Showing papers on "Center frequency published in 1982"

Wide-band distributed rf coupler

Abstract: A wide-band distributed coupler for coupling rf energy from an input waveguide into a tapered interaction waveguide in a traveling-wave amplifier comprising a plurality of channel filters connecting between the input and interaction waveguides, with each filter coupled to the interaction waveguide at the appropriate cross-sectional position along its tapered length where the interaction waveguide cutoff frequency approximately matches the wave frequency propagated by the filter. Each filter comprises, in one embodiment, a main coaxial cavity tuned to a distinct center frequency, a first simple isolation cavity for coupling rf energy between the input waveguide and the main cavity, and at least one second simple isolation cavity for coupling energy between the main cavity and the tapered interaction waveguide. This coupler is compatible both in bandwidth and geometry with the tapered interaction waveguide.

Oscillation center frequency tuning, quantum FM noise, and direct frequency characteristics in external grating loaded semiconductor lasers

Abstract: Simple analytical expressions for the oscillation frequency, quantum FM noise spectrum, oscillation power spectrum, spectral linewidth, and direct optical frequency modulation efficiency in semiconductor lasers with external grating feedback are presented. Experimental results for the grating loaded AlGaAs lasers are in good agreement with the theoretical predictions. Remarkable reduction in spectral linewidth to less than 50 kHz is achieved by feeding back only 10-3of the output power. Oscillation frequency stabilization, frequency jump behavior, and reduction in direct optical frequency modulation efficiency are also discussed.

Ultrasound recognition in house mice: key-stimulus configuration and recognition mechanism

Abstract: 1. We determined the ability of lactating female house mice (Mus musculus, strain NMRI) to recognize natural ultrasonic calls (USC) of their pups or synthesized USC models. Recognition was shown by the mice preferentially responding to these sounds in the presence of an alternative sound signal. 2. Preferred USC models had total durations (flat top + rise and fall times) between 30 and 270 ms. Shorter and longer ones were not preferentially responded to. Response to USC models with major frequency components above 40 kHz was the same as that to natural ultrasonic calls of mouse pups. 3. The key-stimulus configuration for recognition of mouse pup ultrasound in the frequency domain can be characterized as pulses of sound energy in a narrow frequency band in the ultrasonic range with significantly less energy in adjacent frequency bands. The decisive units for call recognition are frequency bandwidths which are almost identical in width with the critical bands of hearing, a measure of frequency resolution in the auditory system. The critical frequency bands for the recognition of USC models have a bandwidth of 22.5 kHz at a center frequency near 50 kHz (the critical band of hearing is 22 kHz wide), and 15 kHz at a center frequency near 40 kHz (the critical band of hearing is 18 kHz wide). We conclude that the discrimination of ultrasonic mouse pup calls from other mouse calls and their recognition is most probably directly related to the critical band analysis in the auditory system.

Single sideband quadricorrelator

Abstract: A supplementary frequency acquisition circuit in the form of a frequency difference detector called a single sideband quadricorrelator is provided. When used in conjunction with a phase-locked loop of a conventional spread spectrum demodulator, this circuit allows for the rapid acquisition and accurate tracking of the center frequency of a spread spectrum suppressed-carrier bi-phase PSK signal. The invention cancels spurious sum and difference frequency components impulsed at the data rate as well as double difference frequency component and other modulation products without filtering. By eliminating the need for supplementary low pass filtering, the present invention provides rapid acquisition of the suppressed-carrier signal and provides a frequency difference output at twice the amplitude of comparable prior art systems. The tracking error or frequency difference (ω i -ω o ) is obtained by differentiating the quadrature signal and multiplying by the in-phase signal component rotated 180° in phase. This product is summed with the output obtained by multiplying the differentiated in-phase signal component with the quadrature signal component.

Method and apparatus for low frequency active attenuation.

Abstract: A low frequency attenuation method based on the virtual earth system has the driver feeding cancelling waveforms into a partially closed volume which contains the microphone of the virtual earth feed-back loop. The volume preferably has a maximum dimensions which lies between one third and one seventh of the wavelength of the highest frequency to be nulled. An outlet port of the volume can be tuned to the center frequency of the band of frequencies to be nulled.

Ultrasonic measuring method

Abstract: A method for measuring the physical characteristics of an object through the use of an ultrasonic wave, which comprises the steps of transmitting an ultrasonic pulse to the object, receiving a reflected wave from the object, analyzing the spectrum of a parameter representing the strength of the reflected wave and obtaining a center frequency of the spectrum to measure the physical characteristics of the object. The center frequency is used as a function of distance or time to obtain its differential or difference coefficient, or a computation similar to that for an X-ray computer tomography is carried out, thereby to obtaining an attenuation slope and other data to be used as the physical characteristics of the object.

Quarter-Wavelength Coupled Variable Bandstop and Bandpass Filters Using Varactor Modes

Abstract: A quarter-wavelength coupled bandstop filter rising varactor diodes for the 6-GHz band has been proposed and tested. Frequency giving maximum attenuation varies from 4.4 GHz-7 GHz. A quarter-wavelength coupled variable bandpass filter using varactor diodes for the 4-GHz band is also proposed and tested. The passband width varies from 730 MHz-1.22 GHz. The center frequency of the filter can also be changed.

Wideband modulation sensitivity compensated voltage controlled oscillator

Abstract: A control oscillator voltage, the modulation sensitivity compensation broadband compensates automatically and continuously over a wide bandwidth modulation sensitivity changes resulting from changes in the center frequency of the oscillations. The oscillator comprises an array direction (30) coupled to the input of a network oscillator (20) for controlling the central frequency. A modulation network (50) is also coupled to the network input oscillator (20) via a compensation network (40). The compensation network (40) continuously varies the coupling between the modulation network (50) and the network oscillator (20) in response to control signals applied to the input (32) of the steering network (30) so as to compensate the variations in modulation sensitivity.

Variable frequency ultrasonic system

Abstract: The ultrasonographer changes the frequency of ultrasound pulses emitted from an ultrasonic transducer as a result of adjusting the RF frequency of the transmitter burst exciting the broadband transducer; this adjustment takes place between pulse transmissions, while examining the patient. In a phased array imager utilizing baseband processing of received echo signals, the same adjustment supplies the corresponding frequency to the demodulator circuits. An alternative method of changing the system spectrum is to have a narrow bandwidth receiver whose center frequency is varied over the available bandwidth.

Frequency stabilization of a diode laser by use of the optogalvanic effect

Abstract: The frequency of an AlGaAs diode laser has been stabilized to the center frequency of the optogalvanic signal corresponding to the 4s′01–4p12 (Racah notation) transition of Ar I at 8408.2094 A. The first derivative curve of the line was used as the error signal to be fed back to the operating current source of the diode laser. Fluctuation of the laser frequency was within 200 kHz for several hours.

Cutoff frequencies in optical fibers of arbitrary refractive index profile using the resonance technique

Abstract: We present a very simple and accurate numerical method for calculating the cutoff frequencies of arbitrary refractive index profile optical fibers, including discrete numerical data from profile measurements. From Maxwell's equations we derive a transmission line equivalent circuit for any mode of an optical fiber which is cutoff frequency dependent. The problem of finding the cutoff frequency of a mode is transformed into finding the resonance frequency of the equivalent circuit. The algorithm uses no Bessel or other complicated functions and could be implemented on small microcomputers.

Measurement of the differential Doppler shift

Abstract: Doppler shifts between narrow-band signals observed at one or more pairs of receivers and originated from a remote source of radiation are useful for estimating source location and track. This paper deals with an instrumentationally attractive approach of estimating differential Doppler shifts by making center frequency measurements at each receiver output and subtracting them in a pairwise fashion. For low in-band signal-to-noise ratio conditions, center frequency measurements at different receiver outputs are weakly correlated. In this mode of operation, therefore, the mean-square error in the differential Doppler estimate equals the pairwise sum of the mean-square errors in each of the center frequency measurement. For high signal-to-noise ratio conditions, the various center frequency estimates are strongly correlated. In this mode of operation, the accuracy of the resulting differential Doppler estimate improves with the first power of the signal-to-noise ratio, even though the accuracy of each center frequency estimate approaches an absolute bound independent of the noise spectrum. The optimal (minimum mean-square error) differential Doppler shift estimate is obtained by simultaneous processing of the receiver outputs jointly. Comparison between the former (indirect) and the latter (direct) estimation techniques yields some interesting insights: the accuracy of the direct estimation procedure is proportional to T-3where T is the observation period. It is basically a coherent procedure. Center frequency measurement and the differential Doppler shift estimate derived from it are basically incoherent procedures and obey the well known T-1dependence. Under high signal-to-noise ratio conditions, the estimation error in both methods decreases with the first power of the signal-to-noise ratio. Under low signal-to-noise ratio conditions, the accuracy of the suboptimal indirect method is inferior to the optimal direct method by a factor proportional to the inverse first power of the individual signal-to-noise ratio.

Frequency controlled hybrid ultrasonic imaging arrays

Abstract: This ultrasonic imaging apparatus has an array (44, 52 or 100) of transducer elements (44, 50 or 104) for transmitting ultrasonic signals having a first predetermined center frequency (fc1) into an object (12) to be analyzed through use of the transmitted signals reflected from within the object. A means (150, 116-1 through 116-X and 120-1 through 120-X) is connected to transmit the ultrasonic signals from the array (44, 52 or 104) in a stepped array mode. A means (150, 116-1 through 116-X and 120-1 through 120-X) is connected to transmit the ultrasonic signals from the array (44, 52 or 104) in an angle scanning mode. There is a means (150, 128-1 through 128-X) for focusing the transmitted signals at a desired depth within the object (12). The reflected signals sensed by the apparatus have a second center frequency (fc2) less than the first center frequency (fc1) as a result of signal attenuation by the object (12). There is a means connected to select between the stepped array transmission mode and the angle scanning transmission mode for operating the array elements based on the second center frequency (fc2). Varying the operating mode of the apparatus on this basis gives improved image resolution over a wider operating range than with prior art systems.

Method and apparatus for detecting tracking error

Abstract: An optical disc player including an automatic tracking control for causing a light spot projected on a rotating optical disc to trace spiral or concentric information tracks is disclosed. A tracking error is detected by a wobbling method in which the light spot is vibrated in accordance with a position modulating signal having a given frequency, an amplitude modulated component due to a positional modulation is derived from a reproduced RF signal by passing an envelope signal of the reproduced signal through a band pass filter having a center frequency equal to the frequency of the position modulating signal, a sampling pulse is produced in synchronism with the position modulating signal and the amplitude modulated signal is sampled by the sampling pulse to derive a tracking error. A phase difference between the amplitude modulating signal and the sampling pulse is detected and a phase of the sampling pulse is modulated in accordance with the detected phase difference in such a manner that the amplitude modulated component can be always sampled at its peak points.

Frequency varied ultrasonic imaging array

Abstract: An ultrasonic imaging apparatus has an array (10 or 100) of transducer elements (14 or 104) for transmitting ultrasonic signals into an object (12) to be analyzed through use of the transmitted signals reflected from the object and sensed by the apparatus. The transmitted signals have a first predetermined center frequency. The reflected signals sensed by the apparatus have a second center frequency less than the first center frequency as a result of signal attenuation by the object. A means (70, 62 or 150, 152-1 through 152-X) is connected to select a number of transducers (14 or 104) in the array (10 or 100) for transmitting and/or receiving the ultrasonic signals based on the second center frequency. Adjusting the number of transmitting and/or receiving transducers (14 or 104) with changes in frequency produced by signal attenuation gives improved image resolution under a wider variety of use conditions than with prior art ultrasonic imaging apparatus.

Cable television subscriber control system including addressable filters having a variable pole

Abstract: A filter for use in a cable television system for filtering out a given channel comprising a two pole filter, said filter including one pole which is fixed at the center frequency to be tuned out and a second variable pole responsive to an input voltage, the second pole adapted to vary in frequency about the first pole. The filter is employed in addressable control system which includes an address generator at a head end, generating address control signals for each of a plurality of remote subscribers, a modulator for modulating a carrier with the address and control signal and coupling it onto cables, circuits at receiving terminals for receiving and demodulating the modulated carrier to recover the address signals, address decoding means for each subscriber to decode the address and control signals and circuits responsive to the decoding means to select the channels which each subscriber will receive. The system also has an encoder for encoding the status of the receive signals and a modulator for modulating a return carrier with the encoded states and putting this on the cable so that the signals may be demodulated at the head end. To carry out the demodulating and also to moduate the return signals, a local oscillator and mixer is used which generates both an intermediate frequency for the mixer and a carrier frequency for the return signal.

An investigation of the validity of high‐frequency audition

Abstract: In this investigation, a masking experiment was utilized to explore the validity of high‐frequency audition. Threshold shifts produced by a narrow‐band noise with sharp filter slopes and variable center frequency were determined for pure‐tone stimuli from 8000 to 14 000 Hz. Subjects were young adults with normal hearing from 250 through 8000 Hz, and with high‐frequency thresholds comparable to those obtained in a previously conducted normative survey. After pure‐tone thresholds were obtained for each test frequency, a narrow‐band masker was presented ipsilateral to the pure‐tone stimulus with center frequency equal to the pure tone. The masker was adjusted to an intensity level necessary to shift the pure‐tone threshold approximately 17 dB. The center frequency of the masker was then decreased in discrete steps with the pure‐tone threshold re‐established at each step. The experimental results, as demonstrated by release‐from‐masking functions, are consistent with the expectation of increased masker effectiveness as the center frequency of the masker approximates the test frequency. The findings of this investigation suggest that responses to high‐frequency auditory stimulation are the result of high‐frequency perception, and not the perception of some lower frequency distortion process.

Band-stop filter for VHF-UHF band

Abstract: A band-stop filter for VHF-UHF band comprises at least three series resonance circuits and at least two transmission lines each connected between the series resonance circuits. One of the transmission lines, which is connected to the input terminal of the band-stop filter, has an electrical length which is shorter or longer than the quarter wavelength of the center frequency of the stop band by more than 20 but less than 50 percent. When a band-stop filter comprises four transmission lines, one of the transmission lines, which is connected to the output terminal of the band-stop filter, has the same length as the transmission line connected to the input terminal. With this arrangement, the band-stop filter exhibits a sharp attenuation characteristic in a frequency range below or above the center frequency. Other transmission lines, which are not directly connected to either the input terminal or the output terminal, may have a length which is shorter or longer than the quarter wavelength by 5 to 20 percent so as to provide a sharper attenuation characteristic.

Method of and apparatus for measuring surface temperature of metallic body

Abstract: Disclosed is a method of measuring the surface temperature of a metallic body. The method comprises: disposing a reflecting member such that the reflecting member constitutes a resonator in cooperation with a substantially flat surface of the metallic body; measuring the mean reflectivity of the resonator over a predetermined frequency band having a center frequency coinciding with the resonance frequency of the resonator, as well as the luminance temperature of the resonator; and computing the surface temperature of the metllic body from these measured values. Disclosed also is an apparatus for carrying out this measuring method. The method and apparatus are suited particularly to the measurement of the surface temperature of a steel sheet heated to a temperature ranging between 500° and 800° C.

Interaction in frequency doubling of ultrashort laser pulses

Abstract: A study of the multiplication of the frequency of picosecond pulses revealed a shift of the central frequency of the second harmonic spectrum dependent on the intensity of the fundamental-frequency radiation It was found that the effect was associated with the cubic nonlinearity of the medium A theory of second harmonic generation was developed in the constant intensity approximation allowing for the quadratic and cubic nonlinearities

Radio receiver apparatus including multipath fade compensating arrangement

Abstract: In a radio receiver a multipath fade compensating circuit comprises a single-pole filter circuit the center frequency and Q of which are controlled in dependence upon the amplitudes of signal components in narrow frequency bands within the band of frequencies passed by the filter circuit. The narrow bands may be selected from an array by a microprocessor, or may be derived using variable frequency filters.

Method and apparatus for compensating non-linear phase shift through an RF power amplifier

Abstract: A device comprising a microstrip including a narrow conductor connected in series between a circuit input terminal and the power amplifier, a film of ferrimagnetic material positioned adjacent the conductor and magnetic biasing means. The biasing means normally biases the ferrimagnetic material to operate at frequencies about a selected center frequency for nonlinearly enhancing RF input signals as a function of input amplitude. The device normally, undesirably provides nonlinear phase shifts to the input signal as a function of input power at frequencies removed from the center frequency. By choice of the amount of the bias, for a particular input signal frequency, the device can be adjusted to produce phase shift which changes as a function of input power to offset the nonlinear phase shift of the RF amplifier.

Small-dimensioned microwave filter with linear resonators

Abstract: 1. A microwave filter comprising n linear hair-pin resonators (H'1 -H'5 ), n being a positive integer, characterized in that the length of each resonator is smaller than lambda/2, lambda being the wavelength corresponding to the center frequency of the filter band, and that a capacitor (C1 -C2 ) is branched between the open ends of each resonator, the capacitance of said capacitor being such that a resonance frequency equal to said center frequency of the filter band is obtained in the resonant circuit constituted by said capacitor and the associated resonator.

A differential narrow-band switched capacitor filtering technique

Abstract: A new resonator loss cancellation technique is described using NMOS technology. It allows the implementation of high Q switched capacitor band-pass filters using single-stage low-gain amplifiers. The approach exchanges the amplifier high DC-gain requirement by a gain matching between amplifiers of the same resonator. A prototype sixth-order bandpass filter with center frequency of 100 kHz and a 5 kHz bandwidth was built to demonstrate the feasibility of the technique. Unloaded resonator quality factors of the order of 400 were achieved using amplifiers with a DC gain of 50.

Method of determining operating characteristics of ultrasonic scanning systems

Abstract: The characteristics of an ultrasonic scanning system, including band-width, center frequency, and spectrum shape of reflected signals, are determined by directing ultrasonic energy from the system into a phantom having known ultrasonic attenuation and detecting the reflected ultrasonic signal for various depths in the phantom. Band-width is measured from the slope of frequency versus phantom depth. Center frequency is determined from the frequency of the signal reflected from the surface of the phantom. Spectrum shape is determined from the change in frequency of the reflected signal with change in phantom depth.

Sounding system of sonar

Abstract: PURPOSE:To increase receiving times of distant marker and to make possible to search repeatedly or continuously by receiving respective different transmission frequencies and by discriminating them. CONSTITUTION:A transmission/reception unit 1 transmits sound wave in water and receives echo sound from the marker. Receiving signal passed through a transmission/receiver converter 2 is phase composed by a receiver 5, amplified, and fed to BPF6-10. Then, receiving signals correspond to respective transmission frequencies f1-f5 are frequency discriminated. Consequently, output of BPF having center frequency which coincides with the transmission frequency is selected and fed to a detection circuit 12. Then, detection signal is displayed on CRT tube by a display circuit 13.

2.2 GHz SH-Mode SAW Delay Line

Abstract: Shear horizontal (SH) waves can be used to build high frequency delay lines because of their high wave velocity. In practice to reduce volume diffraction loss, transducers are embedded and the waves tend to behave like Love waves. In this paper, we describe experimental studies of these SH-type surface acoustic waves on rotated Y-cut Quartz with rotation angle near 36". Delay lines at 2.2 GHz have been designed and constructed, which operate at the 3rd space harmonic. They use embedded transducers and thin Al-metallization. The results at 2.2 GHz show that the acoustic properties such as phase velocity, temperature behavior (turnover temperature - second order temperature coefficient of delay) are quite dependent on the original cut and the metal thickness, as expected from Love type waves. This investigation indicates that low insertion loss devices with god temperature stability can be obtained if the transducer metallization is made closer to 400 d. Experimental results for a 0.13 us delay line with center frequency of 2.2 GHz and 14 dB matched insertion loss are presented.

Dynamic de-emphasis compensation system

Abstract: In color TV receiver for SECAM-encoded signals, a single FM detector (15), subject to line-by-line switching of its center frequency tuning, achieves sequential demodulation of respective SECAM subcarriers. For the purpose of using an identification system of the type shown in U.S. Patent No. 4,240,102, center frequency tuning at the R-Y subcarrier resting frequency is held throughout R-Y line interval and during lead-in burst of B-Y line interval, terminating at beginning of image portion of B-Y line interval. Transient signal component, associated with switching to B-Y subcarrier resting frequency at beginning of that image portion, tends to be stretched into early segment of image portion by de-emphasis circuit (19) following FM detector. To reduce adverse effects of this on colouring of image at left edge, a differentiated version of a pulse (at terminal D) having an appropriately directed trailing edge coinciding with transient is delivered to de-emphasis circuit output terminal (0). Elements (61, 63) of the de-emphasis circuit preferably serve as differentiator.

Matching circuit for a pre-amplifier of SHF band television signal receiver

Abstract: A matching circuit for a pre-amplifier of an SHF band television signal receiver is disclosed. The matching circuit comprises a stub line arranged near a gate terminal of an FET, and a pair of stub lines connected to a transmission line, one being a stub line exhibiting a short circuit impedance at a lower frequency than operating frequencies of the matching circuit and the other being a stub line arranged oppositely to the stub line and exhibiting a short circuit at a higher frequency than the operating frequencies. A distance between the stub line and the pair of stub lines is selected to be approximately equal to 1/4 wavelength of a center frequency of the desired signal band.