摘要:

The radiation pattern in the Fresnel region is expressed as a function of the far-field polar diagram. Following this it is shown how the true side-lobe level may be inferred from amplitude radiation-pattern measurements made in the Fresnel region. This results in considerable shortening of the range at which polar-diagram measurements may be made.

DOI:10.1049/pi-c.1956.0042

出版商:IEE    

年代:1956

数据来源: IET

摘要:

A study is made of the extent to which the high-frequency cyclical direction-finder devised by Earp and Godfrey is subject to three common types of error. First, the result is presented of theoretical computations on the errors given by a practical fixed-aerial system in wave-interference conditions. The variance of these errors as the phase difference between the incident rays is varied is shown to be the same as that given by the ideal rotating-aerial version of this direction-finder; it is appreciably smaller than that of an Adcock for a system aperture of 4λ, and, in general, much smaller for an aperture of 10λ. Secondly, errors due to aerial interaction are considered for a system of 24 unipoles, 9m high and 1.1 m in diameter, placed on a circle of 100m diameter. It is concluded that the errors in indicated bearing are likely to be negligible, provided that the aerials not in use at any instant are terminated by a resistor equal to their nominal characteristic impedance. Finally, the polarization error is examined for such a system in which surface feeders are used, without an earth mat, on ground of moderate conductivity; it is found to be small, being greatest at the low-frequency end of the band, where the standard-wave error is about 1° at 3 Mc/s. With extended feeders the errors at low frequencies are reduced considerably.

DOI:10.1049/pi-c.1956.0043

出版商:IEE    

年代:1956

数据来源: IET

摘要:

Negative-feedback amplifiers are used to supply the currents to the coils of a nickel-iron-cored dynamometer, and by this means, indications proportional to current, voltage or power in an external circuit may be obtained from the dynamometer at any frequency between 50c/s and 20kc/s. The signal voltages required at the amplifier input terminals for full-scale instrument deflection are 2 volts. A voltage divider, having a resistance of 1000 ohms/volt and time-constant ratios of less than 0.02μH/ohm, is used to give eight voltage ranges up to 500 volts. The current ranges are obtained by using four terminal resistance standards of different values and having time-constants of less than 0.02μH/ohm.The overall instrument error at any power factor and any frequency within the working range does not exceed 0.6% of full-scale deflection.Internal switching is provided so that the voltage, current and power in a load may be determined without disturbing the load conditions. The upper limit of frequency is 20kc/s for power measurements, except near unity power factor, but voltage and current may be measured at frequencies up to 30kc/s.

DOI:10.1049/pi-c.1956.0044

出版商:IEE    

年代:1956

数据来源: IET

摘要:

A method is demonstrated for arriving at simple formulae by which the resultant reactive power of overhead lines under any load condition can be quickly calculated, and in which the only line constant necessary to be known is the inductance. Tables of practical overhead-line inductances are given. The method is extended to lines containing series capacitors and also to low-voltage lines. The accuracy of the method, applied both to electrically short and long lines, is discussed fully in the Appendix.

DOI:10.1049/pi-c.1956.0045

出版商:IEE    

年代:1956

数据来源: IET

摘要:

The paper treats of a practical method for calculating the m.m.f. required for a tapered tooth, which is correct over the whole range of flux densities and for all proportions of teeth, slots or ducts. Working curves are given for a typical core steel.

DOI:10.1049/pi-c.1956.0046

出版商:IEE    

年代:1956

数据来源: IET

摘要:

The paper describes the use of the Blackburn a.c. network analyser in analytical and analogue methods of investigating faults on 3-phase power systems. In the analytical approach, after defining the faults in matrix form by symmetrical components, the ensuing equations are solved using the Blackburn analyser without the need for further matrix manipulation.In the analogue method, it is shown how the constraints imposed upon the phase voltages and currents can be applied directly to the sequence networks by the connection of symmetrical-component operational matrices at the fault positions. No knowledge of the relationships between the symmetrical-component currents is required, but it is necessary to know the relationships existing between the phase voltages and currents by virtue of the applied faults.The “equivalent series” connections of the sequence networks, derived recently by Kirschbaum in America for application to the conventionaltype network analyser, are shown to be unnecessary when using the Blackburn machine.Finally, systems containing unsymmetrical simultaneous faults are investigated using both methods.

DOI:10.1049/pi-c.1956.0047

出版商:IEE    

年代:1956

数据来源: IET

摘要:

Measurements on a number of transmitters at ranges from 1000 to 5000 km show that the variance of snap bearings within a period of half an hour is of the order of 10deg2. To reduce this variance by a factor of ten, time averaging over about 5 min is required when the bearings are taken at 10 sec intervals. Bearing changes from hour to hour and from day to day have a variance of about 1 deg2and thus set a limit to the error reduction obtainable by averaging over a halfhour period. The results are consistent with previously published estimates of bearing variances.

DOI:10.1049/pi-c.1956.0048

出版商:IEE    

年代:1956

数据来源: IET

摘要:

The use of a continuous delay-line synthesizer as a means for simulating transfer functions of linear systems by a very simple setting procedure is described. An analysis of the accuracy of this device as a system analogue is given, and the degree of approximation in frequency response is calculated for a number of transfer functions typical of servo systems.It is concluded that a delay-line of 26 sections will give a frequency response with not more than 5% error in the working band of frequencies for all normal servo systems.

DOI:10.1049/pi-c.1956.0049

出版商:IEE    

年代:1956

数据来源: IET

摘要:

The paper considers the frequency response of a feedback-system analogue in which the system is imitated by a discontinuous delay-line synthesizer.The various sources of error in the imitation transfer functions of the delay-line synthesizer and stabilizing network, as compared with the actual transfer functions of system and stabilizing network, are discussed. The contribution of each of these sources is calculated for a feedback system consisting of a multi-capacity process and a 3-term controller.The results of these calculations are used to determine how to minimize each of these contributions. Graphs are included from which the number of delay-line sections required for a prescribed accuracy and the best adaptation of the time scale of the process to that of the delay line may be determined.

DOI:10.1049/pi-c.1956.0050

出版商:IEE    

年代:1956

数据来源: IET

摘要:

The frequency-response method is well established in the analysis of control systems and networks, but has hitherto not been extensively used for analysing rotating machines. The method is of particular value When the magnetic circuit of the machine contains unlaminated iron in which eddy currents are set up when the flux changes. The paper describes a method of calculating the performance of the machine, and shows how the effect of the eddy currents can be taken into account.Several methods of calculating the appropriate frequency-response curves have been worked out and experimentally verified. The application of the frequency-response curves to determine the performance characteristics is illustrated by calculations and tests for several simple transient conditions.

DOI:10.1049/pi-c.1956.0051

出版商:IEE    

年代:1956

数据来源: IET