摘要:

Owing to its larger electromechanical coupling coefficient, the use of lithium-tantalate substrates in place of quartz for the construction of monolithic-crystal filters provides a useful increase in available filter bandwidth. Crystal plate orientations are identified with piezoelectric properties suitable for filter applications, and filterdesign criteria are derived and confirmed experimentally for a number of selected orientations in lithium tantalate. Applying these criteria to the 163° rotated Y-cut plate, third-overtone monolithic-crystal filters have been constructed operating in the frequency range 35–55 MHz with bandwidths up to 0.75%.

DOI:10.1049/piee.1976.0144

出版商:IEE    

年代:1976

数据来源: IET

摘要:

The principle of an inherently simple 8-bit p.c.m. source encoder for video signals is briefly discussed, and a mathematical model of the encoder is developed. Parameters in the model are each assigned a normal probability law in order to simulate the inevitable, small random variations arising from component spreads and alignment error. Monte Carlo sampling of these parameters is then used to relate the degree of instrument error to the degree of chrominance nonlinearity suffered by a PAL colour television signal. The analysis indicates that voltage errors in the encoder should invariably fall within a half-quantum if chrominance nonlinearity is to be acceptable for broadcast quality signals.

DOI:10.1049/piee.1976.0145

出版商:IEE    

年代:1976

数据来源: IET

摘要:

Three years measurements of crosspolarisation and attenuation at 11 GHz are presented. They were taken on a 13.6km terrestrial radio link using horizontal and vertical polarisations. A semi-empirical law based on Oguchi's point-matching attenuation and phase coefficients and relating crosspolarisation discrimination (c.p.d.) to fade depth, is derived. Comparison of this semi-empirical law with measured c.p.d. values shows that the use of an equivalent mean canting angle of 4° gives c.p.d. exceeded for 90% of the time. Typical c.p.d. values for deep fades are given by using an equivalent mean canting angle of 2 or 3°. Yearly cumulative statistics and monthly histograms of c.p.d. and attenuation are presented for the three year period.

DOI:10.1049/piee.1976.0146

出版商:IEE    

年代:1976

数据来源: IET

摘要:

A general method for the design ofRC-active filters that simulate the behaviour of lossless ladder doubly terminated filters is presented. The method is based on the properties of scattering parameters of 2-port networks formulated on a voltage-wave basis from which appropriate active-RCnetworks are derived. The derivation of these networks relies on the interpretation of the incident/reflected voltage waves as voltage-stimulus/voltage-response relationships, and therefore the scattering parameters appear as actual voltage transfer functions.

DOI:10.1049/piee.1976.0147

出版商:IEE    

年代:1976

数据来源: IET

摘要:

The paper describes a d.c. thyristor circuit breaker (t.c.b.) used for high-speed overcurrent protection in low-voltage industrial power installations. The forced-commutation t.c.b. principle of operation, and an industrial model (rated at 600 V d.c., 800 A continuous current) that was subjected to tests under various duty conditions, are discussed. In conclusion, the presented contactless c.b. gives lower peak let-through currents, lower let-throughI2tvalues, and clears faults at least ten times faster than its electromechanical equivalent. It may be advantageously used in networks with a fault-current rise rate up to 107A/s. Therefore the t.c.b. may be considered an effective overcurrent protector for solid-state power devices in industrial applications.

DOI:10.1049/piee.1976.0149

出版商:IEE    

年代:1976

数据来源: IET

摘要:

The paper deals with the rapid determination of the boundary of stability regions which has been the only time consuming step in transient stability studies by Lyapunov's criterion. Three realistic examples, namely a 5-, a 9- and a 15-machine system illustrate and confirm the proposed procedure.

DOI:10.1049/piee.1976.0150

出版商:IEE    

年代:1976

数据来源: IET

摘要:

One of the weaknesses of the small-perturbation theory when applied to power-system stability is that the system differential equations must be linearised with respect to an operating point since they are fundamentally nonlinear. One of the most prominent nonlinear effects is due directly to the loading condition, that is the real and reactive power being transmitted. In the paper, the influence of a generator static-excitation system on the small-perturbation stability of a single-machine infinite system, under widely varying loading conditions, is closely scrutinised by using eigenvalue techniques. The tendency of an unsupplemented static exciter to degrade the system damping for medium and heavy loading is shown in the complex frequency domain. A variable structure power stabiliser (i.e. variable parameters) which is altered to compensate for variations in the system loading is considered. The optimum settings of the stabiliser parameters associated with a selected set of grid points in thePQdomain, are computed offline by minimising a performance criterion. Whereas a stabiliser with fixed parameters is of necessity a compromise, it is shown that one with variable parameters can offer improved dynamic performance under widely varying load conditions.

DOI:10.1049/piee.1976.0151

出版商:IEE    

年代:1976

数据来源: IET

摘要:

An evaluation of the electric field near bundle conductors is essential in e.h.v. or u.h.v. lines. In the paper, the field problem is solved by the integral-equation method. It has the advantage of yielding normal gradients directly with simple computations. The method can be applied to asymmetrical bundles. The presence of earth wires or shielded wires can also be taken into account.

DOI:10.1049/piee.1976.0152

出版商:IEE    

年代:1976

数据来源: IET

DOI:10.1049/piee.1976.0153

出版商:IEE    

年代:1976

数据来源: IET

摘要:

Results of an experimental investigation on an asymmetrical rotor induction motor in developing synchronous torques at any speed other than the ‘synchronous speed’ are reported. It is shown that such torques can be developed at any speed wrelectrical rad/s by injecting additional balanced stator voltages (of proper sequence) of frequencyf−2frwherefis the fundamental line frequency andfris wr/2π. The investigation throws light on the feasibility of using these phenomena for variable speed drives.

DOI:10.1049/piee.1976.0155

出版商:IEE    

年代:1976

数据来源: IET