Showing papers on "Center frequency published in 1971"

Multiparameter sensitivity in active RC networks

Abstract: A new statistical multiparameter measure of sensitivity is presented. The new measure realistically accounts for component tolerances and component tolerance correlations and is shown to be particularly useful in the design of integrated circuits. For illustration the measure is used to analyze several high- Q low-sensitivity networks. It is shown that for high- Q networks the new measure is readily interpreted in terms of the Q and center frequency sensitivities of the circuit elements. The measure is also generalized for high- Q analysis to account for the error in realization due to the ampliler pole as well as the element variations. This enables an evaluation of the circuit response versus center frequency to be performed.

Frequency averaging controlled false alarm rate (cfar) circuit

Abstract: A frequency averaging CFAR circuit having a digital filter bank for receiving radar doppler echoes that are conducted sequentially into serially connected metal oxide semiconductor (MOS) type delay shift register networks with the outputs of shift registers on opposite sides of a center frequency register being summed to produce an average value applied to a threshold circuit together with the output of the center frequency register output to cause the threshold level to vary in accordance with the averaged noise and clutter signals and to detect a target signal whenever the output of the center frequency register exceeds the threshold.

Variable center frequency filter

Abstract: A system for analyzing the frequency response of apparatus such as rotary machinery includes a plurality of vibration sensors which are multiplexed to apparatus utilizing amplitude sensitive phase detection with a two phase clock operating at a selected frequency at which the analysis is to be performed. The two phase-detected waves are passed through vector solution apparatus which provides the summation of the rectified waves and a weighted rectified difference in the rectified waves. Various two phase clock controls and filters are disclosed.

A 360/spl deg/ Reflection-Type Diode Phase Modulator (Correspondence)

Abstract: A 360/spl deg/ phase modulator using two series-tuned varactors in a parallel connection is described. The design minimizes the change in total phase shfit with frequency and gives a small attenuation ripple. The modulator is centered at 2 GHz and gives a total phase shift at 360/spl deg/ at the center frequency, an attenuation ripple of 1.3 dB over a 10-percent bandwidth and a 7/spl deg/ decrease of phase shift at the band edges.

Surface wave transversal frequency filter

Abstract: Elastic waves propagating at the surface of a solid substrate are generated by a transducer-filter of interdigitated electrodes patterned to pass a particular wavelength of frequencies at an established center frequency. Interdigitated electrodes of the filter may be either uniformly spaced one-half wavelength apart or spaced to produce a desired function. The overlapping length of the electrode configuration for each filter varies in accordance with a weighting function usually approximating sin x/x. To generate an output signal having a desired frequency distribution between band pass and band stop regions, each filter comprises two sections of an array of three or more taps of interdigitated electrodes. These taps correspond to a fundamental, third, fifth, etc., time harmonic of the band passband stop periodicity. The two sections are arranged back to back on the substrate, that is, with the fundamental tap of each section adjacent and the highest time harmonic tap of each section at the ends of the filter. An interchange of the band pass and band stop regions is accomplished by splitting each filter and connecting the individual sections to a reversal switch. By selective programming of a plurality of filters, a particular frequency will be selected and passed through an array of such filters.

Coaxial Bandpass Filter Design

Abstract: A technique is described for synthesis of coaxial bandpass filters based on an improved design of impedance inverters. This technique is applicable to filters having bandwidths between approximately 1 percent and 20 percent of the center frequency. The inverter used to realize the filters is a section of either low-Z/sub 0/ line or high-Z/sub 0/ line and is synthesized as a distributed element rather than as a lumped shunt capacitance or lumped series inductance, respectively. Three methods of accommodating the discontinuity capacitance associated with an abrupt change in the characteristic impedance are reviewed. The first two methods are most useful for filters with a fractional bandwidth/spl gsim/ 10 percent and the third for a fractional bandwidths /spl lsim/10 percent. Numerical and experimental verification of the design procedure is provided.

Theory of an ultra-broad-band optical dielectric waveguide coupler system

Abstract: A technique is described for operating a prism to dielectric thin-film waveguide system over a wide frequency band from a conventional broad-band source of the dye-laser type. The continuous coupling bandwidth can extend, typically, over a frequency range of twice to three times the center frequency. The experimental tolerances have been established and are shown to be within the capability of present-day technology.

Adaptive digital frequency discriminator

Abstract: First and second digital filters having similar transfer characteristics are arranged to have their center frequencies tuned to either side of a composite center frequency so that their characteristics are symmetrical relative to that composite center frequency. The digital filters receive a common input signal known to vary slightly in frequency; and each filter generates an output signal representative of the component of the input signal within its bandwidth. The output signals of the filters are detected and one is subtracted from the other to generate an error signal which is representative of the difference between the frequency component of the input signal and the composite center frequency of the digital filters. A feedback loop varies the sampling rate of digital filters to minimize the error signal, indicating that the composite center frequency of the digital filters is equal to the frequency of the input signal. The system thus tracks the frequency of the input signal.

Spectrum analysis systems using optical correlation techniques particularly useful in pulse modulated doppler radar systems

Abstract: System of spectrum analysis using optical correlation in real time with non-coherent light, comprising a moving plan with tracks, each track representing a frequency corresponding to the central frequency of a sample of the spectrum analyzed considered displaced in frequency by a predetermined frequency value DELTA F. Transducer means convert the signal which frequencies are within the spectrum to be analyzed, into an optical modulated beam; photocell receivers in a correlation plane are followed by identical filters centered on DELTA F and having a band corresponding to the width of a sample. The filter is followed by a detection circuit. The invention is particularly applicable to a pulse Doppler radar system.

Process of forming time-variant filters for filtering seismic data

Abstract: The specification discloses a process of forming a set of timevariant filters from an input set of filters having predetermined start times. The center frequency and envelope frequency of the input filters are determined and filters are interpolated between adjacent input filters, based upon the difference in center frequency between the adjacent input filters. In the embodiment disclosed, the number of filters interpolated between adjacent input filters is equal to the number of integer frequency changes between adjacent input filters minus one. The envelope frequencies of the interpolated filters are determined by a linear interpolation between the envelope frequencies of adjacent input filters and the interpolated filters are placed at equally spaced time intervals between adjacent input filters. The length of the input filters and interpolated filters are determined as inversely proportional to their envelope frequencies. The time responses of the filters are determined and truncated with a special truncator.

Digitally controlled rf sweep generator

Abstract: An RF signal is inputted to a digitally controlled RF phase shifter. The RF phase shifter is responsive to digital signal commands and operates to shift the phase of the RF input signal and its frequency in response to the digital signal input. The relationship between change in frequency versus change in phase over a time interval requires that the phase shift rate of change be varied parabolically for the frequency to change linearly with time. The phase change is, therefore, accomplished by parabolically incrementing the digital count, relative to time. The RF frequency is thereby linearly swept about the RF center frequency.

Detector of false vor direction indication

Abstract: A monitoring means for detecting asymmetrical location of intermediate frequency bandpass filter output signal components in a VOR receiver to annunciate a mistuning condition which may give rise to false VOR bearing determinations. A frequency discriminator, at the IF bandpass filter center frequency, determines the general nature of the signal passing the filter, and the discriminator output, either AC or DC, is used to operate threshold sensitive alarm indication means.

Signal seeking tuner control system

Abstract: A tuner control having three discrete states for raising, lowering or maintaining frequency of a voltage controlled tuner. Oppositely phased bi-polar error voltages derived from a discriminator are applied to the input terminals of the control. When the converted frequency outputted by the tuner is at a desired value, indicating reception of a carrier signal, no error voltage is produced and the signal-seeking device is disabled. However, when the converted signal deviates from a desired frequency range, an error voltage is derived. The phase and polarity of the error voltage which is then developed causes the network to produce either a first, higher or a second, lower voltage to cause a controlled voltage applied to the tuner to rise or fall. The tuner is thus caused to home in on a desired, central frequency range. When the desired frequency range is attained, the error voltage recedes to a level which allows the tuner control to become disabled once more.

Highly selective filter circuit

Abstract: A filter circuit providing extremely sharp attenuation at a selected frequency cutoff point. The sharp attenuation is obtained through the use of several ganged or cascaded active filter sections whose characteristics are combined in an additive fashion to provide an extremely flat passband characteristic and a sharp attenuation curve at the desired frequency cutoff value. Filter circuits of this design may be used in combination in the electrocardiograph field to isolate the R-wave of the PQRS complex of an electrocardiogram resulting in trigger signals of a high degree of accuracy for purposes of R-wave detection and evaluation.

Frequency selective network

Abstract: A frequency selective network employing negative and positive feedback in conjunction with an inductorless bandpass or reject filter to provide a stable bandpass or reject characteristic. Sole adjustment of the negative feedback gain varies the center frequency of the filter over a wide frequency range without appreciably affecting the bandwidth. An all electronic frequency selective network is achieved by providing a voltage controlled variable gain stage as the means of adjusting the feedback gain.

Frequency-stabilized laser arrangement

Abstract: A laser arrangement for the stabilization of the frequency of a one or two mode gas laser, particularly a short He-Ne laser, where the stimulated medium is arranged between a fixed mirror and a mirror which is displaceable by means of a piezo-ceramic in the axial direction of the laser, the laser beams discharging from the partially transparent fixed mirror being used to generate a DC voltage control signal which is proportional to the frequency deviation of the laser beams with respect to the central frequency of the amplifying transfer, returning the resonator to the central frequency by way of the piezo-ceramic, in the control circuit which contains a photosensitive element and subsequent amplifiers and phase sensitive demodulators. The stimulated medium is arranged, at least partially, in a magnetic coil which is excited to generate an axis-parallel alternating magnetic field. A lambda 4 plate and a polarization device are arranged between the fixed partially transparent mirror and the photo-sensitive element.

Bandpass filter including monolithic crystal elements with resonating portions selected for symmetrical response

Abstract: A bandpass filter circuit includes a pair of dual coupled monolithic crystal filter elements each formed by a wafer of quartz, or other piezoelectric material, with two pairs of electrodes thereon, each pair cooperating with the wafer to form a resonating portion. The two dual coupled crystal elements are cascade coupled, with the signal to be selected applied to the first pair of electrodes on the first element, then coupled from the second pair of electrodes of the first element to the first pair of electrodes of the second element, and the selected signal derived from the second pair of electrodes of the second element. To reduce the requirement for inductive coupling elements in the filter, the monolithic filter elements are constructed so that the resonant frequencies of certain resonating portions thereof are below the mesh frequencies of the filter, which are at the center frequency of the filter. To provide a filter response characteristic having improved selectivity, i.e. steep skirts, a capacitor is bridged across the electrodes of at least one of the crystal elements. This causes a non-symmetrical response, and to correct this, the filter elements are constructed so that the resonant frequency of one resonating portion of at least one of the crystal elements is increased.

Frequency band shifter

Abstract: A frequency band shifter for shifting a selected frequency band in a complex waveform, which frequency band is translated with its relative frequency, phase and amplitude relationships maintained to a reproduced lower frequency and, if desired, to a smaller frequency band for analysis, which translation is processed by manual or digital control with a master local oscillator control clock that provides protection against drift in frequency and phase throughout the system.

Surface-wave dispersion with a time bandwidth of 1000

Abstract: Experimental results are presented that were obtained in the initial evaluation of a multifunction surface wave delay line designed for a time bandwidth product of 1000. Two types of lines that operate on ST-cut quartz substrates are described. One type utilizes three identical coded 25-Ms transducers symmetrically arranged so that both positive and negative chirp slopes are obtained in addition to zero slope or flat delay. The other type of line provides positive and negative slopes with separate transducer pairs approximately coded. Lines of both types are designed to operate at a center frequency of 60 MHz with a 20-MHz bandwidth and a 50-/spl mu/s time delay. Tests demonstrated time-bandwidth product capabilities of 785 and 900, with time dispersions of 45 and 50 /spl mu/s, respectively, and bandwidths of 18 MHz. Time multiplexing and spectrum inversion were used to measure pulse compression performance. Measured sidelobe levels of -9 to -18 dB indicated nonlinearity and incidential weighting present in these lines. In addition, surface-wave delay-line performance was measured with a 56-/spl mu/ delay, a nominal 10-MHz bandwidth, and -15-dB time sidelobes. The lines were also temperature tested for center frequency time-delay stability. Results indicated time-delay variations of less than 2 ppm//spl deg/C, which is an order of magnitude improvement over those in YX-cut quartz substrates lines.

Large Time-Bandwidth Product Microwave Delay Line.

Abstract: : The objective of the program is to develop a large time-bandwidth product tapped delay line employing acoustic surface waves at microwave frequencies. The essential components of this device include tuned interdigital transducers, surface wave amplifiers and air gap couplers all operating at a center frequency of 1.0 GHz. The report describes achievements in each development area and includes measured data for a five tap 30 microsec long surface wave delay line. (Author)

Maximally linear bandpass frequency discriminator

Abstract: A maximally linear bandpass approximation is introduced for use in frequency discriminator applications It is strictly linear near some center frequency and has a simple cascade active RC realization

Two‐Tone Loudness Summation and the Spectra of Comparison Sounds

Abstract: The loudness of monaural two‐tone complexes centered at 1000 and 2000 Hz was measured as frequency separation varied from 1 to 8 critical bands. Subjects matched these complexes to comparison sounds consisting of (1) a tone at the center frequency of the complex, (2) a two‐tone complex whose components were separated by a single critical band, or (3) a tone set at the same frequency as the higher or lower frequency component of the complex. Measurements were made at an over‐all SPL of 60 dB. Normal amounts of loudness summation were measured when the comparison sound consisted of either a single tone at the center frequency or the critical band complex. Less loudness summation was measured, especially at the widest frequency separations, when the comparison sound was a single tone set at the same frequency as one of the components of the complex. [Supported by funds from the National Institute of Child Health and Human Development.]

Bandwidth and center frequency testing using predetermined amplitude points

Abstract: A frequency responsive device, such as a tuned amplifier, filter, etc., is tested for center frequency and bandwidth. A decreasing sweep frequency signal is applied to the device and the output detected. A waveform analyzer produces a first pulse when the detected signal reaches a predetermined amplitude and a second pulse when the detected signal falls below the predetermined amplitude. The first and second pulses trigger or operate a counter which counts the cycles of sweep frequency signal for a predetermined duration in response to each pulse. The sum in the counter is indicative of the center frequency. The count after the first pulse is multiplied by 2 and added to the complement of the sum in the counter after the second pulse to produce a remainder which is multiplied by 2 to indicate the bandwidth.

Tunable variable bandwidth magneto-elastic filter and method

Abstract: This disclosure involves one or a plurality of cascaded YIG or similar magneto-elastic media propagating elastic waves transduced from a band of electromagnetic waves and having special magnetic field curved profiles and variable bias magnetic fields applied thereto such as to couple out or absorb the energy of specified variable frequencies to-be-filtered, by effecting conversions of the elastic waves of such specified frequencies only to spin waves. Cascaded units enable a bandpass characteristic to be produced that may be varied in width and center frequency.

Method of adjusting electrical filters

Abstract: 1,253,306. Waveguides. STANDARD TELEPHONES & CABLES Ltd. 19 March, 1969, No. 14391/69. Heading H1W. [Also in Division G1] A method of adjusting a multi-cavity filter consists in detuning the sections of the filter and monitoring the frequency characteristic of the energy reflected from the filter as the sections are tuned one at a time starting from the input end. The filter may consist of waveguide cavities coupled by irises, or it may be a comb-line filter forming the output of a frequency multiplier. As a preliminary step, all the sections of the filter are detuned, e.g. by screwing in the tuning screws to their fullest extent, so that all input energy is reflected. A recurrent train of continuous oscillations swept over the intended pass-band is applied to the input and the frequency curve of the reflected signal observed on an oscilloscope. As the first resonator is tuned and becomes transmissive a dip in amplitude is observed and the tuning is adjusted to position this dip at the centre of the frequency characteristic. The procedure is repeated for the second, third &c. cavities, the last cavity being tuned by monitoring the output response of the filter. The frequency characteristic consists of an array of dips which are arranged symmetrically about a central frequency. Further adjustment of the screws is then made to improve the shape of the frequency response curve. The input to the filter may comprise a diode frequency-multiplier fed through an impedance-matching LC network and choke tuned to the output frequency of the multiplier. This prevents feedback of the output. As a preliminary to adjusting the filter, the LC network is adjusted by observing and shaping the frequency response curve of the whole arrangement.

70-MHz Solid-State Frequency Modulator

Abstract: This report describes the development of a wide-band frequency-modulated oscillator with the following design goals: 1) direct modulation at a center frequency of 70 MHz; 2) instantaneous frequency deviation-±10 MHz; 3) linearity-within ±1 percent to ±10 MHz; 4) deviation rate (baseband response)-±0.5 dB from 100 Hz to 10 MHz; 5) provision for automatic frequency control.