Showing papers on "Center frequency published in 1975"

Phase locked loop with circuit for preventing sidelock

Abstract: A side lock detector to prevent side lock in coherent PSK demodulation. For demodulation purposes it is necessary to recreate the carrier at the receiver. This may be accomplished with a phase-locked loop. However, with plural phase PSK modulation the input signal to the phase-locked loop has energy at side bands spaced at modulation rate intervals from the desired lock frequency as well as at the desired lock frequency. To detect side band lock, a band pass filter monitors the phase detector output of the phase-locked loop. The center frequency of the filter is equal to the modulation rate and the filter band width is very narrow. Only during side lock will significant amounts of energy pass the filter. This energy may be detected by a simple diode detector or the like. A lock inhibit means is provided, responsive to the output of the detector, to drive the voltage controlled oscillator out of a side lock condition.

Magnetic recording and/or reproducing apparatus

Abstract: MAGNETIC RECORDING AND/OR REPRODUCING APPARATUS ABSTRACT OF THE DISCLOSURE In recording periodic information signals, such as, the chrominance signal components of color video signals, having first or field intervals which are further subdivided into second or line intervals and which are recorded in successive parallel tracks on a record medium, interference or cross-talk between signals recorded in adjacent tracks is reduced or eliminated during reproduction by recording the information signals in adjacent tracks with first and second carriers having different frequencies Upon reproducing the information signals recorded in adjacent tracks with such first and second carriers, the reproduced signals are reconverted to have a common carrier frequency by means of respective first and second reconverting signals which similarly have different frequencies selected so that, although an information signal reproduced from a particular track and reconverted to the common carrier frequency will pass through a comb filter, the cross-talk signals reproduced simultaneously from adjacent tracks will be reconverted to have carrier frequencies at nodes of the comb filter so as to be eliminated by the latter The circuits by which the first and second carriers and the first and second reconverting signals are produced during recording and reproducing operations, respectively, each include a phase-locked loop having a voltage-controlled variable frequency oscillator whose output frequency is suitably changed in successive field intervals, and preferably in which the center frequency of the voltage-controlled variable frequency oscilator is also changed in the successive field intervals for obtaining rapid stabilization of the respective output frequency ?

A Speckle Pattern Velocimeter Using a Periodical Differential Detector

Abstract: A new method for non-contact velocimeter is proposed. A one-dimensional photodiode array, whose diodes are connected differentially, is used instead of a parallel slit array, in order to remove the low frequency noise. Then, the output signal of the differential detector is restricted to a narrow band signal, whose center frequency is proportional to the velocity of a rough surface. Since the output can be directly fed to a frequency counter, the restriction of the measurement range due to the cut-off frequency of the high pass filter is lifted. The characteristics of the proposed velocimeter are studied with the aid of spectrum analysis and some experimental results are shown.

Frequency discriminator apparatus

Abstract: A frequency discriminator having at least one ferrimagnetic resonator in a band pass or band reject configuration, the frequency of which is swept over a frequency band of interest, a detector receives the filter output, and the timing relationship between the detector output and the swept frequency is compared to generate the discriminator output. The discriminator has a bandwidth variable from a relatively narrow range to a very wide range in which the center frequency is simultaneously tunable over an extremely wide frequency range. The discriminator is insensitive to amplitude variations of the input signal and is capable of demodulating low level signals. The frequency discriminator is particularly useful for microwave frequency applications, for example, as a discriminator in a simple microwave FM receiver.

A Linear Temperature-to-Frequency Converter

Abstract: A new technique to linearize the temperature-frequency relationship of an astable multivibrator using one thermistor is proposed. The center frequency can be adjusted at any set frequency by an adjustable resistance. Furthermore, the oscillation frequency is not affected by the change of supply voltage.

Electronic music synthesizer

Abstract: An electronic music synthesizer is disclosed in which the sound producing chain includes a voltage-controlled oscillator, band-pass filter, low-pass filter, and amplifier in which selected control currents are supplied to low impedance points within the synthesizer circuit from a resistor matrix. The synthesizer produces sounds approximating different acoustic musical instruments or having different tonal qualities by the application of a predetermined voltage to one of fifteen input columns of the resistor matrix with selected other columns being grounded. The currents provided by the resistor matrix in combination with other externally generated currents control the center frequency and bandwidth of the band-pass filter, the cutoff frequency of the low-pass filter, the gain of the voltage-controlled amplifier, the time constants of transient contour currents used to control the filters and amplifier, and the waveform produced by the voltage-controlled oscillator. Specialized keyboard, waveshaping, contour generating and modulating circuits are also provided.

Reflective-Array Matched Filter for a 16-Pulse Radar Burst

Abstract: : A new type of matched filter has been designed and fabricated for a doppler-sensitive burst waveform with 16 equally spaced linear-FM subpulses, each of which has a 60MHz bandwidth and is 3 microsec long. The interpulse period is 5 microsec, and the total duration of the waveform is 80 microsec. The filter consists of 16 reflective-array-compressor sections ion-beam etched in the surface of a 15.2-cm-long Y-Z LiNbO sub 3 substrate. The reflective-array section for each subpulse is depth-weighted according to a Hamming function for range-sidelobe suppression, and the peak responses of successive sections have a Hamming weighting for doppler-sidelobe suppression. A reduction of system complexity and an improvement in dynamic range is expected with filters of this type as compared to conventional doppler burst processors. We have fabricated on one substrate a matched filter for an entire burst, thus providing the full correlation gain inherent in the waveform within a single device. This yields a large dynamic range despite a relatively high insertion loss (43 dB CW at center frequency (200 MHz) for the central section). Within a given section, the phase deviations from quadratic are typically 5 deg. r.m.s. and corresponding range sidelobes are more than 30 dB down from the correlation peak. These phase deviations and the errors in delay between sections can be reduced by metal overlay patterns. A filter for the zero-doppler channel was built to operate at a temperature of 60 C. When the temperature is changed by 0.98 C, the peak response of this filter is shifted by an amount equal to the doppler resolution (18 kHz).

Tracking bandpass filter for conditioning vibrator accelerometer waveform

Abstract: An accelerometer located on the pad of a vibratory seismic source provides a signal for comparison with the sweep signal which controls the vibrator. The error function representing the difference between the phases of these two signals is used to adjust the phase of the vibrator so as to maintain the vibrator in synchronism with the sweep signal. Prior to comparison with the sweep signal, the accelerometer output is conditioned by a tracking bandpass filter having its center frequency slaved to the instantaneous sweep frequency. Those components of the accelerometer output signal having a frequency equal to the instantaneous sweep frequency are passed by the bandpass filter and are subjected to approximately 0° phase shift through the filter.

Light deflector of acousto-optic interaction type

Abstract: A light deflector utilizing the anisotropic Bragg diffraction in an anisotropic medium in which the directions of the wave front normal and the energy propagation of ultrasonic waves are arranged to be different and the frequency range of the ultrasonic wave for causing re-diffraction of light diffracted once by said ultrasonic wave is set outside the driving frequency range. The diffraction efficiency does not fall near the central frequency of the driving ultrasonic frequency range due to the prevention of rediffraction. Further, the driving frequency can be selected over a remarkably wide range compared to that of the conventional light deflector.

Surface acoustic wave filter

Abstract: A surface acoustic wave bandpass filter having a flat frequency response in the passband and an exponentially decaying out-of-band response is realized by designing its transducer electrodes to have an appropriate number of discretely apodized interdigital fingers. The apodization or overlap coefficients H o (N) of adjacent fingers are determined from an analytically derived expression that incorporates factors for the filter time length parameter, the filter center frequency, bandwidth, transition bandwidth falloff, and a ripple reduction parameter.

Coherent component magnitude detector

Abstract: The identification of random and coherent components of an unspecified sil wherein at least a pair of band pass filters, each having the same center frequency but different bandwidths, are employed to make the identification.

Monaural Sensitivity to Dispersion in Impulses and Speech.

Abstract: : Little is known of the ear's phase sensitivity limits outside the well known fact that excessive dispersion in speech signals results in chirp-like sound quality. The limits of phase sensitivity may be determined in reference to the parameters of an idealized dispersion since phase shifts are nothing more than delays in the short-time spectra of a signal. A number of discrimination tests were conducted which contrasted standard stimuli with phase modified variants of the stimuli to determine the limits of phase sensitivity. The idealized dispersion was that of delaying a band of frequency components such that discriminability could be measured as functions of center frequency, bandwidth and delay. The stimuli used in the tests included an impulse, phonemes, words, and a sentence. Sensitivity to dispersion in impulses was shown to be dependent on intensity, center frequency, bandwidth, and dealy. Discrimination scores half way between chance and perfect performance were achieved for dispersed impulses with delayed bands of frequency components centered between 250 and 500 Hz and delayed between 0.0625 and 0.125 milliseconds. Sensation level of the stimulus pairs was 80 dB. The effect of bandwidth on discriminability appears to reach a plateau at 100 Hz, i.e., bandwidths of interest are less than 100 Hz.

Four-cavity velocity modulation tube

Abstract: In a four-cavity velocity modulation tube comprising an electron gun assembly, an input cavity, a pre-intermediate cavity, a post-intermediate cavity, an output cavity, a collector assembly and drift tubes interposed between adjacent ones of said cavities, said input cavity is tuned to the proximity of the lower end of the operating passband of said velocity modulation tube, said pre-intermediate cavity is tuned to the proximity of the upper end frequency of said operating passband, said post-intermediate cavity is tuned to a fundamental resonant frequency that is higher than the upper end frequency of said operating passband but lower than a frequency which is 1.6 times as high as the center frequency of said operating passband, the normalized length of all of said drift tubes being smaller than 90 degrees in terms of the reduced plasma angle, and the normalized length of the drift tube positioned between said pre-intermediate cavity and said post-intermediate cavity being larger than the normalized lengths of the other drift tubes.

Rejection of sonar interference of finite bandwidth by amplitude shading of transducer arrays

Abstract: Following the work reported in an earlier paper, the possibility of rejecting coherent interference of finite bandwidth and distributed direction of incidence by purely amplitude shading of a transducer array is investigated. Using the same linear transducer array immersed in the same distributed interference and ambient noise fields, it is demonstrated that, if the array shading is optimized by assuming all the interference power to be concentrated at its band center, interference of bandwidths up to 10% of its center frequency and intensity 70 dB above ambient noise field can be effectively rejected. This confirms that the theroy reported earlier is adequate for applications in narrow‐band receiving systems. If a broadband interference power quadratic is used in the process of shading optimization, the above interference‐rejecting capability can be extended to a bandwidth equal to 40% of its center frequency. These results further suggest that an optimum/adaptive broadband beamformer for passive sonar typically needs to be amplitude shaded in only eight bands.

Step-servoed tone detector

Abstract: An incoming signal (tone) and the feedback signal of a biquadratic filter are converted into square waves by zero crossing comparators. The phase state of the square waves is decoded and the decoded result is phase compared to determine if a 90° phase shift exists between the incoming and feedback signals. If a 90° phase shift does not exist, a counter is incremented or decremented, depending upon whether the phase comparison indicates that frequency of the incoming signal is greater, or less than the feedback signal. The output of the counter is decoded and utilized through a switching circuit to control the center frequency of the biquadratic filter (determined by the impedance of its feedback path). The switching circuit changes the impedance of the feedback path so that the center frequency is moved toward the frequency of the incoming signal. When the center frequency of the biquadratic filter is at the frequency of the incoming signal, the output of the frequency decoder provides a coded indication of the frequency of the incoming signal.

Multi-channel pressure telemetry system for base pressure measurements on small models

Abstract: : Effects of close proximity on simultaneously operating transducer- telemtry units had been systematically evaluated. Parameters such as the interaction as function of transducer-to-transducer distances, center frequency spread and its effect on the interaction, change of sensitivity in relation to center frequency, center frequency shifts as functions of transducer-to- transducer distances, and the effects of common power supply and shielding have been evaluated. The results showed that the interaction increases approximately as the inverse square of the distance. The center frequency spread has the most significant effect on the interaction. If 7MHZ or larger frequency spacing is maintained the maximum error is plus or minus 8 percent for the pressure range of 0.5 to 2.0 mm Hg. The measured data can be corrected by an interaction matrix method and yield errors in the order of a few percent depending on the accuracy of calibration.