Showing papers on "Center frequency published in 1979"

An electrically-programmable switched capacitor filter

Abstract: Techniques are presented for the design of a second-order switched capacitor filter which has its frequency response parameters programmed by the application of digital control signals. Two different types of weighted capacitor arrays are used to achieve programmability in the center frequency, peak gain, and selectivity. Experimental results are given for an integrated NMOS version with eight logarithmically-spaced center frequencies programmed by a 3 bit digital word, and 64 Q and gain values programmed by two 6 bit words. The filter is designed so that binary changes in the sampling frequency provide new sets of center frequencies which smoothly continue the logarithmic progression. Since the response depends on monolithic MOS capacitor ratios, the accuracy and reproducibility inherent in the switched capacitor approach are retained.

Frequency adaptive, power-energy re-scheduler

Abstract: A frequency adaptive, power-energy re-scheduler (FAPER) that includes a frequency transducer that notes frequency or frequency deviations of an electrical system and logic means which controls and re-schedules power flow to a load unit in part on the basis of the deviations in frequency from a nominal frequency and in part on the needs to the load unit as expressed by an external sensor signal obtained from the physical system affected by the load unit

Optical fiber reflective filter

Abstract: The optical reflective filter is made from a photosensitive optical fiber having a cladding and a core including germanium. Refractive index perturbations are light induced in the fiber in the region of the guided light. The perturbations can be made to have a constant or a varying periodicity, or a series of constant periodicities. The filters are made from single mode or low order mode fibers having germanium doped silica or germania cores. The center frequency for reflective band or bands has a wavelength in the 400 nm to 550 nm range. The reflective band or bands in the filter can be shifted by stretching the filter.

Variable bandwidth filtering and frequency converting system

Abstract: A system which provides frequency conversion and continuously variable bandwidth control uses fixed filters to which opposite edges of the passband of the signal are applied in inverted frequency relationship. A channel contains the filters and three mixers to which injection signals derived from a single variable frequency oscillator and a fixed oscillator are applied to vary the bandwidth of the system without affecting the center frequency of the signal after processing in the system. The system may be designed to obtain either a variable bandpass or rejection band filtering characteristic.

Conversion of acoustic signals into visual signals

Abstract: For displaying spoken words as color pictures on a screen, each audio frequency, i.e. each acoustic sound, is assigned a respective color hue and each audio frequency spectrum a respective color mixture, by conducting acoustic signals through a three-channel triangular filter, each channel having a different central frequency, and controlling the intensity of a respective electron beam of a color television monitor as a function of a respective filter channel output.

Frequency transformations for linear-phase variable-cutoff digital filters

Abstract: The first- and second-order forms of a transformation for implementing a variable-cutoff linear-phase FIR filter are investigated. In the first-order case, correct constraints have been placed on the variable parameter A_0 ; it is pointed out that the cutoff frequency increases, while the cutoff slope decreases, monotonically with increasing A_v; A_0 = 0 corresponds to the prototype filter. The second-order transformation is shown to overcome these drawbacks without increasing the computational load or the number of variable parameters.

Method and device for detecting a specific spectral feature

Abstract: A method and device for detecting a narrow spectral feature in a sample is described. The method includes the steps of providing a beam of light having an optical frequency bandwidth which is narrow compared to the width of the narrow spectral feature and having a center frequency ω C which lies near the narrow spectral feature, phase modulating the beam of light with a single RF frequency to provide a pure FM spectrum having upper and lower sidebands, exposing the sample containing the narrow spectral feature to the modulated light so that only one of the FM sidebands probes the narrow spectral feature, photodetecting the light emerging from the sample to detect a RF beat at the specific RF frequency used for phase modulation, and electronically monitoring the amplitude of the RF beat signal to indicate the strength of the narrow spectral feature. A preferred embodiment of this invention is a multiplex readout device for hole burning memories. The device includes means for using a frequency modulated laser light with widely spaced sidebands arranged so that only one of each pair of upper and lower sidebands probes the frequency location of each hole. The device uses many simultaneous RF frequencies to drive the phase modulator and produce the light with FM sidebands which simultaneously probes all the hole locations of interest. The device includes photodetection means to receive the light after it has passed through the sample and phase sensitive multiplex analyzing means to process the electrical signals from the photodetection means to indicate the presence or absence of holes.

Interference eliminator in communication receiver

Abstract: In a communication receiver, a first mixing circuit, a first band-pass filter responsive to the output of the first mixing circuit, a second mixing circuit responsive to the output of the first band-pass filter, a second band-pass filter with a different center frequency from that of the first band-pass filter responsive to the output of the second mixing circuit, a first local oscillator, the output of which is applied to the first mixing circuit and a second local oscillator, the output of which is applied to the second mixing circuit. Various kinds of interference signals are eliminated by changing the output frequencies of the first and second local oscillators to thereby vary the effective bandwidth and center frequency of the signals which can pass through the receiver and thus eliminate interference. In addition, a third mixing circuit is responsive to the output of the second band-pass filter. The output of the third mixing circuit is applied to a notch filter, the notch frequency of which is effectively made variable by changing the frequency injected into the third mixing circuit and a demodulation circuit. Hence, by varying the effective notch frequency, further interference can be eliminated.

Miniature transmitter and method for making same

Abstract: There is disclosed a miniature hand-held radio-frequency transmitter. An operating frequency is determined by a lumped-circuit oscillator which feeds an antenna etched on the periphery of the circuit board. The antenna is tuned to a frequency which is slightly above the second harmonic of the operating frequency, it being the second harmonic which is radiated. By slightly mis-tuning the antenna, the effects of an enveloping hand are minimized. The clasping of the transmitter by a human hand results in the absorption of some of the radiated power, but hand-capacitance effects also shift the center frequency of the antenna characteristic toward the second harmonic of the operating frequency, thus increasing the radiated power. In this way the signaling range under free-space conditions is the same as that under operating conditions. The oscillator circuit can thus be adjusted for maximum power output under free-space conditions within the guidelines of F.C.C. Regulations, without the signaling range being appreciably reduced under operating conditions. The radiated frequency is not appreciably affected by hand capacitance effects because it is determined by a lumped-circuit oscillator.

Stereophonic sound synthesizer

Abstract: A system is provided which synthesizes stereophonic sound by developing two separate sound channels from a single monophonic sound source. A synthetic stereophonic sound system constructed in accordance with the principles of this invention may be advantageously utilized in combination with a visual display such as a television receiver. A monaural signal is applied as the input signal for a transfer function circuit of the form H(s), which modulates the intensity of the monaural signal as a function of frequency. The intensity modulated H(s) signal is coupled to a reproducing loudspeaker, and comprises one channel of the synthetic stero system. The H(s) signal is also coupled to one input of a differential amplifier. The monaural signal is coupled to the other input of the differential amplifier to produce a difference signal which is the complement of the H(s) signal. The difference signal is coupled to a second reproducing loudspeaker, which comprises the second channel of the synthetic stereo system. In accordance with a preferred embodiment of the present invention, a stereo synthesizer is utilized as the sound reproducing system of a television receiver, with the reproducing loudspeakers located on either side of the kinescope. The amplitude -vs- frequency response curves of the two output channels have crossover points at which the amplitudes of the two response curves are equal, which effectively centers sounds at these frequencies between the loudspeakers. Two crossover frequencies are chosen to occur at approximately the frequency of peak intensity of the human voice, and at the center frequency of the second (articulation) formant frequencies of the human voice so as to effectively center voices on the kinescope while preserving the ambience effect of other, more randomly distributed sound signals. Centering the second formant frequencies also provides increased quality in the reproduction of speech sounds.

Data tracking phase locked loop

Abstract: A counter of modulus n counts the oscillations of a variable frequency oscillator whose center frequency is n-times the nominal frequency of digital data having phase variations. The occurrence of a selected value of the count may be taken as a phase corrected clock for the digital data. Differences between successive values in the counter as pulses of the digital data occur indicate shifts in phase thereof, while the modularity prevents absent data pulses from contributing to the phase error. Successive counts are captured, made available as phase error information in digital form, and used to drive a digital-to-analog converter whose output controls the variable frequency oscillator.

Wave propagation experiments at medium frequencies between two ionospheric satellites, 3. Z mode pulses

Abstract: Intersatellite radio wave propagation in the lower-frequency branch of the extraordinary mode, or Z mode, has been studied using data recorded by the Isis I and Isis II topside sounder spacecraft during a rendezvous near the north pole. The working frequencies, near 1.0 MHz, lay between the gyrofrequency and the upper hybrid resonance frequency, the former being greater than the plasma frequency. In contrast to the 100-µs length of the emitted pulses, the received pulses were stretched to about 10 ms and had sharp rising edges. At any given time the range of transmitted frequencies for the Z mode was limited. The central frequency of this ionospheric passband and the time delay of the leading edge of the pulses both increased monotonically with time as the two-satellite geometry changed. These observations are in good agreement with the predictions of ray optics applied to a smoothly varying medium. However, the detailed pulse shape was quite unlike the theoretical shape predicted under the WKB approximation; this suggests strong scattering. Also, received pulses occasionally had quasi-sinusoidal modulation envelopes. As in previously reported results for the whistler mode, ionospheric irregularities appear to strongly influence the propagation of a wave that can have large refractive indices.

An electrically programmable analog NMOS second-order filter

Abstract: A fully-integrated NMOS electrically-programmable switched capacitor filter will be described. Digital words independently set the filter gain and Q between 1 and 65 in steps of 1, and the center frequency can be set to 1 of 8 values which span one frequency octave.

High speed adaptive clutter filter

Abstract: Method and apparatus for eliminating the effects of clutter in a coherent pulsed Doppler radar including determining the center frequency of the clutter and periodically moving the local oscillator frequency so that the clutter is shifted out of the Doppler filter passband, leaving only targets in the passband.

Microprocessor controlled digital detector

Abstract: of the Disclosure In the digital detector the center frequency and bandwidth of a digital filter is controlled by a microprocessor. Amplitude information for the original input signal may be preserved or a simple threshold of energy may be detected within a bandpass. The microprocessor scans a selected frequency spectrum by digitally changing the decoding data controlled by software. This detector in conjunction with a scanning algorithm permits data acquisition in addition to energy detection, data acquisition being the process of controlling an incoming signal within a bandpass by moving the center frequency and band-pass of the filter and generating a corresponding error signal as the feedback control signal.

PVF 2 Polymer Microprobe

Abstract: This paper describes the design and performance of a PVF2 microprobe for use in mapping the pressure field from arrays. For medical applications, the probe must have short pulse response (i.e., broad, flat bandwidth) in addition to high sensitivity, low noise, and a wide acceptance angle. The factors that influence critical parameters, such as ringing and delayed reverberations, are specifically discussed. The probe has a center frequency of about 3 MHz. It consists of a 1.5 mm diameter disc of PVFZ polymer (30 pm thick) operated well below its resonance to obtain very broad frequency response. The PVFz is completely encased in a metal cylinder to shield it from spurious electromagnetic interference and to protect the polymer from possible corrosion by external fluids. An FET amplifier is integral to the probe housing. The experimental performance of the probe is compared with theoretical predictions, acoustically and electrically. It is also compared with the performance of other probes, including a laser pellicle system, for pulse fidelity and signal-to-noise ratio.

Compensation for Diffraction in SAW Filters

Abstract: It is well known that diffraction can cause serious errors in the response of a SAW transversal filter, and that such errors can be reduced by corrections in the filter tap strengths and positions. In the past these tap perturbations have typically been obtained using calculations made at the center frequency only. However, recent fast methods for the calculation of Fresnel diffraction assuming "parabolic" anisotropy allow iterative algorithms to be practical for optimizing the response. Herein these methods are utilized in an iterative correction method which improves the frequency response by matching bandlimited responses in the tine domain. Trial example designs which initially had severe errors due to diffraction were greatly improved by corrections obtained using this algorithm, whereas the degree of correction achieved using the center frequency method was much less. Both tap position and amplitude corrections are found to be necessary.

Digital filter bank detector

Abstract: Disclosed is a signal detector including a bank of digitally synthesized rowband filters all having the same shape of frequency response and differing only in center frequency and which are implemented by time domain data processing. The invention is comprised of: a signal conditioner, an envelope weighting computer, a Fourier transform processor and a post-detection processor. Resulting therefrom is a bank of 16 contiguous narrowband filters having high selectivity along with a corresponding bank of envelope detectors of wide dynamic range which incorporates center frequency acquisition and tracking. Following detection, a matched filter capability is included to provide correlation and data regeneration so that coded FSK data burst signals can be extracted in real time from noise, interference, and jamming signals which would otherwise affect signal detection.

Jamming wave rejecting device

Abstract: A narrow-band rejection filter inserted in a received signal path is arranged so that its rejection frequency may be changed by a control signal; the narrow-band rejection filter is controlled so that its rejection frequency may substantially coincide with the center frequency of a jamming wave; thereafter, the phase difference between signals on the input and the output side of the narrow-band rejection filter is detected; and the abovesaid narrow-band rejection filter is controlled by a signal corresponding to the phase difference so that its rejection frequency may automatically coincide with the center frequency of the jamming wave.

Time Domain Analysis of SAW Reflectors

Abstract: A time domain analysis of high-reflectivity SAW reflector arrays is shown to yield values of stripe reflectivity, center frequency, and effective reflections plane penetration. An examination of the approach shows that the results are insensitive to device losses, RF coupling, and transducer response. Experimental results confirm the validity of the technique.

Frequency characteristic adjusting circuit

Abstract: In a frequency characteristic adjusting circuit having an arrangement of at least one adder, a filter circuit and feedback and/or feed forward means the transfer factors of which and the peak or dip of the filter circuit are freely selectable. Adjustment of the center frequency and Q are independent.

Microwave moisture measurement device with commutable measuring range

Abstract: The generator for the Mikrowellenmesanordnung consists of a frequency modulated oscillator which feeds a Hohlraummesresonator in a transmission arrangement. The test sample is located in the center of the resonator, from the resonator The transmitted microwave signal is detected as a peak amplitude detector circuit, the change of the signal of the goods factor change by the introduced sample corresponds. To expand the Mesumfanges the center frequency of the microwave oscillator through several stages can be switched. In the frequency switching each be another type of field is then excited in the measuring resonator, so that the sample for measurement of high water contents in a node region of the electrical measuring field for measuring low water contents and is in a maximum of the electrical measuring field.

Influence of atmospheric absorption on the propagation of bands of noise

Abstract: As a band of noise propagates through the atmosphere, atmospheric absorption attenuates the higher frequencies in the band more rapidly than the lower frequencies. For large propagation distances, atmospheric absorption shapes the spectrum such that most of the acoustic energy is in the lower part of the band. When this occurs, the effective atmospheric absorption coefficient for this band of noise is less than when the energy is evenly distributed over the band. When a real filter is used to examine the received spectrum, the problem becomes even more complex since the filter does not cut off completely at the nominal lower frequency limit for the band. The equations governing the attenuation and spectrum analysis of noise under these conditions have been derived and a numerical integration process has been used to obtain quantitative results. It is shown that predicting observed values of atmospheric absorption loss for bands of noise involves two correction factors which are added to single‐frequency absorption loss to define the effective attenuation for the band of noise. The first correction factor ΔI accounts for the difference between the attenuation predicted over a given path in a homogeneous atmosphere for a pure tone at the geometric center frequency of an ideal filter band, and the actual attenuation over the same path for the same ideal band of noise. The second correction factor ΔF accounts for the difference between the band level measured at one point with a practical filter with finite transmission outside the nominal filter pass band and the true band level measured at the same point with an ideal (rectangular) filter. Representative calculations show that the sum of these corrections become substantial when the product of distance, in km, and the square of frequency, in kHz, exceeds about 4 to 40 for octave and one‐third octave band filters, respectively. Although the net effect of such corrections will generally be small for overall frequency weighted‐noise levels (e.g., perceived noise level), the errors in diagnosing spectral detail in noise signatures of distant sources, such as aircraft, can be important.

Amplitude equalizer circuit

Abstract: An amplitude equalizer circuit utilizing active components in which unidirectional functional tuning of the amplitude, bandwidth and center frequency, may each be adjusted by varying a single resistance for each parameter. This eliminates the need for ganged-potentiometers or altering a plurality of interacting components.

Signal processing system

Abstract: An improved system for processing an electrical velocity information signal in a velocity detecting system in which a detector is utilized for developing an electrical information signal, such as a Doppler signal, having a characteristic (e.g. frequency) that varies systematically with the object's velocity. A converter develops an oscillatory signal having a frequency which varies in accordance with the velocity information signal characteristic. A tracking filter having a center frequency that varies with the oscillatory signal filters all frequencies other than the center frequency. A signal generator is responsive to the frequency of the signal passed by the tracking filter for generating an output signal having a frequency which is a preset ratio relative to the center frequency, whereby the output signal of the system is relatively noise-free and has a frequency which represents the velocity of the object being detected. Another feature of the disclosed embodiment of the invention utilizes a switching network comprising a pair of flip-flops and a pair of shift registers which are responsive to the oscillatory signal passed by the tracking filter and to an oscillatory signal generated by a voltage-controlled oscillator for alternately charging and discharging a storage capacitor which is coupled to the inverting input of an operational amplifier used as a comparator. A variable resistance is placed in either the charging or discharging path and the output of the op amp is used as an error voltage to control the frequency of the VCO to thus provide a frequency locked loop.

Multi-pole crystal filter and method of improving the frequency response

Abstract: A crystal filter including at least one acoustically coupled crystal with at least three resonators thereon with an impedance block connected between the input and output of each crystal and the input and output phases of each crystal being adjusted so that attenuation zeros symmetric about a center frequency are produced to improve the frequency response of the filter without increasing the number of poles.

Some recent advances in integrated crystal filters

Abstract: Integrated crystal filters-monolithic, tandem monolithic, and hybrid monolithic (polylithic) quartz crystal filters-are widely used in HF, VHF, UHF, and satellite communications equipments, in both commercial and military, in telephone FDM equipment, and in a number of other applications including frequency synthesizers and airborne navigation aids. Frequencies range from 5 to 180 MHz and occasionally to 250 MHz. Maximum inductorless bandwidths are usually 0.25 to 0.35 percent of center frequency below about 30-35 MHz and less at higher frequencies where overtones must be used. In the past decade, piezoelectric resonator theory has been extended to model accurately the linear and nonlinear behavior of monolithic filter devices. While most integrated crystal filters are all-pole networks, techniques for the design of filters with real and complex frequency transmission zeros are finding increasing application. A number of examples of current production filters are presented.

Compression network displaced phase center electronic correlator

Abstract: A synthetic array processing system which simultaneously develops a plurality of parallel synthetic beams, each beam being spaced in time along a flight path and having different effective phase centers. Means are provided for storing and reading out a plurality of doppler history signals from each of a plurality of range positions and in one embodiment of the subject invention the read out sweep lengths are programmed as a function of the square root of range to allow use of a constant slope focusing oscillator. The center frequency of the doppler histories are offset as a predetermined function of range and applied through a focusing mixer to a time compression filter circuit. A plurality of compressed pulses provided at the output terminal of the compression filter circuit, each represent a doppler history of a point reflector and a synthetic beam and these signals are applied to a display which may be controlled as a function of the square root of range.