Frequency drift

About: Frequency drift is a research topic. Over the lifetime, 5054 publications have been published within this topic receiving 56191 citations. The topic is also known as: chirp rate.

Flux-flow-type Josephson oscillator for millimeter and submillimeter wave region. II. Modeling

Abstract: A theoretical study is made of a travelling‐wave‐type oscillator, which utilizes a flux flow in a long Josephson junction for use as a local oscillator in the integrated superconducting receiver system. An internal electromagnetic field of the oscillator junction in the flux‐flow state is investigated both numerically and analytically. It is shown that the voltage amplitude of the internal oscillation increases gradually in the direction of the flux flow and reaches a maximum value at the junction end. An equivalent circuit of the oscillator is also obtained, which gives dependences of the emitted radiation on frequency, magnetic field, and load. It is shown that the output power attains the value of the order of 10−6 W in the frequency range between 100 and 500 GHz, and that the output power and the radiation frequency can be controlled by both the bias voltage and the applied magnetic field. These theoretical results explain quantitatively the experimental ones with a Pb‐alloy long junction of length 24 λJ.

Subscriber frequency control system and method in point-to-multipoint RF communication system

Abstract: A point-to-multipoint star configured terrestrial radio communication system having at least one base station transmitting to and receiving RF communication signals from a plurality of associated subscriber stations in the 0.3-300 GigaHertz (GHz) range. The system includes means for reducing frequency uncertainty, drift or error of the RF transmissions from each of the subscriber stations to the base station. Each subscriber station has a low cost local reference oscillator, and the system incorporates a reference broadcast signal of high frequency precision from the base station and at each subscriber station there is means for measuring frequency error and compensating for frequency drift/error in the low-cost oscillator at the subscriber station. Moreover, the system can provide an estimate obtained from measuring each subscriber frequency drift or error in the base station and relaying the measured error to the corresponding subscriber station to compensate for that subscriber's transmitter's local oscillator be out of frequency.

Active microscope stabilization in three dimensions using image correlation

Abstract: Super-resolution microscopy techniques are often extremely susceptible to sample drift due to their high spatial resolution and the long time needed for data acquisition. While several techniques for stabilizing against drift exist, many require complicated additional hardware or intrusive sample preparations. We introduce a method that requires no additional sample preparation, is simple to implement and simultaneously corrects for x, y and z drift. We use bright-field images of the specimen itself to calculate drift in all three dimensions: x, y and z. Bright-field images are acquired on an inexpensive CCD. By correlating each acquired bright-field image with an in-focus and two out-of-focus reference images we determine and actively correct for drift at rates of a few Hertz. This method can maintain stability to within 10 nm for x and y and 20 nm for z over several minutes. Our active drift stabilization system is capable of simultaneously compensating x, y and z drift through an image-based correlation method that requires no special sample treatment or extensive microscope modifications. While other techniques may provide better stability, especially for higher frequency drift, our method is easy to implement and widely applicable in terms of both sample type and microscopy technique.

Stable Dual-Wavelength DFB Fiber Laser With Separate Resonant Cavities and Its Application in Tunable Microwave Generation

Abstract: A single-longitudinal-mode dual-wavelength distributed feedback fiber laser with a wavelength spacing of 0.312 nm is proposed and demonstrated. Based on two spatially separated resonant cavities in a single fiber Bragg grating made by a simple method, stable dual-wavelength lasing is established. Then, a 38.67-GHz microwave signal generated by beating the two lasing wavelengths is obtained with a 3-dB bandwidth of ~6 kHz and a frequency drift <5 MHz without any feedback mechanism. As a potential application of this device, a tunable microwave source ranging from 18.67 to 58.67 GHz (with a small discontinuity) is proposed and partially demonstrated

Evolution of the quasi-periodic oscillation frequency in GRO J1655-40 - Implications for accretion disk dynamics

Abstract: Context. Low and intermediate frequency quasi-periodic oscillations (QPOs) are thought to be due to oscillations of Comptonizing regions or hot blobs embedded in Keplerian disks. Any movement of these perturbations is expected systematically to change the QPO frequency.Aims. Our goal is to find systems where such a systematic drifts have been observed. We also try to find the real cause of such drifts and whether they shed some light on the accretion disk dynamics.Methods. Using archival data of the recent outburst of GRO J1655-40, we report the presence of such systematic drifts not only during the rising phase from the 25th of February 2005 to the 12th March 2005, when the QPO frequency monotonically increased from 82 mHz to 17.78 Hz but also in the decline phase from the 15th September 2005 to the 5th of October 2005, when the QPO frequency decreased from 13.14 Hz to 34 mHz.Results. We fitted the frequency drifts with the propagatory oscillating shock solution. In the shock-oscillation solution, the frequency is inversely proportional to the infall time scale from the shock location. We obtained the shock location and strength through such a fit. Conclusions. The astonishing smoothness of the variation of the QPO frequency over a period of weeks directly supports the view that it may due to the drift of an oscillating shock rather than the movements of a blob inside a differentially rotating disk.