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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.


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Patent
30 Oct 1940
TL;DR: In this paper, the multivibrator principle is applied to frequency modulators and more particularly to a frequency modulator using reactance tubes to vary the effective reactance of an oscillator circuit to obtain frequency modulation.
Abstract: The present invention relates to frequency modulators and, more particularly, to a frequency modulator using the multivibrator principle. Most prior art frequency modulators use reactance tubes to vary the effective reactance of an oscillator circuit to obtain frequency modulation. This usually...

24 citations

Journal ArticleDOI
TL;DR: In this article, a cross-correlation analysis is used to quantify the dispersive time delay between each frequency of a chorus element as it arrives at Cluster spacecraft pairs and then compared with a ray-tracing technique in order to identify source locations that are consistent with the observed delays.
Abstract: [1] We report Cluster Wideband Data (WBD) receiver observations of correlated chorus elements with different frequency/time characteristics as seen on multiple spatially separated Cluster spacecraft. Because chorus packets disperse as they propagate, careful comparison of the signals from multiple spacecraft can provide new information about the origin of these waves. A cross-correlation analysis is used to quantify the dispersive time delay between each frequency of a chorus element as it arrives at Cluster spacecraft pairs. This data cross-correlation is then compared with a ray-tracing technique in order to identify source locations that are consistent with the observed delays. We also consider a time-variable source that emits frequencies that increase as a function of time. This frequency drift rate is adjusted to force the frequency/time variation of the simulated chorus element on a single spacecraft to match that observed. This process yields possible source locations for each spacecraft, whose location and extent are a function of the amount of source frequency emission drift. By requiring the individual spacecraft source regions to intersect with the multispacecraft source regions, a common static source region at L ∼ 3.9 (McIlwain parameter) and MLAT ∼ −5.9° (magnetic latitude) is identified for a single event (event 1) and upper and lower bounds are placed on the amount of source emission frequency drift within the source. No common source region is found for a second event (event 2).

24 citations

Patent
26 Mar 1979
TL;DR: In this paper, a programmable frequency divider counter is connected between the output of a reference oscillator and a phase comparator to which the output output of the local oscillator in the tuner also is applied.
Abstract: A television tuning system employs a frequency synthesizer system for establishing the tuning of the receiver. A programmable frequency divider counter is connected between the output of a reference oscillator and a phase comparator to which the output of the local oscillator in the tuner also is applied. The phase comparator output provides a tuning voltage for controlling the tuning of the local oscillator. A microprocessor is used to control the count of the programmable frequency divider and initially to set a count corresponding to the selected channel in a counter connected between the output of the local oscillator and the phase comparator. The AFT discriminator signal is used to sense the presence or absence of a properly tuned condition and to control the operation of the microprocessor for establishing the count in the programmable frequency divider counter. For a localized search, the microprocessor may drive the programmable frequency divider counter to a predetermined maximum count and then step back a fixed number of counts to a lower count and resume counting in the original direction; so that even if the AFT discriminator output is in an ambiguous condition, proper tuning can be achieved. However, if the AFT discriminator output produces the correct tuning direction information initially, the programmable frequency divider is adjusted step by step to the appropriate larger or smaller count that corresponds to correct tuning.

24 citations

Journal ArticleDOI
TL;DR: In this paper, the authors developed a fully kinetic linear theory of the drift mirror (DM) instability accounting for arbitrary particle velocity distribution functions including nonzero electron temperature effects and plasma pressure anisotropy.
Abstract: [1] We develop a fully kinetic linear theory of the drift mirror (DM) instability accounting for arbitrary particle velocity distribution functions including nonzero electron temperature effects and plasma pressure anisotropy. In the quasi-hydrodynamic limiting case the theory reproduces the results obtained for the ion mirror instability. However, for the very low frequency electron DM modes which can develop in a nonuniform plasma of nonzero electron temperature, Te ≠ 0, such an equivalence does not exist. We refer to these modes as slow drift mirror (SDM) modes in order to distinguish them from the conventional ion-DM mode. Two new instabilities, one hydrodynamic and one kinetic, that lead to the growth of SDM modes are found in the fully kinetic regime. The first instability develops for values of the ion anisotropy lower than required for the classical ion-DM instability. The second instability occurs when the conditions for the ion-DM instability are satisfied as well. The frequency of the SDM mode is less than the frequency of the ion-DM mode, ω ≪ ωDM ∼ ωn, where ωn is the density gradient-drift frequency of the ions. However, when the electron temperature is of the order of the parallel ion temperature, the SDM instability growth rate may become comparable or even higher than that of the ion-DM instability. The free energy necessary for these new instabilities is taken from two sources. The main source is the energy stored in the ion pressure anisotropy. The second source is the electron pressure gradient which builds up in a plasma of nonzero electron temperature.

24 citations

Journal ArticleDOI
TL;DR: In this paper, the authors examined the behavior of modulational instability in several classes of high-index glass fibers that are being developed to obtain very high nonlinearities and soften the conditions of generation of highly efficient light sources, namely, telecommunication fibers, air-silica microstructured fibers, tapered fibers, and nonsilica glass fibers.
Abstract: We examine the behavior of modulational instability (MI) in several classes of high-index glass fibers that are being developed to obtain very high nonlinearities and soften the conditions of generation of highly efficient light sources, namely, telecommunication fibers, air-silica microstructured fibers, tapered fibers, and nonsilica glass fibers. We perform a comparative assessment of their respective performances in MI processes on the basis of three major performance criteria: the level of the input pump power, the fiber length, and the magnitude of the frequency drifts. Indeed, we show that the effectiveness of MI processes in such fibers is not merely influenced by the strength of the nonlinearity, but is also strongly determined by the linear attenuation of waves in the fiber material. In those high-index glass fibers, this attenuation acts as a strong perturbation, causing a frequency drift of the MI sidebands. However, we show that this frequency drift can be totally suppressed by means of a technique based on the concept of a photon reservoir, which feeds in situ the process of MI by continually supplying it the amount of photons absorbed by the fiber.

24 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20237
202217
202150
202059
201963
201887