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Dec 2002

Volume 73, Issue 12, pp. 4057-4404

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back to top ELECTRONICS; ELECTROMAGNETIC TECHNOLOGY; MICROWAVES

Low-noise and fast-locking phase-locked loop

S. M. Shahruz

Rev. Sci. Instrum. 73, 4347 (2002); http://dx.doi.org/10.1063/1.1519935 (7 pages)

Online Publication Date: 21 November 2002

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In this article, a phase-locked loop (PLL) is introduced. The proposed PLL, denoted by NPLL, is similar to the standard PLL except that it incorporates a nonlinear element and a low-pass filter in its loop. It is shown that by appropriate choices of these two components, the NPLL outperforms the standard PLL in three respects: (i) it has a large acquisition range, i.e., it can achieve locking in situations where the standard PLL cannot; (ii) it achieves locking fast; and (iii) it has low noise in its output phase. The role of the nonlinear element in enhancing the locking capabilities and noise characteristics of the NPLL is carefully examined. Many tests, results of three of which are reported in this article, show the superior performance of the NPLL. © 2002 American Institute of Physics.
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84.30.Qi Modulators and demodulators; discriminators, comparators, mixers, limiters, and compressors

A programmable log-linear amplifier for wide range nuclear power measuring channels

M. Tahir Khaleeq, Mahmood Alam, and Iftikhar Ahmad Ghumman

Rev. Sci. Instrum. 73, 4354 (2002); http://dx.doi.org/10.1063/1.1518144 (4 pages) | Cited 1 time

Online Publication Date: 21 November 2002

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A programmable log-linear amplifier has been developed for nuclear channels. The amplifier can be programmed for logarithmic, linear or log-linear mode of operation. In the log-linear mode, the amplifier operates partially in log mode and automatically switches to linear mode at any preset point. The log-linear mode is used for wide range operation of nuclear channels and, hence, the amplifier will improve the fault finding capabilities of the nuclear channels used in power range. The amplifier is tested at nuclear reactor and the results are found in very good agreement with the designed specifications. This article presents design and construction of the amplifier and field test results. © 2002 American Institute of Physics.
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28.41.Rc Instrumentation
84.30.Le Amplifiers

Carbon velvet field-emission cathode

D. Shiffler, M. Ruebush, M. Haworth, R. Umstattd, M. LaCour, K. Golby, D. Zagar, and T. Knowles

Rev. Sci. Instrum. 73, 4358 (2002); http://dx.doi.org/10.1063/1.1516853 (5 pages) | Cited 31 times

Online Publication Date: 21 November 2002

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Explosive field emission cathodes comprise an important class of cathodes for high power microwave tubes, having the advantages of light weight as well as requiring no heater for electron emission. Generally, however, this class of cathodes suffers from large amounts of outgassing, nonuniform emission, and very high emittance. This article describes a new class of carbon velvet cathodes that have been coated with a cesium iodide (CsI) salt. We discuss two manifestations of the cathode. We review the lifetime and operation of the cathodes with two different pulse durations, as well as the outgassing from the cathodes during operation. Lifetimes in excess of 980 000 pulses have been obtained, with an outgassing rate of 3.5 atoms per electron. Finally, we discuss the uniformity and emittance of tufted carbon cathodes that have been coated with CsI salt. For comparison, we relate these results to those previously obtained from other cathodes in this class. The cathodes have an emittance of 2.5π mm rad, as compared to the theoretical value, based on computation, of 2.3π mm rad. These new cathodes differ greatly from cathodes such as polymer velvet and tufted carbon fiber cathodes in that no volatiles reside on the cathode and in that a unique coating technique allows the cathodes to function. This new class of cathodes offers a potential replacement for existing thermal cathodes, in that no heater is required for superior operation with low outgassing and long lifetime. © 2002 American Institute of Physics.
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85.45.Db Field emitters and arrays, cold electron emitters
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