• 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.
    • 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.
    • 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.
    • Compatibility Requirements and Considerations of Range Telemetry Tape

      Schulze, G. H.; Pan American World Airways, Inc. (International Foundation for Telemetering, 1968-10)
      Range Telemetry Tape crossplay operations may be arranged into four major classes each with unique compatibility considerations: a. Between like recorders at the same Range. b. Between unlike recorders at the same Range. c. Between unlike recorders at different Ranges. d. Between unlike recorders at Range User facilities and the Ranges. Like model recorders at the same Range are more likely compatible and capable of optimum tape crossplay than any other combination. Sometimes this very fact produces an atmosphere of complacency which can invite problems. The assumption that the recorder manufacturer has properly controlled his production for optimum crossplay or for complete conformance to IRIG1 is naive and should not be a substitute for compatibility testing at the using Range facility. With field use and equipment aging, compatibility can be gradually lost without becoming detected. Adjustment procedures at one' site may not be identical to procedures at other sites and perfectly compatible equipments can unknowingly become incompatible. The absence of adequate compatibility testing is the major cause of difficulty with this class of crossplay. Crossplay between unlike model recorders at the same Range poses unique problems but these can be controlled providing the unlike recorders have individually been strictly specified and tested to conform to IRIG Standards. Compatibility testing by the using Range is a definite requirement as manufactures may differ in their interpretation of the IRIG Document or may differ in the extent to which they conform. No manufacturer appears to be knowledgeable regarding crossplay between competitive recorders, and some appear to be just as uncertain about compatibility between complimenting recorders from their own product line. Crossplay between unlike recorders at different Ranges is being accomplished but many factors stand in the way of automatic success for this type of venture. When different equipments, different tape types, different operational procedures, and different procurement specifications all combine, the compatibility of the whole system is strained. The possibility of different tape types specified by competing equipment manufacturers should produce cautious awareness by the user and compatibility testing with both tapes should be conducted. The question "Which Range is responsible for the incompatibility?" can be difficult to answer. Currently, no central agency exercises control over Range-to-Range crossplay compatibility, and each Range conforms to IRIG Standards on an individual basis. Crossplay between unlike reproducers at Range User facilities and Range copy recorders is probably the most severe test of compatibility that exists. In this type of crossplay IRIG Standards may not have been invoked by the Range User, different bandwidth classes of systems may be involved and the fact that the User, and the Range may be virtually strangers all promote an environment unconducive to compatibility. Anything that can possibly go awry usually does. The major responsibility must lie with the Range who supplies the original or copy tapes to the Users. Ideally, the copy tapes should all be generated identically regardless of individual recipient requirements, and the IRIG Standards should be religiously followed.
    • Buoy Telemetry for Environment Prediction in Fisheries Research

      McAlister, W. Bruce; Bureau of Commercial Fisheries Biological Laboratory (International Foundation for Telemetering, 1968-10)
      A telemetering buoy has been developed for the Bureau of Commercial Fisheries to provide environmental information in support of salmon research. The buoys are designed to be free-drifting units; sensors are inductively coupled to a 200 m. single conductor cable beneath the buoy. Present sensors measure temperature, conductivity and depth. One buoy is equipped to participate in the IRLS satellite telemetry experiment. Present development includes equipment to have the buoys determine their position by use of the U.S. Navy Navigation Satellite System.
    • 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.
    • Communications for the Apollo Applications Programs

      Fordyce, Samuel W.; NASA (International Foundation for Telemetering, 1968-10)
      The Apollo Applications Program will consist of a series of extended duration manned missions in low earth orbit. The initial missions are based upon equipment and techniques proved in previous space flight programs. This is especially true of the communications systems which rely heavily on the Gemini, Saturn, and Apollo communications hardware operating with the Manned Space Flight Network. Following AAP missions may include new spacecraft developments involving television, teleprinters, satellite relays and spacecraft data management systems. These developments are described briefly, but many of them are concepts in early development stages, and it is difficult to specify the configurations that will be flown.
    • 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.
    • 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.
    • 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.
    • 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.
    • 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.
    • 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.
    • 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.
    • 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.
    • 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.
    • The Sun as a Calibration Signal Source for L- and S-Band Telemetry

      Hedeman, W. R.; 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.
    • Design of Airborne S-Band Telemetry Antennas

      Weinschel, H. D.; New Mexico State University (International Foundation for Telemetering, 1968-10)
      The change from VHF to UHF for telemetry requires new antenna designs rather than the scaling of the antennas now used for the UHF frequencies. The reason for this is that the vehicle dimensions at UHF, in particular the rocket diameters, will be of the order of several wavelengths. A common method to obtain a nearly omnidirectional radiation pattern at VHF is to mount two or four element antenna arrays on the vehicle. This is sufficient since the wavelength for the presently used telemetry frequencies is approximately 50 inches and the array spacing rarely exceeds a half wavelength. The radiation pattern from such closely spaced unit radiators exhibits only minor scalloping which does not present a problem in the data acquisition. At the UHF frequencies, the array spacing, in wavelength, is increased by a factor of ten resulting in an interference pattern with narrow lobes and deep nulls. If the mechanical design limitations permit it, it is possible to design unit radiators which will give cardioid or nearly omnidirectional patterns for a single polarization component. Two such antennas are described. They are the axially mounted turnstile and the radial waveguide antennas.
    • 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.