Showing papers on "Frequency drift published in 1986"

Voltage controlled oscillator with frequency sensitivity control

Abstract: A voltage controlled oscillator is tuned with a network comprising two varactor diodes and two transmission lines. By selecting appropriate values of varactor capacitance and transmission line length and width the overall reactance of the network is such that, when a varactor tuning voltage is varied, the output frequency of the voltage controlled oscillator will vary in an fashion with respect to the tuning voltage. Such a voltage controlled oscillator is gain compensated and exhibits a controlled modulation sensitivity over a range of frequencies. If the required frequency range of the oscillator is known beforehand, an alternate embodiment of the invention may be employed in which one of the varactor diodes is replaced with a fixed capacitor having a suitable value for the desired frequency range.

Power saving intermittently operated phase locked loop

Abstract: In an intermittently operative phase-locked loop, in order to prevent the oscillator frequency from significantly changing at the time of turning on of an electric power source, a point in time at which a phase difference between clock signals respectively fed to a reference frequency divider and to a frequency divider for dividing the output frequency of a voltage-controlled oscillator becomes substantially zero is detected, and the two frequency dividers are initialized when the above-mentioned point in time is detected after turning on of the electric power source.

A.F.C. system for broad-band FM receiver

Abstract: An A.F.C. control system for reception of wide-band F.M. transmission such as satellite transmissions, in which a center frequency of an F.M. I.F. signal is repetitively and alternately compared with an upper and a lower frequency limit value so long as the center frequency lies between these values, with the results of the comparisons being respectively stored in two latch memories (28, 29), whose contents thereby indicate any error of the center frequency relative to the frequency limits. Any departure of the center frequency from between the limits is corrected by successive frequency shifts of the local oscillator (4) frequency, with the results of correction being indicated by the latch memory contents and with the number of frequency shifts being determined accordingly.

Method and apparatus for calibrating an adjustable frequency generator

Abstract: A method for calibrating an adjustable frequency generator having a voltage-controlled oscillator which is preceded by a computer via a digital-to-analog converter. The control input of the oscillator is coupled to a calibrating device comprising a series circuit comprising a digital phase detector and a lowpass filter forming a phase-locked loop circuit arrangement. By the computer, a digital-to-analog converter is caused, upon a frequency reference value signal, to deliver a control voltage to the oscillator which corresponds to the output voltage of the lowpass filter prior to the start of the calibrating process. A digital value corresponding to the control voltage is stored in the computer together with a digital reference value corresponding to the given frequency.

Gas density transducer

Abstract: An improved gas density transducer which compares the resonant frequency of an enclosed, reference tuning fork crystal oscillator with the resonant frequency of a detector tuning fork crystal oscillator exposed to the surrounding gas. The frequency of oscillation of the detector crystal oscillator exposed will vary in accordance with the gas density because of the motional resistance of the gas to vibrations of the tuning fork oscillator. The frequency of the detector oscillator can be compared to the frequency of the reference oscillator to determine the gas density.

Stable voltage controlled oscillator

Abstract: A voltage controlled oscillator (VCO) is stabilized against variations in output frequency resulting from changes in temperature or the power supply voltage by trimming the voltage controlled oscillator from a second master VCO which is connected into a phase lock loop. Each of the two voltage controlled oscillators has an output frequency which is a function of two inputs. The signal input to one control input of each of the VCO's is the output of the low pass filter in the phase lock loop. The VCO's may both be implemented by cross-coupled NOR gates with grounded capacitor inputs.

Timing recovery scheme for burst communication systems

Abstract: A timing recovery apparatus for a burst mode communication receiver. The apparatus provides for optimum sampling and digitizing of received data at a plurality of data rates. In particular, a VCO is phase-locked to a local frequency reference prior to data being received. A reference timing preamble transmitted prior to the data is filtered and fed to the VCO causing it to injection lock such that the VCO becomes phase aligned with the preamble. The VCO is then permitted to "free run" during data transmission and continues to operate at substantially the same frequency. A synchronous divider and multiplexer, responsive to the VCO, allows selection of sampling clocks for the plurality of data rates. The divider is forced to a known state during VCO injection locking, to assure that the sampling clocks have maintained the proper phase for optimal sampling at the corresponding data rate. Further, means is provided to monitor the frequency of the VCO. Should the VCO frequency drift more than a predetermined amount an indication of such is produced.

Laser stabilization servo system

Abstract: A method and means for stabilizing the difference in frequencies between the frequency components of a two frequency laser beam influenced by Zeeman effect frequency splitting, accurately determines the frequency separation independently of the individual frequencies or intensities of either of the frequency components. Frequency stabilization is accomplished by mechanical and thermal adjustments to the lasing chamber length of the laser by a closed loop servo control referencing the frequency difference between laser beam components and a reference signal having a frequency equal to the desired frequency difference.

Portable animal control unit

Abstract: A portable animal control unit includes circuitry incorporated in a miniature housing for generating an animal influencing modulated soundwave in the ultrasonic frequency range A first oscillator produces an output signal for driving an ultrasonic transducer, the output signal having a center frequency in the ultrasonic range A second oscillator produces an output control signal for modulating the frequency of the first oscillator, the modulation rate being determined by the center frequency of the second oscillator output signal and the amount of deviation of the second oscillator from the center frequency

Radio frequency signal transmission system with carrier frequencies at opposite edges of the channel

Abstract: A radio frequency transmitter simultaneously transmits both a local oscillator frequency and that frequency modulated by an information content signal. A receiver receives a carrier wave that is at the opposite edge of a channel from that of the local oscillator. The transmitted and received information signals can be of opposite type sidebands.

Multiple frequency horizontal oscillator for video apparatus

Abstract: A deflection circuit for a video apparatus is capable of operating at different horizontal rate frequencies in response to the incoming video information rate In one embodiment, the deflection oscillator input voltage is varied in a cyclical manner to vary the oscillator frequency When the oscillator frequency corresponds to the frequency of the incoming video information, the input voltage is maintained to maintain the desired oscillator frequency In an alternate embodiment, a frequency to voltage converter generates the desired oscillator input voltage in response to the incoming video information rate

A novel digital frequency multiplier

Abstract: This paper presents a digital frequency multiplier having many features not yet found together in existing multipliers. Its acquisition time is within one period of the input signal and it can follow the input frequency over more than three decades. The relative frequency error on its synchronized output signal is independent of the multiplication factor N and is noncumulative. The maximum value of this error is given by f in /f c where f in is the input frequency and f c a master clock frequency. This represents a decrease in the error value by a factor N over many existing digital frequency multipliers.

Analytical microwave spectrometer employing a Gunn oscillator locked to the rotational absorption line

Abstract: A means of locking the frequency of a Gunn effect oscillator operating in the 18-26 GHz range, to the spectral line of a molecular gas which exhibits the quadratic Stark effect, has been developed. The gas is confined within a Fabry-Perot semiconfocal cavity resonator at a reduced pressure of the order 1-10 Pa (0.01-0.1 mbar). A sinusoidal Stark voltage of 6 kV peak-to-peak at 4.5 kHz is impressed upon the gas in the cavity which is coupled to the Gunn oscillator operating at a frequency near to the line frequency. The modulation of the spectral line frequency by the Stark voltage electric field generates amplitude modulation of the microwave radiation particularly at the second and fourth harmonics of the Stark voltage frequency. The second harmonic is used to lock the oscillator which is used in a spectrometer for quantitative determinations of the gas used for locking, employing the fourth harmonic. Working with the ammonia 25.056 GHz (J=6, K=6) spectral line, frequency stability of the order +or-30 kHz standard deviation was achieved over the working day.

Tuning system for television sets

Abstract: An automatic alignment system for the tuner of a television receiver with a controlled high-frequency preamplifier stage and an intermediate-frequency amplifier that has a reference circuit with a resonance frequency that can be switched to the arithmetic mean between the video-carrier intermediate frequency and the audio-carrier intermediate frequency during automatic alignment. The maximum control voltage is employed as a criterion for optimum alignment and an auxiliary oscillator is switched on during automatic alignment and generates through a mixing stage an auxiliary frequency that corresponds to the arithmetic mean of the video-carrier frequency and the audio-carrier frequency from the tuner-oscillator frequency.

A new method for reconstructing type III trajectories

Abstract: A local density approximation (LDA) method is developed for reconstructing the trajectories of type III radio bursts through the interplanetary medium. The method uses the measured source directions and the measured frequency drift rates of the type III burst to determine the locations of the radio source in the interplanetary medium at consecutive frequency levels. The technique is used to reconstruct the trajectory of an actual type III burst and the results are compared to the trajectory obtained from the global density law method. The LDA method represents an improvement in that it utilizes more observed data on the type III burst and that it takes full account of the local density variations at the source locations.

PLL stabilized frequency modulator with extended low frequency range

Abstract: A modulator including a voltage controlled oscillator (VCO) having its center frequency stabilized to a reference frequency using a phase locked loop in which the low frequency range is increased by using frequency translation techniques The VCO output signal is translated relative to the phase locked loop feedback signal so that an increased frequency division ratio can be used in the feedback loop and the effective frequency deviation at the phase comparator can be reduced by an arbitrary factor This has the effect of increasing the allowable deviation at a given information signal frequency by that arbitrary factor Likewise, a given deviation can be maintained for input information frequencies which are an arbitrary fraction of the low end cutoff frequencies of conventional modulators

Fine tuning of atomic frequency standards

Abstract: A predetermined bias voltage is applied to the input of a summing integrator in a frequency lock loop to provide fine tuning control of a voltage controlled crystal oscillator. In this arrangement, the predetermined bias voltage is summed and integrated with a phase error signal to alter the output frequency of the voltage controlled crystal oscillator. Since the servo loop operates to null the net voltage at the input of the integrator, the circuit induces a frequency error which just compensates for the intentional voltage offset bias applied to the integrator. The offset bias arrangement produces incremental offsets within a total range of about three parts in ten to the eleventh power and permits the output frequency of an atomic frequency standard to be accurately and stably adjusted in small increments to agree closely with the frequency of a national standard or other system reference.

Low spurious numerically controlled oscillator apparatus and method

Abstract: Generating a digital signal from the output of a numerically controlled oscillator and delaying certain transitions of the digital to produce an output digital signal having a generally 50% duty cycle and a frequency determined by a frequency select input to the numerically controlled oscillator.

A comparative introduction of a new high voltage resonant oscillator

Abstract: A new high voltage high frequency resonant oscillator switched in push-pull mode for dc-to-ac power conversion is compared with the classical current-fed resonant type. The main advantage of this new oscillator lies in its built-in voltagegain dependence on the load. The ideal dc-to-ac voltage transfer ratio is given and data of an experimental version is presented.

An amplitude modulated laser system for distance and displacement measurement

Abstract: A laser distance and displacement measurement system is being developed to monitor small displacements in large space structures for strain analysis and structural control. The reflected laser beam is focused on a detector and the detected signal is mixed with the reference. Small displacements are indicated by a change in modulation frequency which is adjusted to maintain quadrature between the received signal and the reference signal from the voltage-controlled oscillator in a phase-locked loop. Measurement of absolute distance is accomplished by sweeping the modulation frequency from a quadrature lock point to an adjacent lock point.

Evaluation of Mechanisms for Low-Dose Frequency Shifts in Crystal Oscillators

Abstract: Two possible causes for the observed frequency shift of a crystal oscillator due to a small radiation dose to the crystal have been analyzed. Removal of mass from the surface of the crystal by the radiation does not appear to be a plausible cause for the frequency shift. However, the electric fields and voltages created in the crystal by charge that is photoemitted from the walls of the can around the crystal and is then trapped in the crystal are relatively large and could possibly produce the observed frequency shift. These trapped charges produce both normal and tangential electric fields inside the crystal. Consequently, the difference in this radiation-induced frequency shift for SC-cut resonators, which are primarily sensitive to normal stresses, and for AT-cut resonators, which are primarily sensitive to tangential stresses, is less than the difference in their normal voltage sensitivities.

350‐GHz phase/frequency locked loop for use with a carcinotron backward wave oscillator

Abstract: A phase/frequency locked loop for use in a millimeter‐wave radio‐astronomy receiver is described for locking a carcinotron backward wave oscillator (BWO) operating in the 330–370‐GHz range to a fixed 150‐MHz reference source. The appropriate 29th–31st harmonic of a stable and tunable frequency source around 11.75 GHz acts as the local oscillator to down convert the high BWO frequency to 150 MHz prior to phase/frequency comparison. A double loop is required, whereby the low‐frequency part of the spectrum of the loop error voltage is applied to the line voltage circuit of the carcinotron power supply over more than 30 m distance. The high end of the spectrum is coupled to this voltage via a voltage transformer located next to the carcinotron. Under these conditions a 135‐kHz loop bandwidth is easily obtained. The locked signal shows excellent stability, and the measured performance level in terms of the Allan variance to characterize fractional frequency stability is about 10−16 for integration times in the...

Method and a device for the frequency control of an atomic or molecular beam frequency standard

Abstract: The method realizes the frequency control of a frequency standard including an atomic or molecular beam resonance apparatus with two microwave cavities, to which an electromagnetic field is fed, whose frequency is modulated in time with a sinewave signal about an interrogation frequency near to the characteristic resonance frequency of a selected transition of the atoms or molecules of the beam. In the resonance device a current is generated, proportional to the number of atoms or molecules of the beam which have undergone said transition as an effect of their passing through the cavities. The method includes the step of extracting from said current the component whose frequency is an odd harmonic of the modulation frequency of an order higher than the first, in particular the third. Said component is coherently demodulated, in amplitude and sign, to generate a control signal which is used to steer the frequency of said electromagnetic field, in such a way as to minimize the difference between the interrogation frequency and the characteristic resonance frequency of the atomic or molecular transition.

Circuit for automatic tuning of sharpness in fm receivers

Abstract: The circuit is specially intended for receivers having narrow-band carried filters. Such receivers usually have a mixing phase controlled by an oscillator, at least one filter for filtering out the intermediate frequency signals and a demodulator. The sharpness tuning is effected by way of a closed loop regulation. In one embodiment the mean value of the exit voltage of the demodulator is formed and compared with a desired voltage which gives the reference position of the intermediate frequency signal. The frequency of the oscillator is readjusted on the basis of the difference between the mean value and the desired voltage value. In another embodiment the mean value of the intermediate frequency is formed and compared with a desired frequency which gives the reference position of the intermediate frequency. The frequency of the oscillator is then readjusted on the basis of the difference between the mean value of the intermediate frequency and the desired frequency.

Synchronizer for commonly clocked converters

Abstract: Apparatus for synchronizing the oscillators of several clocked direct voltage converters where each direct voltage converter has a control circuit with the oscillator as an integrated component and each control circuit has a connection for a capacitor and a connection for a resistor for defining the oscillator frequency. Commercial elements TDA 4714 and TDA 4716 are preferred as the control circuit. The synchronization is attained by adjusting the frequency of the oscillator of a first direct voltage converter to be higher than the frequency of the oscillators of the remaining direct voltage converters. A pulse sequence with an impulse frequency proportional to the oscillator frequency of the first direct voltage converter is transmitted by the first direct voltage converter to all of the other converters through an element that provides isolation between the different potentials. The pulses of the pulse sequence adjust a predetermined charging state for the capacitors of the other direct voltage converters. The adjustment is repeated at the frequency of the oscillator of the first direct voltage converter.

Digitally controlled variable frequency synthesizer

Abstract: In a generator whose frequency can be set digitally and connected in a phase-locked loop (PLL) with a frequency divider whose frequency divider ratio is periodically changed, the sum of the phase errors, which are the phase deviations of the individual frequency-divider delivered pulses from the phase of the reference frequency, is calculated and each pulse for which the phase-error sum exceeds a predetermined value is delayed by a time period corresponding to this value before being fed to the phase meter or phase detector of the phase-locked loop. As a result, any drift or oscillatory fluctuations of the voltage-controlled oscillator (VCO) control voltage are confined to substantially high frequencies and only very weak subharmonic components, and the oscillatory fluctuations can be filtered out easily by a low-pass filter between the phase detector or phase meter and the control-voltage input of the VCO. Also the generation of a compensating voltage is possible using digital means at low cost and with the result that high stability and accuracy of the selected output frequency can be ensured.

Injection-locked video frequency oscillator

Abstract: A pair of oscillators (50, 52) controlled by crystal produce respective signals at specific frequencies that are useful in the treatment of a video signal, for example in the production of a clock signal for a line of delay (26, 38) or in the manufacture of a subcarrier signal for an encoder (44). Frequencies are used so that they pass through into the frequency spectrum of the processed video signal. Although multiple frequencies are nominal, they can not be maintained invariant because of the normal circuit conditions, such as variations in ambient temperature and aging of the circuit. Frequencies mix and therefore a differential frequency is developed in the processed video signal. By injecting an appropriate harmonic of the lower frequency signal in the crystal oscillator (50) producing the higher frequency signal, the higher frequency is locked to the variations of the lower frequency, causing the deletion of the differential frequency .

Phase locked loop for locking an oscillator to a noninteger multiple of the reference frequency

Abstract: A method and apparatus for phase locking the signal of a controlled oscillator (1) to that of a reference oscillator (3), a correction quantity depending on the difference between the relative phase angles of the signals being generated at correction instants for correcting the frequency of the controlled oscillator. According to the invention, the phase lock may also be achieved with a controlled oscillator (1), having a frequency which is not a whole number multiple of the reference oscillator (3) frequency by, in one embodiment, the reference oscillator signal or in another embodiment, the controlled oscillator signal being phase shifted such that the phase difference occurring at the correction instants as a result of the controlled oscillator frequency not being a non-integer multiple of the reference oscillator frequency is eliminated at the formation of the correction quantity.

Clock circuit synchronization

Abstract: Synchronization of a local timing signal (Ts) with an incoming reference timing signal (o i (t)) is realized by employing is realized by employing a frequency estimator (l0l) and frequency synthesizer (l02) in conjunction with a local fixed oscillator (l03). The frequency estimator (l0l) includes a first phase-locked loop (ll0-ll5) including an integrator (ll5) for generating a frequency estimate which is the difference between the frequency of the incoming reference timing signal and the frequency of the fixed oscillator signal. The phase value (PHLOL(n)) of the frequency estimate (FRQEST(n)) obtained by integrating the frequency estimate is supplied to a second phase-locked loop (l20-l28) which includes a digitally controlled oscillator (l25,l26) to generate the local timing signal (o o (t)). If the incoming reference timing signal (o i (t)) is lost or if there is too large a variation in a phase error signal (PHIN(n)) in the first phase-locked loop, the value of the frequency estimate is held constant (via l09). Consequently, the second phase-locked loop (l02) never free runs and the local timing signal (o o (t)) remains in synchronization with the reference timing signal (o i (t)).