• RELAY TECHNIQUES FOR MOBILE SERVICES

      Vandenkerckhove, J.; ESRO/ESTEC (International Foundation for Telemetering, 1973-10)
      Dr. Vandenkerckhove will discuss system considerations involved in providing communications services to aeronautical and maritime users via Synchronous Relay Satellite.
    • A REVIEW OF MULTIPLE AMPLITUDE-PHASE DIGITAL SIGNALS

      Smith, Joel G.; California Institute of Technology (International Foundation for Telemetering, 1973-10)
      This 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.
    • RFI ANALYSIS APPLIED TO THE TDRSS SYSTEM

      Jenny, J.A.; ESL Incorporated (International Foundation for Telemetering, 1973-10)
      The effect of radio frequency interference (RFI) on the proposed Tracking and Data Relay Satellite System (TDRSS) was assessed. The method of assessing RFI was to create a discrete emitter listing containing all the required parameters of transmitters in the applicable VHF and UHF frequency bands. The transmitter and spacecraft receiver characteristics were used to calculate the RFI contribution due to each emitter. The individual contributions were summed to obtain the total impact in the operational bandwidth. Using an as yet incomplete enitter base, we have concluded that the 136-137 MHz band should be used by TDRS rather than the whole 136-138 MHz band because of the higher interference levels in the 137-138 MHz band. Even when restricting the link to 136 to 137 MHz, the existing link design is marginal and it is recommended that interference reduction units, such as the Adaptive Digital Filter, be incorporated in the TDRS ground station. RFI is less of a problem in the 400.5 to 401.5 MHz band and can probably be handled by restricting command transmissions to low RFI areas or if that is not acceptable, by using simple automatic notch filters to notch out the few interferers present.
    • SATELLITE-AIRCRAFT DIGITAL TRANSMISSION EXPERIMENT RESULTS AT L-BAND

      Wilson, Stephen G.; Boeing Commercial Airplane Company (International Foundation for Telemetering, 1973-10)
      Results of an experiment involving the synchronous satellite relay of digital information at L-band between a ground station and a jet aircraft are described. Specific tests studied the performance of PSK signalling in conjunction with three distinct detection strategies for both the classical additive noise channels and the composite multipath channel (direct signal plus multipath). Tests were conducted at various signalto-noise ratios and direct signal-to-multipath ratios. Reasonable agreements with available non-fading and Rician fading channel theory is shown. Implications for the operational aeronautical satellite case are discussed.
    • A SHOCK HARDENED PCM SYSTEM WITH DATA STORAGE

      Barnes, D. E.; Sandia Laboratories (International Foundation for Telemetering, 1973-10)
      A miniature shock hardened PCM system with data storage capability has been developed by Sandia Laboratories for use in test where RF transmission either difficult or impossible. The PCM has 16 channel input capacity and encodes the data with 6 bit accuracy. The data rate is selectable from 1k bit per second to 250 k bit per second. The encoder has been harbarized and packaged in a volume of less than 4 cubic inches. The data storage is selected in 6 k bit increments with a maximum storage of 600 k bits. Typical applications involving earth and water penetrating are described.
    • A SHORT RANGE 15 MEGABIT/S LED COMMUNICATOR

      Dworkin, L. U.; Coryell, L.; USAECOM (International Foundation for Telemetering, 1973-10)
      The design, development, and testing of a short range (distances up to 100 ft) data communications equipment that utilizes a GaAs light emitting diode (LED) source is discussed. Data rates of 15 Mb/s are accommodated by a transmission terminal which consists of a line of sight (LOS) atmospheric portion and a fiber optic link. The system has an all weather capability, is relatively inexpensive and is intended for tactical military applications. This is the first attempt at developing a wideband optical communicator that has a similtaneous LOS and cable capability often needed in a tactical military environment.
    • SIMULATION RESULTS FOR AN INNOVATIVE ANTIMULTIPATH DIGITAL RECEIVER

      Painter, J. H.; Wilson, L. R.; National Aeronautics and Space Administration; LTV Aerospace Corp. (International Foundation for Telemetering, 1973-10)
      Simulation results are presented for the error rate performance of the recursive digital MAP detector for known M-ary signals in multiplicative and additive Gaussian noise. The structure of the digital simulation of the innovative receiver, operating in a multipath environment, is generally described. Specific results are given for a quaternary signal, of the type used in air-ground data links, with 2500 symbol per second transmission rate. Plots of detection error rate versus additive signal to noise ratio are given, with multipath interference strength as a parameter. For comparison, the error rates of conventional coherent and noncoherent digital MAP detectors are simultaneously simulated and graphed. It is shown that with non-zero multiplicative noise, the error rates of the conventional detectors saturate at an irreducible level as additive signal to noise ratio increases. The error rate for the innovative detector continues to decrease rapidly with increasing additive signal to noise ratio. In the absence of multiplicative interference, the conventional coherent detector and the innovative detector are shown to exhibit identical performance.
    • A SPACEBORNE RECEIVER FOR MEASURING ELECTROMAGNETIC FIELD INTENSITY

      Reich, B.W.; Van Dusen, M. R.; Habib, E. J.; National Oceanographic and Atmospheric Administration; Airborne Instrument Laboratory; National Aeronautics and Space Administration (International Foundation for Telemetering, 1973-10)
      At the present time, considerable interference with communications to and from spacecraft has been experienced. Consequently, the need for determining the extent of this interference was indicated. NASA contracted AIL to design and build a very accurately controlled receiver to monitor the electromagnetic radiations in both existing and projected space communication bands. Based on analysis of the existing and projected space communication bands, 108 to 174 MHz, 240 to 478 MHz, and 1535 to 1665 MHz were covered. The receiver achieves accurate control via a digitally tuned synthesizer and a wide range of digital control including frequency band coverage and gain control selection. Digital memory was provided to store 16 separate digital command instructions which can be programmed via a command data link. The receiver provides for transmission to the ground of both a predetection signal and signals in digital format, which in turn, were provided by sampling and analog-to-digital conversions.
    • SPECTRUM PROCESSING RECEIVERS FOR TELEMETRY APPLICATIONS

      Van Cleave, J. R.; American Electriconic Laboratories, Inc. (International Foundation for Telemetering, 1973-10)
      When the i-f filter of a telemetry receiver is replaced by a digital processor utilizing an intermediate orthogonal transformation into either the frequency domain using Fast Fourier Transform (FFT) or sequency domain using Fast Walsh Transform (FWT), then much improvement in performance may be expected. This paper discusses both application and results of FFT and FWT processing to: 1) a signal acquisition receiver providing extremely enhanced phase lock loop (PLL) acquisition speed; 2) an adaptive i-f bandwidth receiver providing a large i-f signal to noise ratio (SNR) improvement and also immunity to undesired EMI and/or jamming signals; and, 3) a signal evaluation receiver for measurement of SNR in the range of -30 dB and up. Spectrum processor design considerations and tradeoffs are presented.
    • STANDARDS FOR GOVERNMENT USE OF THE SPECTRUM

      Hull, Joseph A.; IRAC Technical Subcommittee (International Foundation for Telemetering, 1973-10)
    • A SYNCHRONIZED DISCRETE ADDRESS BEACON SYSTEM

      Blake, Neal A.; Federal Aviation Administration (International Foundation for Telemetering, 1973-10)
      The Federal Aviation Administration is developing a Discrete Address Beacon System as a new air traffic control surveillance system. It will solve most of the problems of the present beacon system and will also provide an integral digital data-link for ground to air messages. This paper describes a particular implementation of the DABS concept which also provides air-to-air collision avoidance service and navigation service.
    • TELEMETERING VIA LEAKY WAVEGUIDES

      Hu, A. S.; New Mexico State University (International Foundation for Telemetering, 1973-10)
      Telemetering through leaky waveguides is a combination of cable transmission and atmospheric transmission. This system carries radio signals in a confined space tube thus making signal transmission through tunnels, mines, and buildings possible. This paper discusses the history of development, the types of leaky waveguide, the transmission characteristics, and the performance evaluation methods.
    • TIME DOMAIN ANALYSIS OF AN AGC WEIGHTED COMBINER

      Hill, E. R.; Naval Missile Center (International Foundation for Telemetering, 1973-10)
      The 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.
    • TIMING CORRELATION IN TELEMETRY RECORDING AND PROCESSING SYSTEMS

      Matthews, F. L.; Streich, R. G.; Vandenberg Air Force Base (International Foundation for Telemetering, 1973-10)
      The Space and Missile Test Center (SAMTEC) has conducted tests to correlate independent data stream to within ±10 microseconds. System timing error measurements have been made to determine RF system delays; the delays associated with wideband analog tape recorders in the recording, dubbing and reproducing processes; and uncertainties associated with processed data. Comparison of the time delays between predetection PCM data and post-detection PCM data are made. Several methods of recording IRIG time code formats A and B are evaluated for best resolution. Timing error versus tape recorder head azimuth is plotted. Tape recorder phase delay effects on time code formats and on PCM data are given. The time bias between the time tag and the computer processed data is presented. Sources of timing errors and the calibration and operating techniques available to minimize these errors are discussed. A special time tag technique (Ref 1) has been used in the past to determine the cumulative timing bias for all sources. This investigation is believed to be the first attempt to identify the individual contributions to the cumulative bias.
    • TRACKING AND DATA RELAY SATELLITE SYSTEM (TDRSS)

      Barritt, Paul; Clark, George; NASA (International Foundation for Telemetering, 1973-10)
      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.
    • TRANSMISSION OF RADIOMETER DATA FROM THE SYNCHRONOUS METEOROLOGICAL SATELLITE

      Davies, Richard S.; Philco-Ford Corporation (International Foundation for Telemetering, 1973-10)
      The Synchronous Meteorological Satellite uses a spin scanner radiometer which generates eight visual signals and two infrared signals. These signals are multiplexed and converted into a 28-Mbps data stream. This signal is transmitted to ground by quadriphase modulation at 1686.1 MHz. On the ground, the digital signal is reconstructed to an analog signal. To conserve bandwidth, an analog-to-digital converter with a nonlinear transfer function was used for the visual signals. The size of the quantization step was made proportional to the noise output of the scanner photomultiplier tube which increases as the square root of incident light. The radiometer data transmission link was simulated on a digital computer to determine the transfer function. Some results of the simulation are shown.
    • AN ULTRAHIGH RATE DIGITAL TAPE RECORDER FOR SPACECRAFT APPLICATIONS

      Thompson, C. R.; Treadwell, R. J.; Powell, C.; FICA; NASA (International Foundation for Telemetering, 1973-10)
      Spaceborne 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.
    • ULTRASOUND TELEMETRY OF FETAL CARDIAC ACTIVITY

      Hess, Orvan W.; Litvenko, Wasil; Yale University (International Foundation for Telemetering, 1973-10)
      Patterns of alterations in fetal heart rate provide the earliest clue of jeopardy of the fetus from umbilical cord compression, abnormal uterine contractions, placental dysfunction or impaired fetal reserve. Correlated with uterine contractions, such patterns provide an index of the condition of the fetus and an objective basis for clinical management. The recognition of the value of continuous monitoring of these parameters has resulted in widespread use of electronic apparatus. Telemetry techniques have proved value as an alternative method of surveillance. A system has been devised for telemetry of fetal cardiac activity detected with ultrasound.
    • UNIVERSAL AIR-GROUND DATA LINK SYSTEM

      Williamson, Thomas; Federal Aviation Administration (International Foundation for Telemetering, 1973-10)
      With the implementation of a nationwide Air Traffic Control (ATC) automation system nearly completed the Department of Transportation/Federal Aviation Administration is devoting considerable attention to the integration of a data link capability into the system. This paper presents a description of the universal data link system and details of the system’s characteristics. A possible configuration of the data link system with the ATC automation system is also presented.
    • USER-ORIENTED IMAGE DATA CARTRIDGE RECORDING SYSTEM

      Horton, Charles R.; Radio Corporation of America (International Foundation for Telemetering, 1973-10)
      New generation satellites such as ERTS present a new challenge to the data recording industry. Continuous wideband data creates an enormous storage/retrieval problem. Recently developed high density tape storage solves the volume problem but does not provide fast access. Clearly, some cartridge type device is required. A similar problem faced the broadcast T.V. industry. Cartridge equipment was developed to allow automatic programming of short segments. This paper describes application of this technology to present and future data storage requirements. With the technique described, ERTS data can be segmented into blocks of ten frames each and stored in easily accessed tape cartridges.