摘要:

The paper describes an experimental investigation of the problem of mutual and self-impedances of coupled cylindrical aerials. It is shown that mutual-impedance values, calculated on the assumption that the aerial current distribution is sinusoidal, can be used with some success if appropriate values of self-impedance are used. An approximate method for finding these impedances is suggested.

DOI:10.1049/pi-3.1950.0025

出版商:IEE    

年代:1950

数据来源: IET

摘要:

A brief survey is made of the application of a phase-amplitude theorem, due to Bode, to the design of feedback amplifiers with constant-phase margins, and a graphical method of estimating the phase change at any frequency from a knowledge of the amplitude characteristic is described. The use of constant-phase margin as a design criterion is criticized, and justification is given for a new criterion termed “stability margin.” Using this criterion, a technique is developed for employing several feedback paths, thus enabling an increased amount of feedback to be connected to circuits of increased complexity. A brief account of a miniature audio amplifier with two feedback paths is included, and a 100-watt amplifier covering 300 c/s–108 kc/s with some 35 db of feedback is described which, although it is “conditionally” stable, is suitable for use in a multi-channel telephony system.

DOI:10.1049/pi-3.1950.0026

出版商:IEE    

年代:1950

数据来源: IET

摘要:

The properties of the planar diode with space charge and thermal emission velocities were first calculated by Langmuir. His results cannot be presented in analytic form, but only as a table of data. The comparison of these data with experiment is difficult on account of the well-known uncertainty of the total emission of oxide-coated cathodes.In the present paper the properties of the diode are expressed as thirty partial differential coefficients of five interdependent variables. Using Langmuir's assumptions, the expressions for the differentials turn out to be very simple functions of the five variables and three constants. A table of the relations between the differentials is given.Some of the differentials are experimentally measurable. It is possible therefore to use the table either to calculate properties not accessible to direct measurement, or to use it to verify the assumptions made in deriving them. For example, measurements of the characteristic at two different cathode temperatures enable the effect of changing the distance between the electrodes to be calculated. If, however, the electrode separation is in fact variable at will, a comparison of the calculated and observed results will give an indication of the validity of the assumptions made in the theory.The main interest in the differentials is in the motional transconductance, i.e. the change in anode current for unit change in anodecathode spacing. This differential enters into the theory of scale changes in valves and into the theory of their microphonic properties.

DOI:10.1049/pi-3.1950.0029

出版商:IEE    

年代:1950

数据来源: IET

摘要:

The general problem of radiation from lines is discussed and the theoretical background is sketched. The radiation is calculated by the usual approximate method, i.e. the current distribution of the principal wave in an infinite line is first determined, and the radiation field of a finite line is then calculated on the assumption that the current distribution is the same. The method is applied to lines in free space, to single-wire lines above earth of finite conductivity (earth-return lines), and to multiple lines above earth of finite conductivity. The current distribution and possible wave types in some typical multiple-lines are analysed. It is shown that only the wave in the earth-return line, and the corresponding wave type in the multiple line, will produce appreciable radiation. Formulae for calculation of this radiation field are given, and experimental results are described. Conclusions are drawn regarding interference in carrier-line systems and the use of long-wire transmitting antennae.

DOI:10.1049/pi-3.1950.0031

出版商:IEE    

年代:1950

数据来源: IET

摘要:

When a network is required to give an attenuation which is frequency dependent, the specification is usually given in the form of a graph or a table. If the insertion-parameter theory is to be used in finding the network, the specification has to be converted into a rational function. Known methods of achieving this seldom lead to satisfactory results, and a new method has been developed which is applicable to the most general form of the wanted rational function. The numerator and the denominator are composed of factors, each representing a certain group of permissible zeros in the complex frequency plane. The influence of the single factors can be plotted on log-log paper, the sum of the curves obtained representing the attenuation of the complete function. On the other hand, a given graphical characteristic can be approximated by a sum of curves whose functions are known. It is found that only a comparatively small selection of different curves is needed for the solution of practical problems. By way of example, the function for a network meeting the requirements of the C.C.I.F. (Paris, 1947) psophometer weighting-characteristic for commercial telephone circuits is determined. Although, in principle, the method could be applied to filter design, certain difficulties arise, and the chief application may be limited to the design of equalizers and similar networks, in which the attenuation/frequency characteristics do not exhibit excessively sudden changes of slope.

DOI:10.1049/pi-3.1950.0032

出版商:IEE    

年代:1950

数据来源: IET

DOI:10.1049/pi-3.1950.0033

出版商:IEE    

年代:1950

数据来源: IET

摘要:

The large increase in the radiation resistance of a horizontal dipole at low heights above the ground, predicted by the mathematical analysis of Sommerfeld and Renner, is confirmed by actual measurement for the case of an essentially pure dielectric ground. Measurements carried out above a series of conducting mats of increasing mesh size corroborate the supposition that the large increase in the radiation resistance at low heights is caused by a corresponding increase in the energy radiated downwards into the dielectric ground.

DOI:10.1049/pi-3.1950.0034

出版商:IEE    

年代:1950

数据来源: IET

摘要:

Insulated sleeving and covered wires are to-day so fundamental and so common a part of electronic service equipment that their use has tended to become somewhat of a habit, and at times insufficient importance is attached to their selection.This paper, which is restricted to the field of internal set-wiring, attempts to stress the importance of careful consideration in the choice of the wire covering, and also draws attention to the need for standardization and rationalization of the types and sizes of wire coverings employed.A brief résumé is given of the functions which the wire covering has to fulfil; the materials available to meet these requirements are considered, their limitations indicated and the manufacturing processes reviewed.Whatever method or material is used, the final product is judged on its ability to pass the inter-Service specifications now mandatory; these specifications are fully discussed, the test equipment involved described and test results quoted.It will be seen that there are certain requirements not fully met by the wire coverings available, for which the set designer must make adequate allowance, and the paper concludes with an indication of the likely trend of Service requirements together with suggestions for materials and methods by which these requirements may be fulfilled.

DOI:10.1049/pi-3.1950.0035

出版商:IEE    

年代:1950

数据来源: IET

摘要:

The paper describes an instrument for measuring capacitances from –10 µµF to +10 µµF and resistances from 10 ohms to 10000 ohms at frequencies up to at least 1000 Mc/s. The instrument may be fed from the a.c. mains or from a vibrator unit supplied by a 6-volt battery. The voltage impressed on the unknown impedance is low enough for use on receivers. The two scales are direct reading in micro-microfarads and ohms. The accuracy attained is approximately 1%.

DOI:10.1049/pi-3.1950.0036

出版商:IEE    

年代:1950

数据来源: IET