Browsing International Telemetering Conference Proceedings, Volume 03 (1967) by Title
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Adaptive PCM Pattern Synchronization(International Foundation for Telemetering, 196710)The trend toward more automated PCM decommutation systems demands less operator intervention in their operation. A weak link in this progression has been in the implementation of group synchronizer strategy. A new synchronizer has been developed based on the optimum properties of sequential probability ratio testing which requires only one program based on required worst case decision error probabilities and which is independent of the PCM format being synchronized. A mathematical model is formulated which accurately describes the operating characteristics of this technique. These operating characteristics are then compared to conventional synchronizer characteristics which demonstrate the superiority of this approach. The decision process described inherently adapts to signal conditions by making decisions faster and with less chance of error as bit error rate decreases. Only the Check Mode is discussed, but the same techniques apply to the Lock Mode.

Analysis of Multiplex Systems Based on Orthonormal Function Groups(International Foundation for Telemetering, 196710)Linear multiplex systems may be represented as sequential, invertible transformations on a message set. Such transformations are based on orthonormal functions in the Hilbert space of squareintegrable functions. Demultiplexing is accomplished with the inner product which results in high immunity to noise and bandlimiting. When the orthonormal functions form a multiplicative group, easily generated pulse functions arise. Methods are presented for determining these function groups and their corresponding algebras which yield simple and useful multiplex systems.

Anticipated Problems of ReEntry Vehicle Telemetry at UHF(International Foundation for Telemetering, 196710)Present information on missile range planning indicates that serious UHF telemetry coverage problems are likely to occur during reentry of ballistic vehicles. Flight test experience at VHF has demonstrated that receiving stations experience difficulty in tracking reentry vehicles under conditions of rapid changes of signal strength caused by combinations of vehicle motion, vehicle antenna pattern, and plasma attenuation. Similar but greater variations at UHF coupled with narrow beamwidths and reduced sensitivity of reentry stations portend greater problems at UHF. Conical scan systems may prove inadequate. Comparisons of similar telemetry systems at VHF and Sband are presented, demonstrating that received signal to noise ratios at reentry stations will be 3 to 9 db below levels Presently obtained at VHF for reentry stations. The narrow antenna beamwidths (1° to 3.5°) will also cause problems in acquisition so that some form of acquisition aid will be required at each station. Omnidirectional antennas currently used in aircraft at VHF will be useless at UHF. Ships and aircraft will require stabilized or compensated antennas. Acquisition of hypersonic targets will be a particularly severe problem for aircraft receiving stations. In addition to defining the reentry problem, system limitations, and expected effects, this paper also makes recommendations to range planners and users to minimize or correct the anticipated problems.

Automatic Real Time Data Quality Analysis(International Foundation for Telemetering, 196710)This paper deals with methods of detecting and displaying the quality of received telemetry data automatically and in real time. The most commonly used forms of telemetry multiplexing are considered in detailwith reference to application of the techniques to other similar forms of multiplexing. This paper is a result of a study and hardware development which resulted in equipment now at Cape Kennedy and capable of detecting and displaying bit error rate on PCM telemetry, percentage of channel error on PAM and PDM telemetry and signaltonoise ratio on FM/FM telemetry. The discussion is oriented toward the theory of operation and techniques for automatic real time data quality analysis rather than toward the hardware. Methods of detecting and displaying the various data quality indicators is emphasized resulting in conclusions that in many instances relatively reliable data quality indications are possible in real time, but it must be realized that any indication of quality represents a review of conditions of the received signal over some finite averaging interval and thus no measurement can ever provide instantaneous quality indications.

Carrier Synthesis from Perturbed DSB/SC Signals(International Foundation for Telemetering, 196710)In suppressedcarrier AMbaseband systems, the process of synthesizing carriers necessary for demodulation usually constitutes a difficult problem, especially when noise or recorder flutter is present. In this paper a particular scheme1, which synthesizes a demodulation carrier directly from a DSB/SC signal, is investigated for the purpose of determining the effect of noise and recorder flutter upon each of the various elements in the carrier synthesis loop. Curves are presented which illustrate the relationship between phase error in the demodulation carrier and various system parameters.

Central Data System Concepts for Spacecraft Data Management(International Foundation for Telemetering, 196710)This paper discusses the design concepts of a central data system (CDS) for more efficient" flexible data management and its application in an advanced deep space solar probe. The design features high data sampling rates, programmable data processing, bulk data storage capability (for data sampled during periods of noncommunication), and standard experiment package/CDS interfaces. The basic system concept is based upon sampling each data point at a high rate in a fixed sequence and allowing a central processor to select, process, and format sampled data into a highly efficient format for transmission. The CDS is programmable so that data formatting and processing may be reprogrammed via the command link to optimize data transmission for unexpected conditions. Preliminary design efforts have indicated that a CDS to process data from seven particle and fields experiments can be designed, using present stateoftheart components, to weigh 16.5 lb and consume 5.4 watts (not including bulk data storage unit) from the DC/DC converter.

ComputerControlled Data Compression at 100 KC(International Foundation for Telemetering, 196710)This paper describes a realtime computercontrolled telemetry system that can accommodate a 100 kc sample rate. The system's operating structure allows highspeed, asynchronous PCM data to be simultaneously decommutated, compressed, displayed, and merged. Data generated during test firings of the U. S. Navy's Poseidon missile will be reduced and processed by this system. Emphasis of the paper is on a description of the telemetry system's hardware and software.

Data Collection Station for Automobile Safety Testing(International Foundation for Telemetering, 196710)Increased emphasis on the incorporation of additional safety features in automobile designs has accelerated the adaptation of aerospace telemetry and datahandling techniques to the field of automotive performance testing. Described is a multiple link FM/FM telemetry ground station as used for acquisition of data from an automotive test track. System inputs adhere to aerospace telemetry standards, the output being a computercompatible digital tape. Detailed attention is given to the highspeed sampling, data conversion, and digital tape formatting subsystem.

DeltaT Curves for Measuring Magnetic Tape Link Jitter(International Foundation for Telemetering, 196710)Magnetic instrumentation tape recording links are usually required to be substantially transparent data channels. One of the most important deviations from this requirement, both in FM and direct recording modes, occurs in the area of time delay error. A method for measuring the rootmeansquare time delay error (Δ) between points on a record vs their separation in playback time (T) has been described in the literature (Refs. 1 and 2), but the implications and interpretation of this technique have not been fully developed. This paper derives the theoretical relationships between the ΔT curve and the autocorrelation function of a pure sine wave recorded on the tape, and uses this correspondence to establish a connection between jitter spectra and ΔT curves. A simple instrument for measuring these curves with high accuracy is described, and results of measurements made on a number of intermediateband tape units in use at the Goddard Space Flight Center are presented. These measurements show that a lowmass tape unit may be superior to high mass units by more than an order of magnitude. The utility of the ΔT measurement technique is discussed on the basis of its direct relationship to PCM and coherent recording applications, and its value as a standard means for evaluating time delay error in magnetic tape links is described. It is also shown that the technique can be used to determine FM modulation index.

Description of Computer Program to Analyze Gain Distribution of an Antenna Pattern(International Foundation for Telemetering, 196710)The gain of a radiating antenna is generally a function of the direction in which the antenna is pointing relative to the direction of the received or transmitted signal. The gain distribution over an imaginary sphere surrounding the antenna is called the antenna gain pattern and can be measured experimentally. Under certain circumstances the tolerances associated with the pointing vector make it impossible to determine the antenna gain precisely but rather circumscribe an area on the spherical surface which include a number of different gain values. A computer program called INTGRT has been developed that will determine from measured antenna pattern data the gain distribution within the uncertainty region and will provide a measure of the probability of the gain being above a certain gain value. The boundary of the uncertainty region is described in terms of the coordinate system used in measuring the antenna patterns. Each gain value contained inside this boundary is compared to some reference gain level and a running total is made of the number of values found to be equal to or greater than the reference value and the total number of values inside the region. After weighting each total by an equal area function, the ratio of the number of values above a reference level to the total number of values in the region gives an estimate of the probability that the gain of the antenna will be equal to or above the reference gain. If the region is analyzed in this way for a number of reference levels, the distribution of gain values within the region is obtained. This information is extremely valuable in determining space communication system performance during periods in which the orientation of the spacecraft's antenna with respect to the earth cannot be determined precisely but is known to be within certain limits.

Detection of Orthogonal Sine and Cosine Pulses by Linear Active RCNetworks(International Foundation for Telemetering, 196710)An active RC matched filter, particularly useful for phasecoherent, coded or uncoded, binary or nonbinary communication channels, is described. One detector circuit performs the equivalent of two simultaneous crosscorrelations, avoiding the need for electronic multipliers, reference wave generation and phase synchronization. For example, only I circuits are needed in a receiver that is required to detect the polarity or presence of an orthogonal set of I sine and I cosine pulses. In view of the circuits realizability with linear IC technologies, the sensitivities with respect to circuit component variations are analyzed in detail. The results of the sensitivity analysis are presented in graphical form. Experimental results confirm the predicted performance; i.e. Qfactors in excess of 4000 were obtained with small, generalpurpose operational amplifiers.

The Detection of PCM/FM(International Foundation for Telemetering, 196710)The calculation of the error rate resulting from the detection of PCM/FM is described. Emphasis is placed on characterizing the effect of the FM demodulator (FMD). The works of Schilling(l), Salz(2), and Klapper(3), are summarized and extended to yield error rate expressions when using an FM discriminator, Phase Locked Loop, or Frequency Demodulator Using Feedback (FCF). The "IntegrateandDump" and the Filter Detector are compared. The results indicate that in certain regions the error rate is due primarily to "smooth noise", and the FM demodulator followed by a PCM detector yields an error rate comparable to that obtained with a MatchedFilter (MF) detector. In other regions the error rate is shown to be due primarily to the spikes present at the FM demodulator output. The use of "Spike Detection and Correction" is discussed. It is shown that this technique results in reduced error rate in the "spike regions".

Double Sideband Suppressed Carrier Telemetry System(International Foundation for Telemetering, 196710)Vibration, shock, and acoustic data constitute one of the principal requirements for wideband telemetry. In order to permit a quantitative comparison of DSB/FM with the experimental results on constant bandwidth FM/FM for telemetry wideband noiselike data, a laboratory investigation has been conducted at WSMR. This paper reports experimental data on RF spectrum occupancy, intermodulation, performance against thermal noise, and some preliminary data on the effects of tape recording.

The Effect of Random Threshold Levels on PCM Quantization Noise(International Foundation for Telemetering, 196710)It is common with PCM systems to consider a uniform quantization noise (or error) distribution over plus or minus one half the quantization level. This distribution must be modified to describe the effect of uncertainties in the location of the decision thresholds which separate adjacent quantization levels. The uncertainties exist because electronic decision circuits trigger somewhere within a narrow band surrounding an intended voltage instead of at exactly that voltage. In this paper the encoding error distributions, are calculated in terms of the distributions of the threshold locations. It is shown that the variance of the quantization noise is increased by an amount almost exactly equal to the variance of the threshold uncertainty distribution. The effect of the uncertainty bands becomes noticeable only where the uncertainty band is an appreciable part of the quantization interval. Prime examples are systems with small voltage differences between encoding levels such as lowlevel systems (0 to 50 millivolts) and systems with large number of quantization levels. Because error variance is related to the square of the uncertainty range, a threshold uncertainty range of 1/10 the quantization interval will increase the net encoding variance by approximately (1/10)² or 1.0%.

Effects of Random Fluctuation Noise on FM and FDM/FM Reception(International Foundation for Telemetering, 196710)A tutorial review and analysis of the effects of random noise upon the output of a conventional FM demodulator is presented. The mechanism by which these effects are produced is conveniently brought out with the aid of phasor diagrams. Illustrative computations are given of the smooth and impulsive components of the output noise and of output signaltonoise power ratios for various types of frequency modulation. Various types of thresholds are pointed out and the practical significance of threshold reduction as a system design optimization tool is discussed.

Error Rates in Wide Band FSK with Discriminator Demodulation(International Foundation for Telemetering, 196710)

An Experimental Evaluation of PAMNRZ/FM(International Foundation for Telemetering, 196710)The results of a hardware evaluation of PAMNRZ/FM are presented along with a description of the conditions under which the data were taken. Stateoftheart commutators, transmitters and receivers procured from commercial sources were utilized in the evaluation tests. The principal characteristics of PAMNRZ/FM considered were data channel response, performance at low signaltonoise ratios compared to equivalent FM/FM and PCM/FM systems, linearity, crosstalk, overmodulation, transmission noise, data resolution, decommutator synchronization and a comparison of performance at commutation rates of 25,000, 100,000 and 250,000 samples per second. The test data indicates that PAMNRZ/FM is capable of 2 to 5 percent data transmission accuracy and that performance at low RF levels is comparable to that of FM/FM or PCMJFM under the test conditions specified.

A Family of Linear Integrated Circuits for Telemetry(International Foundation for Telemetering, 196710)Advances in monolithic circuit and process techniques are making available a steadily increasing number of linear integrated circuits especially applicable to telemetry systems. This paper reviews the principal types of telemetry systemsPCM, PAM, PDM, and FM/FM. It demonstrates that a compatible family of monolithic IC's in various stages of development at Fairchild can perform most of the circuit functions required by these systemsnamely: (1) signal conditioning amplifiers, (2) multiplexer, (3) sample and hold, (4) unity gain A/D buffer amplifier, (5) A/D and PDM comparator, (6) D/A reference and switches, (7) D/A summing amplifier. In addition, future integration of functions not performed by the above circuits is discussed.

Graphical Determination of Third Order Intermodulation Frequencies in RF Systems(International Foundation for Telemetering, 196710)A simple discussion is given on the origin of intermodulation distortion in nonlinear devices concluding with reasons for placing primary interest on third order products. Nearby third order products are located at 2f(x) – f(y) and f(x) + f(y) – f(z) where f(x), f(y), and f(z) represent all frequencies in a group. The number of nearby IM products of this type is equal to N(N  1) (1 + (N  2 / 2)) where N is the number of input frequencies to the nonlinear device. For eight input signals, for example, a total of 224 intermodulation products are produced that are located in a bandwidth that is three times the bandwidth between the highest and lowest input frequencies. The graphical method of locating intermodulation products is rapid and simple. Basically, interfering frequencies are found by the alignment of two pieces of paper. On each piece of paper, the spacings between all input frequencies are plotted on a linear scale. Frequencies which may cause interference are easily identified. A guide which will allow the selection of frequencies to avoid third order intermodulation interference is also given.

A High Speed 10 Bit D/A Integrated Circuit(International Foundation for Telemetering, 196710)A new high speed 10 Bit D/A integrated circuit is described as well as the basis for its design. Principal applications are given, notably a successive approximation A/D employing the circuit as its feedback D/A.