摘要:

The paper describes a method of making calculations required in grading resistors for electric traction equipments. The principal features of the method are the use of geometrical progressions in the determination of the resistance grading and the relating of the geometrical progressions to the shape of the motor characteristic curve.It is thought that the clearest way of presenting the method is to work out examples in full, with explanations accompanying each stage of the working. Although the calculations are given in detail, there are many short cuts available to the experienced user.Expedients such as notching at one current in series and at another in parallel have not been introduced, the examples of the method being confined to basic principles only. It is assumed that the notching relay employed is that which has two series coils, one in each motor circuit.Two examples have been worked out, one for a unit-contactor equipment and the other for a cam-operated equipment. In the second example, allowance has been made for the time lag between the release of the notching relay and the closing of the resistance contactor next in sequence.

DOI:10.1049/pi-4.1952.0001

出版商:IEE    

年代:1952

数据来源: IET

摘要:

A general theory of phase transformation by means of static pulsating-flux transformers is presented, i.e.mtonphases on ak-limbed transformer,m, n, andkbeing integers greater than unity. This is derived from the requirements of e.m.f. and m.m.f. balance. Except in the so-called 2-phase case, freedom of choice in selecting the winding elements in each phase always exists and it is always possible to produce a phase transformer for any required transformation ratio and phase shift. It is shown that the effective phase-turns are in general complex and that the ratio of voltage transformation is different from that for current transformation, both being complex and having equal and opposite phase-angles. Equality of primary and secondary power factors is thus established.In the examples given, the Scott and Leblanc connections for 2- to 3-phase transformation are shown to be duals. Two 3- to 4-phase connections are worked out in detail, and the symmetrical phase-transformers used with mercury-arc supplies are discussed briefly.

DOI:10.1049/pi-4.1952.0002

出版商:IEE    

年代:1952

数据来源: IET

摘要:

A microwave valve is considered as a three-dimensional waveguide in conjunction with an electron mechanism. Three spatial axes are chosen and the ways in which they can be terminated are studied. By allotting a symbol to each method of axis termination, all the possible circuit geometries for a given method of interaction can be obtained by permutation. The number of basic valve types is then obtained, after observing that the electron beam may be considered to be subject to the same methods of termination as the spatial axes. Initially 256 symbol groups are found, of which 108 are oscillators and 148 are amplifiers, but these 256 reduce to 104 when considerations of redundancy due to symmetry, of geometrical impossibilities and of the necessity for uniaxial power outflow, are taken into account.These 104 groups are all theoretically possible structures for amplifiers or oscillators, though as 68 contain a certain geometrical complexity which makes them less likely as practical arrangements, only the remaining 36 are considered further and discussed in conjunction with the main types of electron mechanism.The symbolism for many of the familiar valve types is quoted as illustration, but the possible value of the symbolism may lie in the prediction of properties of valves having the same symbol group but different electron mechanisms. An interesting group arises which may be described as “fast-wave” amplifiers, implying that no slow-wave circuit is necessary as with distributed amplifiers of the Kompfner-Pierce type.

DOI:10.1049/pi-4.1952.0003

出版商:IEE    

年代:1952

数据来源: IET

摘要:

Experiments made in Cambridge1, 2during 1933–39 on the reflection of very-low-frequency waves (16kc/s) from the ionosphere have shown that ionospheric propagation at these frequencies differs in important particulars from that at higher frequencies (e.g. 2 Mc/s). There is a large downcoming wave even during a summer day, and the apparent height of reflection is estimated to be about 70 km, whereas on 2 Mc/s, the downcoming wave is relatively weak and the apparent height of reflection is about 100 km. The experiments described in the paper have been undertaken as part of a series of investigations designed to study the transition between these two different conditions, and they have revealed the main characteristics of the behaviour of the downcoming wave on frequencies between 70 and 127 kc/s. The observations have been carried out using c.w. senders situated approximately 100 km from the receiving site.The downcoming wave was found to be approximately circularly polarized with a left-handed sense of rotation viewed along the direction of propagation. Most of the observations have been made on the abnormal component of the downcoming wave field, polarized perpendicular to the plane of propagation; the ratio of its amplitude to that of the “normal” component of the incident field is called the conversion coefficient. At a frequency of 71 kc/s, the conversion coefficient was approximately 0.3 at night, 0.06 on a winter day and 0.002 on a summer day, and at the higher frequencies the values were slightly smaller. These figures are much closer to those observed at 2 Mc/s than those measured at 16 kc/s.The apparent height of reflection is found to decrease over the sunrise period by about 7–8 km on the average. On any one day, the change is very similar at all the frequencies studied, but there are considerable differences from one day to another. This is very different from the observations on 16 kc/s, in which the change of apparent height is about 19 km in summer and 14 km in winter and is very constant from day to day.The decrease of apparent height begins within a few minutes of ground sunrise, but the change of conversion coefficient occurs about one hour before sunrise. The effect of a sudden ionospheric disturbance on the downcoming wave is found to be a decrease in the conversion coefficient and a decrease in the apparent height of reflection. For a sudden ionospheric disturbance which decreases the apparent height by 5 km, the conversion coefficient is decreased by a factor about 0.03.

DOI:10.1049/pi-4.1952.0004

出版商:IEE    

年代:1952

数据来源: IET

摘要:

In a companion paper1the authors have presented the results of a scries of measurements of the characteristics of the downcoming wave observed at a frequency near 100 kc/s at a distance of about 100 km from the sender. In this paper, the results of a complementary series of experiments at greater distances from the sender are discussed. The measurements have been made at frequencies between 70 and 128 kc/s.From measurements of the Hollingworth interference pattern, the apparent height of reflection at oblique incidence (for distances greater than 400 km) has been found to be approximately 70 km at midday in summer, and no definite variation of height with frequency has been detected. The reflection coefficient deduced from the same measurements was found to increase steadily with distance, from 0.02 at 300 km to 0.09 at 800 km from the sender for a frequency of 70 kc/s. The reflection coefficient is found to be less on the higher frequencies. In winter the reflection coefficients at oblique incidence are found to be roughly double the summer values.Up to 350 km from the sender, the diurnal and seasonal variations of apparent height and of absorption appear to be very similar to those reported in the companion paper for 100 km from the sender. The absorption increases about 1 hour before ground sunrise and the apparent height does not begin to fall until very near ground sunrise, when it decreases by about 8 km; this is in good correlation with the observations at shorter distances.When observations are made at distances of 850–950 km from the senders, it is found that both the absorption and the apparent height change about one hour before ground sunrise at the mid-point of the path and that the decrease of apparent height is of the order of 20 km.During a sudden ionospheric disturbance it is found that, at distances of 850–950 km from the sender, the amplitude of the sky wave increases by a factor up to 5 and sometimes reaches its nighttime value. This behaviour is in marked contrast with the observations at short distances, when the amplitude of the downcoming wave is very much reduced. The apparent height of reflection decreases by about the same amount as is observed at shorter distances.

DOI:10.1049/pi-4.1952.0005

出版商:IEE    

年代:1952

数据来源: IET

摘要:

The paper describes three simple impedance bridges for frequencies of the order 50–100 Mc/s. These bridges measure the unknown impedance direct in the formR + jX, whereRis its resistance, andXits reactance.The use of a bridged-T network has enabled the stray admittances to be treated readily. This treatment has been further facilitated in the design by the fact that the impedance standards are all connected in parallel.Two of the bridges described are suitable for the measurement of the “direct” impedance between the two live terminals of a 3-terminal network. They possess the additional advantage that no input or output transformers are required in their construction. The third bridge is suitable for the measurement of impedances which are balanced to earth.

DOI:10.1049/pi-4.1952.0006

出版商:IEE    

年代:1952

数据来源: IET

摘要:

A mathematical analysis of the operation of a phonic motor is presented. Expressions are developed for the motor currents and voltages, power output, efficiency, etc. Both polarized and unpolarized motors are treated, and operation from high- and low-impedance sources is considered. A method for obtaining the motor constants experimentally is given and the predicted power output is compared with experimental results. Power ripple and motor hunting are both analysed. The possibility of multi-phase motors is discussed and some applications of phonic motors are described.

DOI:10.1049/pi-4.1952.0007

出版商:IEE    

年代:1952

数据来源: IET

摘要:

The crosstalk caused by a multi-stage resistance-capacitance-coupled amplifier is determined for time-division-multiplex communication systems using pulse-position modulation (p.p.m.) and pulse-length modulation (p.l.m.). The results are compared with those obtained for pulse-amplitude modulation (p.a.m.). The bandwidth of the amplifier is assumed to be so large that the crosstalk caused by distortion at low frequencies and that caused by distortion at high frequencies can be determined independently. The crosstalk caused by low-frequency distortion is less when p.l.m. is used than when p.a.m. is used and the crosstalk for p.p.m. is less than that for p.l.m. The crosstalk caused by high-frequency distortion is usually negligible except between channels whose pulses are adjacent. The crosstalk for p.p.m. is worse than that for p.a.m., especially if the time constant of the amplifier is either very small or very large. The crosstalk for p.l.m. using front-edge modulation, is worse than that for p.a.m. when the time-constant of the amplifier is small, but better when the time-constant is large.

DOI:10.1049/pi-4.1952.0008

出版商:IEE    

年代:1952

数据来源: IET

摘要:

The effect of mechanical strains introduced in preparing test pieces for magnetic tests in steady fields is discussed, together with the means adopted to minimize them.The need for testing under uniform and strain-free conditions of magnetization is dealt with, and details are given of permeameters which not only produce these conditions but also enable normal testing procedure to be rationalized in order to accelerate the process.A new magnetometer for measuring field strength, which effects a marked simplification in testing without sacrificing accuracy, is described, and the use of a drift-free fluxmeter is mentioned.A new permeameter deriving its excitation from a variable, permanent-magnet source is described. This requires no external electric supply and eliminates problems of overheating.

DOI:10.1049/pi-4.1952.0009

出版商:IEE    

年代:1952

数据来源: IET

摘要:

To generate audio-frequency oscillations, quartz elements vibrating in a flexural mode can be used. Various types of quartz fiexural vibrators are briefly reviewed and two particular types, the + 5° X-cut bar bending in theXY'-plane and the Z-cut gapped ring bending in theXY-plane, are described in some detail.

DOI:10.1049/pi-4.1952.0010

出版商:IEE    

年代:1952

数据来源: IET