• A Double Sideband-Quadrature Carrier Multiplex Telemetry System

      Gutwein, Joseph M.; Annese, Jerald F.; ADCOM (International Foundation for Telemetering, 1968-10)
      A novel FDM telemetry technique was developed consisting of a double sideband-quadrature carrier multiplexing system (DSB-QCM). Each subchannel in the DSB-QCM system carries two completely overlapping DSB data signals, one double-sideband modulated on the subcarrier itself, and the other on a quadrature version of the subcarrier. Demodulation with cophasal and quadrature subcarriers enables simultaneous data extraction from each channel within acceptable distortion levels. The feasibility and practicability of such a DSB-QCM telemetry system is discussed in this paper. Crosstalk levels between the quadrature multiplexed channels were measured and guardband requirements between adjacent channels were assessed for a modem comprised of three pairs of DSB-QCM channels. Crosstalk levels between uniformly loaded DSB -QCM channels were below 2% and guardband requirements equivalent to conventional DSB systems were observed. The DSB-QCM performance was also examined as a function of input SNR with two competing subcarrier synchronization methods. Subcarrier synchronization by means of synthesized reference tones coherently derived from a single pilot was demonstrated to be superior in The presence of noise to a channel reference approach in which each data channel must synchronize its own subcarrier. The major conclusion from this investigation is that DSB-QCM/FM telemetry combines the advantages of both SSB/FM and DSB/FM by accommodating as many data channels as SSB/FM but with low distortion data processing and the dc data response characteristic of DSB/FM.
    • 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.
    • A High-Rate Telemetry System for the Mariner 1969 Mission

      Tausworthe, R. C.; Easterline, M. F.; Spear, A. J.; California Institute of Technology (International Foundation for Telemetering, 1968-10)
      This presentation deals with a multi-mission deep-space telemetry system, its rationale, analysis, development into hardware, and its subsequent planned application to an actual spacecraft mission whose preparation is now in progress. The spacecraft system encodes raw binary data into a comma-free, bi-orthogonal code which antipodally modulates a square-wave subcarrier, which in turn phase-modulates the downlink carrier. There is no separate signal for subcarrier, word, or symbol sync; all transmitted sideband power is thus available for data transmission.
    • 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.
    • Frequency Feed-Forward-An Open Loop Approach for Extending the Threshold and Linearity of FM Demodulators

      Pelchat, M. G.; Boor, S. B.; Radiation Incorporated (International Foundation for Telemetering, 1968-10)
      This paper describes Frequency Feed-Forward, an open-loop technique for lowering the FM threshold. The amount of threshold improvement with standard discriminators is discussed and experimental results with sinewave and gaussian modulation are given.
    • Errors Resulting from Channel Filters and Adjacent Channel Crosstalk in DSB/SC Telemetry Systems

      Salter, W. E.; Frost, W. O.; Sperry-Rand Corporation; Marshall Space Flight Center (International Foundation for Telemetering, 1968-10)
      The waveform distortion resulting from adjacent channel crosstalk and from amplitude and phase nonlinearity in channel filters limits the minimum channel spacing, and hence the bandwidth utilization efficiency of a double sideband/suppressed carrier (DSB/SC) telemetry link. The paper presents results of an analysis defining the minimum achievable mean-square error when Butterworth filters are used in the DSB demodulator/demultiplexer. With data inputs consisting of band-limited random signals, solutions are given for various combinations of data order, filter order, channel spacing, and filter cut-off. The trade-off between waveform distortion and channel spacing is illustrated, and optimum locations for the filter cut-off are defined. The irremovable error based on Weiner optimum filter theory is presented as an interesting basis for comparison.
    • 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.
    • Laser Applications to Biology and Medicine

      Rounds, Donald E.; Pasadena Foundation for Medical Research (International Foundation for Telemetering, 1968-10)
      The unique physical characteristics of coherence, intensity, and monochromatically offered by laser instrumentation has placed renewed importance on studies in photochemistry and photobiology. Sufficient research experience has now been accumulated to demonstrate the potential usefulness of laser energy to fundamental cell biology, and to the diagnosis and treatment of certain pathological conditions. Current progress in laser applications to ophthalmology, oncology, and dentistry is briefly summarized.
    • 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.
    • Cause and Effect of Time Base errors in Coherent Demoudlation of a Suppressed Carrier AM Multiplex

      Nichols, M. H.; Schmitt, F. J.; White Sands Missile Range; Lockheed Electronics Company (International Foundation for Telemetering, 1968-10)
      Two types of time base error, TBE, are discussed. One type results from variations in tape speed (flutter) and the other type is the result of additive noise. Measured data on TBE from a typical tape machine are included. Quantitative effects of TBE on coherent demodulation of DSB, SSB and quadrature DSB are discussed.
    • 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.
    • Flight and Laboratory Testing of a Double Sideband FM Telemetry System

      Richardson, Robert B.; Harney, Paul F.; NASA Flight Research Center (International Foundation for Telemetering, 1968-10)
      This paper discusses the NASA Flight Research Center's laboratory and preliminary flight evaluation of a double sideband suppressed carrier constant-bandwidth telemetry system that will be used as an airborne high-frequency data recorder. Some practical limitations are illustrated, and laboratory and flight-test results are compared. No attempt is made to compare this system with systems using other forms of modulation. Results obtained using an RF link are compared with magnetic tape recording of data. Calibration requirements are included for each system.
    • Bit Error Rates in the Presence of Untracked Time Base Fluctuation

      Roche, A. O.; Mallory, P.; General Dynamics; Dynatronics (International Foundation for Telemetering, 1968-10)
      This paper presents a simple four-step procedure for estimating the error probability of an NRZ PCM Synchronizer and Detector operating on an NRZ Bit Stream in the presence of a fluctuating data frequency source. The four steps are as follows. First, the bit error probability is calculated for Gaussian time base fluctuation as a function of the energy per bit to noise power density ratio. The second step is to model the synchronizer as an ordinary linear servo for small phase errors and a closed loop bandwidth, small compared to the bit rate, so that effect of the randomness of the data is averaged out. With the linear model, the time base error in tracking the input signal is calculated also utilizing this approximation as if there were no additive noise. The third step is to calculate the mean squared time base error due to the additive Gaussian noise alone. The fourth step is to combine the errors found in steps two and three as if they were independent and use the graphs found in Step 1 to determine the error rates. It is assumed that the total untracked time base fluctuation is Gaussian. The calculated error probabilities are compared with measured data. There appears to be good correspondence between the calculated and measured error probability.
    • 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.
    • Miniature Power Amplifier for Telemetry Transmitters

      Winkler, R. H.; Amelco Semiconductor (International Foundation for Telemetering, 1968-10)
      There is continuing emphasis to reduce the size and weight of telemetry transmitters and to increase the frequency at which the power is generated. An approach to achieve this goal is discussed. A power amplifier stage designed specifically for a telemetry transmitter is described. It produces 1 watt output at 500 MHz with 7-10 db of gain. Typically it is midpoint in a series of similar amplifier stages. An extraordinarily small size is achieved by using microstrip transmission lines on an alumina substrate. The dielectric constant of alumina is relatively high; which makes the transmission lines relatively short. Furthermore, the judicious use of lumped capacitors results in a further foreshortening of the transmission lines. The transistor die is attached directly to the microstrip transmission line. This minimizes any stray inductances and makes the circuit reproducible and broadband. This amplifier is composed of three basic component types: 1) a transistor 2) four microstrip transmission lines, and 3) three lumped capacitors. Of special importance is the fact that the entire amplifier, that is, the transistor plus the matching network, is enclosed inside a hermetic envelope. The terminals are 50 ohm microstrip input and output. The hermetic envelope is less than 1.100" x .830" x .085". Complete with a heat sink the unit is no higher than .150". Useful design information for this type of amplifier is presented.
    • The Effects, Measurement, and Analysis of Flutter in Instrumentation Recorders

      Moore, Laurence; Micom, Inc. (International Foundation for Telemetering, 1968-10)
      As instrumentation recorders are improved to provide wider bandwidths and shorter recorded wavelengths, the effects of flutter and attendant time base distortion severely limit the potential for accurate recording and retrieval of data. The effects of flutter on typical classes of data is given and the measures necessary to determine flutter with high accuracy shown. Since the degrading effects of flutter depend upon the application and the characteristics of the flutter, means of analyzing flutter both in the time domain and in the frequency domain are necessary. A self contained instrument for accurate measurement and analysis of flutter sensitive enough for the most sophisticated transports is described, as are necessary conditions for its use.
    • 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.
    • Miniature Current Discontinuity Device Antennas

      Bittner, Burt J.; Kaman Nuclear (International Foundation for Telemetering, 1968-10)
      Flush and semi-flush, Current Discontinuity2 antennas have been developed for VHF and UHF frequencies that exhibit good efficiency and minimum structural disturbance. Typical antennas are .02 wavelengths high, 1/8th inch at "L" band. An airborne, electronically steerable array for VHF, satellite applications is described.
    • 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.
    • Communications Between Satellite and Ballons for the Eole Mission

      Bourdeau, J. P.; Debray, P.; Namy, X.; CNES (International Foundation for Telemetering, 1968-10)