Showing papers on "Frequency drift published in 1980"

Frequency stabilisation of semiconductor lasers for heterodyne-type optical communication systems

Abstract: In the somewhat distant future, heterodyne-type optical communications will appear, increasing channel capacity and repeater separation. At present, the greatest difficulty is the frequency drift of lasers. The letter describes an a.f.c. (automatic frequency control) experiment using a Peltier cooling element; it is shown that the frequency fluctuation can be reduced to below 10 MHz.

Optical heterodyne detection of directly frequency modulated semiconductor laser signals

Abstract: Frequency modulated semiconductor laser signals are demodulated by optical heterodyne detection using an independently temperature stabilised semiconductor laser local oscillator and a square law detector followed by electrical frequency discrimination circuitry. Beat frequency stability of the free-running semiconductor laser transmitter and local oscillator and characteristics of direct frequency modulation and optical heterodyne detection are delineated.

Broadband superheterodyne tracking circuits for millimeter‐wave measurements

Abstract: Superheterodyne stimulus‐response measurements can be made with high dynamic range, but are often sensitive to oscillator frequency drift and noise. The usual techniques for reducing this sensitivity often become impractical at millimeter‐wave frequencies and above. This paper describes a feedforward tracking technique and its application to single frequency millimeter‐wave interferometry and Doppler‐shift scattering measurements on tokamak plasmas. Swept frequency transmission measurements can also be made with high dynamic range using this technique.

Digitally controlled temperature compensated oscillator system

Abstract: A crystal oscillator that is temperature compensated by digitally substrang a correction frequency from the running frequency of the crystal oscillator to provide the required operating frequency. The correction frequency is generated by a digital frequency synthesizer circuit which is controlled by the output of a programmable read-only memory which has been programmed to generate the required correction frequency for each temperature code over the operating temperature range. The temperature code is generated by gating a digital counter with the output of a monostable multivibrator which utilizes a thermistor to make its gate interval proportional to temperature.

Microcomputer-controlled one-step-back automatic frequency control tuning system

Abstract: An electronic, microcomputer-controlled television tuning system capable of acquiring channels offset by as much as 3.25 MHz from the designated frequency while also being able to accurately tune in channels operating at the designated frequency. After synthesizing the correct channel frequency, the microcomputer looks at AFC discriminator information from which local oscillator tuning voltage direction is determined. To achieve automatic fine tuning the tuning voltage is then stepped by the microcomputer in small frequency increments which vary from 28 KHz for channel 2 to 90 KHz for channel W in the direction of the desired frequency until the center video carrier frequency is passed. The tuning voltage is then returned to the preceding step to which frequency the receiver is then locked. With essentially all broadcasting stations operating at, or very close to, the FCC-designated frequency, highly accurate tuning to the selected channel is thus permitted. Video carrier verification is accomplished by microcomputer analysis of AFC discriminator and vertical sync states.

Analysis of Aging Data on SAW Oscillators

Abstract: Test oscillators including delay lines and resonators in the 300-400 MHz range have been investigated with reference to the long-term stability (aging) characteristics All devices were fabricated on rotated Y-cut quartz plates (40 deg), and either gold or platinum metallization was used; all packages were high-quality hermetic enclosures, and the mounting was strictly mechanical, with no organics or silicone rubbers used It is shown that drift of less than 2 ppm in the first year can be obtained on a significant fraction of the devices when reasonably clean packages are used The data also suggest that the transducer metallization (at least for aluminum) is very likely the source of the relaxation mechanism that causes the frequency drift

Optimum Gaussian Filter and Deviated-Frequency-Locking Scheme for Coherent Detection of MSK

Abstract: Predetection Gaussian bandpass filtering effect on the coherent detection of minimum-shift-keying (MSK) is theoretically anlayzed on the basis of the worst signal pattern which brings the maximum intersymbol interference. The optimum 3 dB-down bandwidth (B)-bit duration (T) product of the Gaussian bandpass filter is proved theoretically to be BT = 0.5887 , which degrades the required E_{b}/N_{0} (signal-energy-per-bit to noise-power-density ratio) only by 0.14 dB from that of antipodal coherent PSK using differential encoding. The degradations due to the phase errors of reference carrier and decision timing and the frequency drift of the received input signal are also shown. In addition, an alternative coherent detection using the reference carrier having the frequency deviated from the center frequency by the frequency deviation, which is called the deviated-frequency-locking scheme, is presented, and its error-rate performance is proved to be substantially identical with that of the conventional center-frequency-locking scheme.

Wideband, millimeter wave frequency Gunn oscillator

Abstract: A tunable millimeter wave frequency Gunn oscillator operates efficiently beyond the normal Gunn oscillator frequency range through the use of a second harmonic enhancement circuit. The enhancement circuit is tuned to the fundamental frequency of the oscillator and is tracked with a second harmonic circuit to provide a wide tuning range. Lumped element circuitry is used to aid in providing the wide tuning range and to facilitate adjustment and fabrication.

Power supply having automatic frequency control for ultrasonic bonding

Abstract: A power supply is provided for an electromechanical device of the type employing ultrasonic frequency vibratory energy for bonding materials. An automatic frequency control varies the output frequency of the power supply until the ratio of the maximum to minimum amplitudes of a standing wave produced in the mechanical vibratory member falls below a pre-set maximum. The frequency of the power supply is set by a voltage controlled variable frequency oscillator. A sweep generator produces a periodic voltage signal having a frequency substantially less than the frequency range of the voltage controlled oscillator. Means are provided for coupling the voltage signal from the sweep generator to the control input of the voltage controlled oscillator whenever the standing wave ratio exceeds a pre-set value, and for holding the last voltage signal received by the control input of the voltage controlled oscillator whenever the standing wave ratio is equal to or less than the pre-set value. Thus, the power supply frequency will be automatically varied to maintain the standing wave ratio below a pre-set value which is deemed to be an acceptable value for efficient transfer of power.

Signal generator including high and low frequency oscillators

Abstract: A signal generator includes a high frequency oscillator such as a quartz crystal oscillator at a frequency of 4.19 MHz, a low frequency quartz oscillator with a frequency of 32 kHz, a beat frequency generator for producing a correction signal which is transmitted to a programmable frequency divider, and an electronic switch for periodic switching of the high frequency quartz oscillator. By periodically switching-on the high frequency quartz oscillator, comparing its frequency curve with that of the low frequency quartz oscillator and and appropriately adjusting the programmable frequency divider, the advantages of long term stability, temperature of behavior and aging of a high frequency oscillator are combined with the low current consumption characteristics associated with the low frequency quartz oscillator, whereby the life of a battery powering the signal generator can be substantially extended.

Integrated circuit FM local oscillator with AFC control and temperature compensation

Abstract: A FM local oscillator circuit suitable for integrated circuit fabrication, the frequency of which responds to a first current component for reducing frequency drift of a tuned frequency as a function of temperature and to a second current component for providing automatic frequency control of said tuned frequency. The circuit comprises a cross coupled differential pair of transistors, adapted to be coupled to a tuned circuit manually tunable over a given frequency range, which exhibit a negative conductance substantially controlled by said first current component for sustaining oscillations over said given frequency range and which further exhibit a variable capacitance controlled by said second current component for providing electronic fine tuning of the oscillator circuit. The emitters of the differential transistor pair are joined and coupled to first and second current sources, the first of which is temperature compensated for generating said first current component and the second of which is selectively controlled by an AFC control signal for generating said second current component.

Tuning control apparatus of receiver

Abstract: The output of a voltage controlled oscillator serving as a local oscillator is frequency divided by a prescaler and a programmable frequency divider, and the frequency divided output is applied to a phase locked loop including a phase comparator and a charge pump. An S curve signal obtained from a frequency discriminator is applied to an automatic frequency control loop including a window comparator and a charge pump. The outputs of these two charge pumps are applied through an analog switch to a common low-pass filter and the output of the low-pass filter is applied to the voltage controlled oscillator as a control voltage. A state of reception by the tuner is detected based on the output of an intermediate frequency amplifier and the analog switch is responsive to the detected output and a lock detected output of the phase locked loop. Accordingly, a control voltage obtained from the phase locked loop on the occasion of a station selecting operation or a control voltage obtained from the automatic frequency control loop on the occasion of the reception of the electric wave by the tuner, is switchably selected and is applied to the voltage controlled oscillator.

Metal object locator including frequency shift detector

Abstract: A frequency shift responsive metal detector having a sense oscillator coupled with an inducer loop. When the inducer nears a metal object, the effective inductance is changed which correspondingly shifts the natural frequency of the sense oscillator. The sense oscillator couples with a frequency shift detector. The detector produces a d.c. feedback signal which is proportional to the sense oscillator shift and acts therewith to re-establish the oscillator to it's original natural frequency by way of a voltage controlled reactance. The detector also produces a d.c. output that serves to drive an audio frequency rate voltage controlled oscillator wherein the pitch, or resultant frequency therefrom produced is proportional to the effect of the metal object on the inducer loop. A d.c. signal from the detector also serves to drive a visual indicator, such as a meter. The change in the loop inductance may be either positive or negative, resulting in a unique indication distinction between diamagnetic materials, and those which are ferromagnetic or paramagnetic. The use of a dual channel, stereo-like apparatus also provides the operator with directivity, which may be coupled with an enhancement gate signal which alternates the stereo-response back and forth between the earphones of a stereo-headset, thereby improving operator acuity.

Controlled oscillator having random variable frequency

Abstract: Method and apparatus for varying the output signal frequency of a controlled oscillator. The oscillator control signal is formed by filtering the output of a random number generator in such a way that the oscillatory output signal has a random frequency walk phase characteristic having predetermined, controlled characteristics.

Circuitry for switching effective electrode area on a crystal in a crystal oscillator to vary the oscillation frequency

Abstract: An oscillator comprises plural electrodes formed on a piezoelectric vibrator, and the oscillation frequency is controlled by varying the duty factor of the pulses for switching an effective electrode area of the plural electrodes. The frequency-temperature characteristic of the oscillator is compensated by varying the duty factor of the switching pulses according to temperature variations. No trimmer condenser is needed, and the frequency-temperature characteristic is compensated over a wide temperature range.

Phase locked loop frequency modulator

Abstract: A frequency modulator including a free-running oscillator which is frequency modulated and which is frequency stabilized by means of a reference oscillation by way of a phase control loop having a phase detector and a loop filter. In order to be able to process d.c. components with such a frequency modulator, given a keyed modulation signal, and without abandoning the limitation of the modulation spectrum, the modulation signal is supplied to a control input of the oscillator both by way of a modulation filter and by way of the phase control loop. For this purpose, the phase control loop includes, between the oscillator output and the phase detector, a frequency divider having a division ratio controlled by the modulation signal.

Pulsed coherent doppler radar with frequency agility

Abstract: A pulse coherent Doppler radar allows both transmission frequency agility and pulse repetition frequency agility in association with phase encoding which accomplishes the transmission frequency agility by the use of a transmission oscillator, the nominal frequency which may be modified by a microcomputer, a local oscillator, a reference oscillator, and a phase-locked loop having a phase comparator with the oscillator and a mixer for receiving the signals issued by the oscillator and the signal issued by the local oscillator.

Swept frequency oscillator with compensation for variations in tuning sensitivity

Abstract: In a swept frequency oscillator arrangement compensation is provided for the non-linearities in the tuning sensitivity of the oscillator. The non-linearities are initially measured and stored. Subsequently the stored values are used to control the rate at which the clock pulses are integrated to produce a control signal for the oscillator.

Variations of type III burst parameters during a decametric solar storm

Abstract: An analysis has been made of type III bursts recorded during a decametric solar storm observed from July 29 to August 16, 1975 with the UTR-2 antenna (Kharkov, IRE Acad. Sci. Ukr. SSR). The bursts were recorded with a dynamic spectrograph and radiometers at 25.0, 20.0, 16.7, and 12.5 MHz. Daily observations have yielded histograms of the type III burst distribution with respect to the frequency drift rate in three subbands between 25.0 and 12.5 MHz. During the middle stage of the storm the drift rate was about twice as high as at the onset and the final stage of the storm. Abrupt changes in the mean frequency drift rate were registered some two to three days after the active region McMath 13790 had come onto the limb and also before it disappeared behind the solar disk. Sudden changes in the drift rates of the type III bursts were accompanied by sudden changes of their mean duration. The rather long burst durations observed at 25.0 MHz at the beginning and the end of the radio storm coincided with such at the twice lower frequency, i.e. 12.5 MHz, during the period when an increased drift rate was observed.

Random power controller

Abstract: The frequency of a reference oscillator is controlled by a reference voltage which is altered at the beginning of an output cycle to equal the instantaneous value of the averaged outputs of a first oscillator and a second oscillator. In a preferred embodiment, the outputs from the reference oscillator and the second oscillator are summed, and this voltage is used to control the power output to a load.

JFET Reflection oscillator

Abstract: A high frequency oscillator circuit is provided using a low cost junction type field effect transistor (T1) with a tuned circuit connected to its gate. The frequency of operation is determined by the tuned circuit and the capacitance reflected from the source to the gate. The transistor is matched to the frequency of operation so that this frequency falls within the roll-off portion of the transistor's transconductance verses frequency curve, preferably somewhat above the 3 db point in frequency. Phase shifting necessary to sustain oscillation occurs due to the operation of the transistor in the roll-off portion of the curve and the addition of a phase shifting network (R1, C1) at the source. The resulting oscillator is small, stable, linear and inexpensive.

Temperature compensated signal generator including two crystal oscillators

Abstract: A signal generator having a digital temperature compensation circuit contains high and low frequency quartz oscillators (HF and NF), the low frequency oscillator being used for temperature compensation. Both oscillators are manufactured such that the descending portion of the temperature dependent parabolic frequency curve of the low frequency oscillator passes through the temperature inversion point of the parabola of the high frequency oscillator. The frequencies of both oscillators are first adjusted such that the ratio thereof is inversely proportional to the ratio of the parabolic temperature coefficient, i.e., f 1 :f 2 =β 2 :β 1 . Subsequently two substantially identical reference frequencies are adjusted and, by feeding back the output frequency, combined in such a manner that an output frequency independent of temperature is produced which is determined substantially by the high frequency oscillator. The signal generator is thus temperature compensated and, due to the use of a high frequency oscillator, has much better properties with regard to aging and frequency stability than a low frequency oscillator.

Radio receiver with system for maintaining optimum tuning

Abstract: A radio receiver comprises a voltage-controlled oscillator acting as a local oscillator, a capacitor to supply a control voltage to the voltage-controlled oscillator, a phase locked loop incorporating the voltage-controlled oscillator and adapted for a preset selection of a broadcast station, a charge/discharge control circuit to charge or discharge the capacitor adapted for automatic or manual selection of a broadcast station, and an automatic frequency control circuit adapted for maintenance of a local oscillator frequency when the broadcast station is received. A control circuit is provided which couples the phase locked loop or charge/discharge control circuit to the capacitor in response to the selection of one of the station select modes and couples the automatic frequency control circuit to the capacitor in response to the reception of the broadcast station in a good receiving condition.

Radio receiver having phase locked loop frequency synthesizer

Abstract: A radio receiver comprises a frequency conversion circuit connected between a frequency-variable local oscillator and a divide-by-N programmable counter incorporated in a phase locked loop frequency synthesizer and adapted to continuously change the frequency to be divided by the programmable counter. Owing to the frequency conversion circuit, the local oscillator frequency is permitted to continuously change in the locked state of the phase locked loop so that the intermediate frequency offset adjustment of receivers, that is, the adjustment of the intermediate frequency of each receiver to the center frequency of an intermediate frequency filter used in the receiver can be made easily, and that a reception of such a broadcast station as having a carrier frequency which is not an integral multiple of a channel spacing frequency also can be made.

Device for inspecting an individual high frequency signal selected according to frequency from a broad frequency band

Abstract: A device for inspecting an individual high frequency signal selected according to frequency from a broad frequency band comprises a voltage controlled oscillator which can be controlled with respect to frequency by a periodic sweep voltage, in particular a linear sawtooth voltage, in such a manner that all signals occurring in the frequency band can be displayed as a spectrum in the picture screen of a cathode ray tube. The device further comprises a frequency marker generator which has a device for generating a frequency mark voltage and a voltage comparator for, given sweep operation and equality between an adjusted frequency marker voltage and a momentary sweep voltage, generating a frequency mark on the picture screen which is adjustable to identify a corresponding fixed frequency after termination of the sweep operation for inspecting an individual frequency-selected signal. The oscillator is a phase controlled oscillator of a synthesizer in whose control loop a transfer switch is provided and operates in such a manner that the sweep voltage switches off in a first position of the switch and the control loop is closed, and the momentary tuning voltage of the control loop is stored. Subsequently, the control loop is opened in a second switch position and the sweep voltage is connected to the control input of the oscillator. In this mode, the stored tuning voltage is compared to the sweep voltage in the voltage comparator of the frequency mark generator for generating the frequency mark. The transfer switch is held in the first switch condition for evaluating the individual signal.

Pulsed radio frequency transmitting and receiving system

Abstract: A radio frequency transmitter-receiver alternately transmits signal pulses of frequency F 1 and receives return echo signals of frequency F 1 . The transmitter signal of frequency F 1 is generated by mixing signals of frequencies F 2 and F 3 . A signal of frequency F 3 is generated by mixing signals of frequencies F 4 and F 5 . The return signal of frequency F 1 is mixed with frequency F 2 which is continuously generated by the transmitter to produce a signal of intermediate frequency F 3 . Frequency F 5 and therefore frequencies F 3 and F 1 are only generated during signal transmission and therefore do not interfere with the return signal of frequency F 1 and the produced intermediate frequency F 3 .

Receiver for high frequency electromagnetic oscillations having a frequency readjustment

Abstract: A receiver for high frequency electromagnetic oscillations, having frequency readjustment with a voltage-control oscillator, includes a phase control loop for regaining the carrier in the signal path of the receiver. The phase control loop comprises a device for recovering the carrier, a phase-locked loop oscillator and phase detector which receives the output signal of the carrier recovery device and the oscillations of the phase-locked loop oscillator as a reference, and a demodulator which receives the modulated input signal and the output of the phase-locked loop oscillator.

Passive masers having oscillator and cavity control loops

Abstract: The maser of the invention is particularly suitable for forming a frequency standard, by virtue of its excellent degree of frequency stability. The stimulating signal injected into a hydrogen maser cavity 10 is phase modulated at a single modulating frequency from a source 34 by a modulator 2. Nevertheless, the envelope detected signal picked off from the cavity and detected by a detector 13 includes two error signal components which respectively represent the difference between the carrier frequency of the injected signal and the frequency of the stimulated emission and the difference between the resonance frequency of the cavity and the said carrier frequency. These components are distinguished by their phases and phase shifters 42 and 44 and bring them respectively into phase with the modulating signal for detection in detectors 23 and 33 whose integrated outputs are used to control the oscillator 1 (and hence the said carrier frequency) and the cavity tuning respectively.