摘要:

The chirp-signal data-communication system, and the application in communication to civil aircraft via satellite relay, are outlined. A vital part of the receiver is the dispersive network, which processes the chirp signal; the problems encountered in the realisation and utilisation of this network are examined.

DOI:10.1049/piee.1974.0045

出版商:IEE    

年代:1974

数据来源: IET

摘要:

A decision-directed delay-lock loop is described using the fast Fourier transform (f.f.t.) for cross-correlation, together with decisions based on maximum likelihood. The f.f.t. produces a complete set of lagged products of the received echo and the delayed replica of the transmitted signal. This enables the loop to realise a wide dynamic range. Another useful feature of the loop is that it has the ability to detect unlocking and to switch automatically between the modes of acquisition, tracking, and detection of unlocking and reacquisition.

DOI:10.1049/piee.1974.0046

出版商:IEE    

年代:1974

数据来源: IET

摘要:

The paper describes several circuits, which include subsystems switched with alternating polarity. Practical applications are shown. The analysis of such circuits is presented in a companion paper (Proc. IEE, 1974,121, (2), pp.(88–90). The circuits considered in the paper are for a high-power oscillator, for power-factor control by means of a switched coil, and for load-power regulation by means of a switched capacitor.

DOI:10.1049/piee.1974.0047

出版商:IEE    

年代:1974

数据来源: IET

摘要:

The finite-size belt-generator representation of coaxial-line excitation is used for analysis of cylindrical monopole antennas driven by a coaxial line and immersed in a conducting medium. Whereas the existing theories are inaccurate for σ/ωε > 1, the results for admittance and current distribution obtained by the present theory are in excellent agreement with available experimental results for all the conductivities of the medium.

DOI:10.1049/piee.1974.0048

出版商:IEE    

年代:1974

数据来源: IET

摘要:

The antenna arrays considered consist of identical parallel dipoles equally spaced around, and perpendicular to, a circle. The method of polynomial decomposition used to determine the phase sequence currents has proved to give excellent results. Moreover, the accuracy of the results can be very easily increased by simply increasing the order n of the polynomial. The other main advantage of the method over the other existing methods is its very simple programming logic. A comparison of theoretical and experimental results is presented.

DOI:10.1049/piee.1974.0049

出版商:IEE    

年代:1974

数据来源: IET

摘要:

Scattering by rain is often neglected when evaluations of attenuation are made from aerial-noise temperatures observed by radiometers. Calculations show that values may be significantly low if the attenuation is assumed to be due only to absorption in the rain. Curves are given for estimating errors at frequencies of 37, 72 and 110 GHz.

DOI:10.1049/piee.1974.0050

出版商:IEE    

年代:1974

数据来源: IET

摘要:

The results of a statistical investigation of the variation of E-region critical frequency f0E with solar activity, solar zenith angle and season, are synthesised to obtain a describing function of f0E in terms of geographic latitude, solar zenith angle and 10°7 cm solar radio-noise flux, for the design of ionospheric transmission paths. The reliability of the f0E expression is assessed by comparing predicted and observed values at various stations, and the standard error of estimate is determined.

DOI:10.1049/piee.1974.0051

出版商:IEE    

年代:1974

数据来源: IET

摘要:

Alternating currents will generally be present in a d.c. traction supply owing to the action of synchronously switched power-control equipment and also to the presence of mains-frequency-harmonic voltage ripple. This paper describes the factors that determine the magnitude and frequency of such current in the power rails, for various conditions of d.c.-chopper operation. Models that describe the introduction of harmonic current into track circuits are developed from power-circuit considerations, and theoretical predictions are compared with practical results obtained from measurements undertaken by London Transport. The use of multiphase chopper equipments to reduce the size of the input filter is considered, and it is shown that, when normal-load unbalance conditions are considered, no advantage is gained by using more than two phases.

DOI:10.1049/piee.1974.0052

出版商:IEE    

年代:1974

数据来源: IET

摘要:

The amplitudes of saturation harmonics in an induction machine are evaluated by performing a nonlinear field calculation over a radial cross-section of the machine. The approach is more direct than existing methods, and has certain advantages with regard to convenience and accuracy. Overrelaxation is used to solve the field equations, and particular attention is paid to the problems that arise from the introduction of variable permeability into this procedure.

DOI:10.1049/piee.1974.0053

出版商:IEE    

年代:1974

数据来源: IET

摘要:

To reduce computational effort when evaluating the transient response of multiconductor transmission lines, a simplified means of obtaining frequency responses is described. The method employs the concept of frequency-independent modal matrices, and in this respect involves an approximate application of the theory of natural modes. Together with the modified Fourier transform, it is used to provide the transient-response characteristics of typical line configurations found in practice. Furthermore, these results are compared with those obtained more precisely, so as to indicate the high order of accuracy that is possible.

DOI:10.1049/piee.1974.0054

出版商:IEE    

年代:1974

数据来源: IET