational transponders for tactical communications with and among mobile users. FLEETSATCOM is a logical outgrowth of earlier experimental projects, principally the Tactical Satellite Communication (TACSATCOM) project of the late 1960’s. When the globe-girdling system goes operational in calendar year 1976 it will quite literally revolutionize both Air Force and Navy tactical communications by providing availability and reliability of over-the-horizon communications that can never be matched by conventional high-frequency circuits.
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RELAY TECHNIQUES FOR MOBILE SERVICESDr. Vandenkerckhove will discuss system considerations involved in providing communications services to aeronautical and maritime users via Synchronous Relay Satellite.
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RECONSTRUCTION OF DISTORTED SAMPLES IN DIGITAL TELEMETRYThe problem of processing of an analog-digital message, that is transmitted via the noise channel is digital form, is considered. A simple algorithm of correction of distorted samples is proposed with the use of one symbol for even parity checking and linear interpolation. The expression for a resulting mean-square error is obtained, that allows to evaluate the influence of noises in a channel. Possible generalizations of the formulated problem are presented.
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AN ALL DIGITAL LOW DATA RATE COMMUNICATION SYSTEMThe advent of digital hardwares has made it feasible to implement many communication system components digitally. With the exception of frequency down conversion, the proposed low data rate communication system uses digital hardwares completely. Although the system is designed primarily for deep space communications with large frequency uncertainty and low signal-to-noise ratio, it is also suitable for other low data rate applications with time-shared operation among a number of channels. Emphasis is placed on the fast Fourier transform receiver and the automatic frequency control via digital filtering. The speed available from the digital system allows sophisticated signal processing to reduce frequency uncertainty and to increase the signal-to-noise ratio. The practical limitations of the system such as the finite register length are examined. It is concluded that the proposed all-digital system is not only technically feasible but also has potential cost reducation over the existing receiving systems.
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MULTIMEGABIT OPERATION MULTIPLEXER SYSTEMThe Multimegabit Operation Multiplexer System (MOMS) is a high data rate PCM telemetry unit capable of sampling and encoding 60 scanning radiometer and 4 vidicon channels at 250 kilosamples/second and 5 megasamples/second, respectively. This sampling capacity plus the 7-bit quantization requires a total throughput rate of 40 megasamples/second and 280 megabits/second. To produce these rates efficiently, the system was divided into a pair of identical 140-megabit blocks. A low-power 20-MHz analog multiplexer and analog-to-digital converter were developed together with a video sample-and-hold that features an aperture time error of less than 50 picoseconds. Breadboard testing of these basic building blocks confirmed the design prediction that the total system would consume 27 watts of power. Two 140-megabit output ports are suitable for quadraphase modulation.
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TRACKING AND DATA RELAY SATELLITE SYSTEM (TDRSS)Coincident with the advent of the Space Shuttle era in the late 1970’s will also come a new era in space communications. The NASA Tracking and Data Relay Satellite System (TDRSS), consisting of satellites in synchronous orbit relaying data between mission spacecraft in low altitude earth orbit and the various mission control centers, will change the character of tracking and data acquisition operations from the short duration, intermittent contacts characteristics of the world wide network of ground stations of the Space Tracking and Data Network (STDN), to nearly full time contact. This capability will expedite interaction between ground based scientists and their spaceborne instruments, reduce dependence upon data tape recorders, and in general improve the reliability and versatility of space communications. This paper will discuss the requirements for TDRSS service and the characteristics of the system and subsystems that NASA studies have shown best meet those requirements.
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A PCM DATA SEQUENCE CONTROLLERThe PCM Data Sequence Controller described in this paper is used to interface a memory-controlled PCM encoder with a plated wire memory to form a unique digital data compression and storage system. The memory-controlled PCM encoder is used to select formats and convert input analog data channels into a PCM bit stream which is both transmitted and stored in a plated wire memory. The encoder is also used to retrieve information from the plated wire memory and retransmit it. The system provides both temporary and permanent data storage for the telemetering of data in a severe environment.
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INTERFEROMETER SIGNAL DEMODULATION IMPROVES TRACKING SENSITIVITYA considerable improvement in signal to noise ratio has been achieved in narrow band interferometer trackers by demodulating the telemetry signal prior to the final stage of i-f amplification. This system has an effective signal bandwidth much greater than the noise bandwidth. Signal to noise improvements of 10 dB are typical.
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TIME DOMAIN ANALYSIS OF AN AGC WEIGHTED COMBINERThe conventional agc weighted diversity combiner is implemented on the assumption that the agc system of each receiver is tracking the rf fading envelope perfectly (i.e., such as to maintain the linear i-f output amplitude constant). The departure from optimum (maximal-ratio) combining which results from imperfect tracking is determined by computer solution of the nonlinear differential equation of the agc system for particular deterministic rf fading envelopes. The performance of the agc weighted combiner is compared with maximal-ratio and equal-gain combiners, both as a function of time and fade rate. It is shown that under certain conditions the equal-gain combiner outperforms the agc weighted combiner. It is also shown that by using both the a-m (detected linear i-f envelope) and the agc voltages for weighting the combiner the limitations arising from the response time of the agc system can be overcome. It is also indicated how an optimum diversity selector can be implemented by using both the a-m and agc voltages.
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HIGH DENSITY PCM MAGNETIC TAPE RECORDINGThe Bell & Howell Enhanced-NRZ™ recording reproducing technique for bit packing densities up to 40,000 per track inch is described in this paper. Utilization of the pulse code modulation format of Enhanced-NRZ achieves this high density with a bit error rate of one in ten million. Bell & Howell’s standard VR-3700B instrumentation tape recorder and wideband instrumentation recording tape are used. This same technique permits parallel recording of data rates up to 10 megabits per second at a tape speed of 120 in./s. The merits of the unique encoding/decoding method, factors affecting bit error rate, and future opportunities for development are discussed.
