• PLANETARY PROGRAM DATA SYSTEMS STANDARDS

      Glahn, Earl W.; Planatary Programs Data Systems Working Group (International Foundation for Telemetering, 1973-10)
    • PRINCIPLES AND HEAD CHARACTERISTICS IN VHF RECORDING

      Krey, K. H.; Lieberman, A. G.; Harry Diamond Laboratories; University of MD (International Foundation for Telemetering, 1973-10)
      Concepts of VHF analog magnetic recording are discussed; problem areas are reviewed; and solutions are outlined. Attention is drawn to the conductive-gap-spacer recording head. The unique field contours of this recording head with Alfesil pole faces are analyzed in relation to the recording of very short wavelengths. The field gradients of the unloaded head are computed for various conditions such as maximum magnetization depths, positions in the tape coating, and gap lengths. Comparison of the driven-gap-spacer head using Alfesil pole faces with the ferrite driven-gap-spacer head and the conventional ring-core head shows the Alfesil type to be the most effective for a-c bias VHF recording at very short wavelengths. Problems associated with short-wavelength recording and reproduction are reviewed. In spite of good short-wavelengths capabilities of the Alfesil head, the requirement for a high head-to-tape speed continues to be mandatory to minimize wavelength reproduction losses.
    • A PROGRAMMABLE SAMPLING FORMAT TELEMETRY SYSTEM

      Peterson, Max B.; Johns Hopkins University (International Foundation for Telemetering, 1973-10)
      This paper describes the programmable sampling format telemetry system to be used by the near-earth Small Astronomy Satellite-C (SAS-C) and possible future SAS missions. The concept of the programmable sampling format is introduced and the features of the system are illustrated by an example. The SAS-C telemetry system is described at the block diagram level and redundancy of the system is discussed briefly.
    • RCC TELEMETRY STANDARDS

      Reynolds, R. Stanton; Range Commanders Council (RCC) Telemetry Group (International Foundation for Telemetering, 1973-10)
    • A REAL-TIME HADAMARD TRANSFORM SYSTEM FOR SPECIAL AND TEMPORAL REDUNDANCY REDUCTION IN TELEVISION

      Noble, S. C.; Knauer, S. C.; National Aeronautics and Space Administration (International Foundation for Telemetering, 1973-10)
      A digital Hadamard transform system has been developed for the real-time compression of standard NTSC television signals. The system digitizes the video signals and subdivides four successive frames of data into suppictures of sixty-four picture elements. The subpictures are cubes four elements on a side, in horizontal, vertical and temporal directions. Subpictures are transformed and processed to reduce special and temporal redundancy. Implementation and performance results of the system will be described and discussed.
    • RECONSTRUCTION OF DISTORTED SAMPLES IN DIGITAL TELEMETRY

      Berezin, V. I.; Sviridenko, V. A.; Trofimov, A. M.; Shtarkov, Yu. M. (International Foundation for Telemetering, 1973-10)
      The 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.
    • THE REDUNDANCY OF A SIMPLE SYNCHRONIZATION METHOD FOR VARIABLE LENGTH CODES

      Shtarkov, Yu. M.; Academy of Sciences of the USSR (International Foundation for Telemetering, 1973-10)
      Prefix insertion prior to the coded representation of every fixed length block of data provides a simple synchronization method for variable length coding. Unlike fixed length coding where the prefix appears with a set period, the appearance time of each prefix word in the variable length coded representation is a random variable. At the receiver a synchronization decision is made whenever a pattern within a threshold Hamming distance of the prefix is received. In this paper an expression is found for small synchronization error probabilities. This egression depends on the coded block length only through its average value L. The optimal value for the recognition threshold is found. The necessary and sufficient condition for an arbitrarily small synchronization error probability is shown to be that the prefix length grows as log L. The results are discussed from the viewpoint of data compression and source encoding.
    • 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.