摘要:

A new radio transmitting station has recently been built by the Post Office on a 700-acre site adjacent to the original Rugby station. The 28 transmitters installed are suitable for independent-sideband operation in the frequency range 4–27.5 Mc/s, provide 30kW peak envelope power and can carry both multi-channel telephone and multi-channel telegraph signals. Upwards of 70 aerials (mainly rhombics) will be provided and will cover transmissions beamed on all the main traffic routes.In the design of the station attention has been focused particularly on flexibility, whereby the maximum use can be made of the plant with the minimum staff. This has been achieved by careful attention to the design of the building; by the maximum standardization of equipment; by the segregation of low-and high-power equipment; by the provision of remotely controlled frequency-changing and aerial-switching; and by the inclusion of a central control position from which the station is operated. Staff at this position can start and stop any transmitter, switch to any one of six predetermined frequencies and to the required aerial, fully monitor its performance and quickly locate a fault.The new station was brought into service in October, 1954, and formally opened on the 28th July, 1955; experience of its operation has fully justified the basic design considerations employed in its planning.

DOI:10.1049/pi-b-1.1956.0155

出版商:IEE    

年代:1956

数据来源: IET

摘要:

A communication system is described which enables three music circuits and an engineer's circuit to be combined. The combination is effected by using pulse time modulation in four time-division multiplexed channels. The purpose of the system is to enable a microwave link, intended for the transmission of television signals, to carry audio signals of broadcast-programme quality as an alternative. The radio equipment, primarily intended for television transmission, need not be specially designed for this particular service.Measurements of the performance of the equipment indicated very satisfactory signal/noise and signal/crosstalk ratios. When the terminals were directly connected the figures obtained were better than those recommended by C.C.I.F. When the terminals were operated in conjunction with a 25-mile radio link there was a 20dB margin in the signal/noise ratio over the recommended value. This margin was allowed for fading of the radio signal.The choice of time division as a multiplexing method is discussed, and the selection of the pulse repetition frequency, duration and time deviation is explained.A detailed description of the multiplexing circuit is given, and both the performance specification and actual measured performance figures are tabulated. Finally, the signal/noise ratio obtained with the radio link working over a 25-mile path is discussed, and the improvement which results from the use of pulse time modulation is explained.

DOI:10.1049/pi-b-1.1956.0158

出版商:IEE    

年代:1956

数据来源: IET

摘要:

Using a wide-aperture spaced-loop direction-finder, measurements have been made of the direction of arrival of high-frequency radio waves propagated over 2100 km. Pulse transmissions were used for most of the experiments, and first- and second-order F-reflections could usually be identified at 11 Mc/s. The bearing fluctuations of these echoes included a lateral deviation component of approximately the magnitude expected from previous experiments at shorter distances. The rapid fluctuations were appreciably larger than they were at 700km, and this appears to be associated with an increased complexity of the individual pulses. This effect was very marked in the night-time observations on 5 Mc/s and resulted in a standard deviation of 1.5° for individual bearings in an hourly period. The corresponding figure for the 1F echo in the day-time on 11 Mc/s was only 0.6°.The results were unaffected by such changes in the transmitting aerial as were practicable, or by ionospheric or magnetic storms.

DOI:10.1049/pi-b-1.1956.0161

出版商:IEE    

年代:1956

数据来源: IET

摘要:

The conventional treatment of propagation coefficients in lossy periodic waveguides suffers from certain major defects. It gives no information about the effects of the losses on the phase-change coefficient, it breaks down when the frequency approaches the edge of a pass-band from within and it does not work at all in a stop-band. A new treatment is described which removes all these defects. It is based on the following result: the propagation coefficient of a mode in a lossy guide at the frequency ω is equal to the propagation coefficient of the corresponding mode in the lossless guide at the frequency ω(1 —j/2Qc). Here,Qcis the “complex Q-factor” of the mode at the frequency ω. It is given by an explicit formula which holds good at all frequencies when the losses are small. When ω lies within a pass-bandQcis equal to ω times the mean energy stored in a period of the guide divided by the complex power dissipated in the same period. When ω lies in a stop-bandQcis equal to the analytic continuation of its values in the pass-bands.

DOI:10.1049/pi-b-1.1956.0162

出版商:IEE    

年代:1956

数据来源: IET

摘要:

The problem of launching and supporting the radial form of surface wave over a flat surface is examined both theoretically and experimentally. The arrangement discussed consists of a vertical dipole aerial erected at different heights above the centre of a large horizontal metal plate inductively loaded at the surface, either by coating it with a thin layer of dielectric or by corrugating it with a series of concentric ridges. The earlier theoretical work of Cullen on the launching of a plane surface wave has been extended to the present case, and the results obtained have been substantially confirmed by the experimental observations recorded. In particular, the practicability of securing launching efficiencies approaching 80% for a particular height of aerial above a given surface has been fully demonstrated.

DOI:10.1049/pi-b-1.1956.0163

出版商:IEE    

年代:1956

数据来源: IET

摘要:

The paper describes a method of deriving numerical values for quantities such as characteristic impedance, attenuation and wavelength with the aid of an electrolytic tank. Numerical results are given for two principal forms of strip transmission line for a range of dimensions for which rigorous solutions by direct analysis are not readily available. This range is nevertheless of considerable practical interest as it encompasses characteristic impedances between 20 and 150 ohms. The recent findings of Black and Higgins in regard to the inaccuracy of the formulae due to Maxwell and Palmer for the strip-above-ground system are confirmed. A new and simple method is derived for calculating approximate values for the pseudo-TEM impedance, wavelength and attenuation of a non-homogeneous dielectric-slab-supported strip-above-ground system (e.g. Microstrip). The numerical results obtained by this method, which depends only on a knowledge of the values for air-spaced lines, are in good agreement with measured results. As a result, it appears that the dominant mode propagating in a Microstrip line is more closely TEM in character than was hitherto supposed. In theory, however there must exist a longitudinal component of the electromagnetic field if the boundary conditions are to be satisfied. Measurements on the electrolytic tank of coupling between adjacent conductors and of field spread are also described. From the analysis as a whole it would appear that the tri-plate (sandwich line) has certain theoretical advantages over the strip-above-ground system. However, these are likely to be offset by a number of important practical disadvantages.

DOI:10.1049/pi-b-1.1956.0164

出版商:IEE    

年代:1956

数据来源: IET

摘要:

The probable causes of the development of stable bombarding potentials on the glass envelope of an oxide-cathode pentode are analysed and subjected to experiment. A photo-electric effect is examined in some detail and shown to give rise to dangerous potentials under certain conditions which may be of interest to electronic switching engineers.

DOI:10.1049/pi-b-1.1956.0165

出版商:IEE    

年代:1956

数据来源: IET

摘要:

The Q-factors of a resonant-cavity magnetron are usually estimated, in terms of the frequency bandwidth of a resonance curve, from measurement of the standing wave which exists in a feeder through which power is supplied to the magnetron at, and near to, its resonant frequency. The accuracy of this method is high, but when changes in Q-factors are to be measured which, for example, may result from changes in the output coupling or tuning of the magnetron, its application is tedious.The use of a directional coupler replacing the standing-wave indicator to monitor the reflected power is well known. Such a coupler may be used in conjunction with a frequency-swept oscillator and cathode-ray tube to give a visual display of the magnetron resonance curve. The paper describes an apparatus of this type which was used for the qualitative examination of magnetron resonances in the 3 cm wave-band, and details of an improved equipment which may be used to measure magnetron Q-factors are given, with a discussion of the accuracy of measurement which may be achieved.

DOI:10.1049/pi-b-1.1956.0166

出版商:IEE    

年代:1956

数据来源: IET

摘要:

The paper deals with the application of the X-ray image-intensifier tube in industrial fluoroscopy and radiography. It considers the factors governing resolution—i.e. brightness, blurring and contrast—and discusses the improvement expected from the use of the image intensifier.Industrial fluoroscopy with this technique is compared with conventional fluoroscopy and contact radiography. Results are given of measurements obtained with D.I.N. penetrameters for steel and aluminium in the voltage range 30–200kV.The conclusion drawn is that the image intensifier allows new applications of industrial fluoroscopy and miniature radiography owing to the enhanced resolution which brings it near to contact radiography. It therefore permits more economical X-ray testing.

DOI:10.1049/pi-b-1.1956.0169

出版商:IEE    

年代:1956

数据来源: IET

摘要:

The paper describes the comprehensive instrumentation scheme recently developed and applied on the new 14 in experimental rolling mill in the British Iron and Steel Research Association (B.I.S.R.A.) Sheffield Laboratories. Roll force on each side of the mill, front and back tensions and strip gauge, using the B.I.S.R.A. gaugemeter principle, are continuously indicated on high-speed servo-operated potentiometric indicators fitted with large pointers and dials. The supply voltage to all measuring elements and transducers in the system is at a frequency of 400 c/s and a rational system of electronic units has been worked out which enables identical amplifiers to be used for all channels. Some of these amplifiers are already in quantity production for other purposes.In the a.c. gaugemeter system used the normal gauge-setting control is situated on the main control desk, and a device is included for automatically setting the zero of the gauge-deviation indicator. Also the mill-screw setting data are fed into the gaugemeter system by Magslip transmission from the screw top. The five indicating dials are mounted in one unit on the mill housing. The whole instrumentation scheme is designed and laid out as a model system for industrial mills of this class.Facilities are provided for experiments with various systems of automatic gauge control previously developed by the B.I.S.R.A.1A simple method of on/off control of the existing a.c. screw motors according to the gauge deviation has been successfully operated with a tolerance zone of only ± 0.0005 in.Facilities have also been provided for switching to automatic tension control based on measured tensions as an alternative to the present method of control of coiler-motor current with correction for radius of build-up.The accuracy of the various measuring systems is discussed in the light of experience gained so far, and attention is drawn to possible sources of error, particularly in the gaugemeter system.

DOI:10.1049/pi-b-1.1956.0172

出版商:IEE    

年代:1956

数据来源: IET