Showing papers on "Frequency drift published in 1990"

Adaptive estimation of power system frequency deviation and its rate of change for calculating sudden power system overloads

Abstract: A novel Kalman filtering-based technique is presented for estimating power system frequency deviation and its average rate of change during emergency operating conditions that may require load shedding. This method obtains the optimal estimate of the power system frequency deviation from noisy voltage samples and the best estimate of the mean system frequency deviation and its rate of change while accounting for low-frequency synchronizing oscillations which occur during large disturbances. The proposed technique is a two-stage algorithm which uses an adaptive extended Kalman filter in series with an adaptive linear Kalman filter. The extended Kalman filter calculates the frequency deviation, magnitude, and phase angle of the voltage phasor, which may change during the time period covered by the estimation window. Both the measurement noise variance and the system noise covariance associated with the voltage samples are calculated online. The instantaneous frequency deviation is used as the input to a linear Kalman filter, which models the frequency deviation as a random walk plus a random ramp process. The estimated average rate of frequency decay is represented by the slope of the random ramp. Results for both single and multiple measurements are reported. >

Video dot clock generator

Abstract: A video dot clock generator includes a phase-locked loop (PLL) which includes a voltage controlled oscillator, a frequency divider, a phase comparator and a loop filter. The voltage controlled oscillator (VCO) is programmable to provide multiple frequency ranges for a given range of control voltages applied to the oscillator. The programming affects both the frequency range and the gain of the VCO. The phase comparator includes circuitry which simulates a predetermined minimum phase error which, when compensated for, substantially eliminates jitter in the dot clock signal. The frequency divider used in the PLL and a similar frequency divided used to generate the reference signals for the phase comparator are programmable via an internal memory which also holds programmable control signals for the VCO. The memory, in turn, may be programmed by the user to achieve desired frequency and loop again characteristics for a given application.

Receiver for terrestrial AM and satellite FM-TV broadcasting signals

Abstract: Receiver for terrestrial AM and satellite FM-HF-TV signals in first and second frequency ranges, respectively, of mutually predominantly equal dimensions, which succeed each other in frequency, comprising, arranged one after the others, a HF-AM-FM section (2-6), a mixing circuit (8) common for the AM and FM-TV signals and an IF device (10-20), oscillator mixing signals being applied from a tuning oscillator (9) to that mixing circuit for a frequency conversion of the AM and FM-HF-TV signals into a first AM and an FM intermediate frequency signal, respectively, having a first AM and an FM intermediate frequency, of which at least the first AM intermediate frequency is located above the first frequency region In order to enable a simple and cheap realisation, in which a tuning oscillator having a comparatively narrow-band tuning range can be used, the first AM intermediate frequency is of the order of magnitude of twice the highest frequency of the first frequency range and the FM intermediate frequency is of the order of magnitude of half the lowest frequency of the second frequency range, the IF-device including an AM (13-19) and a FM-IF (10,11) section whose inputs are coupled to an output of the mixing circuit for a separate selection and processing of the first AM and the FM-intermediate frequency signal respectively

Power supply frequency regulating device for vibration wave driven motor

Abstract: A vibration wave driven motor comprise a comparator for comparing a resonance frequency of the motor with a power supply frequency and a frequency setter for setting the power supply frequency according to a predetermined algorithm in response to the output of the comparator. The frequency setter is provided with an algorithm which, if the power supply frequency is identified lower than the resonance frequency by the comparator, brings the power supply frequency toward an optimum frequency through a predetermined frequency higher than the resonance frequency.

Phase-locked loop with pulse-duration modulation fine frequency control

Abstract: A phase-locked loop includes an oscillator controlled by means of a switching network and a microprocessor which generates, in response to the output of a phase detector, two groups of output signals. A first group (Q1 . . . QN) is for adjusting the frequency of the oscillator in steps by selectively switching in frequency determining elements, and a second group (P1 . . . PM) for feeding a pulse duration modulator. The pulse duration modulator produces a control signal for a frequency determining minimum element of the switching network. The control signal has a duty cycle indicative of the frequency determination contribution by the minimum element.

Elimination of phase noise and drift incident to up and down conversion in a broadcast communication system

Abstract: Phase noise and drift in a broadcast communication system caused by imperfections in transmitter and receiver local oscillators used for up and down conversion of a frequency or phase modulated information signal is eliminated from a downconverted component that is provided for demodulation by adding a pilot frequency component to the modulated signal for mixing by the local oscillator in the transmitter and by frequency locking the local oscillator in the receiver, so that a signal at a frequency equal to the sum of the intermediate frequency and the pilot frequency provided by a phase-locked loop that tracks the pilot frequency component of the downconverted signal is maintained at a desired value. The downconverted signal is mixed with the sum signal provided by the phase-locked loop to provide a component for demodulation at the difference between the pilot frequency and the modulation frequency that is free from the phase noise and drift caused by the local oscillators. Since the phase noise and drift caused by the local oscillators affects the phases of the modulation frequency information component and the pilot frequency component equally, the frequency modulated information is proportional to the difference between the pilot signal frequency and the modulation frequency, and the effect of phase noise and drift is eliminated.

Development and operation of a backward wave oscillator based FIR scattering system for DIII-D

Abstract: The laser‐based far‐infrared scattering system (λ=1.22 mm) on DIII‐D is to be upgraded by the addition of a backward wave oscillator or carcinotron. By supplying up to 300 mW at λ=1.06 mm, the carcinotron is expected to increase the scattered power and signal‐to‐noise ratio by more than ten times. In addition, the laser has suffered from significant frequency pulling during high density discharges which has necessitated using undesirable geometry to obtain accuracy in the low‐frequency part of the fluctuation spectrum. However, the carcinotron‐based system will use an IF tracking system to simultaneously remove the excessive phase noise, frequency drift typical of high‐frequency tubes, and the effects of frequency pulling. This should allow more reliable measurements of low‐frequency asymmetric spectra under all discharge conditions. The local oscillator will be provided by a frequency doubled and locked klystron, to enable heterodyne detection of the scattered signal. Results of extensive laboratory tests of the carcinotron‐based scattering apparatus are to be presented.

Swept frequency domain relectometry enhancement

Abstract: An improved swept frequency domain reflectometry instrument has an input/output terminal coupled to one end of a cable. A radio frequency at the input/output terminal is converted to an intermediate frequency using a swept local frequency. The radio frequency is derived from the swept local frequency and a variable offset frequency. A controller controls the variable offset frequency, monitoring the amplitude of the intermediate frequency. A period counter counts the intermediate frequency at a first maximum response of the intermediate frequency and further counts the offset frequency at a second maximum response of the intermediate frequency. The location of a discontinuity in the cable is calculated from the counted frequencies.

Apparatus and method for sensing the presence of moving objects

Abstract: A sensor, especially for detecting misfeeds in a stream of sheets of paper, comprises a pair of sensing plates sensing changes in the capacitance between the plates, a first oscillator providing an output signal at a frequency representative of the capacitance, a second oscillator set to a reference frequency which is the same as or close to that frequency generated by the first oscillator when no object is between the sensing plates, gating means to produce an output representative of the frequency difference between the oscillator outputs, a low-pass filter, and a microprocessor which responds to changes in the difference frequency.

Performance of internal-mirror frequency-stabilized He-Ne lasers emitting green, yellow or orange light

Abstract: A comprehensive control system has been developed for the stabilization of internalmirror He-Ne lasers to their power envelopes. It is designed particularly for use with lasers emitting at 552, 505, or 490 THz (543, 594, 612 nm). The aim has been to combine convenience in routine operation with good day-to-day resettability and minimal frequency drift during a day. The lasers are observed to emit in up to four modes simultaneously and their tuning behaviour is highly alignment-sensitive. They also tend to flip between modes having orthogonal linear planes of polarization. Reliable control of polarization and mode frequency are possible using permanent magnets and active length control through thermal expansion. The stabilized single-frequency outputs have frequency drifts of about 2×10−8 per year, and powers of between 150 μW and 850 μW.

Station selecting apparatus

Abstract: A station selecting station apparatus having a first mixer and a first local oscillation circuit for frequency converting the input signals (television signals) into a first intermediate frequency signal, a second mixer and a second local oscillation circuit for frequency con­verting the first intermediate frequency signal into the second intermediate frequency signal. A variable voltage device capable of varying, outputting by stages the direct current fixed voltage as the signal for controlling the second local oscillator is provided, the minimum potential width of the direct current fixed voltage is set so that the frequency displacement (unit variation amount) of the second local oscillator to be obtained by the potential difference may become smaller than the frequency resolution of the first local oscillator.

Phase locked loop frequency modulator using data modulated digital synthesizer as reference

Abstract: In a frequency-modulated frequency generator comprising an oscillator connected in a phase control loop, the reference frequency is generated in a digital frequency synthesizer which is adapted to be frequency-modulated by digital data signals; under control of the data signal, numerical values are alternately read out from a register to result in corresponding different frequency deviations; the register stores further predetermined additional numerical values which result in frequencies adjacent to said frequency deviations; the register is controlled by the data signal so that for every edge of the data signal predetermined additional numerical values are initially read out in such an order that the frequency values produced thereby will compensate for any overshooting which occurs upon switching between the drift frequencies.

Suppression of laser frequency drifts caused by thermal transients in optical WDM packet switching systems

Abstract: Frequency drifts caused by laser thermal transients have been identified as a major impairment in packet switching networks using multisection tunable lasers. They are induced by the heating changes caused by current steps used to switch the carrier frequency. A method to suppress this frequency drift in a FSK-WDM direct detection system through the use of a passive equalisation circuit is presented.

Sinusoidal oscillator with voltage controlled frequency and amplitude

Abstract: A sinusoidal oscillator is considered of which both the frequency and amplitude are electronically controlled The control of frequency is obtained with two multipliers used as controlled amplifiers The circuit for amplitude control also uses multipliers; the output voltages of the oscillator are squared and summed and the resulting DC voltage is compared with the reference This approach provides fast frequency and amplitude control The practical range of frequency control depends on the distortion level requirements A detailed consideration of non-linear distortion is given The main sources of the distortion are the non-linearity and mismatch of the multipliers and the offset of operational amplifiers in the oscillation loop The frequency can be controlled in the range 16 Hz–16 kHz (in three overlapping bands) with a level of distortion that varies between − 40 dB and − 55 dB

Auto-centered phase-locked loop

Abstract: A multi-band processing system for automatically tuning the oscillator of a phase-locked loop to the frequency and phase of an applied input. The system includes an error detection circuit, a frequency controller, a scaling circuit, and a phase and frequency controller. The applied input and the oscillator output are coupled to the error detection circuit whose error output drives a charge pump/filter circuit. An error signal is derived from the difference between the loop charge pump output V1 and a preset charge pump zero error reference signal Vref, wherein the frequency controller regulates the oscillator output frequency according to a frequency error component of V1 -Vref, the scaling circuit scales the oscillator output frequency according to a system scaling signal N, and the phase and frequency controller adjusts the oscillator output frequency and phase according to V1 -Vref, when a 1/N multiple of the frequency of the oscillator output is compared in the error detection circuit to the frequency of the applied input.

Electro-optic line narrowing of optical parametric oscillators

Abstract: In the present invention a nonlinear crystal of an optical parametric oscator is provided with a pump pulse and electrodes for applying a high voltage to the crystal during the pump pulse. The high voltage is switched from one level to another during the pump pulse duration. The initial value of the high voltage determines the position of the frequency center of the optical parametric oscillator gain profile because the indices of refraction are a function of the applied voltage due to the electro-optic effect. During the pump pulse, when the high voltage is switched to some other value, a new set of momentum and energy conservation conditions results. This causes a frequency shift in the gain profile. Thus the oscillator is provided with two differing gain profiles during the pump pulse. The output frequency of the oscillator is only those frequencies in both gain profiles.

Transmitters and transmitter circuits

Abstract: The invention relates to small low voltage transmitters for transmitting at a single frequency, preferably in the VHF range, suitable for use in the location or tracking of birds, animals, vehicles, people or other objects where the transmitter is required to be small and light. The transmitter circuit includes an oscillator stage (61) based on a crystal oscillator XL1 having a predetermined nominal frequency, a frequency multiplying and amplifying circuit (62) arranged to double the nominal frequency and pulsing circuit (60) designed to give a pulsed output at a predetermined frequency, the pulsing stage (60) includes a pair of transistors TR11, TR12 having effective negative resistance, which transistors are separate from the transistor TR3 in the oscillating circuit and which are off during an Off Period and on during an On Period, with the Off to On period in the ratio of at least 15 to 1. The oscillator circuit (61) includes a tuning capacitor C3 by which the tolerances of the crystal frequency and other components of the oscillator stage can be compensated. The frequency multiplying and amplifying circuit (62) includes a distinct tuning capacitor (66) by which the final desired frequency of the amplifier stage can be tuned to compensate the component tolerances in the amplifying stage. The transmitter circuit together with batteries (30) are located in a casing (18, 20) all of which components weigh no more than 7 grams.

Millimeter wave oscillator with flicker (1/f) noise suppression

Abstract: Flicker (1/f) noise is suppressed in an oscillator by reducing oscillator voltage-frequency pushing to zero. A varactor (56) is incorporated in the resonator circuit and is biased with a tuning voltage setting the varactor to a capacitance value providing the zero oscillator pushing at a given frequency. A common bias connection (62) is provided between the varactor and the active element (64) such that a random perturbation voltage change across the active element also causes a change in voltage across the varactor, to compensate a change in oscillator frequency otherwise caused thereby. The varactor capacitance versus voltage characteristic is shaped such that a change in active element voltage provides a change in varactor voltage, and the combination of these voltage changes results in a zero change in oscillator frequency. The tuning slope of the oscillator provided by the varactor is opposite the tuning slope of the oscillator resulting from a change in active element voltage.

Quantum-well SEED optical oscillators

Abstract: Oscillation at 110 MHz in a GaAs-GaAlAs quantum-well SEED (self-electrooptic effect device) optical oscillator is considered. Optimization of device length and optical pump wavelength for high-frequency oscillation is discussed. Frequency tuning is obtained by adjusting the oscillator bias voltage or optical pump power, and the oscillator can be injection locked to modulated optical signals. Frequency fluctuations caused by perturbative Gaussian noise and 1/f frequency noise are observed; the 1/f noise in an 8.5-MHz oscillator limited the minimum frequency variance to 230 Hz/sup 2/. >

Overtone crystal oscillator having resonance amplifier in feedback path

Abstract: In an overtone crystal oscillator comprising a crystal oscillator having a feedback loop and a resonance amplifier whose amplitude characteristic has an overshoot in the range of the resonant frequency of the resonance amplifier and which is arranged in the feedback loop of the crystal oscillator, the resonant frequency of the resonance amplifier is between the frequency of the overtone to be generated and the next lower oscillation frequency of the crystal oscillator, while signals in the frequency range of the next lower oscillation frequency(ies) in relation to signals in the frequency range of the overtone to be generated in the feedback loop, particularly in the resonance amplifier, have such a phase shift that the overtone crystal oscillator cannot oscillate at the frequencies of the next lower oscillation frequency(ies) and that it only oscillates at the frequency of the overtone to be generated.

Stability detection method and apparatus for a tuning system

Abstract: An indication of stability of a tuning system after changing, the local oscillator frequency to a predetermined frequency, such as a frequency corresponding to a new channel during a channel changing operation or to a new search frequency during a search, is provided by monitoring an AFT signal during the frequency changing operation and determining when it remains consistent for a predetermined time.

Single oscillator FSK pulsed radar receiving transmitter

Abstract: An improved radar receiver transmitter uses a single oscillator frequency shift keyed system in which the oscillator shifts rapidly between a pulsed output frequency and a local frequency such that the system can transmit at one frequency and shift fast enough such that when the echo pulse is received, the transmitter is operating at the local frequency desired. The two signals are demodulated in a mixer to establish the desired intermediate frequency which then may be processed to produce the desired output. Extremely fast shifting is accomplished by a gallium arsenide oscillator in conjunction with a varactor diode which responds to a modulator pulse.

Automatic optical frequency acquisition and tracking apparatus for optical coherent communication system

Abstract: An automatic frequency control system, for an optical coherent communication system, in which an output frequency of a local oscillator is swept by a frequency sweep signal FM-modulated with a frequency shift signal. The FM-modulated local frequency is combined with an input optical signal and heterodyne-detected. A frequency shift signal component derived from a heterodyne detection output is compared with the frequency shift signal to verify whether or not the local oscillation frequency is in a predetermined range with respect to the input signal frequency. When it is in the predetermined range, the system operates to terminate the frequency sweep signal and remove the frequency shift signal and is switched to oscillation frequency control of the local oscillator by using a d.c. component of the hterodyne detection output.

Frequency-modulated transceiver

Abstract: A frequency-modulated transceiver in which modulation caused by the transmitter part of the transceiver in the output signal of the receiver i.f.-mixer is decreased. The transmitter comprises a frequency-modulated high-frequency oscillator (1) having a modulation input and an output, and the receiver comprises in a cascade: a high-frequency mixer (13) having a local oscillator input functionally connected to the output of the high-frequency oscillator (1) of the transmitter; a first intermediate frequency filter (12); an intermediate frequency mixer (11); a second intermediate frequency filter (10); and a detector (9). The receiver further comprises a frequency-modulated local oscillator (8) having an output functionally connected to a local oscillator input in the intermediate frequency mixer (11), the local oscillator being modulated with the modulating signal of the transmitter. Modulation caused by the transmitter part of the transceiver in the output signal of the intermediate frequency mixer is decreased by providing means (5, 6, 7) for adjusting the modulation sensitivity of the high-frequency oscillator (1) or the local oscillator (8), or for adjusting the level of the modulating signal supplied to one of these oscillators, on the basis of the correlation between the output signal of the detector (9) and the modulating signal of the transmitter.

Method for setting the absolute frequency of a tunable, 1.5 mu m two-section DBR laser

Abstract: A technique for setting the absolute frequency of a 1.5- mu m two-section distributed Bragg reflector (DBR) laser using an Er:YAG optical filter as a frequency discriminator is described. The absolute frequency of the laser was controlled with an accuracy better than 300 MHz over a tuning range of several hundred gigahertz. The frequency drift with laser temperature was -130 MHz/ degrees C, and the tuning rate with current in the active region was 40 MHz/mA. >

A method and circuitry for automatic control, according to the counter principle, of the frequency of a radio telephone.

Abstract: The invention relates to a method and circuitry for automatic control of the frequency of a radio telephone, according to the counter principle and on the basis of the reception frequency, in which case the reception frequency (fin) is mixed with the output frequency of a phase-locked loop (7) in a first mixer (1), the output frequency (if1) of the first mixer (1) is mixed in a second mixer (2) with the frequency derived from a local oscillator (5), and the frequency of the phase-locked loop (7) is controlled on the basis of the frequency deviation of the output frequency (if2) of the second mixer (2). Whereas in prior-art circuitries at least two oscillators are needed, one of which must additionally be very precise, in the present invention one local oscillator (5) suffices, which is an oscillator having a controllable frequency and is controlled on the basis of the said frequency deviation, the reference frequency (fr) of the phase-locked loop (7) being derived from the frequency (f) of the local oscillator (5). The frequency deviation of the second mixer (2) can be determined, for example, by counting pulses within a certain time interval, the time interval being determined by counting a certain number of pulses of the local oscillator (5).

A voltage step up regulator

Abstract: A voltage step-up regulator produces a frequency control voltage for a frequency synthesizer in a radio transmitter using a low operating voltage. To minimize the disturbances conveyed elsewhere in the radio device, the step-up regulator comprises an amplifying transistor controlled by an oscillator signal which operates as a class A amplifier, the output of amplifying transistor (Q1) including a diode and two selectively coupled capacitors for rectifying and filtering the amplified signal. The step-up regulator further comprising a feedback circuit for stabilizing the output voltage by adjusting the amplitude of the amplified signal.

Low parts count transmitter unit

Abstract: A frequency modulated (FM) transmitter for use in the 100 to 300 megacycle band is described having a low parts count topology. The disclosed topology requires the use of five tank circuits tuned to various frequency multiples of a crystal oscillator to achieve a twelve fold multiplication of the natural frequency of the crystal oscillator.