Showing papers on "Bandwidth (signal processing) published in 1973"

Filtering of Dispersed Wavetrains

Abstract: Summary The filtering problem with dispersed signals is examined and an equation relating the duration of the filtered signal to the bandwidth of the filter and the dispersiveness of the dispersing system is established. This equation is applied in two domains: one, the optimization of the multiple filter technique, a method used for a time-frequency analysis of a signal; and two, the choice of parameters in a ‘time variable filter’, a technique used to isolate from a signal a wavetrain related to a dispersion curve. We give an application of this ‘time variable filter’ technique to isolate the fundamental mode of Rayleigh waves from a record of an earthquake 650 km deep.

High-power linear-beam tubes

Abstract: High-power klystrons, coupled-cavity traveling-wave tubes (TWT's), and hybrid tubes, all of which utilize the microwave cavity as the basic circuit element, are described. These amplifiers are used in communications, radars, electronic countermeasures, and other applications at power levels from a few hundred watts to megawatts, at frequencies from ultrahigh frequency on up, and are particularly suited for high average powers. High gain, 30 to 60 dB, is normally achieved, and bandwidth usually lies in the 1-30-percent range. Elementary theory of operation is described, together with design considerations and systems interface information. Typical tube designs and data are presented. Recent developments are discussed, including high-efficiency techniques (to 75 percent), improvements in bandwidth, periodic focusing, and beam control electrodes. Most of the basic design techniques are well developed, and emphasis is being shifted to improvements in the detailed performance characteristics such as gain and phase resolution ripples, noise, and the sensitivities to operating voltages and currents.

Applications for quantum amplifiers in simple digital optical communication systems

Abstract: Previously published results on the performance of optical direct detection digital receivers using avalanche detectors are extended to the case where incoherent noise due to quantum amplifiers in the transmission medium is present at the detector. These calculations are applied to determine the usefulness of quantum amplifiers in simple digital transmission systems where the optical source instability results in a required amplifier bandwidth which may be orders of magnitude greater than the modulation bandwidth. It is concluded that practical applications exist where quantum amplifiers can be used in analog repeaters between regenerating repeaters in a hybrid digital system; and also as front ends of regenerating repeaters to increase their sensitivities.

Theory of minimum mean-square-error QAM systems employing decision feedback equalization

Abstract: Decision feedback equalization is presently of interest as a technique for reducing intersymbol interference in high-rate PAM data communications systems. The basic principle is to cancel out intersymbol interference arising from previously decided data symbols at the receiver, leaving remaining intersymbol interference components to be handled by linear equalization. In this work we consider the application of decision feedback equalization to quadrature-amplitude modulation (QAM) transmission, in which two independent information streams modulate quadrature carriers. Extending Salz's treatment in a companion paper of decision feedback for a baseband channel, we derive the form of the optimum receiver filters via a matrix Wiener-Hopf analysis. We obtain explicit analytical expressions for minimum mean-square error and optimum transmitting filters. The optimization is subject to a constraint on the transmitted signal power and assumes no prior decision errors. The class of QAM transmitter and receiver structures treated here is actually much larger than the class usually considered for QAM systems. However, our results for decision feedback equalization show that, for nonexcess bandwidth systems, optimum performance is achievable without taking advantage of the most general structure. If the transmitter is required to have the conventional QAM structure, study of the time continuous system that gives rise to the sampled data system considered here demonstrates that under quite general assumptions a nonexcess bandwidth system is optimum. Finally, the explicit description of the optimum transmitting matrix filter follows from an information-theoretic “water-pouring” algorithm in conjunction with the determination of the form of the points of maxima of a determinant extremal problem.

Statistics of the myoelectric signal from monopolar and bipolar electrodes

Abstract: With the aid of some simplifying assumptions, a model is proposed that describes certain statistics of the myoelectric signal detected with a bipolar electrode. It is shown that these statistics are determined by the statistics of the monopolar signal and the spacing of the bipolar electrode pair. In particular, the dependence of the bipolar-signal bandwidth on electrode spacing is derived. The experimental results agree reasonably well with those predicted by the model.

A bandpass filter using the operational amplifier pole

Abstract: The pole of an operational amplifier and a grounded capacitor are used for obtaining a high Q bandpass function. The utilization of the pole of the operational amplifier enables the extension of its useful frequency range. The gain and the bandwidth of the operational amplifier are the primary factors determining the filter performance. The experimental results of a low-sensitivity filter circuit are presented. The circuit is suitable for integration.

A new approach to optimum pulse shaping in sampled systems using time-domain filtering

Abstract: A new approach to time-domain pulse shaping in digital sampled systems is described. The proposed method allows time-limited impulse responses with optimum specified energy distribution in the frequency domain to be generated. Additional constraints to guarantee zero intersymbol interference are easily taken into account. Nyquist-type pulses which have the maximum possible amount of their total energy concentrated below some given frequency are one particularly important application. An example of such an impulse response with only 6 percent excess bandwidth is presented which shows that 99.96 percent of the energy can be concentrated in the desired bandwidth with a pulse 16 baud intervals long that can be generated using a read-only memory (ROM) with only 256 bits of storage. This new class of signals can be used advantageously for waveform generation and processing in digital data systems.

Simultaneous Two-Way Data Transmission Over a Two-Wire Circuit

Abstract: Simultaneous two-way (full-duplex) data transmission in the same bandwidth normally requires separate channels, and in the telephone network is realized by using a four-wire circuit. This paper reports on investigations directed toward full-duplex operation on a two-wire circuit using a hybrid coupler and a passband automatic transversal filter at each end of the circuit to separate the two signals. Full-duplex binary transmission at a rate of 2000 Bd in each direction has been experimentally demonstrated on a limited number of twowire circuits. Photographs of eye patterns are provided to illustrate the substantial improvement over operation with hybrids alone. Limitations on performance due to unstable distant echoes are described.

Adaptive digital filters

Abstract: Both analog and equivalent digital filters having adaptive capability are discussed. The analysis is restricted to second order sections but is extendable. Simple to implement gradient procedures using energy or phase information are used. Neither require supervised adaption. Applications include tracking nonstationary signals such as in seismic and acoustical sensing. Aside from the results shown, the tutorial nature of the paper establishes the need for further study to determine the optimum transformation that will minimize the interaction of the analog parameters (center frequency and bandwidth) in the transformed digital domain. It is suggested that this be realized by adaptive decorrelation, modification of the topological structures, and design of sm appropriate equivalent transformation.

The IMCON Pulse Compression Filter and Its Applications

Abstract: The IMCON is a reflection-mode dispersive delay line capable of high performance in large time-bandwidth product pulse compression systems. As developed in this paper, the unique characteristics of the IMCON are obtained by reflection from a double grating array that is applied to the surface of a strip. Current models of the device have center frequencies in the 4-30-MHz range with bandwidth up to 15 MHz, dispersion to 320 /spl mu/s time sidelobes on the order of --40 dB (with equalization), and other spurious signals at least 70 dB below the compressed output. The characteristics of IMCON operation are developed from a consideration of the device's transfer function. In particular, the IMCON'S high linearity and low sensitivity to fabrication and propagation problems are shown to be due to a unique error rejection effect. By comparison, the error rejection characteristics of single grating and dispersive transducer devices are found to be inferior to the IMCON. Data derived from operating pulse compression systems are utilized to demonstrate the low time sidelobe and high time-bandwidth capability of the IMCON.

Delphinid sonar: measurement and analysis

Abstract: Problems in acquisition, storage, and analysis of delphinid echolocation signals are described and illustrated. It is shown that adequate bandwidth is the prime requisite for validity in measurement. However, idiosyncracies of the detector and recorder may alter the signal and, therefore, its derived characteristics. Uncertainty about the signal leads to ambiguous results in analysis.

Practical considerations for analog operation of bucket-brigade circuits

Abstract: The bucket-brigade circuit offers a means of implementing a clock-controlled analog delay line in monolithic form. Operating in the sampled-data domain, it combines some of the advantages of both analog and digital circuits and appears to have a strong application potential in analog signal processing systems. In this paper, the analog operation of bucket-brigade circuits is described with respect to such practical operating considerations as bandwidth, dynamic range, linearity, power dissipation, baseband, signal recovery, a clock waveform noise. Experimental results from p-channel MOSFET and n-channel JFET brigades are presented.

On the transition width of finite impulse-response digital filters

Abstract: Several properties of finite-duration impulse-response (FIR) digital filters designed to have the maximum possible number of ripples are discussed and illustrated with examples. Such filters have been called extraripple filters. Among the properties of such filters are as follows. 1) Extraripple low-pass filters with fixed passband ripple δ 1 and stopband ripple δ 2 achieve the local minimum of transition width in the class of linear phase filters with fixed impulse-response duration of N samples. 2) For the case δ 1 = δ 2 the minimum transition width is roughly independent of F p , the passband cutoff frequency. 3) For the case δ 2 1 , the minimum transition width decreases with increasing bandwidth. Several figures are included to show the relation between the transition width and bandwidth for low-pass filters.

Note on minimizing the bandwidth of sparse, symmetric matrices

Abstract: The case where more than one initial numberings is possible when minimizing the bandwidth of a given sparse symmetric matrix by a directed method, is discussed. It is shown that for a little extra cost there is a significant reduction in the bandwidth.

Peaked power coherent pulsed laser transmitter/receiver system

Abstract: In a coherent pulsed laser radar system employing state-of-the-art laser technology, optical technology and microwave radar video signal processing technology, the radar receiver is provided with a bandwidth which is commensurate with doppler frequencies in radar return signals resulting from unresolved target return signal doppler shifts. These unresolved doppler shifts are on the order of magnitude of those resulting from targets having ground speeds on the order of tens of miles per hour. The above said bandwidth being orders of magnitude larger than that required for the data rate of return signals. The pulsewidth of the transmitter is designed to be matched (substantially the reciprocal) to the aforementioned large bandwidth, whose function is determined by the shape of the transmitted pulse. The PRF is chosen to be the lowest possible commensurate with the data rate. In one embodiment, a 10.6 micron carbon dioxide laser transmitter is passively Q-switched by a low pressure gas saturable absorber, such as a sulfer hexafluoride cell, giving an output pulse having a pulsewidth on the order of roughly one tenth microsecond to one microsecond, and the receiver has bandwidth of approximately one half to three MHz, operating at a nominal IF center frequency of 30 MHz, with receiver information rates on the order of 20-50 KHz, the local oscillator being adjusted with respect to the ground velocity of the laser radar so as to provide radar video at substantially the IF frequency falling within the bandwidth, as described hereinbefore.

On The Minimum-length Property Of One-sided Signals

Abstract: Apart from a visual inspection, the length property of a signal is mostly judged by its amplitude spectrum (e.g., bandwidth or “roughness” of the spectrum). However, due to the important influence of the phase spectrum. a sensible yardstick for signal length should consider both amplitude and phase. In addition, a complete investigation should also include evaluation of the length of the (partly) deconvolved signal. In this paper, signal duration and signal length are introduced as two different concepts. Unlike signal duration, giving the minimum time interval outside of which the signal equals zero, signal length gives some information as to how the signal energy is distributed within this interval. An objective yardstick for signal length is proposed, and it is shown how signal length depends on both the amplitude and phase spectrum. The minimum‐length signal is introduced and it is shown that for one‐sided signals the minimum signal‐length property implies the minimum‐phase property and vice‐versa. Th...

Use of markov-encoded sequential information in numerical signal detection

Abstract: Twelve Ss made binary decisions with feedback on numbers from one of two normal distributions with equal variances and unequal means. Sequences of distribution choices corresponded to first-order two-state Markov processes with probabilities of change of state of p1 = p2 = .50, p1 = p2 = .75, and p1 = p2 = .25. Performance was best (in d’ terms) when p1 = p2 ≠ .50. First-order sequential response dependencies tended to mirror the first-order stimulus dependencies. Violations of a fixed cutoff point decision rule were concentrated in the region of the average critical point, with a bandwidth of about 1/2σ, in which violations were strikingly more frequent than would be expected if they had occurred randomly. These results imply that in this task Ss are using a criterion-band decision rule instead of a fixed cutoff point rule, and that they are basing decisions in the region of the criterion band on information extracted from the sequence of decisions presented to them. The average bandwidth is generally different from the optimum bandwidth used by an ideal O in combining the two sources of information.

Ranging and Data Transmission Using Digital Encoded FM-"Chirp" Surface Acoustic Wave Filters

Abstract: A digital encoded multislope chirp modem/demodem unit has been implemented using two 3-port surface acoustic wave filters. Each filter operating at a 30-MHz center frequency provides either positive or negative slopes as digital 1's or 0's with a time-bandwidth product of 280, an unweighed bandwidth of 5.6 MHz, and a time dispersion of 50 /spl mu/S.The modems were used to calibrate and compare the operational performance of the conventions multitone CW ranging system with a multislope chirp ranging system. Range measurements and range-rate observations were made to a synchronous satellite with both systems using a ground communication satellite terminal. Both ranging techniques provided accuracies well within the predictable satellite range of 20 000 nmi; the multitone system provided a theoretical range resolution of 1 m, and the chirp system 0.4 m. Data transmission was also accomplished, using 12-bit binary code at a 1.25-Mbit rate. The significant advantage to be noted with the chirp system is the ability to obtain continuous range data from the satellite repeater simultaneously while other modes of information are being transmitted, and to combine the ranging and data-link transmission on a time-order basis using digital encoded chirp sequences. The chirp system was found the more desirable technique, since it provides a more direct range measurement, with minimal calibration requirements, and provided greater processing gain with relative ease and reliability. The data transmission at low data rates provided little deterioration in theoretical compressive gain. However, at the higher data rate a greater loss was encountered due to power sharing of the overlapping chirp coded carriers in the limiting satellite.

On linear parasitic array of dipoles with reactive loading

Abstract: Center loaded linear parasitic arrays of dipoles are examined. It is shown that capacitive loading increases the phase velocity of the slow wave on the structure while inductive loading reduces it. For the infinite array, used as a transmission line, this has the effect of modifying the cutoff frequency and the bandwidth. This is experimentally verified for the capacitive loading. For a simple finite array without a reflector, due to end effects only a small bandwidth widening is observed. However, when the finite array is attached with a suitable reflector, a significant widening of bandwidth is observed. In both these cases the loading causes a significant shifting of the center operating frequency. This effect is utilized to build a tunable Yagi array with varactor loading. With variable bias this loading can effectively be adjusted to double the operational bandwidth. Also it is shown that it is possible to sustain the optimum array directivity over a very wide bandwidth without bias adjustments, by a special loading network.

Distortion produced by band limitation of an FM wave

Abstract: The bandwidth required to transmit an FM wave is related to how much distortion is allowed in the signal. Here expressions are developed for the distortion (interchannel interference) produced when an FDM-FM wave passes through an ideal filter. The signal is represented by a flat (PM) band of Gaussian noise. The formulas obtained hold only for small rms frequency deviation, but fortunately this is an important case in microwave communication systems. The theoretical expressions agree well with Monte Carlo results published recently by Anuff and Liou.

Wireless portable tachometer

Abstract: Apparatus for measuring the operating speed (RPM) of an internal combustion engine without attachment to the engine. The apparatus basically includes antenna input means having a resonant frequency for receiving the radiation signals emitted by the engine with each spark plug firing and for generating a resonating voltage signal in response to each radiation signal, tuning or filter means for passing frequencies within a bandwidth including the resonant frequency, amplitude detection means for discriminating the resonating voltage signal from accompanying noise and for generating a control pulse in response to each resonating signal, and output means for displaying the measured RPM in response to the control pulse repetition rate.

Efficient use of the radio spectrum and bandwidth expansion

Abstract: Using the definition that the most efficient use of the radio-frequency spectrum is that which produces maximum communication with a point or into and through an area, it is shown that considerable bandwidth expansion is required to achieve optimum communication capacity. The effectiveness of digital modulation in trading bandwidth for interference protection is demonstrated in the environment of a dense urban network. The considerable benefits obtained from the use of highly directive antennas with small off-angle response are demonstrated. Effects produced by reflection and scattering from objects on or near the radio path are studied parametrically. It is concluded that very large amounts of communication can be realized in a restricted area and bandwidth if bandwidth expanding digital modulation techniques are employed in combination with high-quality antennas mounted so as to minimize effects of the environment.

An Analysis of Helicopter Rotor Modulation Interference

Abstract: In satellite-to-helicopter communications, interference exists on the incoming signal when the receiving antenna is located below the rotor blades. A bound is established for the performance of a coherent fixed-tone ranging system operating at L band in this interference environment. The scalar diffracted field beneath the rotating blades, at L band and above, is found to satisfy the criterion of Fresnel diffraction, and is computed using the techniques of Fourier optics. The diffracted field is expressed in terms of a narrow-band signal. The amplitude and phase components are calculated from a Fourier Series expansion using the FFT algorithm. The significant harmonics of the phase component of the interference combine with the baseband of the narrow-band, phase-modulated ranging signal. This results in CW interference, and in rearrangement of the first-order, sideband, ranging-tone channel powers. The degradation in ranging accuracy is evaluated by computing the signal-to-interference (SIR) ratio for a set of ranging tones. The post-detection (SIR)PD at the output of the correlator is shown to be a function of the amplitude of the phase harmonics of the interference, the relative difference between the ranging tone and interference center frequencies (a function of rotor speed), the rangetone modulation indices, and the post-detection filter noise bandwidth.

Static-split tracking radar systems

Abstract: A static-split tracking radar system with substantially improved performance. The system includes parallel signal processing channels for processing sum and difference signals from a target-seeking aerial array, to produce target tracking signals. Novel means are provided for trimming relative phase and gain of these channels to achieve substantially perfect matching, which gives a receiver stability sufficient for homing head use in a guided missile system. The system also includes a receiver for acquiring a reference frequency signal, the receiver having novel bandwidth adaptation and doppler tracking facilities. Other novel features provide improved clutter rejection and jamming immunity.

A New Digital Coherent Demodulator

Abstract: A coherent demodulator is described which is particularly well suited to digital implementation. Its important features are that no low-pass filter is required to eliminate double-frequency terms and that the passband signal need be sampled at only twice the highest frequency of the baseband signal, rather than at twice the highest frequency of the passband signal. A demodulator of this type will be useful in those systems that do not require passband digital signal processing for other purposes.