摘要:

The signal/noise performance of a colour picture source is known to be an extremely difficult parameter to measure and specify. Owing to the complexity of signal processing within the picture chain, conventional methods of measuring r.m.s. noise levels at the outputs of the picture source can give a figure of merit that is substantially different from that obtained by direct observation of the subjective noise impairment of the final displayed picture. The paper describes the results of research to establish standard test procedures for the measurement of noise in picture sources. It is shown that noise-measuring equipment may be designed that yields a figure of merit termed ‘the display signal/noise ratio’ for the source under test. This figure of merit corresponds well with the subjective noise performance of the equipment.

DOI:10.1049/piee.1978.0251

出版商:IEE    

年代:1978

数据来源: IET

摘要:

A method of detecting and identifying the total symmetry of ann-variable Boolean functionFwith the use of decimal combinational tables is presented. Instead of using maps, charts or truth tables, with permutations and complementations of variables, this method uses a table which gives for each mintermmi(that makesF=1) the number of adjacenciesw1ranging from 0 ton. The detection of the variables of symmetry is based on finding out from the table a pair of mintermsm* and its is complementm*(or pairs of similar minterms) that among all minterms appearing inF(or in F̄) are distinguished by havingw1equallingnor 0. The parameterw1is the total number of other minterms appearing inF(or in F̄) that differ from any function minterms, e.g.mby one complementation of literal, and is easily determined from the table of combinations. The mintermsmandm* are likely contenders to define the literals of symmetry and merit further investigation. The identification ofFas a totally symmetric function is completed if and when a set ofa-numbers is determined from the combinational table. The paper describes the construction of the combinational table and illustrates the method with example.

DOI:10.1049/piee.1978.0252

出版商:IEE    

年代:1978

数据来源: IET

摘要:

Simulation results of a multiple-instruction multiple-data-stream (m.i.m.d.) organisation are presented. The results deal with the behaviour of throughput performance with respect to variations in cache-memory parameters, number of processors and processing time, of a m.i.m.d. system in which a pipelined binary switch is used as the interconnection network. The results indicate the viability of systems utilising cache memories and pipelined switches which exhibit performance comparable to systems with crosspoint switches. This aspect is attractive, since it is likely that m.i.m.d. systems with pipelined binary switches can be implemented at a lower cost than those with crosspoint switches.

DOI:10.1049/piee.1978.0253

出版商:IEE    

年代:1978

数据来源: IET

摘要:

Interference from other users can be an important source of errors in aeromobile h.f. data transmission and is often more detrimental than the effects of multipath propagation and atmospheric and receiver noise. This paper describes briefly an initial investigation into the frequency and time characteristics of interfering signals within aeronautical h.f. voice channels and considers modem proposals that can improve the performance of slow-rate data transmissions in the presence of such interference.

DOI:10.1049/piee.1978.0254

出版商:IEE    

年代:1978

数据来源: IET

摘要:

The development of an I-shaped novel geometry for radiating slots entirely in the narrow wall of a waveguide is outlined.I2Rlosses in the metal of the waveguide wall are identified as an undesirable feature of impedance-loaded slots or slots of reduced height. The I-shaped geometry developed does not include these features, and is demonstrated to be a useful low-loss waveguide array element, offering a wide range of coupling values.

DOI:10.1049/piee.1978.0255

出版商:IEE    

年代:1978

数据来源: IET

摘要:

The principle of network analysis by scattering matrix renormalisation, described in earlier papers, is extended to 5- and 6-port networks. The 5-port renormalisation transforms are given in detail and the 6-port transforms in symbolic form. A new method of deriving the transforms is briefly described.

DOI:10.1049/piee.1978.0256

出版商:IEE    

年代:1978

数据来源: IET

摘要:

The paper describes a method of minimising the material cost of starting windings for split-phase induction motors. The quantities considered as variables are the number of turns and the wire diameter. The method is considered in the context of a typical starting specification for this type of motor, and the effect of various constraints is discussed.

DOI:10.1049/piee.1978.0258

出版商:IEE    

年代:1978

数据来源: IET

摘要:

The performance of large linear induction machines with nonlinear secondaries is predicted utilising the principle of electromagnetic similitude and small-scale models. A set of scaling factors is derived and confirmed initially using a pair of physically similar solenoids with solid iron cores. Static and dynamic characteristics of the model are scaled and compared with the full-size machine for both dynamic a.c. and dynamic d.c. braking modes. It is concluded that the technique can be used, instead of analysis, to give adequate prediction of performance.

DOI:10.1049/piee.1978.0259

出版商:IEE    

年代:1978

数据来源: IET

摘要:

Radial tooth-ripple forces that are associated with tooth-ripple flux pulsations give rise to undesirable effects in induction motors. The relation between these pulsations due to the main flux and the airgap geometry is considered. By evaluating the amplitude of the tooth-ripple carrier, for a wide range of parameters, general conclusions are drawn that help in the understanding of design problems.

DOI:10.1049/piee.1978.0260

出版商:IEE    

年代:1978

数据来源: IET

摘要:

The magnetic flux in a generator induces a voltage between adjacent laminations of the stator core. These voltages are uniformly low (less than 50 mV) along the length of the core, and so only light interlamination insulation is required to prevent troublesome heating in the core. However, near the end of the core, additional interlamination voltages are induced by the axial magnetic fields in the core-end region and the radial leakage field at the core back. These voltages result from the segmentation of the laminations, and their magnitude depends on the way in which individual laminations are earthed to the stator building bars. These ‘segmentation voltages’ are calculated by considering the eddy currents induced in the laminations by the axial magnetic fields, the currents flowing from the laminations to the stator building bars and the currents induced in these bars by the radial leakage fields. It is shown that, if the contact resistance between the laminations and the building bars is relatively high, and varies from contact to contact, the segmentation voltages are an order of magnitude higher than those induced by the main generator flux and hence sufficient to cause troublesome heating in damaged areas of the core.

DOI:10.1049/piee.1978.0261

出版商:IEE    

年代:1978

数据来源: IET