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Proceedings of the IEE - Part III: Radio and Communication Engineering

Issue 74 • Date November 1954

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Displaying Results 1 - 13 of 13
  • R.F. conductivity in copper at 8 mm wavelengths

    Page(s): 357 - 359
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (342 KB)  

    Measurements of r.f. conductivity in copper have been made at 8mm wavelengths. It is shown that, in addition to the known effect of surface roughness, the conductivity may be considerably reduced below the d.c. value by surface layers of low conductivity and stress in the bulk material. This can be overcome by etching and annealing, or by a process designed to cover the surface layers. Under suitable conditions the d.c. conductivity can be obtained. View full abstract»

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  • Ionospheric absorption at vertical and oblique incidence

    Page(s): 360 - 367
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1135 KB)  

    Measurements of the ionospheric absorption of radio waves of frequency 9.15 Mc/s over an 800-km path, and of frequency 5.455 Mc/s at vertical incidence at the mid-point of this path, have been made simultaneously over a period of 14 months. A discrepancy between the observed results and those predicted by Martyn's absorption theorem is found, which varies diurnally. The oblique-incidence results are examined in detail, and empirical formulae for diurnal and seasonal variation of absorption are derived. View full abstract»

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  • On the optimum illumination taper for the objective of a microwave aerial

    Page(s): 371 - 382
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1328 KB)  

    The Fourier-transform description of the radiation pattern from an aperture is used to obtain curves relating the overall gain of an idealized aerial system, comprising an objective and waveguide flare, with the size and illumination of the aperture of the latter. For rectangular objectives the dimensions of the aperture of the flare may be varied independently in the two planes of symmetry and the overall gain obtained by multiplying together the gain factors for the distributions across the objective in these two planes. In the case of the circular objective this no longer applies, but curves are drawn showing the variation of the gain of the system as the size of a symmetrical feed is varied by equal amounts in the two planes of symmetry. It is shown that maximum overall gain is obtained with a rectangular objective when the size of the feed is adjusted to give a primary pattern such that the illumination intensity at the edges of the objective is 8¿ dB below that at the centre. The corresponding optimum taper for circular objectives is 11¿ dB. Primary radiation-patterns are drawn for ¿constant,¿ ¿cosine¿ and ¿double-cosine¿ illuminations of the feed aperture. The variations of secondary beam-widths and first side-lobe levels with feed size for rectangular and circular objectives are discussed. View full abstract»

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  • The accuracy of the location of sources of atmospherics by radio direction-finding

    Page(s): 383 - 390
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1218 KB)  

    In recent years, increasing importance has been attached to the use of radio direction-finders for the location of thunderstorms. A large number of stations for this purpose are now in operation, and for the planning of further networks it is necessary to assess the accuracy to which storms may at present be located, and to delimit the areas in which location is satisfactory with the existing networks. An investigation of the accuracy of the United Kingdom network of twin-channel cathode-ray direction-finders, operating at frequencies near 10 kc/s, has shown that instrumental errors other than polarization errors are small, but that at particular stations, errors of several degrees have been caused by the hilly nature of the terrain and by buried cables. When the equipment is on a level site, free from obstructions, polarization errors are likely to be the main limitation to accuracy, particularly at distances of a few hundred kilometres and at night. Maximum errors of 2? or 3? may be expected in summer day-time and rather more in winter day-time. The magnitudes of polarization errors at night are not accurately known. Over a limited range of distance, around 400km, observations on continuous-wave stations exhibit, at times, r.m.s. errors of more than 20?, but there is evidence that errors of this magnitude do not normally occur with atmospherics. At distances greater than 1 000km, polarization errors may be expected to be no greater than 2? or 3?, even at night. At these distances there are also significant errors caused by interference between the atmospheric under observation and others arriving almost simultaneously. Although knowledge of the errors is far from complete, preliminary estimates of their magnitudes have been made and an estimate of the accuracy of storm location has been derived. It is not possible to express the potential accuracy in simple terms, since it depends not only on the bearing errors, the spacing of the stations and the distance of the - storm, but also on the number of observations made and the manner in which they are interpreted. As an indication of the order of magnitude, it is estimated that with the present network and observation technique the probable error in position of a storm centre at a distance of 1 000km is about 20km by summer day, 50km by winter day and 100km by night. These preliminary estimates, particularly that for night-time conditions, must be regarded as approximate because knowledge of the bearing errors is still lacking in some important respects. In particular, a more complete knowledge is required of their amplitude distribution and of the degree of correlation, if any, between polarization errors at the different stations. The types of error discussed are liable to occur with all atmospherics direction-finders in current use; polarization errors, in particular, may be expected with any instrument with an aerial system incorporating either a single rotating loop or a pair of fixed crossed-loops. View full abstract»

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  • The Circuit Development of the Ampliphase Broadcasting Transmitter

    Page(s): 391 - 399
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1271 KB)  

    The paper describes the circuit design of a new type of broadcasting transmitter believed to be the most economical in equipment and valves and of the smallest dimensions and weight for a given power. It has an overall electrical efficiency and a modulation performance at least equal to that of the best known types. This latest type exploits phase-modulation internally in the transmitter to give a normal amplitude-modulated output¿hence the term ¿ampliphase system¿¿amplitude-modulation derived from phase-modulation. View full abstract»

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  • A Radio-Frequency Transformer Attenuator for use with a Level Recorder

    Page(s): 401 - 403
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (414 KB)  

    A transformer-type attenuator is described which is designed to operate at 10.7 Mc/s. It can be substituted for the potentiometer of a commercial high-speed level recorder, no modifications to the recorder itself being necessary. A method of recording field strength is described, using the attenuator and level recorder with a receiver having an intermediate frequency of 10.7 Mc/s. The same apparatus could be adapted to control counters indicating the times during which the field strength exceeds specified levels. View full abstract»

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  • Dielectric measurements with H01n resonant cavities having appreciable loading

    Page(s): 404 - 406
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (341 KB)  

    Modifications to the usual formulae for dielectric measurements in H-mode cavities are suggested to allow for damping due to coupling irises. The correction permits the use of low-level sources. It is suggested that the correction may also be worth while in accurate high-frequency conductivity determinations. View full abstract»

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