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.

Millihertz Oscillation Frequency Drift Predicts the Occurrence of Type I X-ray Bursts

Abstract: Millihertz quasi-periodic oscillations reported in three neutron-star low mass X-ray binaries have been suggested to be a mode of marginally stable nuclear burning on the neutron star surface. In this Letter, we show that close to the transition between the island and the banana state, 4U~1636--53 shows mHz QPOs whose frequency systematically decreases with time until the oscillations disappear and a Type I X-ray burst occurs. There is a strong correlation between the QPO frequency $ u$ and the occurrence of X-ray bursts: when $ u\gtrsim9$ mHz no bursts occur, while $ u\lesssim9$ mHz does allow the occurrence of bursts. The mHz QPO frequency constitutes the first identified observable that can be used to predict the occurrence of X-ray bursts. If a systematic frequency drift occurs, then a burst happens within a few kilo-seconds after $ u$ drops below 9 mHz. This observational result confirms that the mHz QPO phenomenon is intimately related with the processes that lead to a thermonuclear burst.

Disciplined oscillator system with frequency control and accumulated time control

Abstract: A disciplined oscillator system having a standard oscillator which is automatically corrected for both frequency errors and time error accumulation to a constant frequency signal which is derived from the WWVB carrier frequency and the WWVB TIME CODE to maintain overall frequency accuracy within one part in 10 9 notwithstanding oscillator aging and in spite of jitter and distortion due to propagation delays and noise which may cause loss of, or time jitter in, the WWVB signals. Frequency errors are detected through the use of a counter (24) having a measurement accuracy greater than one part in 10 10 . An error detector (26) derives correction signals by averaging a plurality of frequency variances obtained in successive measurement cycles. Timing errors are corrected by dividers (34, 40) controlled by a timing discriminator (36) which responds to timing variance between signals from the standard oscillator and from the WWVB reference which are phase locked to those TIME CODE signals which are substantially free of noise and jitter. The timing correction is inhibited after the standard oscillator is corrected. Frequency correction is applied continuously.

Optoelectronic oscillator with improved phase noise and frequency stability

Abstract: In this paper we report on recent improvements in phase noise and frequency stability of a 10 GHz opto-electronic oscillator. In our OEO loop, the high Q elements (the optical fiber and the narrow bandpass microwave filter) are thermally stabilized using resistive heaters and temperature controllers, keeping their temperature above ambient. The thermally stabilized free running OEO demonstrates a short-term frequency stability of 0.02 ppm (over several hours) and frequency vs. temperature slope of −0.1 ppm/°C (compared to -8.3 ppm/°C for non thermally stabilized OEO). We obtained an exceptional spectral purity with phase noise level of -143 dBc/Hz at 10 kHz of offset frequency. We also describe the multi-loop configuration that reduces dramatically the spurious level at offset frequencies related to the loop round trip harmonic frequency. The multi-loop configuration has stronger mode selectivity due to interference between signals having different cavity lengths. A drop of the spurious level below −90 dBc was demonstrated. The effect of the oscillator aging on the frequency stability was studied as well by recording the oscillator frequency (in a chamber) over several weeks. We observed reversal in aging direction with logarithmic behavior of A ln(B t+1)-C ln(D t+1), where t is the time and A, B, C, D are constants. Initially, in the first several days, the positive aging dominates. However, later the negative aging mechanism dominates. We have concluded that the long-term aging behavioral model is consistent with the experimental results.

Low-Drift Coherent Population Trapping Clock Based on Laser-Cooled Atoms and High-Coherence Excitation Fields

Abstract: Atomic clocks based on coherent population trapping (CPT) are of great interest for portable applications, due to their high performance, low power requirements, and potential for miniaturization. Slow frequency drift, however, limits their holdover ability on long time scales. This study reports a CPT clock that minimizes long-term drift, with a fractional frequency stability of $3\ifmmode\times\else\texttimes\fi{}{10}^{-13}$ over the span of an hour---ten times as good as previous CPT clocks. After successful shrinking of the laser-cooling apparatus, this clock could see commercial use, as the atoms fall just a few millimeters during a typical probe period.

Random number generator using sampled output of variable frequency oscillator

Abstract: A random number generator designed for use with an electronic key uses a triangular output analog oscillator to vary the frequency of a higher frequency voltage controlled oscillator. The output of the voltage controlled oscillator is sampled at a rate much less than the rate of oscillation of the voltage controlled oscillator to produce random digital values.