• The Signal-to-Noise Ratio Estimation Techniques for PCM Signals

      Sos, John Y.; NASA/Goddard Space Flight Center (International Foundation for Telemetering, 1968-10)
      Reliable estimation of signal-to-noise (S/N) ratio in a demodulated PCM telemetry signal can be useful in evaluating the performance of the complete telemetry link, including its signal detection and data processing portions. This paper describes three potentially practical methods developed at Goddard Space Flight Center for estimating the S/N ratio in a PCM signal. One method referred to as "spectral null" method uses spectral characteristics of PCM' signals to estimate the S/N ratio, the other two use statistical properties of the signal, i.e., its mean value and variance. These two methods are known as "variance estimations and "null zone." The implementation of each method is discussed. The spectral null method takes the least amount of equipment, but is more difficult to calibrate and operate over a wide range of bit rates, than the other two systems. All three approaches, however, are uncomplicated enough to be included into almost any existing PCM data handling system. An analysis of the performance characteristics of each system is made. It is shown that the variance estimation method is the most versatile. It can reliably estimate the S/N ratio to within 1.5 db over a range of S/N ratios from 0 db to +10 db. (The S/N ratio is defined as the ratio of signal energy per bit/noise power density.) Under certain conditions all three methods can provide estimates to within 1 db, especially over a S/N ratio range from +3 db to +10 db.
    • Single RF Carrier Time-Sharing by Remote Locations

      Stadler, S. L.; United Aircraft Corporation (International Foundation for Telemetering, 1968-10)
      It is of vital national interest to know the essential real-time factors involved in the evaluation of an air attack versus a ground defense. This need led military planners to request the development of a computerized system to determine the victors and the vanquished in a war game on a par with an actual combat situation. From an engineering point of view, the evaluation system would permit all "combatants" full scope of operation and would not introduce, of itself, any "artificialities" into a complexity of split-second duels taking place over a wide geographical area. This paper discusses a unique time-division telemetry technique that was designed to resolve the data and control flow to and from remote locations, in this case, tactical aircraft. The actual system that evolved from this approach transfers all "aim and fire" events, coming from a group of aircraft engaged on a "mission", to a central communications and data processing facility. The control in the form of timing synchronization is sent from the facility to all aircraft. It should be noted that this time-sharing method could not utilize classical time-division multiplexing, e.g., PAM or PDM, since the test elements were all physically separate from one another (up to 120 miles). Preliminary test data is presented herein as an indication of the validity of this new technique. The paper concludes with a brief description of this method as applied to air and water pollution control and other posited applications.
    • The Small Astronomy Satellite (SAS) Program

      Townsend, Marjorie R.; NASA/Goddard Space Flight Center (International Foundation for Telemetering, 1968-10)
      One of NASA's newest Explorer class satellite programs, the Small Astronomy Satellite (SAS), will provide much-needed information in the most recently studied fields of astronomy, X-ray, Gamma-ray, UV and IR. This paper will describe the basic spacecraft functions with emphasis on its key feature, the SAS control system, as proposed for early sky surveys, and the changes needed in it for later flights which will require a pointing capability of one arc-minute or better. Its flexibility and versatility for application to many different types of astronomy experiments will be examined.
    • The Sun as a Calibration Signal Source for L- and S-Band Telemetry

      Hedeman, W. R., Jr.; Aerospace Corporation (International Foundation for Telemetering, 1968-10)
      One of the major problems confronting a telemetry receiving station is that of self calibration, particularly an end-to-end calibration, on a frequent and routine basis. For this purpose an external signal source is needed, preferably one in the far field of the antenna. The sun is such a source for L- and S-band systems--its usefulness depends on knowledge of its emission at the time it is used, since it is a variable source. Examined here are the characteristics of the sun as a source of electromagnetic energy in the 10 centimeter region, and the methods by which it could be used to determine receiving system noise temperature. Limitations of the methods are also described.
    • Synthesis of High Data Rate Coherent Telemetry Systems

      Ma, L. N.; Stone, M. S.; Sullivan, D. P.; TRW Systems Group (International Foundation for Telemetering, 1968-10)
      For high data rate telemetry (above 100 Mbits/sec) multiphase modulation effectively trades transmitter power to alleviate the RF bandwidth requirements. This paper presents a unified method of synthesizing and analyzing multiphase systems. In particular, the design of multiphase modulators and three types of coherent demodulators are discussed in detail. Included is a description of 400 Mbits/sec quadriphase system fabricated by TRW which employs direct modulation and demodulation of an 8.5 GHz carrier and a transversal filter to effect matched data filtering. This system operates within 2.5 db of theoretical performance of coherent quadriphase.
    • Telemetry with Unrestrained Animals

      Baldwin, Howard A.; Brumbaugh, Donald L.; Sensory Systems Laboratory (International Foundation for Telemetering, 1968-10)
      Telemetry from animals in their natural environment requires simple but efficient data coding methods. The problems common to behavioral or physiological studies with wild animals include immobilization techniques, harness design and ruggedized instrumentation development. Radio tracking experiences with the lion, elephant and buffalo and other game animals are summarized and an outline of instrumentation requirements for a study of long range goal finding ability in the green sea turtle is presented.
    • Tranmission of Cardiovascular Data from Dogs

      Rader, R.; Meehan, J. P.; Henry, J. P.; Krutz, R.; Trumbo, R.; University of Southern California (International Foundation for Telemetering, 1968-10)
      Prolonged acquisition of dynamic blood pressure data from animal subjects in various experimental conditions has become a special research area in numerous institutions. To properly conduct many of these experiments, the subject must be instrumented with blood pressure sensors and a means of conveying the indicated pressure level to a remote station. Quite often data must be obtained over several weeks in which recalibration can not be conducted. Telemetry techniques are quite adaptable to these problems and in many instances are the only solution available. To illustrate the special applications of telemetry, several experiments are described along with the hardware required to conduct these experiments.
    • A Two-Channel Monopulse Telemetry and Tracking Antenna Feed

      Yaminy, R. R.; Radiation Systems, Inc. (International Foundation for Telemetering, 1968-10)
      The two-channel monopulse telemetry and tracking antenna feed operates over the frequency range from 1435 to 2300 MHz. The feed was designed and developed for a 7-foot parabolic reflector located in the nose cone of an EC-135N aircraft. This airborne system maintains in-flight voice and telemetry communications with Apollo spacecraft during the injection and reentry phases of the Apollo missions. The feed consists of a planar multimode dual-polarized cavity-backed spiral radiator and two printed circuit comparators. The spiral radiator is excited in the sum and difference modes at both its inner and outer filament terminals. This allows the simultaneous reception of right-hand and lefthand circularly polarized signals. The sum and difference modes of excitation are precisely controlled to provide the proper reflector illumination functions for improved sidelobes and efficiency. Sidelobe levels in excess of 22 db, null depths greater than 40 db, boresight shifts of less than 0.25 degree, and system efficiencies of greater than 40 percent have been achieved.
    • Wideband PCM-FM Bit Error Probability Using Discriminator Detection

      Hayes, J. J.; Chen, C. H.; Kubicki, W. J.; AVCO Corp.-MSD (International Foundation for Telemetering, 1968-10)
      The expression for bit probability of PCM/FM is derived for a receiver with an IF bandwidth equal to or greater than the data rate, limiter-discriminator detection; followed by a post-detection filter with bandwidth equal to the data rate. The optimum deviation ratio is shown to be essentially constant regardless of the IF bandwidth-to-data rate ratio and system performance is shown to degrade when this ratio is greater than unity. Pre-modulation filtering of the transmitted PCM data is experimentally tested and the analytical results are shown to good agreement with experimental data.