摘要:

When two waveguide modes are coupled uniformly along the direction of propagation, power is partially transferred from one mode to the other. This transfer is only complete if the phase velocities of the modes are equal. If the phase velocities differ, complete transfer of power is still possible if a certain spatially periodic coupling is provided. The exact conditions for complete transfer for a square-wave and raised-square-wave coupling function are derived. To illustrate the theory, experimental results for coupling between the TE10and TE20modes in an overmoded X band guide are presented. Experimental results for a sinusoidal function are also presented. These results provide strong support for the theory of periodic-mode coupling.

DOI:10.1049/piee.1970.0371

出版商:IEE    

年代:1970

数据来源: IET

摘要:

The paper describes a ferrite-core unit serving both as memory and line scanner in a 64-subscriber electronic telephone exchange used as a p.a.x. (private automatic exchange). This dual function is realised by ferrite cores with a rectangular hysteresis loop, using working points different from those of conventional computer core memories and determined by m.m.f.s produced by currents in the appropriate windings. The cores are arranged in a square matrix and are scanned by a ‘linear-selection’ mode. A special bridge amplifier, with logic-controlled switches in its four arms and the reading winding at its centre, permits the reading currents to be directed as required by actuating a pair of opposite arms.

DOI:10.1049/piee.1970.0372

出版商:IEE    

年代:1970

数据来源: IET

摘要:

The paper presents a detailed study of a combined delay- and loss-queuing system which has limited waiting capacity. The queuing system considered is one with Poisson input, exponential servers and first-come-first-served queue discipline. The stationary-state probabilities of the system and the distribution function of the waiting time are obtained in explicit form. It is shown that many results obtained by other workers can be derived from those presented in the paper. In addition, the operational control of queuing systems is also discussed.

DOI:10.1049/piee.1970.0373

出版商:IEE    

年代:1970

数据来源: IET

摘要:

The paper describes the progress of the public mobile-telephone service in the island of Newfoundland from its inception to 1970. A description of the mobile telephone service and the systems of control equipment used are given.

DOI:10.1049/piee.1970.0374

出版商:IEE    

年代:1970

数据来源: IET

摘要:

The case for the use of pulse-code modulation for radiotelephony is summarised. The nature of the problem of achieving clock synchronisation for a time-division-multiplexed/pulse-code-modulation system with mobile terminals is discussed. The problem is first shown to be soluble under the ideal (noiseless) conditions of a perfectly synchronised slave-clock system. Noise in the system has two deleterious effects. It may cause two mark indications to be fed into the system where only one exists, this effect can be eliminated by circuitry arrangements. It may also cause a mark indication to vary its position in the time frame from frame to frame, this effect can be overcome by a clock-phase reversal at a mobile terminal. The parameters used in an experimental system are included as an Appendix to the complete paper.

DOI:10.1049/piee.1970.0375

出版商:IEE    

年代:1970

数据来源: IET

摘要:

A theoretical method is formulated for calculating input and mutual impedances, total field radiated, and power gain of a Wullenweber antenna above a lossy flat earth. The Wullenweber antenna considered here is essentially an array of two concentric rings of discrete elements. Each ring is placed in front of a concentric screen. The inner ring is designed to operate at 3–10MHz, and the outer ring at 8–32 MHz. The radiator used for the highband ring is a sleeve antenna, and that for the lowband ring is a 3-wire folded monopole. Numerical results are given as a function of frequency, ground constants, elevation and azimuth angles with a specified set of element and array dimensions.

DOI:10.1049/piee.1970.0376

出版商:IEE    

年代:1970

数据来源: IET

摘要:

The paper is concerned with an investigation of the propagation characteristics relevant to the operation of digital v.h.f. radiocommunication systems with mobile terminals. Appreciable information already exists regarding the statistics of signal-strength distribution as a function of range and aerial heights. However, comparatively little information can be found concerning the signal distortions likely to be produced by multipath propagation, by operation with a moving terminal, or by signal reflections from aircraft. Such information is required in order to assess the relative merits of different modulation and multiplexing methods and to permit prediction of performance against range. The digit rates of primary interest were about 20k bit/s, 150 bit/s and 75 bit/s. The complete paper describes relevant details of the equipment, an investigation of propagation characteristics with the receiving terminal in a moving vehicle, an investigation of the effects of aircraft reflections, and the possibilities of application of the propagation results to the design of digital transmission systems.

DOI:10.1049/piee.1970.0377

出版商:IEE    

年代:1970

数据来源: IET

摘要:

It is shown that the important performance criteria of conversion gain and intermodulation and cross-modulation distortion performances can be predicted for the double-balanced crosscoupled transistor mixer, driven by a high-level local-oscillator source, to close approximation by extending analysis previously developed for a single-transistor mixer. Good agreement is demonstrated between the theoretical and practical results for a typical high-frequency mixer.

DOI:10.1049/piee.1970.0378

出版商:IEE    

年代:1970

数据来源: IET

摘要:

RCactive filters have been constructed using various kinds of active elements, such as negative-impedance convertors, gyrators and amplifiers. The paper shows a new synthesis method which can independently control the coefficients of both numerator and denominator of a transfer function ofnth degree. The conventional method which has the above ability needs many integrators, but the proposed circuit contains only amplifiers of finite gain and anRCmultiport network. First, the synthesis method of anRCmultiport network, which is necessary to fulfil the above condition, and the circuit configuration using feedback and feedforward techniques, are given. We then apply the method to biquadratic transfer functions. The results show that, in view of the sensitivities and the number and values of the elements, it is desirable to construct the function in a cascade of biquadratic functions rather than to construct the whole function in one circuit. As an example, the 4th-degree lowpass filter with one attenuation pole is synthetised, and experimental results show quite good agreement with the theory. The filters designed by this method are intended for use as controlled equalisers in communication systems, speech synthetisers etc.

DOI:10.1049/piee.1970.0379

出版商:IEE    

年代:1970

数据来源: IET

摘要:

The optimisation of power-system operating conditions is formulated as a dual linear programming problem. This suboptimal model allows fast solutions to be obtained dependably by applying the revised simplex l.p. method to the problem of minimising total generation costs subject to the constraints imposed. These constraints include the network equations, the inequalities restricting generator loading, runningspare capacity and transmission-line loading under normal and outage conditions. The fast speed of solution and low computer-storage requirements result from the reduced mathematical model developed by means of the variable eleimination and the computing strategy used. The computational procedure automatically adjusts the size of the problem to be solved according to indications obtained of the likely critical lineoutage security constraints, a small number in relation to the prohibitively large number of possible outage constraints. A sample application of the method is given for a 2700MW, 275/132kV system of 23 busbars, 30 lines and transformers, supplied by 24 generators. Using ALGOL 60 on the Atlas computer, solutions were obtained in 5s neglecting line-outage security, and 11.5s including security under all possible single-line-outage conditions. For accuracy, comparisons are also made with the network-flow technique and the full nonlinear programming solutions.

DOI:10.1049/piee.1970.0382

出版商:IEE    

年代:1970

数据来源: IET