A recent paper1 has described the design and performance of a waveguide-fed parallel plate lens which provides five beams from a sixteen element antenna array, with sidelobes ≈ − 20 dB and beam crossovers ≈ − 10dB, in the frequency band 8–12 GHz. A microstrip version of this lens has been designed, constructed and tested, with the addition of a beam port overlap network to now provide nine beams with crossovers ≈ − 2 dB. Fair performance is achieved at midband, but internal reflections are found to limit the bandwidth of the microstrip lens design.
Results are presented of observations extending over a decade of propagation by means of sporadic-E ionization at frequencies in the range 59 to 77 MHz. The seasonal, diurnal and longer term trends in the data are discussed. Cumulative distributions of event durations are presented for different groupings of the data. A limited study of possible polarization discrimination at these frequencies is also described. The results are discussed in terms of their potential use in spectrum planning at frequencies around 70 MHz.
The general properties of hybrid networks are described and two main types, the quadrature and the 0¿180° types, are identified. A list of uses of hybrid networks in radio frequency circuits follows. Seventeen configurations of hybrid networks are given with diagrams showing the variations of their input and output parameters with frequency. The 3 dB transmission line coupler is described in more detail and multiplexers are mentioned.
The paper describes a technique for implementing moving target indication (m.t.i.) in an independent bistatic radar receiver. Conventional techniques for m.t.i., and the particular features and advantages of the bistatic radar configuration are also reviewed.The technique of phase priming by clutter echoes is suggested as a means for providing a coherent reference at the receiver, without need for any link between radar transmitter and receiver. An oscillator at the receiver is primed at the instant of switch-on at the beginning of each p.r.i. with a small sample of echo signal from close-in stable clutter, such that its phase is determined by that of the clutter echo. This enables m.t.i. processing to be obtained, just as with a conventional monostatic radar system.An experimental system using this principle is described, and results demonstrated and discussed.
Radio waves can induce currents in electrical firing circuits used for blasting in quarries, and for similar industrial purposes, and could cause premature detonation if sufficiently strong. The paper describes an experimental and theoretical study of the currents in typical circuits, and a set of maximum-current curves is presented. These curves form the basis of a set of safe field-strength curves contained in the British Standard guide to the prevention of inadvertent initiation of electro-explosive devices by radio-frequency radiation.
The GEC Hirst Research Centre was formally opened just over 60 years ago. This paper reviews the origins of the Laboratories, records their early history, and describes some of the technical work which they have undertaken. Although the Laboratories were set up to serve all the diverse activities of GEC, the present paper concentrates on electronics and communications.
Binary phase-coded waveforms are widely used in modern radar systems. In linear receivers the sidelobes present at the output of the compression filter cause a reduction of the useful dynamic range. Many procedures have been developed to reduce the sidelobes based on a compensation of their Fourier spectra or on a design of an optimum single mismatched filter. The present paper uses linear programming technique to define an optimum sidelobe reducing network which introduces small mismatching losses when cascaded to a matched filter. The influence of quantization in a digital implementation is evaluated.
A receiver is described that sampled the 1 GHz radio field distribution along a horizontal line of length 32 m. The field distributions were recorded as one-dimensional, offset reference holograms. Computer processing of the holograms formed focused images of scatterers near the line-of-sight path between a c.w. transmitter and the receiving aperture. These images took the form of reconstructed wavefronts, which were further processed by a technique involving complex division and subtraction. Some test results are presented, in which a near-by signal source and an obstacle casting a shadow were imaged.
Videotex is an electronic information service which allows the sighted user to access a vast amount of information via the telephone line, to be viewed on the screen of the domestic television receiver in a compact and colourful layout. In this paper, the development of a microprocessor based system for converting videotex pages to synthetic speech in real time, for the benefit of blind people, is described. The system has been successfully used by some blind people to access the British Telecom videotex service (Prestel).
This paper describes the philosophy and principles of Integrated Services Digital Networks (ISDN), reviews the CCITT standards activities and outlines the plans and strategies for evolution to an ISDN.
This paper describes a joint BBC/BT pilot scheme involving the transmission of broadcast quality sound and vision signals and other services over a 140 Mbit/s digital bearer between London and Birmingham. Terminal equipment, designed and constructed by the BBC, is described which assembles one PAL television signal, including teletext and associated stereo signal, with 12¿5 Mbit/s available for further high quality audio channels, telephony, data and error correction. The means of transmission involves the use of an optical fibre system, a radio relay channel and a coaxial line system. Initial evaluative studies are briefly outlined.
The data collection and analysis system has been developed for a factory producing beam deflection units for colour television picture tubes. The existing factory information system is described and the requirements of a system more suited to a proposed new product are discussed. The production process for the new deflection coil is described in some detail. The collection of production data during the assembly process is then outlined and the computer-based system is described. An indication is given of the performance achieved.
Over the past decade or so, travelling-wave-tube amplifiers for communications have advanced from field replaceable glass bodies to packaged metal ceramic tube construction and from large, fully adjustable, linear power supplies to miniature, highly efficient, preset switched mode units. The principal features of modern tube design are based on metal ceramic technology, dispenser cathodes, two-stage depressed collectors and samarium cobalt magnets.Equally important, though often neglected in the literature, is the design and construction of the power supply and in particular the interface between tube and supply. These problems and their solutions in development and manufacture are discussed in this paper and a case is presented for a more integrated design approach.
A linear active RC network with two capacitors is sufficient to realize a 2nd-order transfer function. By making equal the time-constants which consist of one capacitance and the resistance seen across this capacitance with the other capacitance open circuited, minimum network sensitivity can be obtained.
The paper starts with a summary of the techniques available for implementing digital satellite transmission systems, then goes on to discuss current and probable new error performance objectives that will be consistent with the requirements of the Integrated Services Digital Network (ISDN). The main body of the paper discusses factors which affect performance, including capacity/quality trade-offs, satellite and Earth station parameters, atmospheric propagation conditions, interference and intermodulation. The conclusion indicates briefly the techniques available to a system designer to meet performance requirements.
