摘要:

The generation-recombination noise of junction-gate field-effect transistors is calculated taking into account the variable mobility. The field dependence of mobility suggested by Trofimenkoff is used, and the resultant spectral intensity of the drain-noise fluctuations shows no signs of a logarithmic singularity at saturation. The need for any cutoff procedure to remove the logarithmic singularity at saturation is therefore removed, and it is thus an improvement over earlier methods.

DOI:10.1049/piee.1974.0306

出版商:IEE    

年代:1974

数据来源: IET

摘要:

The paper presents a pole-zero diagram which is applicable to m.t.i. radar filters operated with a staggered p.r.f. Such a diagram is readily constructed from the pulse transfer function of the filter, and may also be used when time-varying coefficients are employed. It enables the potential performance of a given filter to be quickly assessed, and affords the designer a convenientmethod of obtaining optimum stopband performance from staggered p.r.f. filters without the use of computer optimisation techniques.

DOI:10.1049/piee.1974.0307

出版商:IEE    

年代:1974

数据来源: IET

摘要:

The paper describes an analytic theory of the IMPATT diode, based on the well known Read model. The inclusion of finite avalanche pulse width and space-charge effects in the treatment yields a relatively simple theory that compares well with a computer simulation such as that of Scharfetter and Gummel, or the University College London full-simulation program. The use of such diode admittance calculations in the prediction of oscillator locking characteristics is described. The circuit of a reflection-type locked oscillator is analysed for steady-state conditions and stability limits. After allocation of practical parameter values to the theory, the resulting predicted variation of locked output power with frequency shows good agreement with experimental measurements on a low-power X band IMPATT oscillator.

DOI:10.1049/piee.1974.0308

出版商:IEE    

年代:1974

数据来源: IET

摘要:

The skewing that is found to occur in the amplitude distributions ofmsequences subjected to lowpass filtering is discussed. An analysis is presented which establishes a systematic relationship between the extent of skewing and the characteristic polynomial. The results show that the extent of skewing varies considerably for differentmsequences of the same length. It is shown howthe skewing can be minimised by the choice of a sequence having an appropriate characteristic polynomial.

DOI:10.1049/piee.1974.0309

出版商:IEE    

年代:1974

数据来源: IET

摘要:

Two procedures for modifying linear block error-correction codes are proposed. The first is based on the deletion ofxrows andycolumns from the parity-check matrix of a given (n, k) code, in such a way that the minimum Hamming distance of the resulting (n−y,k+x−y) code remains equal to that of the original. It is shown that ifxis unity, thenymay be as low asthe minimum Hamming distance of the (n, n−k) dual of the original (n, k) code. This procedure of deleting rows and columns when applied to the known linear binary block code yields a family of codes, some of which have better rates than those of the best previously known codes of identical Hamming distance and the same number of paritycheck digits. 17 examples of such new codes are derived and included in the paper. It is also shown that apart from appropriate slight modification, the coding and decoding algorithms for this family of modified codes are similar to those of the original code. The second proposed procedure of code modification entails lengthening the original (n, k) linear block code by annexingk′message digits. If the original code is capable of correctingtrandom errors or less, then the resulting modified (n+k′,k+k′) code has a rate higher than that of the original (n, k) code. Moreover, its error-correcting capability is such that it will correcttrandom errors or less if at least one of these occurs in the block ofkmessage digits andsrandom errors or less, where 1≤s<t, if none of the errors occur in any of thekmessage digits. Five examples of such codes are given.

DOI:10.1049/piee.1974.0310

出版商:IEE    

年代:1974

数据来源: IET

摘要:

The theory of a permanent-magnet d.c. machine that has an axial field and a disc-shaped armature is discussed. Consideration is given to the effect that the distribution of magnetic field inthe airgap will have on the generation of e.m.f. The machine parameters in the angular and radialdirections are related to this distribution, so that a pole shape may be chosen that maximises the output power.

DOI:10.1049/piee.1974.0311

出版商:IEE    

年代:1974

数据来源: IET

摘要:

Several features which could cause an unsaturated 3-phase induction motor to draw nonsinusoidal currents from a supply of negligible harmonic content are examined. An analysis is developed which provides a simple method for the prediction of the harmonic-current magnitudes and frequencies. A comparison of predicted and measured current harmonics is presented to substantiate the theory.

DOI:10.1049/piee.1974.0312

出版商:IEE    

年代:1974

数据来源: IET

摘要:

The conventional theory of the synchronous machine is based on the assumption that the mutual inductances between the three direct-axis windings are all equal. The method is satisfactory for a calculation of the armature current, but the value of field current is considerably in error. Better results are obtained if another reactance is included in the equations to allow for additional coupling between the field and damper windings. The paper shows how the value of the additional reactance can be deduced from the short-circuit oscillograms.

DOI:10.1049/piee.1974.0313

出版商:IEE    

年代:1974

数据来源: IET

摘要:

Invertor-fed brushless synchronous motors are described, in which the harmonic content of typical invertor-supply waveforms is utilised to produce rotor excitation in wound rotors with shaft-mounted diodes. Particular attention is paid to a 3-phase star-connected rotor, connected to two diodes, and a salient-pole rotor with a single diode. Approximate analyses of synchronous performance are presented which provide a clear understanding of the special modes of operation of these systems, and results of full digital simulations are shown to be in excellent agreement with measured performance characteristics. Practical developments are reported which demonstrate the influence of design features, including saturation and skew, and which typify the high levels of performance attained with these motors.

DOI:10.1049/piee.1974.0314

出版商:IEE    

年代:1974

数据来源: IET

摘要:

A mathematical model of a 3-phase synchronous machine, connected to the infinite bus through a delta—star transformer and a transmission line, is given. Symmetric and asymmetric faults on the low-voltage side and on the high-voltage side of the transformer are analysed by using 3-phase variables. Since the simulation is in terms of the direct-phase quantities, the digital-program solution can very easily simulate simultaneous fault conditions as well as sequential faults on either side of the power transformer. By applying proper constraint conditions, the model can be readily used to include symmetric and asymmetric faults for an unloaded alternator, and power-frequency transients following the closure of the generator circuit breaker. The validity of the analysis developed is examined by comparing the digital results with the theoretical results for 3-phase faults on a generator on open circuit, and with a number of experimental results. Versatility is demonstrated by the range of experimental results considered and by further studies.

DOI:10.1049/piee.1974.0315

出版商:IEE    

年代:1974

数据来源: IET