• DEMODULATION OF FM SIGNALS BY A DISCRETE PHASE LOCKED LOOP

      Reddy, C. P.; Gupta, S. C.; SMU Institute of Technology (International Foundation for Telemetering, 1972-10)
      This paper discusses the discrete-phase locked loop for demodulation of an incoming frequency modulated analog signal imbedded in white noise. The discrete samples admitted into the system adoptively, represent an estimate of the message at the discrete instants of time which can be improved further with a correction factor. The work is in two parts: (1) even without the noise, perfect demodulation is not possible. To arrive at the best estimate, requirements are specified regarding the ratio of carrier frequency to maximum frequency deviation, taking into consideration the lock range and the Nyquist sample rate. A simulation study is performed to specify the bounds for the estimate to be accurate enough. (2) With the above considerations, the receiver is analyzed with noise. For high carrier to noise ratio, it is shown that the performance is at least as good as an analog discriminator. The only requirement being that the condition specified in (1) is more stringent. Digital computer solutions of the system check the above and provide a qualitative picture of the threshold behavior comparable to analog feedback discriminators.
    • A NEW VHF-INTERFEROMETER WITH THREE STEERABLE HIGH-GAIN-ANTENNAS FOR SATELLITE-TRACKING

      Fogy, W.; German Aero-Space-Research Establishment (International Foundation for Telemetering, 1972-10)
      The German-Central-Ground-Station near Weilheim, Bavaria, called Z-DBS, operates now on VHF-Telemetry and Telecommand. Its monopulse-autotrack-subsystem measures one way doppler datas and medium-precise (~0,25° RMS) direction angular (AZ,EL) datas. For precise orbital tracking the station will now be completed by a VHF-Interferometer with three steerable high-gain-antennas, using the angular information of the existing system for initial acquisition and ambiguity resolution. Such a system is applicable to track most near-earth-satellites in orbit without needing a global network even with a relatively low percentage of contact time because of its large angular- and distance-coverage from one topos. The interferometer, now under construction, will be ready for operation at the end of 1973. The present paper gives a brief description of the parameter requirements, the system itself and the methods used to overcome the very high technical difficulties. The total residual direction error is predicted not to exceed (10÷15)”, including nearby ground reflexions but excluding residual athmospheric propagation effects. High side-lobe-suppression-antennas with extremly stable phase characteristics as well as a 3-channel-piloting-receiver-system are used to make the antenna’s difference-phase errors small enough and to eliminate phase changes throughout long cables and receivers. A computer operates the whole system to a high degree of automacy and evaluates and smoothes the direction datas.
    • BIT SYNCHRONIZATION

      McRae, D. D.; Smith, E. F.; Radiation Incorporated (International Foundation for Telemetering, 1972-10)
      In this paper the trade off between acquisition and noise performance for several bit synchronizer techniques are examined. Results are presented for random NRZ input data with an initial frequency offset between the incoming bit rate and the a priori estimate of this rate.
    • A NARROWBAND, CRYSTAL CONTROLLED BIOMEDICAL TELEMETRY SYSTEM

      Westbrook, Richard M.; Fryer, Thomas B.; National Aeronautics and Space Administration (International Foundation for Telemetering, 1972-10)
      A miniature, single-channel, crystal-controlled transmitter has been developed for biomedical applications. A narrowband frequency modulation (±7 kHz) of the RF is used to achieve maximum operating range with minimum transmitting power. The radiated power is limited to stay within the 50 μv/m at 15 m FCC requirement for low power transmitters (Part 15.212 FCC Regulations) in the 88 to 108 MHz band. This technique offers a number of advantages. First only manufacturer’s type approval is required for the device and the user does not need a license. Second maximum operating range can be achieved within the FCC power limitations by using a narrowband that is consistent with the required medical information bandwidth. A third advantage in using the 88 to 108 MHz band is that the commercial FM stations are relatively widely spaced and carefully regulated so that by selecting the transmitter’s frequency in the guard band between stations, minimum interference from other transmitter sources is encountered. For EKG and EEG applications, where an information bandwidth of 0.1 to 150 Hz is adequate, a subcarrier with a fixed frequency (approximately 1 kHz) is used with differential pulse width modulation (DPWM). This type of subcarrier has the advantage of simple circuitry for both the transmitter and demodulator. Since DPWM is self-aligning, it can be handled effectively by magnetic tape recorders having relatively high tape speed errors. For EMG and other high frequency data signals the RF can be directly frequency modulated without the use of a subcarrier.
    • DATA COMPRESSION FOR EARTH RESOURCES SATELLITES

      May, C. L.; Spencer, D. J.; TRW Systems (International Foundation for Telemetering, 1972-10)
      This paper concerns an information-preserving data technique which is applicable to multi-spectral imagery such as that obtained by earth-resources satellites. The requirements for data compression in such missions is discussed and a rationale is presented for the use of distortion-free information-preserving compression. The selected compression technique involves the use of the spectralspatial-delta-interleave (SSDI) algorithm, a form of DPCM, to eliminate gross spectral and spatial redundancies. This reduced data is then coded for transmission using either the Huffman or the Rice coding algorithms. The coding algorithms have been simulated using a portion of frame 3698 taken during the Apollo S065 experiment and, the results are presented. A parametric study presents the compression achieved by the SSDI-Rice algorithm as a function of block size and split-pixel mode used. Implementation considerations are also given.
    • SELF-CORRECTING DIFFERENTIAL PCM

      Anglade, P.; Hawkes, T. A.; Durand, J. J. (International Foundation for Telemetering, 1972-10)
      Differential PCM (DPCM) systems are characterized by an accumulation of transmission errors in the signal regenerated in the receiver. The use of a normalization procedure before transmission appears to permit suppression of these errors. This normalization must be carried out with respect to the limit value toward which the signal is evolving. The error reduction is not immediate, but is a function of signal value and signal activity. For constant signals there is no reduction. Reduction is more rapid the more widely the signal varies, and is also more rapid as the frequency of signal reversals increases. This method of coding requires adaptation to each application, since the basic quantization interval varies with signal magnitude.
    • AN ALL DIGITAL PHASE LOCKED LOOP

      Greco, J.; Garodnick, J.; Schilling, D. L.; City College of CUNY (International Foundation for Telemetering, 1972-10)
      An All Digital Phase Locked Loop for FM Demodulation is presented. The system operates synchronously and performs all required digital calculations within one sampling period, thereby performing as a real time special purpose computer. The signal to noise ratio is computed for frequency offsets and sinusoidal modulation and experimental results verify the theoretical calculations.
    • DIGITAL FM DEMODULATION TECHNIQUES

      Garodnick, Joseph; Goldmark Communications Corp. (International Foundation for Telemetering, 1972-10)
      Digital systems have been heavily emphasized over the past decade because of their intrinsic trouble free operation, multiplexed signal handling capabilities, and the complex processing techniques possible through the use of small special and general purpose digital computers. The digital evolution has also allowed system cability to increase, while size, cost and power consumption decrease. Functions previously deemed impossible to implement are now being constructed in production facilities. When digital techniques are used for source encoding in a wide band communications network (such as two-way CATV), information is transmitted and received digitally with Small error probalility compared to analog signals, especially when carriers and media take the form of cable, laser beams and fiber optics where line repeaters are used in lieu of amplifiers.
    • L-ORTHOGONAL SIGNAL TRANSMISSION AND DETECTION

      Lindsey, W. C.; Simon, M. K. (International Foundation for Telemetering, 1972-10)
      This paper investigates the detailed capabilities and performance characterization of systems that employ L-orthogonal signaling techniques. L-orthogonal signals represent a unified set of signals wherein the polyphase and orthogonal (bi-orthogonal) signal sets are included as special cases. This fact is important since orthogonal (bi-orthogonal) and polyphase signaling sets r e present opposing forces as far as tradeoffs between error probability, energy - to-noise ratio, and bandwidth requirements are concerned. Bounds on the performance of the optimum receive r and the performance of various suboptimum (practical) receiver structures are given. Coherent and differentially coherent detection of differentially encoded signals re also pursued. Various comparisons and tradeoffs are made by means of numerical evaluation of the error probability expressions.
    • ADAPTIVE LINE BY LINE ENCODER FOR IMAGE TRANSMISSION

      Algazi, V. R.; University of California at Davis (International Foundation for Telemetering, 1972-10)
      A simple adaptive algorithm is applied to the line by line encoding of images. Among its desirable properties the algorithm includes a control of encoding errors independently of the image statistics. This block transform encoder, because of its adaptive nature gives rise to non-stationary errors and end of block effects. Two methods are proposed to reduce these effects and thus improve the subjective quality of reconstructed images. The performance of the algorithm is image dependent and several illustrative examples are given.
    • International Telemetering Conference Proceedings, Volume 08 (1972)

      International Foundation for Telemetering, 1972-10
    • MICROPROGRAMMABLE PROCESSORS APPLIED TO TELEMETRY PROCESSING SYSTEMS

      Karleskint, Daniel J. (International Foundation for Telemetering, 1972-10)
      This paper briefly analyzes the application of modern microprogram techniques in the computerized telemetry processing environment. It shows these technique s can attain a flexibility in design and application previously unavailable.
    • POLICY ISSUES IN CABLE COMMUNICATIONS

      Hinchman, Walter R.; Office of Telecommunications Policy (International Foundation for Telemetering, 1972-10)
      Cable communications constitutes a complex and dynamic new medium for both selective and mass distribution of entertainment and information programming, as well as new information exchange services. The complexity of technical, operational, social, political, and economic issues relating to cable probably exceeds that of any electronic communications development to date. Fortunately, there are relevant experiences from many other communications operations -- common carriers, broadcasters, the publishing industry, etc. -- which provide insights into the probable evolution of cable communications and into the many policy issues which exist or will arise. By carefully selecting from among several options for industry structure and integration, it should be possible to achieve -with minimal detailed regulation -- a cable communications industry which encourages diversity of information and entertainment services, guarantees access by all responsible interests, avoids excesses of monopoly powers, and is truly responsive to public needs and interests. That, at least, is the objective of the Administration’s current Cabinet-level policy review.
    • BIOTELEMETRY IN THE 1970’S

      Rader, D. R.; University of Southern California (International Foundation for Telemetering, 1972-10)
      A date cannot be pinpointed for the concept of using telemetry for acquiring biological data; however, it is known that the birth of biotelemetry in the form of hardware occurred about 1921--with the report of a heart sound transmitter. Biotelemetry matured only slightly from the twenties to the early fifties. During the fifties and sixties large amounts of money were administered through the money pipeline of the federal government. As a consequence, the growth during this period was bath rapid and grotesque, with tentacles reaching into scores of industrial and educational institutions. Duplication of efforts was quite common during this period and hundreds of miniature biotelemetry systems were built, but results deriving from practical application were quite limited. During the last few years, much of the chaff was shucked from this new growth, a root system developed, and biotelemetry found limited use as a tool in clinical medicine and in medical research. In the past biotelemetry has not lived up to the expectations. What about the future--will it really occupy an important place in clinical medicine and medical research? What is the economic outlook--how many jobs will it support? Which areas will require new talent? And, finally, what are the most common problems and haw can they be solved?
    • 10-MICROMETER BAND COMMUNICATION TERMINALS IN SPACE

      McAVOY, N.; Goddard Space Flight Center (International Foundation for Telemetering, 1972-10)
      10-micrometer band communication systems using CO2 lasers for space to space links are discussed. Particular emphasis is on low earth orbiting earth observation satellites to geosynchronous satellites at high data rate. Four key technology areas are discussed: Wideband mixers for Doppler tracking; tunable laser local oscillators; high data rate modulators; laser transmitters.
    • EFFECT OF FLUTTER ON THEORETICAL BIT ERROR RATES FOR DIGITAL RECORDING SYSTEMS

      Byers, R. A.; Jet Propulsion Laboratory (International Foundation for Telemetering, 1972-10)
      Tape recorders employed to record and eventually reproduce digital data introduce errors into the data. It is desirable to understand the sources of these errors so that predictions may be made of the resultant error rate. While specific predictions are difficult to apply to whole classes of machines and their respective electronic systems, it is possible to make general predictons which give insight into the problems and processes involved. The intent will not be to suggest improvements in recorders, but to supply a heuristic viewpoint for understanding the problems involved in machines and systems that now exist.
    • ULTRA-WIDEBAND, LONGITUDINAL MAGNETIC-TAPE RECORDING

      Krey, Karl H.; Harry Diamond Laboratories (International Foundation for Telemetering, 1972-10)
      Signal frequencies from 100 kHz to 30 MHz with bias frequencies of 120 MHz and higher have been recorded longitudinally on magnetic tape with a SNR better than 15 dB. The upper frequency of zero-bias-recorded signals was 36 MHz at a tape velocity of 2800 ips. The recordings were reproduced on a standard Mincom wideband recorder/reproducer at 60 and 120 ips. This laboratory recording system includes a Newell-type tape transport, which has been redesigned to comply with requirements of higher tape velocity and faster acceleration. At present, this transport accelerates tape at a rate of approximately 8000 in/sec^2 to a maximum speed of about 3000 ips. The magnetic recording heads developed for this system represent the state-of-the-art in head design., These are combination heads having a ferrite core with Alfesil pole tips and an insulated conductive gap spacer.
    • SATELLITE NETWORKS FOR EDUCATION

      Singh, J. P.; Morgan, R. P.; Rosenbaum, F. J.; Center for Development Technology (International Foundation for Telemetering, 1972-10)
      This paper is concerned with satellite-based educational networking. It is based on work performed in a continuing study of the potential uses of communications satellites to help meet educational needs in the United States. The paper is divided into four main sections. The first is concerned with the characteristics and structure of networks. The second section contains a discussion of pressures within the educational establishment that are providing motivation for various types of networks. This latter section also identifies studies in which networking needs for educational sectors and services are defined. Section three examines the current status of educational networking for educational radio and television, Instructional Television Fixed Services, inter- and intrastate educational communication networks, computer networks, cabletelevision for education, and continuing and proposed educational experiments using NASA’s Applications Technology Satellites. The fourth section describes possible satellite-based educational telecommunication services and three alternatives for implementing educational satellite systems. The paper concludes with some remarks concerning public policy aspects of future educational satellite system development.
    • THE USE OF MATCHED FILTERS FOR SYNCHRONIZATION

      Halpern, Peter H.; General Dynamics Corporation (International Foundation for Telemetering, 1972-10)
      Matched filters are derived for best extracting synchronization. This is done for a somewhat general class of signaling systems as well as for NRZ and SO/ PCM. The approach is based on the synthesis of finite time duration trigonometric pulses. The solution of simple calculus of variations problems yield a description of the matched filters.
    • DIGITAL PHASE LOCKED LOOPS WITH SEQUENTIAL LOOP FILTERS: A CASE FOR COARSE QUANTIZATION

      Cessna, J. R.; National Oceanic and Atmospheric Administration (International Foundation for Telemetering, 1972-10)
      A class of digital phase locked loops exists for which performance can be demonstrated to be comparable to that of the linear analog model, yet the use of coarse quantization seems to be favored. This class is characterized by the use of (1) a phase detector with quantized output, (2) a sequential loop filter, and (3) a discrete phase adjustment clock. The sequential filter is an inherently nonlinear device which operates on a sequence of inputs and provides a sequence of outputs, usually fewer in number and with a variable interval between outputs. Operation of these loops is decidedly nonlinear and a conventional linear loop bandwidth cannot be defined. Although higher than first order loops of this class may be constructed, their analysis, so far, has been limited to first order types by random walk techniques. A quasi-bandwidth measure can be defined for these loops in terms of their transient response which serves as an absolute basis for comparison of different digital loops. Using this tool, examples of 3- and 4-level quantization in these loops are found to have no obvious advantages over the binary quantized model and in some cases striking disadvantages.