摘要:

Following the development of the earliest low-noise travelling-wave tubes, some 20 years ago, there was a period of great activity in this field. Until about five years ago, a great deal of work was published both on the theoretical aspects of low-noise behaviour, and on the attainment of low noise factors under laboratory conditions. Since then, the major effort has been directed towards translating these laboratory models into reliable commercial devices, and, in the paper, a review is made of current work on low-noise travelling-wave tubes. After discussing, in some detail, the design requirments of a minimum-noise-factor t.w.t., the paper shows the interrelation between the noise factor and the other prime requirements of a t.w.t.,—gain, power and bandwidth—with particular emphasis on the practical considerations involved. The implications of the choice of permanent-magnet focus mount and r.f. coupling system on the optimisation of the size, weight and performance, are considered, together with the compromises that are available. The final sections of the paper are devoted to cosideration of some of the other characteristics of low-noise t.w.ts. which are of interest to a systems designer. These include the dynamic range, gain and phase tracking, environmental performance and life behaviour.

DOI:10.1049/piee.1970.0062

出版商:IEE    

年代:1970

数据来源: IET

摘要:

Measurements are reported on current limitations induced by single cylindrical-hole grids in mercury-vapour valves. It is shown that, over a wide range of time scales, a single equation may be used to predict the onset of ‘chop’ for a variety of current waveforms. The values of the two parameters in the equation are estimated for grids of different diameters and depths. The neutral-number density under prescribed conditions of pool temperature and excitation anode current is measured so that dependence on this parameter is also determined.

DOI:10.1049/piee.1970.0063

出版商:IEE    

年代:1970

数据来源: IET

摘要:

The computer is a small desk-top machine designed for teaching schoolchildren how computers work and how to use them. It works in decimal notation and has a powerful instruction set which includes 3-address floating-point instructions implemented as ‘extracode’ subroutines. Addressing can be absolute, relative or indirect. For input it uses a capacitive touch keyboard, and for output and display, a perfectly normal t.v. receiver is used. Another input/output device is an ordinary domestic tape recorder, used mainly for long-term storage of programs. To make the operation of the machine easy to follow, it can be made to stop at certain stages in the processing of an processing of an instruction and automatically display the contents of all registers and storage locations relevant at that time. The paper gives a description of the machine and a discussion of the factors that have influenced its design.

DOI:10.1049/piee.1970.0064

出版商:IEE    

年代:1970

数据来源: IET

摘要:

The fully compelled signalling sequence is frequently used for interregister signalling in telecommunications. The sequence is reasonably reliable, but erors can be experienced when interruptions arise in the transmission path between registers. The paper examines every possible effect of line interruptions, and produces constraints which enable every source of error to be positively eliminated. The constratints govern the application and setting of the timing circuits which, in one form or anothe, are employed with existing fully compelled signalling equipment. The timing circuits do not have stringent requirements, and a standard setting is applicable to all environments.

DOI:10.1049/piee.1970.0065

出版商:IEE    

年代:1970

数据来源: IET

摘要:

The instrument, which was built for the study of solar radiation in the band 2–4 GHz, is capable of measuring the intensity and state of polarisation of the received energy as a function of time and frequency. Energy is received by a 6ft-diameter, paraboloid reflector with a broad band feed. The receiving system consists of four superheterodyne receivers, from which the desired outputs are generated by crosscorrelation processes. Correlation is performed at the intermediate frequency of 30MHz using a type of diode-ring multiplier. The system has a gain stability of ±2% and adequate incremental sensitivity. The paper discusses the general requirements of a solar polarimeter and describes the design and construction of the instrument. Difficulties caused by r.f. coupling between the receiver inputs are discussed, and some preliminary results are given.

DOI:10.1049/piee.1970.0067

出版商:IEE    

年代:1970

数据来源: IET

摘要:

A method has been developed for measuring the common-emitter short-cicuit current gain of transistors at frequencies in the range 10–500MHz. The measurement is made by comparing the voltage outputs of two parallel channels, one of which contains the transistor and a standard attenuator; at balance, the transistor gain equals the attenuator loss. The best absolute accuracy obtainable is within ±0.1 dB, but is limited in practice by the quality of available commercial attenuators to within about ± 0.2dB. The method is suitable either for accurate routine meaurements or to give a precise ‘go-no-go’ indication of whether a required specification is met. The method has been realised in two versions, both using lumped components: a single-frequency version and a wideband version. The single-frequency version will accept transistors with long leads, and imposes no practical upper limits on the d.c. bias which may be applied. The wideband version is inherently less accurate as a result of stray cpacitance from the base terminal to earth; if the stray capcitance is regarded as an essential part of the transistor, the accuracy is not much less than that of the single-frequency version. The d.c. bias in the wideband version is fed through resistors, which may limit the maximum allowable current.

DOI:10.1049/piee.1970.0068

出版商:IEE    

年代:1970

数据来源: IET

摘要:

The nonlinearity of the voltage-frequenc characteristic of a frequency modulator is a factor of primary importance when designing, for example, high-quality modulators for large-capacity microwave links. The nonlinearities of a varactor-controlled oscillator are derived. A theory of various distortion-conpensation circuits is developed. Distortion compensation is applied to push-pull modulator, and 1800–2700-channel radio links, are shown.

DOI:10.1049/piee.1970.0069

出版商:IEE    

年代:1970

数据来源: IET

摘要:

The equivalence properties of nonuniform transmission lines with different parameter distributions are analysed in detail. BothLC(lossless) andRClines are treated. The formulation adopted may be considered as an appilication of the method of spatial-variable transformation to differential equations that govern the transfer-matrix parameters of these lines. The principal result is an equivalence theorem which establishes a general method of equivalent transformation for nonuniform transmission lines. Emphasis is placed on the derivation of the transformation function which plays a key role in the equivalent transformation. The generality of the proposed method of equivalent transformation lies in the fact that there is a large freedom of choice of the form of the transformation function which is pertinent to the problem in hand. Details of the procedure of equivalent transformation are described, and the quantities which are invariable under equivalent transformation are discussed. Furthermore, as an application of the equivalent transformation, the relationship between two particular classess of nonuniformLClines is elucidated, namely, semiuniform lines having uniform series inductance, and reciprocal lines having a constant propagation factor. On the basis of this relationship, it is possible to design various inhomogeneous-layer components by the direct use of the available data on corresponding nonuniform-line components.

DOI:10.1049/piee.1970.0070

出版商:IEE    

年代:1970

数据来源: IET

摘要:

A modified reciprocity theorem is formulated for general bianisotropic media through the definition of a complementary medium. A bianisotropic medium is one in which the field vectorsDandHdepend on bothEandB, and a moving mediucm appears bianisotropic to the laboratory observer even if it is isotropic in its rest frame. The conditions under which the modified reciprocity relationship will hold for moving gyrotropic and biaxial media are discussed.

DOI:10.1049/piee.1970.0071

出版商:IEE    

年代:1970

数据来源: IET

摘要:

The paper shows that it is possible to compensate for the effects of mechanical profile errors in large parabolic reflectors, by means of a specially designed multielement feed array situated in the focal plane of the reflector. The factors relating the magnitude and period of these profile errors to the size and complexity of the compensating feed are discussed, and a novel method is described for achieving this compensation by controlling the phasing of the array. The system employs a spatial Fourier-transforming device, and its use is mainly restricted to long-period profile errors. Experimental results of this process, derived from a small-scale laboratory system employing a 1-dimensional 5ft parabolic reflector incorporating an 8-element feed, are presented. These results demonstrate compensation for profile errors up to π/2 radians. The possible application of this technique to existing and new reflectors is discussed.

DOI:10.1049/piee.1970.0072

出版商:IEE    

年代:1970

数据来源: IET