• A PCM-Telemetry System for Sounding Rock Payloads

      Hommel, R.; Deutsche Versuchsanstalt für Luft- und Raumfahrt e.V. (International Foundation for Telemetering, 1968-10)
      Complex sounding rocket payloads require on-board data processing and channel capacity which frequently exceed the capability of the standard FM-FM-telemetry system. To obtain the full benefit of the accuracy and information density of sounding rocket experiments a PCM-telemetry system has been developed which provides sufficient flexibility in the choice of channel number, bit rate, time resolution, and accuracy. A first version with Bo channels for scientific data, and 62 channels for technical data will be flown on board of five Black Brants from the Esrange in Kiruna.
    • Performance Characteristics and Specification of PCM Bit Synchronizer/Signal Conditioners

      Peavey, B.; NASA/Goddard Space Flight Center (International Foundation for Telemetering, 1968-10)
      The PCM BR Synchronizer/Signal Conditioner, hereafter called "synchronizer," plays a vital role in telemetry data recovery, and is perhaps the most important and complex component of telemetry data processing systems (DPS). The synchronizer, being the "front end" of the system, makes an irrevocable decision as to the binary value of each data bit, and provides the fundamental timing signal (clock) for the entire DPS. Thus, the performance characteristics of the synchronizer substantially determine the system's capabilities, and it may be said that the system is as good (or bad) as the synchronizer. This paper presents and discusses test data obtained on synchronizers available to date, and used at Goddard Space Flight Center (GSFC) and its satellite tracking and data acquisition network (STADAN) stations. Performance characteristics such as bit synchronization (bit sync), bit sync acquisition, tracking, bit error rate, and intersymbol interference have been measured with respect to split-phase (SP) and NRZ-L input signals between 500 bps and 300 Kbps, perturbed by "white" Gaussian noise plus jitter. The effect of tape recording and band limiting of these signals on synchronizer performance is also discussed. It is shown that bit error rate alone does not "tell the whole story" about synchronizers, particularly when operating with low (less than 7 dB) SNR's plus jitter. The test data indicate that there is no single synchronizer excelling in all respects. For example, a synchronizer which operates well down to SNR of -3 dB has inferior acquisition, and slippage characteristics when jitter is added to noise. Generally, the performance threshold for random jitter (defined later) is at SNR greater than 10 dB. Some synchronizers seem to perform better with SP than NRZ-L signals, and vice versa. Finally, discussed and suggested are definitions of performance parameters which would uniformly and unambiguously describe and specify synchronizers. A lack of precisely defined and measurable performance parameters and characteristics has caused misinterpretation and misunderstanding of specifications presented by both vendor and customer.
    • Performance of a Bandwidth Limited PCM/PSK/PM Telemetry System

      Miller, G. E.; Jennings, V. A.; The Boeing Company (International Foundation for Telemetering, 1968-10)
      This report investigates the use of coherent and non-coherent FM/PM detectors as applied to recovery of PCM telemetry data. Given a PCM Manchester II encoded FM carrier, a theoretically perfect bit detector was derived. A laboratory prototype was built and evaluated under simulated threshold conditions. Agreement with theory was obtained within 1.50 db, using a coherent demodulator without a limiter stage. Amplitude and phase characteristics are shown in addition to the filter circuit and component values. Several commercial demodulators are compared against the theoretical model. The results of the comparisons are discussed, and recommendations concerning deficient areas are submitted.
    • Performance of Binary PSK Communication Systems

      Oberst, J. F.; Schilling, D. L.; Polytechnic Institute of Brooklyn (International Foundation for Telemetering, 1968-10)
      The degree of RF coherence which can be established between transmitter and receiver greatly influences the performance of binary communication systems. Practical systems are partially coherent; the main classes are transmitted reference (TR) and single channel (SC). Although SC systems are potentially superior, they are difficult to analyze and have an inherent mark-space ambiguity problem. In this paper, four SC PSK systems have been studied using Monte Carlo simulation on an IBM 360/50 digital computer. Differential data encoding was used. The systems investigated include Decision Feedback (DF), Squaring (SQ), and a variation of SQ called Absolute Value (AB). In addition, a new Maximum Likelihood (ML) SC system, which is optimum in a restricted sense, is derived and simulated. The simulation results show that all of these systems yield comparable average probability of error. This is in contrast with results which have been published previously. Furthermore, the systems can all be shown to reduce to Differential PSK when the number of reference bauds is one. Finally, a method is introduced for studying the effects of various methods of data encoding on SC system operation.
    • Performance of Block-Coding Systems When Transmitting Through a Ary Discrete Channel in the Presence of White Gaussian Noise

      Okkes, R. W.; European Space Technology Centre (International Foundation for Telemetering, 1968-10)
      The basic problem of transmitting digital (PCM) data with the least signal to noise ratio per bit of information is considered if the data is encoded into code words consisting of a finite number of symbols where each symbol belongs to an alphabet of N elements. For quantitative results the error probability of the decoded data has been taken as equal to or below one out of 10⁵ bits of information in the case where the transmitted symbols are corrupted by additive white Gaussian noise and are detected "symbol per symbol" by correlation methods. Mainly coherent detection is considered. After the derivation by a geometrical method of the upper bounds (based upon random coding) of the minimum signal to noise ratio per bit, the performance of several constructive code methods are compared with these bounds. The amount of hardware and the number of operations required respectively for encoding and for decoding the most promising class of codes (binary and N-ary Bose-Chaudhuri codes) are indicated. Considerations are given to synchronous demodulation requirements using a "Costas" phase lock loop type of demodulator.
    • Preliminary Experiment Results from the Omega Position Location Equipment (OPLE)

      Horiuchi, H. S.; NASA/Goddard Space Flight Center (International Foundation for Telemetering, 1968-10)
      The analysis of data taken during the fixed platform, road and aircraft tests indicates that the OPLE system can locate a fixed or moving platform with reasonable accuracy. During the fixed platform interrogations, it was found that the error in the OPLE-derived position estimates were consistently correlated with the error in the position estimates of the OCC as derived from the local Omega monitors; that is, latitude and longitude errors of corresponding magnitudes were received at the OCC both from the PEP's and from the Omega receiver located at the control center. Based on the data analyzed thus far for the fixed platforms, the overall contribution to the mean position error by the OPLE equipment ranges between 50 to 400 feet in latitude and 300 to 500 feet in longitude. The results have shown that the longitude errors are consistently greater than the latitude errors. The results of the road test indicated that a moving vehicle could be located with good accuracy. Men the OPLE-derived position estimates were adjusted for the navigational errors of the Omega system, the vehicle was located to within 1500 feet of the roadway. The results of the aircraft tests showed that an airborne platform moving at 160 knots could be located with reasonably good accuracy. During the daytime test, the position of the aircraft could be placed to within approximately 5 miles of GSFC. During the evening tests, the position of the aircraft was located to within 10 miles of the estimated center of the aircraft's circular flight pattern, the position being consistently to the east of the center of the circle. During these evening tests, the position of the OCC was calculated to be 4 miles east of its actual location.
    • Presampling Filtering

      McRae, D. D.; Davis, R. C.; Radiation Incorporated (International Foundation for Telemetering, 1968-10)
      Sampled data systems often employ lumped-parameter lowpass filters both prior to and following the sampling operation. The purpose of these filters is to reduce the error between the input and output data waveforms. The present paper discusses the effect of presampling filters on the rms interpolation error for two types of sampled data systems and gives some thumb rules for choosing such filters. The two types of sampled data systems considered are: (1) one employing only zero-order hold interpolation, and (2) one employing zero-order hold followed by the best lowpass lumped-parameter interpolation filter. The resulting expressions for rms interpolation error for sampled data systems employing lumped-parameter filters from a detailed time domain analysis are given.
    • Results of the UHF Telemetry System R & D Flight Tests at White Sands Missile Range

      Chin, Ball; Hamilton, James W.; White Sands Missile Range (International Foundation for Telemetering, 1968-10)
      This paper describes results of UHF telemetry R&D tests conducted at White Sands Missile Range (WSMR), New Mexico. UHF telemetry problems, such as multipath and target scintillation, are discussed. Several recommendations which may improve the reliability of telemetry data transmission at UHF frequencies are made based on experience and data gained from many UHF telemetry tracking operations.
    • RF Telemetry from a High Speed Subterrain

      Caffey, T. W. H.; Hale, W. R.; Sandia Corporation (International Foundation for Telemetering, 1968-10)
      The telemetry of the deceleration loading upon a vehicle which deeply penetrates the earth at high speeds is described. The technique consists of using a single-channel, narrow-band FM transmitter to drive a magnetic dipole so that RF communication with above-ground receivers is provided. A 260-kHz, 340-watt system with a 2-kHz bandwidth is described along with design considerations. The reduction of the conductivity along the signal path by the penetration tunnel with consequent signal enhancement is discussed.
    • Rician Intersymbol Interference in Frequency Shift Keying

      Vencill, J. J.; McDonnell Douglas Astronautics Company (International Foundation for Telemetering, 1968-10)
      Many communications links involve a reflected signal which is Rician in nature. In troposcatter systems, this reflection constitutes the entire received signal while in communications between satellites or aircraft, such a reflection from the surface corrupts the direct signal. Other such situations involve low elevation tracking or intentional coherent jamming. This paper derives the bit error probability for a non-coherent binary FSK link in this environment for any order of diversity and any ratio of specular to diffuse reflection assuming orthogonal signalling frequencies, matched filter detection and perfect bit synchronization. The interfering signal may represent the same datum as the direct signal (Mark-Mark interference) or, for delays longer than a bit period, the interference may appear in the opposite receiver channel from the direct signal (Mark-Space interference). Results are stated in terms of the direct signal energy to noise density ratio and factors determined by the geometry of the situation; the ratio of direct signal to interfering power, the ratio of specular to diffuse reflected power and the relative carrier phases of the direct signal and the specular reflection in the Mark-Mark case. These geometric parameters are most conveniently treated separately from the modulation and detection problem.
    • 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.