Showing papers on "Frequency band published in 1968"

Linear polarization in pulsating radio sources.

Abstract: The mechanism of emission from the pulsating radio sources reported by Hewish et al.1 seems to be quite different from that of any other celestial radio source, particularly because of the wide frequency band over which intense radiation is emitted simultaneously2. An analogy may be found, however, in the radio pulse emitted by a cosmic ray shower3,4, in which a sheet of particles moving relativistically may emit linearly polarized radiation when they are deflected by the Earth’s magnetic field. It seemed appropriate therefore to search for linear polarization in the pulsating stars, and we here report the successful detection of linear polarization in all of the four known sources.

Speech recognition as a function of channel capacity in a discrete set of channels.

Abstract: There have been many attempts to perform a frequency analysis of speech and to use the outputs of this analysis to provide cutaneous stimulation. The results of these tests have left in doubt the issue of whether or not cutaneous recognition of speech is actually possible. In addition to other difficulties, an optimum frequency analysis has never been achieved. Instead, filtering configurations have been chosen essentially arbitrarily. The systems considered may well have had insufficient channel capacity for speech recognition even in the event that the tactile stimulators were arranged in an optimum manner. In this paper, several sets of finite frequency band to discrete channels filters were considered. The frequency of each discrete channel was constrained to the fixed center frequency of the corresponding band so as to be directly translatable to the position of a tactile stimulator. Tests were conducted to measure the auditory recognition rate of speech, resynthesized as the sum of these discrete channel signals. From these measurements with different numbers of channels, a representation of recognition rate as a function channel capacity was obtained. It is anticipated that these results will be helpful in the choice of the optimum filtering configuration for test in actual tactile recognition.

Electromagnetic Microinstabilities of Plasmas in a Uniform Magnetic Induction

Abstract: Electromagnetic instabilities associated with transverse plasma waves propagating perpendicular to an external uniform magnetic induction B0 are investigated for a two‐temperature Maxwellian distribution function. The analysis shows that no instability develops if V‖e2 V⊥e2 an instability develops if ωce2/ωpe2 < V‖e2/c2 [1 − (32)12 (V⊥e/V‖e)] where ωce and ωpe are the cyclotron and plasma frequency, respectively, and c is the velocity of light. The allowable frequency regions for this type of electromagnetic wave to exist across B0 are studied. It is found that below the plasma frequency there is always a narrow allowable frequency band just below any harmonics of the ion or electron cyclotron frequencies. Each width of the allowable frequency band is calculated.

Minimum rms bandwidth of M time-limited signals with specified code or correlation matrix

Abstract: The minimum rms (root-mean-square) bandwidth of M real equi-energy time-limited signals is derived for the case of either a specified code or a specified correlation matrix. The minimum bandwidth depends only on the nonzero characteristic roots of the correlation matrix, or equivalently, of a matrix derived from column properties of the code. The optimum waveforms depend additionally on the characteristic vectors of the respective matrix and are given by linear combinations of a time-limited fundamental sine wave and its harmonics. An upper bound on the minimum rms bandwidth is approximately proportional to the rank of either matrix. Applications to several codes and correlation matrices are given, including some best binary group codes, which indicate a worthwhile saving of bandwidth for the optimum waveforms as compared with conventional waveforms. The energy concentration of these optimum rms waveforms compares very favorably with that of the time-truncated prolate spheroidal wave functions, which concentrate most energy in an assigned frequency band. Furthermore, the optimum rms waveforms are easier to generate and process.

High power-wide frequency band electroacoustic transducer

Abstract: An electroacoustical transducer assembly employs a plurality of focused poelectric elements. Each of said elements is made of a plurality of individual sections and energized to produce a radiation pattern having desired geometrical properties. The individual piezoelectric elements are figured to improve the frequency bandwidth and to provide for improved electrical connection thereto.

Wide deviation voltage controlled crystal oscillator

Abstract: A variable frequency harmonic oscillator including a voltage tunable crystal controlled resonator incorporating a quartz crystal unit with precisely antiresonated (neutralized) static capacitance operating substantially at the series resonant frequency of the quartz crystal as opposed to the antiresonant frequency thereof and a voltage variable reactance network coupled thereto having a linear reactance vs. voltage characteristic, the coupling being by means of a reactive transformer, two elements of which are absorbed in combination with elements of the neutralized crystal and variable reactance networks. Additionally a maintaining circuit is coupled to the resonator forming an oscillator thereby and including a circuit providing a means for suppressing spurious oscillations at undesired frequencies below the desired frequency band of operation.

On the correlation between wide-band arrays and array simulators

Abstract: A ninety-six element scanning array, which operates over an octave bandwidth, has been built and tested. The array beam is steered with digital latching ferrite phase shifters, which have low insertion loss and essentially constant phase shift over considerably more than an octave. A reasonable match has been achieved through the use of dielectric transformers at both the input and radiating apertures. The array performs properly over nearly an octave bandwidth for scan angles up to 60°, but at the upper end of the frequency band, the thick dielectric transformers caused a surface wave-type phenomenon and a subsequent loss of the main beam. An examination of the occurrence of `lost beams' at scan angles of 60° showed that these effects could be predicted from simulator measurements performed at higher frequencies and smaller scan angles

Acceleration dependent phase control seismic exploration

Abstract: SEISMIC WAVES ARE DETECTED AND RECORDED BY GENERATING ACCELERATION SIGNALS THROUGH PRESTRESSED PIEZOELECTRIC CRYSTALS OF WIDE BAND FREQUENCY CAPABILITY AND PASSING THE WIDE BAND SIGNAL TO A MULTI-STAGE AMPLIFIER HAVING WIDE BAND INPUT AND PROGRESSIVELY NARROWED FREQUENCY BAND THROUGH SUCCESSIVE STAGES OF THE AMPLIFIER WHILE RETAINING SIGNALS OF FREQUENCY IN THE RANGE OF ABOUT 100 CYCLES PER SECOND AND ABOVE.

Method and apparatus for the recognition of errors at the receiver in a data transmission system

Abstract: An error recognition process for a system in which data is transmitted in a one out of m different modulation characteristics (e.g. frequencies) code and wherein errors at the transmitter, or in the transmission system can cause a plurality of modulation characteristics to exist simultaneously at the receiver. The method of the invention takes advantage of the fact that modulation products outside of the assigned frequency band result when two different modulation characteristics are combined in a nonlinear device. Frequencies outside of the assigned band are detected to furnish an error voltage which blocks the decoded output at the receiver to prevent errors.

Tuning circuit for multi-band receiver using variable capacitance diodes

Abstract: A RECEIVER ADAPTED TO RECEIVE SIGNALS WITHIN TWO FREQUENCY BANDS COMPRISES SEPARATE TUNING MEANS, EACH MEANS BEING ADAPTED TO RESONATE AT FREQUENCIES WITHIN ONE OF THE FREQUENCY BANDS. THE TUNING MEANS ARE EACH PROVIDED WITH SIGNAL SENSITIVE CAPACITANCES HAVING THE CHARACTERISTIC OF BEING OPERATIVE OR INOPERATIVE AS A CAPACITOR DEPENDING UPON THE POLARITY OF A CONTROL SIGNAL APPLIED THERETO. THE POLARITY OF THE APPLIED CONTROL SIGNAL THEREBY DETERMINES WHICH OF THE TUNING MEANS WILL BE OPERATIVE THEREBY RENDERING THE RECEIVER EFFECTIVE TO RECEIVE ONLY SIGNALS WITHIN THE SELECTED FREQUENCY BAND. WHEN A GIVEN CAPACITANCE IS OPERATIVE AS A CAPACITOR, THE VALUE OF ITS CAPACITANCE MAY VARY DEPENDING UPON THE MAGNITUDE OF THE CONTROL SIGNAL APPLIED THERETO. HENCE CONTROL SIGNAL APPLYING MEANS CAN SELECT A DESIRED BAND AND CAN EFFECT TUNING WITHIN THAT BAND.

Non-coherent multi-channel optical spectrum analyzer

Abstract: A system for simultaneously analyzing the frequency content of a plurality of complex input signals. The input signals are converted to optical signals and recorded on photographic film. Each input signal is assigned a discrete track on the continuous film. Each track appears as a density modulated series of bands across the track. The optical representation of the signal as it appears on the track is analyzed by superimposing on the track a pattern representative of the frequency band of interest. When the superimposed image corresponds to the frequency of the track, light projected through the film is modulated and is picked up by photo-detectors which transform the modulated optical signals to electrical signals for recording or viewing on a cathode-ray tube.

Varactor diode tuned circuit having substantially constant loaded q-factor

Abstract: A tuned circuit arrangement comprising a tuned circuit having varactor diode means for the tuning thereof over a band of frequencies, and compensation means operative for providing selective damping to said tuned circuit so that the loaded Qfactor of the tuned circuit arrangement remains substantially constant over the frequency band.

Human frequency response as a function of visual feedback delay.

Abstract: This paper uses a light-matching tracking study to determine the human frequency band pass characteristics in the presence of significantly large external transmission delays which are introduced into the stimulus-response information loop. Such delays occur in real time operation of vehicles and other equipment which is at some distance from the operator (near earth or deep orbit, surface of the moon, etc.). When information in the visual sensory channel is delayed because of transmission times between man's controlling action and the displayed results, this interacts with the relatively short normal delay of the other sensory feedback loops such as tactual and kinesthetic information loops, causing substantial phase interference problems between otherwise in-phase parallel sensory information channels. A representative model was used for the human transfer function for the system studied, which matched the experimental data reasonably well. The maximum frequency at which a person could meaningfully acce...

Acoustic-gravity waves produced by energy release

Abstract: : A complete asymptotic analysis is carried out for the flow field produced by the instantaneous release of energy, at a point on the ground, in an isothermal atmosphere A double integral representation of the flow is constructed from Laplace-Handel transforms of the linearized equations An asymptotic approximation to the integral is obtained by two successive applications of the method of stationary phase It is found that there are three principal groups of dispersive waves behind the spherical acoustic front One of these groups is contained in a high frequency band, and the other two are contained in a low frequency band The spatial domain of the low frequency waves is cut off by a front (caustic), the location of which is calculated Some of the characteristics of the flow are discussed

Line defects in three-dimensional lattices

Abstract: In the presented paper localized modes near a line defect in a simple cubic lattice with interaction among the nearest neighbours are studied. For the case of a row of atoms with a changed mass and interaction among them, criteria for the occurrence of localized modes are given. It is shown that the frequency band of acoustic localized modes beginning at the frequencyω=0, insofar as it deals with the frequency spectrum, is very similar to that of a linear chain. This leads, when studying crystal properties which are any additive functions of eigenfrequencies (thermo-dynamical functions, etc.), to the appearance of the contribution characteristic for the linear chain.

Color video pickup system with means for generating a frequency modulated indexing signal higher in frequency than the video information

Abstract: In a color video signal generating apparatus in which a filter having regions respectively selecting light of different wavelength ranges and a screen having separating lenses are optically interposed between an object to be televised and a single image pickup tube to cause such separating lenses to coact with the filter in dividing an image of the object into color components which are projected onto said tube in such manner that said color components when successively encountered in the line scanning direction can respectively become chrominance signals having a predetermined color subcarrier frequency and being of the same frequency band, there are provided index image forming means to form index images on the image pickup tube which, when successively encountered in the line scanning direction, produce in the tube output frequency or angle modulated index signals having a carrier frequency which bears a predetermined relationship to the color subcarrier frequency and a frequency band which is different than the frequency band of the chrominance signals, and the positions of the respective color components in the chrominance signals are indicated by the index signals to permit the extraction from the tube output of color video signals.

A wideband circular array for h.f. communications

Abstract: This paper describes a study of the use of a single ring array of monopoles for a wideband multiple-beam aerial system for communications.Directional patterns are calculated for 24- and 32-element circular arrays over the frequency band 1-5-10 MHz and for different types of array excitation (or element combination in the case of a receiving array).The calculations are backed by experimental measurements on a model circular array operating over the band 200?1365 MHz. The study shows that low side-lobe levels (?6 to ?9 dB) and acceptably small variations of beam-width, can be achieved over the above frequency band.

A space-time filter for seismic models

Abstract: A space‐time filter has been designed and constructed for use with arrays of transducers on seismic models. The filter allows real time, space‐time operations. Adjustments to change the filter parameters are simply performed. The device can be considered an analog implementation of the techniques used in “digital filtering.” The space‐time operator is capable of handling ten spatial (receiving transducer) inputs, and each input can be filtered with up to 20 feedback and feed‐forward filter points. The time operators are composed of lumped constant, electric delay lines tapped every 0.5 μsec with total delays up to 28 μsec available. The outputs from the delay line taps are summed in an operational amplifier summing circuit. The frequency response of the device is from approximately 10 kHz to 500 kHz, which covers the frequency band normally used in two‐dimensional seismology. Some simple experiments have been performed to demonstrate the utility of the device. These experiments are: a) feedforward time op...

Design of waveguides and transmission lines by the distributed maximum principle.

Abstract: Waveguide and transmission line optimal design to minimize reflected power due to mismatch over frequency band, using distributed maximum principle

Improvements in or relating to the measurement and testing of electrical circuits

Abstract: 1,123,193. Measuring circuit characteristics. MULLARD Ltd. 6 May, 1966 [14 July, 1965], No. 29848/65. Heading G4H. In apparatus for measuring the electrical transfer characteristic of a circuit in a desired frequency band, input pulses having an energy spectrum including said band are generated repetitively and applied to said circuit, the waveforms of the input pulses and output pulses from said circuit being approximately reconstituted on an extended time scale by sampling successive input and output pulses, the samples then being digitized. Thus the samples required at successive points within the typical input (or output) pulse are obtained from respective successive (identical) versions of the pulse. The digitized samples are used by a computer for Fourier analysing the input and output pulses to derive their amplitude and phase components, the ratio of respective amplitudes (input and output) and the difference of respective phases being obtained. The group time delay (rate of change of phase with frequency) can also be calculated.

A wideband array of non-uniformly spaced directional elements

Abstract: This paper discusses the design of an economical wideband array suitable for low-frequency radio astronomy applications. The array consists of 32 non-uniformly spaced, uniformly excited, log periodic antennae designed to operate over a 2 : 1 frequency band. At the highest operating frequency, the array has a beam-width of approximately 1° and side-lobes at least 16–5 dB below the main beam level. The theoretical limit to which the'side-lobes of an idealized array, having the same gain and length, can be suppressed is 17 dB.

Application of Dinoseis in Canada

Abstract: An experimental program was conducted to determine if a seismic system consisting of a Dinoseis, a digital recorder, and digital processing was adequate for solving exploration problems in Alberta and Saskatchewan. Aspects to be considered when using a low power, low frequency, surface source are: ambient and coherent noise reduction, resolution of reflected events, and penetration of subsurface. Field procedures and processing techniques used to attack these problems include stacking of multiple pulses taken at each shotpoint, selection of appropriate source and receiver arrays, common-depth-point coverage, and application of deconvolution and velocity and frequency filtering in the processing sequence. A match was obtained between central Saskatchewan Dinoseis traces and a synthetic seismogram over a frequency band width of 20-65 cps. Dinoseis sections were comparable to processed dynamite sections in two Alberta areas.

Basic Concepts and Definitions of Infrared Radiation Theory

Abstract: The infrared energy emitted by thermal sources covers a wide frequency band in the spectrum of electromagnetic waves. Like light, infrared radiation is now understood to have both wave and corpuscular properties. The properties complement each other and never manifest themselves separately. The wavelength λ or the wave number v is usually taken as the parameter to differentiate the types of radiation.

Improvements in or relating to electric combining networks

Abstract: 1,109,227. Diversity reception systems. GENERAL ELECTRIC CO. Ltd. 27 Jan., 1967 [27 Jan., 1966], No. 3705/66. Heading H4L. In an electric network for selectively connecting in a diversity radio communication system the signals from two receivers applied at 7, 8 respectively, to an output circuit 10, a pair of relays (not shown) are controlled by the two receivers so that if the signal strength or quality of one path, e.g. path 8, falls, below an acceptable level a switch 19 is closed and a switch 22 opened, whereby the signal from this path is absorbed in a dummy load 4, and only the signal from input 7 is applied to the output circuit. Similarly, if the signal from the path 7 is unacceptable, switch 18 is closed and switch 20 opened so that the signal from 7 is dissipated at 4 and the output at 10 is provided by the input signal at 8. At other times the two input signals are added in the output circuit 10. The quality of the received signal may be determined in known manner by measuring the noise level in a frequency band adjacent to that used for the intelligence signals.

Formant frequency extractor

Abstract: 1,250,393. Formant vocoder analyser. PHILCO-FORD CORP. 23 Jan., 1969 [25 Jan., 1968], No. 3860/69. Heading H4R. A formant frequency tracking circuit for a vocoder has a variable frequency tuned filter, 4, whose tuning is controlled by the output of the formant frequency detector, 8, to provide an emphasis of the frequency band around the detected formant. The band pass filter 2 provides selection of the formant frequency range 14 as shown in Fig. 2 with direct coupling via resistor 6 to the frequency meter, the resistor being by-passed at the frequency of the tuned filter to provide a peak 16 in the response. The arrangement provides a sort of hysteresis effect in the frequency tracking.

Wide-band transducer for seismic modeling

Abstract: A linear piezoelectric transducer with a wide-band frequency response has been designed for use as a seismic model source. The wide bandwidth is achieved by a transducer configuration that is constant for discrete scaling changes. This gives a log-periodic design that is a subclass of frequency-independent designs. A six-step log-periodic transducer with a scaling ratio of 1.25 was constructed and tested. The measured electrical impedance compares favorably with a theoretical electrical impedance obtained using an approximate analysis. The electrical impedance of the transducer mounted on an aluminum semicircle was measured and found to be relatively independent of frequency over the frequency range from 90 to 300 kHz. The elastic waveform from the transducer compared with that from a standard simple transducer shows that the wideband transducer is more efficient in electromechanical conversion over a broader frequency band.

Improvement of System Compatibility through Coupling Reduction

Abstract: This paper deals with various techniques in the form of modifications or additions which were developed to produce additional coupling reduction in existing systems. Although this has been the prime purpose, due consideration has been given to the effects of the different methods on the original objectives of the systems. Some of the techniques alter the radiation patterns and gains of the antennas involved. Consideration has been given to developing techniques which are operable over a broad band of frequencies in order not to restrict the operational requirements of the systems involved. Both analytical and experimental results are presented. Experiments were performed in convenient microwave frequency bands. However, by proper scaling with respect to frequency, it is possible to use the results given in this paper at other frequencies. One of the methods of coupling reduction described here is the compensating bridge. This bridge is formed with the addition of a cancellation link between two interfering systems. The bridge is balanced by adjusting the amplitude and phase of the power transmitted through the link to obtain high isolation. The distinct achievement here is the reduction of interference between two systems over a broad range of frequencies. This method is one of the most versatile since it can be readily extended to almost any frequency band. The use of corrugations in the form of circumferential trenches around the aperture of an antenna was found to offer a substantial reduction in coupling.