摘要:

This paper describes measurements designed to study the effect of very short pulses on aircraft echoes. A method is described for making simultaneous comparative echoing-area measurements on aircraft in flight, for different pulse durations. Experimental results indicate a reduction in echoing area as the resolution cell becomes small compared with the aircraft dimensions. Photographs of high-resolution video responses are given for three types of aircraft. Separate radar returns from different parts of the airframe can be clearly distinguished.

DOI:10.1049/piee.1969.0240

出版商:IEE    

年代:1969

数据来源: IET

摘要:

Experimental data on v.l.f. propagation taken during aircraft flights from the United Kingdom over the North Atlantic have shown that, at night, waveguide-mode interference is appreciable at distances of at least 7000km from the transmitter, for frequencies between 10 and 14kHz. The implications of these propagation results on the lane-resolution ability of the OMEGA v.l.f. navigational aid is discussed.

DOI:10.1049/piee.1969.0241

出版商:IEE    

年代:1969

数据来源: IET

摘要:

The geostationary-satellite orbit is uniquely useful for communication satellites. There is, however, an ultimate limit to the number of communications channels which the orbit can support in a given bandwidth owing to the effects of interference between adjacent satellites. By calculating the minimum separation angles between satellites, the capacity of a 10° arc of orbit and a 500 MHz bandwidth is determined as a function of earth-station-aerial diameter and satellite-transmitter power. Results are given for frequency modulation and pulse-code modulation for telephony, and for frequency modulation only for television. The effect on the results of variations in some of the basic assumptions made are discussed in some detail. These include the interference noise permitted, the interleaving of channel carrier frequencies, the use of narrow-beam satellite aerials, and the use of frequency bands higher than those at 4GHz and 6GHz which are used at present. It is shown that capacities of 2000 telephone circuits per degree of orbit might be expected using earth-station aerials 20–30m in diameter. It is further concluded that one of the most significant ways to increase the efficient use of a given arc of orbit is to carefully co-ordinate the characteristics and methods of operation of systems using adjacent satellites.

DOI:10.1049/piee.1969.0242

出版商:IEE    

年代:1969

数据来源: IET

摘要:

The paper presents results which enable the designer of a mobile radio network to allocate channel frequencies which give freedom from interfering third- or fifth-order intermodulation products. The general rules for the selection of third- and fifth-order mutually compatible channels are developed, and Tables of channel-difference sequences are presented for direct use in channel allocation. An extension of the theory for immunity to higher-order products is also given.

DOI:10.1049/piee.1969.0243

出版商:IEE    

年代:1969

数据来源: IET

摘要:

The principles of a method of random access for distributed static stations to a synchronised pulse-code-modulation multiplex system has been described. This paper explains the instrumentation used to build a model to demonstrate the automatic switching of stations to operate in a free channel, and the cross-connection required to apply a store-and-forward technique to pulse-coded signals. The system, which is adapted from one designed for operation with mobile outstations, has a number of limitations. These are considered, and an indication given of the solutions adopted to overcome them in a new demonstration model. The name WISDOM has been derived from ‘Wing's self-synchronising delayed-delta orthogonal-channel modulator’.

DOI:10.1049/piee.1969.0244

出版商:IEE    

年代:1969

数据来源: IET

摘要:

An important problem in the design of v.h.f. and u.h.f. transmitting aerials is the provision of a vertical radiation pattern, which gives an approximately uniform field strength over the prescribed service area. A good solution is provided by a beam-tilted cosecant-shaped radiation pattern. Several methods are described for synthetising radiation patterns of this type by varying either the amplitudes or the phases (or both) of the radiating currents in a linear column of equispaced elements. Some examples are given of the application of these techniques to the types of multitiered aerials employed at v.h.f. and u.h.f. broadcasting stations. Consideration is also given to the problems of realising the required current distributions, and important design factors such as aerial-impedance matching and pattern bandwidth are discussed. Recommendations are made for selecting v.r.p.-shaping techniques to satisfy a range of design requirements.

DOI:10.1049/piee.1969.0245

出版商:IEE    

年代:1969

数据来源: IET

摘要:

This paper describes the development of the stereophonic gramophone pickup since 1958. The basic requirements for such a pickup are given. The characteristics of the early pickups and improvements over the past ten years are discussed. Emphasis is placed on tracing and tracking distortion, mistracking and frequency response. The paper concludes with a list of problems which must still be resolved.

DOI:10.1049/piee.1969.0246

出版商:IEE    

年代:1969

数据来源: IET

摘要:

The phenomenon of second breakdown in transistors is analysed when the breakdown process is initiated by a thermal mechanism. An expression is developed relating the characteristic delay time to the power dissipated in the collector junction. For short delay times, a simple relationship is shown to exist between the parameters describing the breakdown. Experimental results are presented which indicate a reasonable correlation with the theoretical predictions.

DOI:10.1049/piee.1969.0247

出版商:IEE    

年代:1969

数据来源: IET

摘要:

Series and parallel combinations of resistance and inductance are investigated theoretically under maximum-transient conditions, to find alternative representations of the replica impedance employed in distance-protection applications for which the line current is converted to an equivalent voltage. When the primary-system-impedance angle exceeds the replica-impedance angle, the parallel configuration is shown to develop a significantly reduced transient component of the output voltage, and a lower transient flux is required in the core of the energising current transformer.The parallel-tuned-filter circuit is employed in differential current-protection schemes to allow a reduction in the transient component of the relaying quantity derived via a current transformer. The circuit parameters are investigated with a view to minimising the transient-flux requirements of the current transformer and developing an output approaching proportionality with the a.c. component of the primary current. The treatment includes energisation at nonresonant frequencies.

DOI:10.1049/piee.1969.0248

出版商:IEE    

年代:1969

数据来源: IET

摘要:

A theoretical treatment of the mechanical forces developed in power cable conductors as a result of temperature changes is presented, using equations based upon classical beam theory. From considerations of flexural rigidity, it is shown that, in most practical cases, such conductors should have very little bending stiffness and possess considerable longitudinal stiffness. It is also proposed that a joint may be effectively represented as a very stiff spring. For single-core cables, the theory is in good agreement with previously published work, under most practical conditions. A brief extension of the analysis to cover the mechanical behaviour of multicore cables is given.

DOI:10.1049/piee.1969.0249

出版商:IEE    

年代:1969

数据来源: IET