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Showing papers on "Frequency response published in 1970"


Journal ArticleDOI
TL;DR: In this article, the authors presented a design for recursive and non-recursive wide-band differentiators based on the magnitude of the frequency response, and the coefficients were optimally chosen to minimize the peak absolute error between the obtained frequency response and the response of an ideal differentiator.
Abstract: Designs for recursive and nonrecursive wide-band differentiators are presented. The coefficients for the recursive differentiators were optimally chosen to minimize a square-error criterion based on the magnitude of the frequency response. The coefficients for the nonrecursive differentiators were chosen using a frequency sampling technique. One or more of the coefficients were optimally selected to minimize the peak absolute error between the obtained frequency response and the response of an ideal differentiator. The frequency response characteristics of the recursive differentiators had small magnitude errors but significant phase errors. The nonrecursive differentiators required on the order of 16 to 32 terms for the magnitude error of the frequency response to be as small as the magnitude errors for the recursive differentiators; however, there were no phase errors for the nonrecursive case. The delay of the recursive differentiators was small compared to the delay of the nonrecursive differentiators.

89 citations


Journal ArticleDOI
TL;DR: In this paper, the construction and performance of mechanical transducers suitable for generating and detecting second sound in pure 4He, and also in dilute 3He-4He mixtures at millidegree temperatures, are described.
Abstract: The construction and performance of mechanical transducers suitable for generating and detecting second sound in pure 4He, and also in dilute 3He–4He mixtures at millidegree temperatures, are described. It is shown that when the normal fluid density is small, the behavior of the transducers can be explained by a simple acoustical model which enables their sensitivity, frequency response, and reflection coefficient to be calculated in terms of easily measured parameters.

71 citations


Journal ArticleDOI
TL;DR: Compliance is the most troublesome variable in obtaining high frequency response and factors such as occult air bubbles and leaky connections cause the greatest difficulty.

57 citations


Journal ArticleDOI
P. Payne1
TL;DR: An improved curve fitting technique, based on modification of work by Levy and Sanathanan and Koerner, incorporating known physical constraints is described, showing that there is a much better guarantee of obtaining stable transfer functions and of predicting responses in other domains.
Abstract: An improved curve fitting technique, based on modification of work by Levy and Sanathanan and Koerner, incorporating known physical constraints is described. A comparison with experimental results on high-order systems shows that there is a much better guarantee of obtaining stable transfer functions and of predicting responses in other domains.

43 citations


Journal ArticleDOI
01 May 1970
TL;DR: In this paper, the frequency response of a high-power grid-controlled convertor system is deduced, using the concept of "conversion functions" introduced to systematise and simplify the calculations.
Abstract: In high-power grid-controlled convertor systems large parallel capacitor batteries are usually installed and connected to the a.c. busbar at the same point as the convertor. They can be used either for filtering harmonics, e.g. as parts of tuned filters, or for the generation of reactive power, or both. The capacitive components introduced complicate the dynamic behaviour of the convertors considerably, and thus the system cannot be described by simple convertor theory. In the paper, the frequency response of such a system is deduced, using the concept of ‘conversion functions’ introduced to systematise and simplify the calculations. The frequency response for the current-control loop is deduced with reference to h.v. d.c. transmissions, but the results are applicable to any kind of rectifier load. The numerical calculations are laborious and require the use of a digital computer. The comparison between calculated and simulator-measured frequency responses for two practical h.v. d.c. transmissions shows satisfactory agreement. The calculated transfer functions are useful for the synthesis of the current-control system and allow an inexpensive study of the effects of system changes on the achievable speed of response.

42 citations


Journal ArticleDOI
TL;DR: It is shown that DDA speed and accuracy can be greatly improved by using increment word lengths which are approximately one-half the length of integrand registers providing that integration formulas more accurate than Euler integration are used.
Abstract: In conventional digital differential analyzers (DDA), the word length used for the transmission of information between integrators is restricted to at most a single magnitude bit and a sign bit. This restriction seriously limits integrator frequency response and has to a large extent been responsible for the failure of DDAs to achieve widespread acceptance as general purpose differential analyzers. In this paper it is shown that DDA speed and accuracy can be greatly improved by using increment word lengths which are approximately one-half the length of integrand registers providing that integration formulas more accurate than Euler integration are used. The programming of such machines for the solution of both linear and nonlinear differential equations is discussed and a quantitative evaluation of performance improvement is presented. At the same time, an effort is made to isolate the principal difficulties in hardware implementation which result from extending the integrator increment resolution.

35 citations


Proceedings ArticleDOI
01 Dec 1970
TL;DR: The structure and the simulated performance of nonlinear adaptive filters appropriate for high speed serial data transmission over time-dispersive and slowly time-variant channels, obtained by means of Monte Carlo computer simulation are presented.
Abstract: This paper describes the structure and the simulated performance of nonlinear adaptive filters appropriate for high speed serial data transmission over time-dispersive and slowly time-variant channels. The filters are designed to combat the two major obstacles in high speed digital signaling over such channels, namely, the presence of intersymbol interference due to the non-ideal frequency response of the channel and the slow, randomly time-variant response characteristics of the channel. Some results on the error rate performance of the adaptive filters, obtained by means of Monte Carlo computer simulation, are also presented.

32 citations


Patent
16 Dec 1970
TL;DR: In this article, the output frequency is controlled by varying the number stored in the updown counter, which is obtained by applying the output pulse train to a dividing circuit, which sets the overall multiplying factor of the system, and comparing the time of occurrence of the output pulses from the dividing circuit and the input pulses to the system to provide an appropriate change in the up-down counter.
Abstract: A frequency multiplier in which an output pulse train is obtained, at a frequency related to the frequency of a sequence of input pulses. A counter is connected to a fixed oscillator and an output pulse generated each time the count reaches the same number as that stored in a separate up-down counter. The output frequency is controlled by varying the number stored in the updown counter. This control is obtained by applying the output pulse train to a dividing circuit, which sets the overall multiplying factor of the system, and comparing the time of occurrence of the output pulses from the dividing circuit and the input pulses to the system to provide an appropriate change in the number stored in the up-down counter.

29 citations


Proceedings ArticleDOI
01 Jan 1970
TL;DR: In this article, the authors developed models to describe delay lines and compared the predictions of these theories with several experimental filters, including band-pass filters and dispersive delay lines, in the UHF range, and the frequency response is determined by the finger spacing and overlap of the interdigital comb structures used as input and output transducers.
Abstract: Acoustic surface waves offer several advantages in the construction of delay lines and filters in the UHF range. In these devices the frequency response is determined by the finger spacing and overlap of the interdigital comb structures used as input and output transducers. Models are developed to describe these devices, and the predictions of these theories are compared with several experimental filters, including band-pass filters and dispersive delay lines.

23 citations


Dissertation
01 Oct 1970
TL;DR: In this article, an analysis of static frequency changers with finite internal impedances is presented and the results obtained are verified by appropriate computer simulations, and the output voltage unbalance is computed under various conditions.
Abstract: The thesis is concerned with static frequency changers, using solid-state switching devices, capable of directly (i.e. without an intermediate dc link) converting polyphase ac power of a given frequency to single or polyphase power of a chosen frequency. The thesis consists of two parts. The first part, comprising five chapters, is devoted to the study of ideal frequency changers operated from ac Sources having zero internal impedance. The second part, comprising two chapters, considers sources with finite internal impedances . Chapter 1 introduces the basic concepts of static frequency conversion, outlines the basic mathematical models representing static frequency changers and defines the output and input performance indicators. Chapter 2 presents a detailed investigation of that class of three-pulse frequency changers which will be studied in the thesis. A large portion of the chapter is devoted to the study of output waveform generation. The mathematical tools of the investigation, existence matrices and modulating functions, are introduced and defined. Analytical expressions for output waveforms corresponding to various practical modulating functions are derived and the related performance indicators are computed. Assuming a given desired output performance, criteria for an optimal modulating function are established. It is proved that only one system can generate an output waveform conforming to the postulated prerequisites. This system is termed the "Unrestricted" Frequency Changer. Expressions for the input current waves are also derived in this chapter and the corresponding input performance indicators are determined . The concept of a new frequency changer having the unique property of providing unity input power factor, regardless of the load, is introduced. This system is termed the "Unity Power Factor" Frequency Changer. In Chapter 3 the previous results are extended to systems having pulse numbers which are integral multiples of three. Chapter 4 is devoted to the study of output voltage control. Three basic methods are analysed and detailed quantitative data for output voltage and input current waves, and the related performance indicators, are presented in graphical form. In Chapter 5 special aspects of static frequency changing are investigated. It is shown that the input displacement factor is variable. The concept of the "Controlled Displacement Factor" Frequency Changer is introduced It is proven that the naturally commutated cycloconvertor is theoretically equivalent to a particular "Controlled Displacement Factor" Frequency Changer. Chapter 6 presents a detailed analysis of the "Unrestricted" Frequency Changer, operated from an ac source with finite internal impedance. The basic conditions are defined and an outline is given of the techniques of symmetrical components used for the analysis. The input current, input terminal voltage and output voltage waveforms are expressed in terms of the input terminal impedance and the positive, negative and zero sequence components of the output currents. The equivalent sequence impedances and the output impedance matrix are derived . The output voltage unbalance is computed under various conditions and presented in graphical form. The relationships between the amplitudes of the unwanted components in the output waveform and the resonant frequency of the input terminal circuit are also graphically presented. The results obtained are verified by computer simulations. In Chapter 7 a similar analysis of the "Unity Power Factor" Frequency Changer is carried out . The computed data are also graphically presented. Again, the results are verified by appropriate computer simulations.

20 citations


Journal ArticleDOI
TL;DR: In this paper, it is shown that conventional methods of least squares polynomial curve fitting in the frequency domain allow estimates to be made of the moments of the impulse response of a linear system and a method by which the moments may be obtained from a perfect step response is proposed.


Patent
15 Apr 1970
TL;DR: In this paper, a system for transmitting binary information in the form of a frequency modulated signal is presented, which includes a digital-to-analog converter for converting a series of input pulses into an output signal consisting of incremental voltage changes.
Abstract: A system for transmitting binary information in the form of a frequency modulated signal is provided The system includes a digital to analog converter for converting a series of input pulses into an output signal consisting of a series of incremental voltage changes which is approximately in the form of a sine wave having a frequency determined by the frequency of the input pulses The system also includes a frequency selecting circuit for controlling the frequency of the input pulses to the digital to analog converter The frequency selecting circuit is operated by a binary input signal and controls the frequency of the output signal produced by the digital to analog converter A filter is connected to the output of the digital to analog converter to eliminate discontinuities from the output signal of the converter

Journal ArticleDOI
TL;DR: In this article, the authors measured the steady-state frequency response of air and water-filled aluminum spheres and cylinders in water and found that the non-dimensional frequency range is 24 ≦ka≦60.
Abstract: Measurements of pulse‐echo forms and steady‐state frequency response of air‐ and water‐filled aluminum spheres and cylinders in water are presented. These compare favorably with theoretical results. The nondimensional frequency (ka) range is 24≦ka≦60. Scattering paths defined by the cross‐sectional geometry of the targets are identified, and it is shown that it is constructive and destructive interference between the energy returned along the different scattering paths that generates the frequency response of the target as frequency is changed. Similarities in the backscattered echoes from spheres and cylinders at normal incidence due to similarities in the scattering geometry are described. Measurements of circumferential waves in spherical shells, believed to be the first reported for this target form, are presented.

Journal ArticleDOI
TL;DR: In this paper, a graphical display is given of numerical solutions of Iberall's theory over a wide range as a function of the Stokes number and of a dimensionless frequency.
Abstract: Air, carbon dioxide, and helium test data are presented for the experimental verification of Iberall’s analysis of the dynamic pressure response of viscous compressible fluids in rigid tubes with deadened volume termination against oscillatory frequency. A graphical display is given of numerical solutions of Iberall’s theory over a wide range as a function of the Stokes number and of a dimensionless frequency. Rapid engineering solutions are presented for the following problems: Given a tube, a chamber volume, and a fluid, determine the maximum frequency to be transmitted at ±10 percent amplitude distortion. Given a tube, a chamber volume, and a fluid, sketch the dynamic pressure response curve. Given a chamber volume, a fluid, and a specified frequency to be transmitted within ±10 percent amplitude distortion, plot allowable tube length against tube diameter.

Patent
03 Aug 1970
TL;DR: In this paper, a parametric frequency conversion is proposed for a sample of material, such as an alkali vapor, having an energy level system including first and second energy levels with a first transition frequency between them, and a third energy level with a second transition frequency in between the third level and one of the first level.
Abstract: Parametric frequency conversion is effected in a sample of material, such as an alkali vapor, having an energy level system including first and second energy levels with a first transition frequency between them, and a third energy level with a second transition frequency between the third level and one of the first and second levels. The sample of material is disposed in a resonant structure resonating at a frequency substantially equal to the first transition frequency, so as to be within an oscillating electromagnetic field of frequency substantially equal to the first transition frequency, established and maintained by application of a signal to the resonant structure. With a population imbalance between the first and second levels established in the sample as by optical pumping, a carrier beam of energy at a frequency substantially equal to the second transition frequency is directed through the sample. The resonant structure is designed to provide a wavelength within the structure for the field frequency that satisfies a phase-matching condition such that sidebands of the carrier beam are produced by modulation of the index of refraction of the sample, these sidebands differing from the carrier frequency by integral multiples of the field frequency. By appropriate polarizing means, the generated sidebands can be detected, or alternatively, a polarized component of the carrier beam modulated in intensity at the field frequency can be detected. Devices providing this parametric frequency conversion may be arranged to operate as stable, self-oscillating frequency standards or for other purposes such as microwave photon detection.

Patent
19 Mar 1970
TL;DR: In this paper, a frequency shift relaying system utilizing at least one transmitter which is normally transmitting its signal at a first or normal frequency and operable to shift the frequency of its output signal to a second or a third frequency is defined.
Abstract: A frequency shift relaying system utilizing at least one transmitter which is normally transmitting its signal at a first or normal frequency and operable to shift the frequency of its output signal to a second or a third frequency one of which is above and the other of which is below the normal or first frequency in response to a first or a second fault condition and utilizing at least one receiver means tuned to receive the transmitted signal at the first and second and third frequencies; the receiver means including a pair of output circuits operable in accordance with frequency of the transmitted signal, and effective to maintain a first of the output circuits in a first or a second operating condition in response to the transmission of the signal at the first or the second frequency and to maintain a second of the output circuits in a third or a fourth operating condition in response to the transmission of the signal at the first or third frequency.

Patent
C Hartmann1
12 Aug 1970
TL;DR: In this article, a plurality of interdigitated surface wave transducers are formed on a piezoelectric substrate along a common acoustic channel and the signal from the output transducers is rectified and then filtered to separate the r.f. component from the audio signal.
Abstract: Disclosed are apparatus for constructing a frequency discriminator utilizing surface wave devices. A plurality of interdigitated surface wave transducers are formed on a piezoelectric substrate along a common acoustic channel. The signal from the output transducers is rectified and then filtered to separate the r.f. component from the audio signal. A frequency discriminator having a preselected frequency response characteristic may be synthesized by constructing the individual interdigitated transducers to have the appropriate center frequency and number of pairs of electrodes.

Journal ArticleDOI
TL;DR: In this article, the theory of noise in transistors is applied to microwave transistors at microwave frequencies and an expression for the noise figure is obtained in terms of easily measurable parameters of the transistor.
Abstract: The theory of noise in transistors is applied to microwave transistors at microwave frequencies and an expression for the noise figure is obtained in terms of easily measurable parameters of the transistor. By making some simplifying assumptions, the expression for the noise figure can be reduced to a simple form containing only one parameter, which is useful for engineering applications. The effects of feedback and parasitics introduced by the encapsulation are taken into account. Friiss' formula is modified in order to take the effects of image frequency response on the measurements into account. A method of measuring gain and noise figure simultaneously is also described. Experimental verification of the theory up to 4 GHz is presented.

Journal ArticleDOI
TL;DR: In this paper, it was shown that the maxima of the combined response occur in clusters of micromaxima and that the distribution of all maxima is estimated by accounting for the number of micro-maxima introduced at each macromaximum.
Abstract: When a lightly damped linear oscillator responds to stationary wide‐band Gaussian excitation, the root‐mean‐square level and average frequency of the response are relatively insensitive to increases in the bandwidth of the excitation, but the average rate of maxima increases without limit. This phenomenon is interpreted by reexamining the exact distribution of the maxima and by giving a heuristic explanation based on decomposing the response into macroscopic and microscopic components. It is shown that the maxima of the combined response occur in clusters of micromaxima. The distribution of all maxima is estimated by accounting for the number of micromaxima introduced at each macromaximum.

Patent
Robert R. Hay1
04 Mar 1970
TL;DR: In this article, a variable frequency receiver scans a spectrum of frequencies from a signal source, and a cathode-ray tube (CRT) system detects and displays the amplitude of the signal source as a function of the frequencies scanned.
Abstract: A variable frequency receiver scans a spectrum of frequencies from a signal source, and a cathode-ray tube (CRT) system detects and displays the amplitude of the signal source as a function of the frequencies scanned. At any selected point of the amplitude response curve, the frequency scanning is momentarily stopped to produce a marker spot on the CRT screen. During the stop time, a digital counter counts the frequency of the variable frequency generator. Timing and logic circuitry controls the intensity of the marker spot and the length of the stop time in response to the counting time and the frequency scanning rate.

Journal ArticleDOI
TL;DR: In this article, the frequency response and electrical equivalent circuit of piezoelectric sources and detectors were derived from a one-dimensional formulation of the piezo-lectric relations, and Green's functions were used to obtain solutions for the generated stress waves in terms of the Fourier transform of the spatial distribution of piezolectric stress.
Abstract: This paper develops a theoretical method of obtaining the frequency response and electrical equivalent circuit of piezoelectric sources and detectors in which the piezoelectric stress hD is not spatially uniform. A wave equation is derived from a one‐dimensional formulation of the piezoelectric relations, and Green's functions are used to obtain solutions for the generated stress waves in terms of the Fourier transform of the spatial distribution of piezoelectric stress. Both acoustically matched and unmatched sources are treated. The complex electrical impedance is also developed. Expressions are obtained for the voltage and current generation in detection, and conditions for maximum power transfer are considered. Illustrative examples include sources with uniform, sawtooth, and Gaussian distributions of piezoelectric stress, both matched and unmatched. Optimization of response by choice of source distribution is illustrated. Arrays of sources are also treated, both with and without piezoelectric interactions between sources.

Journal ArticleDOI
TL;DR: In this paper, a complete solution for the small-signal high-frequency response of an idealized model of the insulated-gate field effect transistor is presented, and simple approximate results that apply only beyond the point of pinch-off are derived for operation at moderately low frequencies.
Abstract: A complete solution is presented for the small-signal high-frequency response of an idealized model of the insulated-gate field-effect transistor. The y parameters are found by solving Bessel's equation and are plotted as functions of signal frequency and the quiescent conditions. In addition to these general results, simple approximate results that apply only beyond the point of pinch-off are derived for operation at moderately low frequencies.

Journal ArticleDOI
J. Lamb1
TL;DR: A method is presented by which the frequency response of a system may be obtained directly from the response to a pseudorandom binary sequence without recourse to the calculation of the cross correlation function and its subsequent Fourier transformation.
Abstract: A method is presented by which the frequency response of a system may be obtained directly from the response to a pseudorandom binary sequence without recourse to the calculation of the cross correlation function and its subsequent Fourier transformation. The technique is ideally suited to digital computer processing but could also be carried out by equipment having a combination of features available in present day transfer function analyzers and noise generators.

Journal ArticleDOI
TL;DR: In this paper, a pressure transducer is described which was specially developed to measure wind pressures exerted on buildings, which gives an electrical output suitable for measuring pressures in the range ± 1200 N m−2 (± 25 lb ft−2).
Abstract: A pressure transducer is described which was specially developed to measure wind pressures exerted on buildings. The instrument, which gives an electrical output, is suitable for measuring pressures in the range ± 1200 N m−2 (±25 lb ft−2). The frequency response is such that pressure fluctuations lasting only 0·1 s can be recorded.

Journal ArticleDOI
P.N. Bapat1
01 Mar 1970
TL;DR: In this article, the effect of stator resistance on the damping and sychronsing torques and on the frequency response of an induction motor was investigated, and expressions for the frequency responses of the slip, torque and current fluctuations were developed for each fluctuation.
Abstract: This paper analyses the hunting nature of induction motors when driving oscillating loads. Proceeding from the equation of motion of the oscillating system, it is shown that the electrical torque developed by an induction motor has two components; the damping torque and the synchronising torque. Neglecting, at first, the effect of the stator resistance, and limiting the investigation to small oscillations, these two characteristic torques are functions of the mean relative slip and the hunting frequency. Expressions are developed for the frequency responses of the slip, torque and current fluctuations. Resonance frequencies are defined for each fluctuation. The effects of the stator resistance on the damping and sychronsing torques and on the frequency response are shown.

Journal ArticleDOI
TL;DR: In this article, an L-shaped chamber is proposed for minimizing the energy content of wind waves reflected from a floating bridge, where a linearized differential equation describing the hydraulics of the system has the form of a forced, damped oscillator; here, the term analogous to the natural frequency contains the key dimensions of the breakwater and an added mass.
Abstract: One method proposed for minimizing the energy content of wind waves reflected from a floating bridge incorporates an L-shaped chamber as a structural part of the bridge. The basic chamber has a vertical leg perforated with circular holes, the bottom is solid. A linearized differential equation describing the hydraulics of the system has the form of a forced, damped oscillator; here, the term analogous to the natural frequency contains the key dimensions of the breakwater and an “added mass” term. Solutions show the quantitative dependence of reflection coefficient upon the ratio of wave frequency to system (natural) frequency, wave camber, wall porosity, and chamber dimensions. The breakwater is most efficient (reflection coefficient as low as 0.2) when the frequency of the incident wave is near the system frequency, which provides a design link between incident wave and optimum breakwater dimensions. A prototype design example is included.

Patent
10 Aug 1970
TL;DR: In this paper, a phase comparator detects the drift and compares the phase thereof with a provided reference signal, the resultant error signal is then fed into the frequency generator to shift the frequency back to its original value.
Abstract: A digitally controlled frequency generator is provided having a selectively variable output frequency with crystal controlled accuracy and stability. Should the desired output frequency drift, however, a phase comparator detects the drift and compares the phase thereof with a provided reference signal. The resultant error signal is then fed into the frequency generator to shift the frequency back to its original value. In addition, should it be desired to change the output frequency of the frequency generator, a new program is applied to a variable program counter which produces an electronic response representative of the new program. This response is sensed by both the phase comparator and an acquisition circuit, the acquisition circuit providing signals to the phase comparator to achieve a "lock-in" of the system at the new desired frequency.

Patent
29 Jan 1970
TL;DR: In this article, a variable frequency audio frequency field modulator is employed for producing a variable-frequency sideband which can be stepped through the resonance line under analysis in precisely controlled small audio frequency increments under the control of a digital computer.
Abstract: The radio frequency spectrometer is disclosed employing a variable frequency audio frequency field modulator for producing a variable frequency sideband which can be stepped through the resonance line under analysis in precisely controlled small audio frequency increments under the control of a digital computer. The precisely controlled audio frequency for the modulator is derived from a radio frequency crystal and is divided by a certain divisor as determined by a computer which feeds the number into a counter which serves as the divider. The quotient output of the divider is employed to trigger a square wave generator, the output of which is filtered to produce a sinusoidal audio frequency output which is fed to the field modulator. The computer calculates new divisors for each of the successive audio frequency outputs.

Journal ArticleDOI
TL;DR: From the results of input-impedance measurements of a transmission-line system, the location, nature and magnitude of individual reflections can be calculated by using a finite Fourier transform as discussed by the authors.
Abstract: From the results of input-impedance measurements of a transmission-line system, the location, nature and magnitude of individual reflections can be calculated by using a finite Fourier transform. Resolution depends only on the frequency range. A computer program calculates and plots the distribution of reflections.