Showing papers on "Center frequency published in 1989"

Multi-antenna gas receiver for seismic survey vessels

Abstract: Method and apparatus are disclosed for accurately determining position from GPS satellites and received on a ship using observations of C/A code group delay, L1 band center frequency carrier phase, L1 band 5115 MHz implicit carrier phase, and L2 band 5115 MHz implicit carrier phase A precise measurement of the range to each satellite is made based upon the L1 center frequency carrier phase A correction for ionospheric effects is determined by simultaneous observation of the group delays of the wide bandwidth P code modulations in both the L1 and L2 bands These group delays are determined by measuring the phases of carrier waves implicit in the spread-spectrum signals received in both bands These carriers are reconstructed from both the L1 and L2 band signals from each satellite without using knowledge of the P code The unknown biases in the L1 center frequency carrier phase range measurements are determined from simultaneous, pseudorange measurements, with time averaging The instantaneous position of the antenna receiving these signals, and therefore the ship, may then be determined from the ranges so determined, with both the bias and the ionospheric effects having been eliminated Additional antennas are positioned on the ship and a seismic streamer towed by the ship to reject false signals, compensate for blockage of signals by the ship's structure, and determine the position of sensors in the streamer

Temporal window shape as a function of frequency and level

Abstract: In an earlier article [Moore et al., J. Acoust. Soc. Am. 83, 1102-1116 (1988)], preliminary work on the temporal-window model of temporal resolution in the auditory system was described. The temporal window is conceived of as a temporal integrator that slides in time and that is implemented as an intensity-weighting function. The shape of the temporal window was estimated by measuring the threshold for a brief sinusoidal signal presented in a temporal gap between two bursts of noise as a function of the duration of the gap and the position of the signal within the gap. In this paper, a much more thorough examination of the effects of level and frequency on the shape of the window is presented, using the same basic technique. Temporal window shapes were measured at four different frequencies (300, 900, 2700, and 8100 Hz) and at three different masker levels covering a 20-dB range at each frequency. The shape of the temporal window was well described by modeling each side as the sum of two rounded-exponential (roex) functions. The equivalent rectangular duration (ERD) of the window decreased from about 13 to 9 ms as the center frequency increased from 300 to 900 Hz, but decreased only slightly, to 7 ms, as the center frequency increased to 8100. The greater ERD at 300 Hz does not seem to be explicable in terms of "ringing" in the auditory filter. The ERD decreased somewhat with increasing level, for example, having a value of about 10 ms at 2700 Hz with a 20-dB masker spectrum level and about 7 ms with a 40-dB masker spectrum level.

Dynamic measuring of frequency and frequency oscillations in multiphase power systems

Abstract: Instantaneous system frequency is defined, and a method of frequency measurement is proposed which determines the angular velocity of the rotating voltage space phasor. Impulses in frequency caused by steps in phase are blanked out, whereas harmonics and noise are suppressed by FIR filters. Using an optimized observer-based filter, frequency modulations are split into and frequency drift and frequency oscillation signals, which can be used in power control and power system stabilization. >

Capacitively compensated high performance parallel coupled microstrip filters

Abstract: A capacitive compensation technique is described for the design of microstrip parallel coupled filters with improved passband symmetry and very low spurious response up to 2.5 times the center frequency. The compensated structure does not require any extra computer-aided design tools and is compatible with monolithic microwave integrated circuit technology. The technique is useful for the design of filters on alumina as well as GaAs substrates. Two design examples are considered. >

Spread spectrum-time diversity communications systems and transceivers for multidrop local area networks

Abstract: Messages are transmitted on pairs of frequencies that are orthogonal, that is the frequencies have no least common denominator (are prime to each other). A message is transmitted on the first of the pair of frequencies and, simultaneously, its complement is transmitted on the second of said pair of frequencies. The message is then retransmitted on another pair of orthogonal frequencies. In the second transmission, the message is remapped, such that, adjacent bits in the first transmission are not adjacent in the second transmission and the same bit in the first transmission and the second transmission are not spaced 1/120th of a second apart. Information is collected on the data error rates at each receiver. This information is periodically transmitted to a central frequency controller which collects this error information and determines the error rates on the frequencies being used. A hill-climbing technique is used to choose pairs of frequencies having the lowest current data error rates. The frequency controller transmits the identity of these frequencies to the various transceivers in each message. The transceivers comprise a frequency controlled carrier frequency generator, appropriate data keying for the carrier, a pair of digital state machines, each having a frequency controlled filter connected thereto, appropriate microprocessors for control and broad band coupling networks for coupling the transceiver to a communications channel, which may be an AC power line, a private line, the floor loop of an automatic guided vehicle system, or the like.

A 12.5 MHz CMOS continuous time bandpass filter

Abstract: The authors describe a continuous-time bandpass filter integrated in a 3- mu m CMOS technology, with an f/sub 0/ of 12.5 MHz and a 2% fractional bandwidth. The four-pole filter is modeled on two L-C resonators coupled by mutual inductance, resistively terminated at the input and output for maximum power transfer. Each resonator is simulated on the IC by two tunable integrators in negative feedback and is terminated by MOS resistors to define the filter bandwidth. Regulation of f/sub 0/ is obtained by locking an oscillating, consisting of a third identical integrator pair without termination resistors, to an externally supplied reference frequency. The circuits were fabricated on a double-metal, single-polysilicon, 3- mu m CMOS IC. Operation of the chip at a 12.5-MHz center frequency was verified, showing the desired 2% fractional bandwidth. >

Wideband scanning of a guided‐light beam and spectrum analysis using magnetostatic waves in an yttrium iron garnet‐gadolinium gallium garnet waveguide

Abstract: Wideband scanning of a light beam through the use of magnetostatic waves has been accomplished for the first time. Specifically, a guided‐light beam at a wavelength of 1.317 μm in an yttrium iron garnet‐gadolinium gallium garnet waveguide was Bragg diffracted by magnetostatic forward volume waves (MSFVWs) operating at a frequency range of 2–7 GHz. Wideband scanning of the light beam was accomplished simply by changing the frequency of the MSFVW continuously from center frequencies of 2.5 and 6.0 GHz while keeping the dc magnetic field fixed or by continuously tuning the dc magnetic field while keeping the frequency of the MSFVW fixed at the center frequencies. A large number of resolvable scan spot positions were obtained in both cases. The resulting wideband magneto‐optic Bragg cell or light beam scanner was also used to perform spectral analysis of wideband rf signals at a center frequency of 3.2 GHz. Potential advantages of the magneto‐optic Bragg cell and scanner over the existing acousto‐optic counte...

Tuning strategies in high-frequency integrated continuous-time filters

Abstract: Three approaches for tuning integrated continuous-time filters are discussed and compared. Results are presented that refer, but are not limited to, second-order bandpass filters implemented with transconductance amplifiers and capacitors (OTA-C filters). It is shown that tuning with two frequencies has superior performance over single-frequency tuning: in this first case, center frequency, bandwidth, and midband gain of a biquad can be tuned exactly; in the second case, only center frequency and midband gain can be so tuned. >

X‐band magneto‐optic Bragg cells using bismuth‐doped yttrium iron garnet waveguides

Abstract: Guided‐wave magneto‐optic Bragg cells at X‐band microwave frequencies using magnetostatic forward volume waves (MSFVWs) in bismuth‐doped yttrium iron garnet‐gadolinium gallium garnet (Bi‐doped YIG‐GGG) waveguides are reported for the first time. Performance figures that have been obtained at an optical wavelength of 1.303 μm include a center frequency tuning range of 3.7–12.0 GHz, a diffraction efficiency of 12% at the magnetostatic wave power of 56 mW, a linear dynamic range >40 dB, and a −3 dB magneto‐optic bandwidth of 150 MHz. These results represent a significant improvement over those obtained previously with the Bragg cells using pure YIG‐GGG waveguides. Maximum scan angle of 6° and 5.3° were also measured, respectively, by tuning the rf frequency ∼10.0 GHz at a fixed dc magnetic field of 3660 Oe and by varying the dc magnetic field ∼3660 Oe at a fixed rf frequency of 10.0 GHz. A frequency resolution of 30 MHz was measured with rf spectral analysis experiments carried out at 12 GHz. Finally, a Fara...

High-frequency phase-locked loops in monolithic bipolar technology

Abstract: Circuit design techniques for realizing high-frequency, low-power phase-locked loops (PLLs) in monolithic silicon bipolar technology are discussed. A varactor-tuned voltage-controlled oscillator (VCO), an analog phase detector, and a bandgap reference have been utilized as building blocks. A test circuit fabricated in a 2- mu m bipolar process exhibited a maximum center frequency of 350 MHz, and the PLL pull-in range was larger than +or-1%. The circuit operates from a 5-V supply and dissipates 270 mW. >

Integrated selectivity for narrow-band FM IF systems

Abstract: An 18th-order all-pole continuous-time bandpass filter for IF filtering purposes has been designed and integrated in a 3 ?m CMOS process. Implemented using nine fully-balanced, transconductor-capacitor coupled resonators, the filter features 20 kHz bandwidth at 200 kHz center frequency, 54 dB dynamic range (IM3 ≪ - 40 dB) and consumes 300 ?A from a single 4 V supply.

Widely tunable single-longitudinal-mode pulsed dye laser.

Abstract: We have developed a simple cavity-length-stabilization method appropriate for single-longitudinal-mode pulsed lasers that use grazing-incidence gratings. Our technique relies on the detection of aminute (<0.5-mrad) angular variation in the output beam direction caused by a detuning betweenthe cavity-mode frequency and the center frequency of the grating passband. In a prototype systemimplementing this stabilization scheme we have generated single-longitudinal-mode scans of up to 290cm(-1).

Electrically-tunable bandpass filter

Abstract: A bandpass filter is disclosed which may be used in a superheterodyne receiver in front of the first mixer. The bandpass filter provides a narrow front end filter which is tuned automatically as the local oscillator frequency is changed. In the present exemplary embodiment, a series tuned reflective notch filter is coupled to a node of a balanced resistive bridge in such a manner that the tuned circuit presents a short circuit to the node at the filter's resonant frequency to thereby assure a maximum transfer of signal from the input to the output of the circuit at a desired frequency. At all other frequencies, the series tuned reflective notch filter will present essentially an open circuit across the node of the resistive bridge so that the node is balanced and no transmission occurs. The inclusion of the series reflective notch filter thereby produces a bandpass characteristic from the circuit input to output. By using back to back varactor diodes in the reflective notch filter, the center frequency of the passband can be changed by changing the tuning voltage applied to the varactors. In the configuration of the present invention, the varactor diodes are protected from high signal levels which are not within the narrow passband of the filter. For this reason, the filter is inherently less susceptible to the generation of intermod products than filters of a conventional design.

A noise insensitive solution to an ambiguity problem in spectral estimation

Abstract: The instantaneous frequency measurement (IFM) receiver is capable of measuring the center frequency of single frequency pulses over a wide range (bandwidth) of center frequencies. Because of various constraints, the frequency resolution requirement results in long correlator delay times that reduce the single correlator bandwidth. A large bandwidth can be achieved only if two or more correlators are used. The problem of estimating frequency is then reduced to the simultaneous congruence problem of number theory. A design procedure is presented for solving the congruence problem for a given amount of noise protection, a stated frequency resolution, a minimum bandwidth, and a fixed level of precision (bits) in the IFM receiver. >

A synthesized method to improve coherence in semiconductor lasers by electrical feedback

Abstract: A method for improving coherence in semiconductor lasers by negative electrical feedback is proposed for stabilization of the center frequency of the field spectrum, linewidth reduction of the field spectrum, frequency tracking to another highly coherent laser, and stable and wideband frequency sweep. Experimental center frequency stabilization of the master laser showed that the magnitude of frequency fluctuations was reduced to 50 kHz at the integration time tau =3 s. The linewidth of the master laser was reduced to 100 kHz, which was 1/50 that of the free running laser. Under these frequency control conditions, the frequency of the slave laser was controlled so that the phase of the heterodyne signal between the master and the slave lasers could be locked to that of a stable microwave synthesizer. The slave laser frequency tracked accurately to the master laser frequency. >

Proximity reading of coded tag

Abstract: In a proximity-reading coded-tag system, a coded tag (10) responds to a high-frequency interrogation signal by providing a binary signal of a predetermined low frequency and bearing a code that is unique to said tag; and by transmitting a high-frequency response signal of a given high frequency, with the response signal being modulated with the uniquely coded low-frequency binary signal; and a coded-tag reader (12, 12a) receives and demodulates the high-frequency response signal to detect the uniquely coded low-frequency binary signal. The modulator (24) of the coded tag modulates the response signal by shifting the center frequency of the response signal during each pulse of the low-frequency uniquely coded binary signal to thereby vary the amplitude at the given high frequency in the response signal in accordance with said unique binary code and at the rate of the predetermined low frequency; and the demodulator (36, 37) of the coded-tag reader is tuned to the predetermined low frequency of the coded binary signal for detecting the unique binary signal code in accordance with amplitude or phase variations at the given high frequency in the received high-frequency response signal caused by the frequency shifting.

Self-injection locking technique

Abstract: A self-injection locking system is disclosed that internally narrows the prepulse of a laser cavity before it is replicated as the laser output using: two quarter wave plates, an air spaced etalon, and a polarizing beam splitter The air spaced etalon will separate the off-center frequency signals from the center frequency signals of the prepulse by inducing a phase shift Following this, the polarizing beam splitter impedes the off-center frequency signals by a power loss of about ten percent while the center frequency signals are unaffected In operation, this can cause the off-center frequency signals to fail to reach the threshold at which stimulated emission takes place The result is that the laser replicates only the center frequency signals as the laser output

Radiation source for helium magnetometers

Abstract: A radiation source (12) for optical magnetometers (10) which use helium isotopes as the resonance element (30) includes an electronically pumped semiconductor laser (12) which produces a single narrow line of radiation which is frequency stabilized to the center frequency of the helium resonance line to be optically pumped. The frequency stabilization is accomplished using electronic feedback (34, 40, 42, 44) to control a current sources (20) thus eliminating the need for mechanical frequency tuning.

Computationally generated velocity taper for efficiency enhancement in a coupled-cavity traveling-wave tube

Abstract: A computational routine has been created to generate velocity tapers for efficiency enhancement in coupled-cavity traveling-wave tubes (TWTs). Programmed into the NASA multidimensional large-signal coupled-cavity TWT computer code, the routine generates the gradually decreasing cavity periods required to maintain a prescribed relationship between the circuit phase velocity and the electron-bunch velocity. Computational results for several computer-generated tapers are compared to those for an existing coupled-cavity TWT with a three-step taper. Guidelines are developed for prescribing the bunch-phase profile to produce a taper for high efficiency. The resulting taper provides a calculated RF efficiency 45% higher than the step taper at center frequency and at least 37% higher over the bandwidth. >

A novel all-MOS high-speed continuous-time filter

Abstract: A new continuous-time transistor-only bandpass/lowpass filter based on g/sub m//C integrators that is capable of realizing critical frequencies in excess in 10 MHz is described. The center frequency, Q, and voltage gain are all voltage-tunable over a 10:1 range. The integrators use a novel, fully balanced, source-degenerated transconductor which maintains less than 1% nonlinearity for differential inputs up to 2 V. A second-order state variable filter with a nominal f/sub 0/=3.2 MHz and Q=5 consumes only 20 mW from a single-ended 5-V supply. >

Video detector employing PLL system

Abstract: A PLL video detector comprises a phase detector circuit receiving a video intermediate frequency signal and an oscillation output of a VCO for phase-detecting the same. The phase of the oscillation output of the VCO is controlled by a signal obtained by smoothing a detection output of the phase detector circuit by a low-pass filter. In addition, a trap circuit having a center frequency of fH is provided between the phase detector circuit and the VCO, so that an unecessary component having a frequency of fH is removed from an output signal of the low-pass filter. Consequently, the VCO stably oscillates, so that occurrence of a buzz sound in a sound output and degradation of the picture quality can be prevented.

Dielectric receiving filter with sharp stopband using an active feedback resonator method for cellular base stations

Abstract: The development of an 800-MHz-band dielectric receiving filter with a sharp stopband is presented. The filter is composed of a conventional dielectric antenna filter and thee active band-stop filters, each sharply eliminating one band in the passband. In the active band-stop filters, small dielectric resonators, in which the unloaded Q is raised to about 50000 by means of an active feedback resonator method, are used. These filters are designed to obtain optimum stability and an optimum noise figure. One of them has a center frequency of 845.75 MHz, a stopband width of 1.0 MHz, and an attenuation of 30 dB. Deviation of the resonant frequency is held without +or-30 kHz, and the noise figure at passband is adequately small. The size of the dielectric receiving filter is 480*250*44 mm/sup 3/, and the volume is less than 1/20 that of a conventional filter using cavity resonators. >

Wigner distribution analysis of SAW filters

Abstract: The application of a mixed time-frequency representation, the Wigner distribution (WD), to the analysis of the transfer function of a surface acoustic wave (SAW) filter is discussed. The utility for signal analysis and practical aspects of the computational implementation of the WD and of two smoothed versions of the WD are discussed. Criteria for the separation and identification of second-order effects are listed. Second-order effects of a broadband delay line incorporating chirped transducers with a center frequency of 380 MHz and a fractional bandwidth of 52% are analyzed. Signals overlapping in the time and frequency response are separated and the origin of these spurious signals is identified using the WD. >

A 2.5 GHz low noise phase locked surface transverse wave VCO

Abstract: A hybrid VCO (voltage-controlled oscillator) at 2.488 GHz which is phase locked to a crystal oscillator operating at 75.4 MHz is described. Acoustic surface transverse wave (STW) delay lines operating at the fifth harmonic are used as the frequency-controlling element of the VCO. In order to reduce the delay-line electromagnetic feedthrough a three-transducer-type STW filter design is combined with a microstrip rat-race coupler. The filters were designed using advanced analysis methods and fabricated on rotated Y-cut quartz substrates with a standard photolithographic process. The delay lines were characterized by a center frequency of 2.49 GHz, an untuned insertion loss of 22 dB, an unloaded Q value of 1280, and a group delay time of 158 ns. The signal of the VCO is mixed with the local (crystal) oscillator signal multiplied by 32, thus providing an IF (intermediate frequency) signal of 75.4 MHz that feeds the phase-locked loop, which has a bandwidth of 300 kHz. A single-sideband phase-noise-to-carrier ratio of -112 dBc/Hz at 1-kHz offset has been attained. >

Detection and discrimination of frequency modulation of complex signals

Abstract: Detection and discrimination of frequency modulation were studied for harmonic signals with triangular spectral envelopes. The center frequency of the stimuli was near 2 kHz; the fundamental frequency was near 100 Hz. To prevent the possibility that the discrimination was based on differences of initial or final frequencies, these frequencies were equal within and across modulations in each individual experiment. Differences between modulations consisted of differences in the trajectories between the initial and final frequencies. Performance worsened as the slopes of the spectral envelopes decreased. Addition of noise also impaired modulation discrimination. The dependence on the signal‐to‐noise ratio was similar to what is found for stationary stimuli: Discrimination of frequency modulation deteriorated more rapidly with decreasing signal‐to‐noise ratio when stimuli had shallow spectral slopes than when they had steep spectral slopes. In spite of the precautions taken (i.e., initial and final frequency the same), the discrimination of these stimuli was more likely based on quasistationary frequency discrimination than on discrimination of modulation rate. This conclusion is consistent with previous findings for pure tones presented in quiet that frequency discrimination is more acute than modulation‐rate discrimination.

A novel integrated acoustooptic frequency shifter

Abstract: An integrated optical frequency shifter that utilizes guided-wave acoustooptic Bragg diffractions in cascade from two tilted- and counterpropagating-surface acoustic waves is reported. The doubly and frequency-shifted diffracted light propagates in a fixed direction, but spatially resolved from the incident light, irrespective of the magnitude of frequency tuning. A device fabricated in a Y-cut LiNbO/sub 3/ planar waveguide has demonstrated desirable characteristics, including single-sideband suppressed-carrier properties, a frequency shift centered at 1 GHz, a tunable bandwidth of 165 MHz, a linear dynamic range greater than 41 dB, and high efficiency at the optical wavelength of 0.63 mu m. These preliminary results suggest that a compact integrated acoustooptic frequency shifter module capable of multigigahertz center frequency and gigahertz bandwidth can be realized in a common LiNBO/sub 3/ substrate 0.2 cm*1.0 cm*1.5 cm in size. >

Stabilizing circuit for optical fsk frequency deviation

Abstract: PURPOSE:To stabilize frequency deviation by controlling the frequency deviation of respective FSK signal light beams in a frequency range corresponding to the half cycle of a transmissivity cycle in a periodical filter. CONSTITUTION:A selection means 24 extracts one FSK signal light beam from signal light beams (FSK signal light beams) 151-15n with a frequency corresponding to an injected current which is optical frequency-multiplexed. The periodical filter 25 and control means 261 and 26n make the frequency whose transmissivity is to a maximum value or a minimum value to coincide with the central frequency of the FSK signal light beams 151-15n. Then, an output signal 17 corresponding to the frequency deviated amount of the FSK signal light beams 151-15n of the transmissivity cycle is taken out, and the output signal 17 is fed back to corresponding light sources 221-22n through a switching means 28. Thus, the deviation of the frequency of FSK signal light beams can be stabilized.

Notch filters with variable center frequency and attenuation

Abstract: The author describes notch filters whose center frequencies and maximum attenuation are variable. Three different types of such filters using varactor diodes and GaAs field-effect transistors (FETs) are proposed and tested at 2-4 GHz. The tunability over 2.2-4.0 GHz is obtained by changing the junction capacitances of the varactor diodes, and a maximum attenuation over 15-60 dB is obtained by changing the inner resistances of the FETs. >

High-frequency and high-Q tunable active filters

Abstract: Investigation of the performance of classical second-order bandpass active filters has shown that since they use low-gain elements, they can be divided into two classes at high frequencies: low-selectivity stable filters and low-stability selective filters. The author presents structures that realize a good compromise between both classes, so that high Q can be achieved with good stability. Verifications have been carried out with experimental Si hybrid high-frequency filters and with computer simulations of GaAs microwave integrated filters. The center frequency of the GaAs filters is tuned with MESFETs used as voltage-controlled resistors and can exceed 2 GHz. >