Showing papers on "Sampling (signal processing) published in 1971"

Sidelobe blanking system

Abstract: A logarithmetic sidelobe blanking system operable in a pulse compression radar system in which the dynamic range of the blanking system is not limited by the compression dynamic range. A sidelobe blanking receiver is provided to process the sidelobe signals in a manner identical to the processing in the radar receiver. The uncompressed IF pulses in both the sidelobe receiver and the main lobe receiver are sampled prior to their being amplitude limited, and are applied through logarithmetic amplifiers whose dynamic range capability is at least equal to the dynamic range of the preceding circuits. The output signals of the logarithmetic amplifiers are then compared and if the sidelobe signal is larger than the main lobe signal the compressed pulse at the output of the pulse compressor is located and used for blanking to ensure that only the time interval of the compressed pulse width is removed. As sampling is made prior to the threshold or amplitude limiting circuit, the full dynamic range of the receiver is processed. The sidelobe receiver system in accordance with the invention also includes an arrangement for selecting the above described sampling prior to threshold operation when the input signal is limited and for selecting operation with normal sidelobe blanking comparison of compressed sidelobe signals when the input signal is at a level lower than the limiting amplitude of the channels.

Sampled data control

Abstract: A sampled data controller responsive to a derived error signal which sums the error signal with a feedback signal. A sample buffer store is arranged in response to a sampling command to sample and hold the combined error and feedback signal. A plurality of serially-connected memory stages are connected to receive the output of the sample buffer store. The feedback signal is obtained from the output of the memory stages. The outputs of each memory stage and that of the buffer store are summed to derive a signal for adjusting a variable.

Frequency Interleaved Sampling of a Color Television Signal

Abstract: In the transmission of color television signals over a digital communications system, the analog TV signal must first be converted to digital form. This paper treats the first step in this conversion, sampling of the analog waveform. A significant reduction in sampling rate can be achieved by using several properties of the television signal. The spectrum of the TV signal has the energy concentrated at harmonics of the line and field rates. By choosing a sampling rate that is less than twice the bandwidth and a frequency that is an odd multiple of one-half the line rate, the aliased energy resulting from the sampling process falls in the gaps of the video signal energy. A comb filter is then used to remove most of the aliased energy. The resulting signal shows no appreciable deterioration. The subjective effects of noise added between harmonics of the line rate are discussed. These results are used to determine the requirements of the comb filter. The key parameters of one form of a comb filter are developed. A quantitative evaluation of the comb filter parameters shows that adequate suppression of the aliased energy can be achieved.

Adaptive processor for an rf antenna

Abstract: The elements of an RF antenna array are individually connected to mixer circuits to produce a plurality of distinct IF signals. Each signal is fed to a multi-tapped delay line which makes available an increasingly delayed IF signal at subsequent points therealong. The delayed signals are independently converted from an analog to digital form so that they may be accepted by subfrequency sampling input lines of a digital computer. A pilot signal can also communicate with the computer or be generated internally to produce a control signal for varying weights that control the amplitudes of the IF signals transmitted from the tapped delay line. The weighted signals are fed to a summing circuit which sums these signals to form a system output. The system output is employed for achieving null steering of the array by controlling system gain in the ''''look direction'''' and rejecting noise.

Signal sampling circuit

Abstract: A current-mode amplifier is connected in series with a current source which turns the amplifier on or off in response to signal voltages connected to the current source. The current-mode amplifier samples signals from a source of signals only when the amplifier is turned on. Diodes, connected between a source of signal voltages and the current source, store electrical charges which aid the current source in providing fast turn on and fast turn off so that a high rate of sampling is possible.

Clock recovery system

Abstract: A clock recovery circuit for a data communication system, wherein the eye pattern for the data is sampled (by sampling the outputs of the slicer circuits ) and logic circuitry utilized to select only those transitions, i.e., slicer axis crossings, which should be located midway between the desired time sample points and to advance or retard the local clock in accordance with the samples for these transistions. The ratio of advance to retard decisions is utilized to generate, through use of a D to A converter, a control signal for correcting the frequency of the voltage controlled oscillator which serves as the local clock, so that both frequency and phase error correction is provided.

Exact model for delta-modulation processes

Abstract: A mathematical model is described which generates a pulse waveform identical to that of a single-integrator delta modulator, provided that the input signals to the latter do not cause slope overloading. The model uses analogue techniques of angle modulation and sampling to generate time- and amplitude-quantised signals, thus readily lending itself to exact analysis. The delta-modulation process is treated in a general manner that is equally applicable to delta-entry and sigma-entry systems. By this means, a central delta modem is defined which includes both pulse modulation and local decoding (prior to final filtering) of the pulse waveform. The model formulation is such that it is equivalent to the delta modem. The equivalence of the delta modem and model is proved analytically. It has also been verified by simulation on a digital computer and demonstrated experimentally. The model can be extended to simulate a double-integration network, provided that the necessary prediction is included. The model can also be extended to represent pulse-code modulation, because a linearly quantised p. c. m. siganal can be obtained by suitable sampling of the output of a delts modulator.

Traffic volume computer

Abstract: The output of a vehicle detector which provides an indication for each vehicle passing a point on a roadway is multiplied by an appropriate scaling factor. This scaled signal is then divided by factors in accordance with a predetermined sample cycle length and the number of sampling cycles used to form a complete sampling period. The signal so derived is then divided by a selected scale factor which represents a standard or reference vehicle volume per unit of time. A signal is thus derived which represents the volume of traffic per unit of time as a percentage of the selected standard or reference volume, this information being digitally accumulated during each sampling period and read out for display or use in computing circuits.

IF versus video limiting for two-channel coherent signal processors

Abstract: Intermediate frequency (IF) and video limiting are evaluated and compared for a two-channel coherent digital signal processor, where the video limiting is that of the analog-to-digital (A/D) converters, occurring separately in each channel. The input is a narrow-band random signal. Video limiting is shown to produce considerably higher distortion sidebands outside the input signal band. Within the input signal band, video-limiting distortion is about 1 dB worse. The results are useful for both the radar moving target indicator (MTI) and mapping applications.

A 36-Mbit/s Television Codec Employing Pseudorandom Quantization

Abstract: The paper describes an experimental system constructed to allow investigation of pseudorandom dither signals for coarse quantization of 625-line monochrome television siginals. The system employs a separate encoder/decoder for the television synchronizing pulses so that the picture signal can be allowed to occupy the full nonsaturating range of the video encoder. Dither samples are added to the video signal before coding and subtracted at the decoder and are negatively correlated to maximize the picture signal-to-noise ratio according to a subjective noise weighting function. The power spectral distribution of the quantizing noise is derived and, assuming this to be picture independent and random, pre- and deemphasis networks are used to increase the signal-to-noise ratio. Empirical methods are used to determine the network parameters. The results of preliminary subjective experiments with the 3 bits/sample pseudorandom codec are given for a sampling frequency of 12 MHz and indicate the practical limitations of a theory which predicts a high standard of picture quality.

Single bit doppler processor for guidance missile system

Abstract: Hybrid digital processor of a missile guidance system in which the input spectrum is mixed, limited, sampled, and fed to a recirculating shift register. Sampled values of the shift register, with the same oscillator controlling the sampling rate of the limiter and the shift register, are mixed with a signal from a voltage controlled oscillator and fed to a threshold pulse generator which is connected to a sampling logic circuit that feeds a series of counters.

Digital generation of quadrature samples

Abstract: A method and apparatus for generating digitized quadrature samples which approximate the sampled complex envelope of an input waveform by digitally sampling the input signal and applying the resultant digital samples to a digital processing system to obtain pairs of quadrature samples of the input signal. The input digital samples are digitally combined, delayed, and multiplied by the digital processor to form the quadrature samples. An alternative method and apparatus takes digital samples from a plurality of input signals, applies the digital samples to an alternative form of digital processor, and generates multiplexed quadrature samples of the input signal.

Digital to analog conversion apparatus

Abstract: A digital to analog converter which improves the accuracy of reconstruction of a sampled analog signal without requiring that the sampling rate of the original signal be increased to obtain such accuracy.

Magnetic susceptibility mud log

Abstract: Relative to the mud system used in a well drilling operation, a monitoring system is provided from which a log of the magnetic susceptibility of earth formations traversed by a borehole can be obtained. The system employs a mud sampling channel where the flow of mud is temperature stabilized and passed through a sampling coil so that the entrained formation particles can influence the value of the magnetic field induced by a signal generator in the sampling coil by virtue of their magnetic susceptibility. The sampling coil is a part of a bridge detecting system which is driven with a standard excitation signal so that a change in the permeability (or susceptibility) of the material on the interior of the coil produces an output voltage signal. The amplitude of the output voltage signal which is in phase quadrature with the excitation signal is detected by a phase sensitive detector. A corresponding deviation signal is generated by amplifying this voltage signal to drive a clock operated chart recorder. The chart recorder is connected to the traveling block of the drilling rig for producing a depth recording also. Thus, the recorded deviation signal which is indicative of magnetic susceptibility is correlatable in a well-known manner to the drilling depth. Identical systems may be used to monitor the mud input and output to the well, so that a differential value of the magnetic susceptibility signal can be obtained. Reference liquids can also be supplied to the system for obtaining calibration values having known magnetic susceptibilities.

Estimating frequency-response function using periodic signals and the f.f.t.

Abstract: A technique for estimating a frequency-response function using a periodic pseudorandom binary sequence which is compatible with the fast-Fourier-transform algorithm is presented. A method of synchronising the p.r.b.s. and the sampling for the f.f.t. using a single clock source and two binary counters is described. A simple check on the synchronisations and the identification of an 8th-order lowpass Butterworth filter is provided.

Amplitude quantized signal transmission method

Abstract: A signal transmission method which reduces the frequency band of a transmission channel by sampling the input signal, quantizing each sampled pulse, combining the quantized pulses into a group of pulses, combining the quantized pulses in each group into a single pulse the quantized amplitude of which is uniquely determined from the quantized amplitude of each component pulse. The signal transmission method is used for transmitting video, facsimile, audio, data or other similar signals characterized by a high density of information with sufficient recognizability at a comparatively slight cost of signal-noise ratio.

Method and apparatus for high-resolution spectral analysis

Abstract: A method and apparatus for high-resolution power spectral analysis employing a digital computer is provided without stringent stability requirements on the sampling rate by using a pair of balanced mixers to combine one signal directly and in quadrature with a second signal, and alternately sampling the outputs of the mixers through an analog-to-digital converter. The computer then carries out computations of a convolution spectrum from two autocorrelation and two cross-correlation functions which can be computed from the two sequences of samples with compensation for variations in gain of the signal channels by normalizing correlation functions, and known deviation from - 90° in the quadrature mixing of signals by using φ in place of - 90° in the analysis and dividing the sum of the cross-correlation functions by - sin φ.

Digital to sin/cos converter

Abstract: In a radar system, an arrangement for converting digital information representative of the rotational (azimuthal) position of the radar antenna to sine and cosine of azimuth waveforms for use in a display such as a plan position indicator. Azimuth change pulses indicative of the antenna's rotation and azimuth reference pulses indicating the 0 DEG reference direction are applied to a first counter, the individual outputs of each stage of which are in turn coupled to a comparator arrangement. The state of the first counter is compared with that of a second counter which is fed by a pulse source standard. The output of the last stage of the second counter is treated and filtered to provide a pure sinusoidal reference waveform to be sampled in a sample/hold detector arrangement. From the comparator arrangement sampling pulses are derived in accordance with the rotational position of the antenna relative to the digital reference as represented by the count in the second counter, with these sampling pulses then being applied to the sample/hold detector in order to produce a sine of azimuth waveform. A cosine of azimuth waveform is also derived via an adder stage in conjunction with the comparator arrangement, which adder counts the equivalent of 90 DEG from the first derived sine sampling pulse to produce the priming condition for a cosine sampling pulse.

Neuroelectric Signal Analysis Using Nuclear Instrumentation Techniques

Abstract: A real-time system for nerve spike recognition and separation has been developed. The system is based on the techniques, commonly used in nuclear instrumentation, which have been adapted here for biological signal measuring and processing. Techniques used are signal shaping and optimum noise filtering; pulse peak stretching; peak sampling; pulse shape discrimination and multichannel pulse height analysis. Spectra for nerve pulse heights of the cockroach are shown, for the case of spontaneous activity as well as for evoked activity (e. g. for a living object exposed to radiation wind or light). Similarities and contrasts between nuclear and biomedical signal analysis are discussed.

Simplified digital to sin/cos converter

Abstract: The invention provides a conversion arrangement, particularly applicable to radar, for converting digital information representative of the rotational (azimuthal) position of the radar antenna to sine and cosine of azimuth waveforms for use in a display such as a plan position indicator. A frequency oscillator standard is coupled to an n-stage reference counter the square wave output of which is subsequently filtered to provide a reference cosine wave of predetermined frequency. Azimuth change pulses representative of the antenna positional rotation are mixed with the frequency oscillator standard and coupled to a second n-stage or n-bit counter operating in like manner to the reference counter. The content of the second counter is advanced with respect to the reference counter by one count per azimuth change pulse, the second counter in turn serving to generate cosine and sine sampling pulses. These pulses sample the reference cosine wave to provide an output signal which when filtered derives cosine phi and sine phi positional information signals respectively. System reference is obtained by presetting the second n-stage counter to equal the reference counter in dependence upon each received azimuth reference pulse.

Circuitry for detecting low amplitude rapid variations in a high amplitude output signal

Abstract: Measuring circuitry is described having the capability of providing output signals indicative of low amplitude, rapid variations in a higher amplitude, slowly changing signal. The circuitry includes a transducer upon which the signals are imposed, a storage device such as a capacitor which is intermittently connected to output terminals of the transducer, means for coupling the capacitor to a data recovery system, and a sampling relay for changing the capacitor connection between the transducer and the data system whereby the average input voltage to the data system is reduced to zero but any variations in the signal are faithfully indicated.

Noise properties of the dynamic crossed-field photomultiplier

Abstract: Experimentally measured noise power spectra of the dynamic crossed-field photomultiplier are presented, along with data which describe the sampling characteristics of the device. Sampling is shown to introduce excess noise of the order of 3 dB.

Image Quality in Sampled Data Systems

Abstract: : The paper deals with aliasing, an important effect of one-and two- dimensional sampling on image quality. Aliasing changes the normal criteria of utility of the modulation transfer function (MTF) as a measure of system quality. Aliasing can be eliminated by letting the MTF fall to zero at one-half the sampling frequency. This, of course, markedly reduces the signal-to-noise ratio at the display (SNR(D)) near cutoff and thus reduces operator performance. Several factors control the amount of information an observer extracts from an image and the rate at which he extracts it. The paper presents the results of a series of experimental programs relating observer performance to the modulation transfer function area (MTFA) and to the SNR(D) and derives the relationship between MTFA and SNR(D). The paper discusses the tradeoffs as they are presently understood.

Reconstructions of signals of a known class from a given set of linear measurements

Abstract: This paper investigates the error in reconstructions of a signal based on a given finite set of linear measurements, and presents two schemes that, if there is available a priori knowledge of the class of signals of which the measured signal is a member, can achieve a reduction of this error beyond the best that could be done without such knowledge. The error measure used is the supremum over the class of the \mathcal{L}_2 distance between a signal and its reconstruction. The essence of the proposed reconstruction techniques is a coordinate transformation from the sampling subspace to a new reconstruction subspace known to be efficient for representation of signals of the given class. This study applies the theory of extremal subspaces and n widths of signal classes originated by Kolmogorov. Results are applied to the much studied class of time-concentrated band-limited signals. The measurement process is here assumed to be the convenient one of Nyquist rate time sampling. For this problem, plots of the error bounds and of several test functions and their reconstructions are presented, both for the proposed reconstructions, and for conventional cardinal-sampling-theorem reconstructions.

Sweep-frequency measurement of structural return loss by a carrier-burst method

Abstract: Errors due to hybrid unbalance and reflections from connectors and terminations are eliminated by using a burst of carrier as the test signal. A sampling oscilloscope extracts that part of the signal which is proportional to the reflection from the cable alone.

Adaptive 2nd-order delta-modulation system with 1-bit memory

Abstract: A system of companding is described, as applied to a 2nd-order delta-modulation system, which has a memory of only one sampling interval, leading to a fast response to overload, and improvement in dynamic range and signal/noise ratio.

Method and system for compressing bandwidth

Abstract: A method and system for compressing required bandwidth for signals possessing redundancy, without substantial loss of intelligence or signal-to-noise ratio. This is effected by sampling the input signal to yield an appropriate first group of samples, transforming the said group into a second group of samples displaying reduced power but yet retaining intelligence and signal-to-noise ratio, and then operating upon the transformed sample group to recover original power levels-and in the process reducing required bandwidth. A system is disclosed wherein these operations are effected by applying the input signal to a tapped delay line-the outputs from said line comprising the aforesaid first group of samples. Such outputs are each applied through weighting networks to derive the transformed, low-power, second sample group. After being passed through analog-to-digital converters, the low-power samples, then in parallel binary form, are gated and passed through a suitable delay line to effectively combine the low-power samples into higher power signals of number per unit time reduced in comparison to the original sampling rate.

Visual recording system for video signal

Abstract: A system for the visual recording of a video signal records one field or frame of the video signal on a rotary magnetic recording medium, such as a magnetic disk, and then repeatedly reproduces the recorded signal. A portion of the repeatedly reproduced signal is sampled at each horizontal synchronizing signal period thereof, and controls a recording element, such as a discharge electrode, which discolors or otherwise visually alters a recording paper in correspondence with the amplitude of the sampled signal. The recording paper is supported on a cylindrical surface for relative movement with respect to the recording element both axially and in rotation by a mechanical interconnection to the rotary magnetic recording medium, and the position of sampling of the reproduced signal is sequentially shifted at every relative rotation of the recording paper and element while the relative axial movement is synchronized with such relative rotation.

Automated analyzer of machine operation

Abstract: An automatic analyzer of the operation of machinery having sensors coupling various machine components to produce electrical signals which sensor output signals are applied to the analyzer in accordance with a program of sampling by a taped program controlling relay switches to compare the voltage amplitude of an electrical signal from the machine component or to compare the harmonics of noise from the machine component with a predetermined reference to shut down the analyzer to further sampling and to indicate a fault whenever the machine component signal is in excess of the reference until the fault is corrected.

Sampling of flowing liquids

Abstract: 1,255,625. Sampling liquids. COTTON SILK & MAN-MADE FIBRES RESEARCH ASSOCIATION. 17 Jan., 1969 [17 Jan., 1968], No. 42339/70. Divided out of 1,255,624. Heading B8N. [Also in Division G1] The rate of flow of a liquid is determined by measuring the depth of the liquid passing over a weir C, using a float A attached to the slider of a potentiometer 1 and modifying the signal in accordance with the known relationship between depth and rate of flow for a weir of the given shape. The rate of flow signal controls pump 3 to feed a tipping device 4 at a proportionate rate, predetermined quantities in device 4 being fed into a mixer 5 and collected periodically in bottles D assembled on a turntable 6.