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Spectrum analyzer

About: Spectrum analyzer is a research topic. Over the lifetime, 12217 publications have been published within this topic receiving 101851 citations.


Papers
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Journal ArticleDOI
TL;DR: In this paper, a three-phase total demand distortion index and a total unbalance index are proposed to characterize the time-varying data to simplify their representation, and the exposed procedures are applied to the data registered from an electrical power system, to show the performance of the proposed methods.
Abstract: Voltage and current waveform distortion are more prevalent on power systems today related to nonlinear loads. The proliferation of loads of this kind and their interaction with the power supply system is increasing the need to use power monitoring equipment to evaluate electric power quality. Measurements show that waveform harmonics and unbalance are variable over time due to changes in load conditions and in the system configuration. Thus, the electrical engineer has a large amount of data available from each phase, acquired using commercial Analyzers. Therefore, it is necessary to find ways to characterize this group of recorded data, to allow proper evaluation of the situation. Two indices, which can be calculated with these measurements, are proposed in this work: a three-phase total demand distortion index and a total unbalance index. In addition, this paper proposes an easy way to characterize the time-varying data to simplify their representation. The exposed procedures are applied to the data registered from an electrical power system, to show the performance of the proposed methods.

30 citations

Patent
12 Nov 1997
TL;DR: In this paper, a multi-modal waveguide-based spectrum analyzer is used to analyze the spatial mode spectrum of radiation received from a scene, where a portion of the laser light is directed towards a mode generator which selectively converts the laser radiation into one of a series of modes.
Abstract: A radiation field analyzer (10) provides means for analyzing the spatial mode spectrum of radiation received from a scene. In a multimode waveguide embodiment, light from a laser (24) is directed towards a scene through an alumina waveguide structure (12). A portion of the laser light is directed towards a mode generator (28) which selectively converts the laser radiation into one of a series of modes. Laser light returning from the scene is mixed with the light from the mode generator to produce interference signals. These signals are measured by a detector (34) and analyzed by a programmed computer (36). By sequentially altering the mode generated by the generator (28) and analyzing the resulting signals, a spectrum of the modes returning from the scene is obtained.

30 citations

Journal ArticleDOI
TL;DR: The design and development of a palm-sized, cost-effective, microcontroller-operated analyzer for direct amperometric measurements is described, and its utility was assessed by performing experiments for the determination of ascorbic acid in standard solutions and pharmaceutical tablets.
Abstract: The design and development of a palm-sized (9 cm × 11 cm × 3 cm), cost-effective, microcontroller-operated analyzer for direct amperometric measurements is described. The low-power-consumption electronics used allow 8 h of autonomous operation with a 9 V battery (110 mAh), making thus this unit suitable for in-field measurements. Its operation is based mainly on the simple two-electrode potentiostatic mode, although the three-electrode mode is an option. The use of a microcontroller combined with analog and digital supporting circuits allows: (i) generation of the applied potential and the acquisition of analog signals with a gain auto-scaling capability; (ii) interaction with the operator for setting the measurement parameters; (iii) processing of data and displaying result on an LCD screen. Numerical data are automatically stored in memory and they can be retrieved by a personal computer through an RS232 port, either for creating measurements archives or for advanced processing. For this purpose, a program has been developed (on the LabVIEW platform) to provide a user-friendly graphical interface. The utility of this amperometric analyzer was assessed by performing experiments for the determination of ascorbic acid in standard solutions and pharmaceutical tablets.

30 citations

Journal ArticleDOI
TL;DR: In this paper, a short-time cepstrum analyzer for vocal pitch detection has been simulated on an IBM-7094 digital computer, where the amplitude spectrum of a signal is defined as the square of the Fourier transform of the logarithm of the amplitude of the signal, which is inversely proportional to the fundamental frequency of the speech.
Abstract: A short‐time cepstrum analyzer for vocal‐pitch detection has been simulated on an IBM‐7094 digital computer (The cepstrum of a signal is defined as the square of the Fourier transform of the logarithm of the amplitude spectrum of the signal) Since temporal periodicities in a speech signal cause periodic ripples in the amplitude spectrum, Fourier transformation of the spectrum gives the “frequency” of the ripple, which is inversely proportional to the fundamental frequency of the speech Taking the logarithm of the amplitude spectrum makes the effects of the vocal tract (spectrum envelope) and the vocal source (spectrum fine structure) additive, thereby separating the low “frequencies” of the spectrum envelope from the usually higher frequencies of the spectrum fine structure Cepstrum pitch detection is insensitive to phase distortion, amplitude distortion, additive noise, and the absence of the fundamental speech frequency A general description of the technique and some recent results and examples are

30 citations

Journal ArticleDOI
TL;DR: A procedure for measurement of fluorescence lifetimes with picosecond time resolution is described, and with the spectrum anlyzer and 170-MHz light modulation frequency, the team has achieved 4-ps lifetime resolution.
Abstract: A procedure for measurement of fluorescence lifetimes with picosecond time resolution is described. A cw laser beam is modulated with a standing‐wave acousto‐optic modulator. The modulated beam is split; one part serves as a reference beam, the other part excites the fluorescent sample. The sample flourescence and the reference beam, attenuated and delayed optically to be equal in amplitude and opposite in phase to the fluorescence, are incident onto a single photomultiplier tube. The thus achieved photodetector ac null is monitored either by an AM radio, whose intermediate‐frequency signal is displayed on an oscilloscope, or by a spectrum analyzer. With 30‐MHz light modulation and the radio, lifetimes could be determined with resolution better than 15 ps. With the spectrum anlyzer and 170‐MHz light modulation frequency we have achieved 4‐ps lifetime resolution. Correction for photomultiplier transit time versus incident wavelength is made.

30 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20241
2023256
2022568
2021155
2020287
2019361