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

Volume 98, Issue 54, July 1951

Volumes & issues:

Volume 98, Issue 54

July 1951

Design considerations for a radiotelegraph receiving system
  • Author(s): J.D. Holland
  • Source: Proceedings of the IEE - Part III: Radio and Communication Engineering, Volume 98, Issue 54, p. 253 –262
  • DOI:  10.1049/pi-3.1951.0052
  • Type: Article
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  • p. 253 –262 (10)
    The paper discusses some of the difficulties encountered in the reception of frequency-shift and amplitude-modulated telegraph signals over radio links. Comparison between both methods of signalling leads to the conclusion that greater transmission efficiency can be obtained by the use of f.s. signalling. Fading and interference affect both systems and give rise to distortion characteristics which depend not only on the type of modulation used but to some extent on the particular shape of the modulating waveform. The three main components of distortion are defined, and bandwidth requirements before and after demodulation are discussed. The use of direct printing circuits introduces difficulties during long marking periods and some methods of overcoming this problem are given. The need for exceptional frequency stability in relation to the reduction of errors for both methods of signalling is stressed, and methods of minimizing the effects due to frequency drift by the use of automatic frequency control and other means are discussed. The means of obtaining the greatest benefit from a diversity system are considered, and mention is made of an effective method of diversity working using a.m. signalling. Some observations are made on the effects of noise, and the main features of a satisfactory system for the reception of high-speed signals using either method of signalling.
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Discussion on “Design considerations for a radiotelegraph receiving system” before the Radio Section, 7th March, 1951
The author's reply to the discussion on “Design considerations for a radiotelegraph receiving system”
Radio valve life testing
Discussion on “Radio valve life testing” before the Radio Section, 7th February, 1951
The author's reply to the discussion on “Radio valve life testing”
Discussion on “The space-charge smoothing factor”
Crosstalk in amplitude-modulated time-division-multiplex systems
  • Author(s): J.E. Flood  and  J.R. Tillman
  • Source: Proceedings of the IEE - Part III: Radio and Communication Engineering, Volume 98, Issue 54, p. 279 –293
  • DOI:  10.1049/pi-3.1951.0059
  • Type: Article
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  • p. 279 –293 (15)
    Crosstalk arises in a time-division-multiplex system using amplitude modulation when some of the energy proper to one channel arrives during the time allocated to another channel. Networks inserted in the transmission path will almost always introduce crosstalk, the more so as their bandwidths are increasingly restricted.Analyses of the crosstalk produced by those networks of amplifiers most commonly met with in the transmission path show that no one method of analysis is satisfactory for all networks. Coupling and decoupling networks, producing attenuation distortion at low frequencies, are conveniently tackled by Fourier methods. The use of both networks simultaneously can result in a reduction of crosstalk. The simplest anode loads and those improved by inductance compensation are much better treated by the operational calculus. Experimental results confirm the analyses. Cable problems can also be analysed by operational methods.Because practical low-pass filters introduce serious difficulties in analysis most of the data presented for them are experimental. The oscillatory response found with filters brings new problems. The crosstalk depends on the shape of the transmitted pulse and the duration of the demodulating pulse. Practical systems show little advantage from the use of pulse shapes other than rectangular when the number of networks in the transmission path which distort the pulse shape is small; when the number is large, however, the improvement can be worth-while. The demodulating pulse should not normally be much wider than the transmitted pulse; if it is narrower there may be an increase in crosstalk attenuation.
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Is there an optimum speed for a gramophone record? Radio Section discussion meeting, 19th February, 1951
A phase-comparison method of measuring the direction of arrival of ionospheric radio waves
  • Author(s): W. Ross ; E.N. Bramley ; G.E. Ashwell
  • Source: Proceedings of the IEE - Part III: Radio and Communication Engineering, Volume 98, Issue 54, p. 294 –302
  • DOI:  10.1049/pi-3.1951.0061
  • Type: Article
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  • p. 294 –302 (9)
    The most convenient research method of measuring completely the direction of arrival of waves reflected at the ionosphere appears to be that in which the phase differences of the signals received in an assembly of aerials are measured. If two pairs of similar aerials erected on lines perpendicular to each other are used, two independent phase angles may be obtained from which both angle of elevation and azimuth may be deduced.The apparatus described uses spaced coaxial loop aerials at a separation of 100 m. The signals from the aerials in a pair are amplified by means of matched receivers. The phase difference between the output signals from these receivers is displayed direct on a cathode-ray tube as the angle of inclination of the trace. With pulsed signals emitted from a suitable transmitter and with corresponding timing equipment in the receiver, the individual rays making up the total ionospheric signal may be separated from each other. The apparatus covers the frequency band 4–15 Mc/s, and the r.m.s. error of phase measurement is about 1°. Site errors, however, set a more severe limit to the accuracy of the directional measurements than do instrumental errors, and in practice it is found that, for example, over an oblique path corresponding to a range of 700 km, bearings can be measured with an accuracy of about 1° while the angle of elevation can be measured with an accuracy better than about 1½° so long as it exceeds 30°.These limitations mean that angles of elevation of E-layer reflections cannot be measured accurately at long range; it is possible, however, to obtain measurements of useful accuracy of the angle of elevation of F-layer reflections at ranges up to 1000 km or more. Bearings can be measured accurately at all ranges and for all reflections. The apparatus has so far been used principally for the study of F-layer reflections.
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The measurement of permitivity and power factor of dielectrics at frequencies from 300 to 600 Mc/s
  • Author(s): J.V.L. Parry
  • Source: Proceedings of the IEE - Part III: Radio and Communication Engineering, Volume 98, Issue 54, p. 303 –311
  • DOI:  10.1049/pi-3.1951.0062
  • Type: Article
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  • p. 303 –311 (9)
    The paper describes a resonance method of measuring permittivity and power factor which is essentially a development of the Hartshorn and Ward apparatus, suitable for use at the higher frequencies. The method is one of capacitance variation, and the disc form of sample, the circular plate electrodes and the cylindrical form of micrometer capacitor are retained but reduced in linear dimensions. The capacitive elements are mounted in a re-entrant cavity, and the micrometer capacitor is so placed that the voltage across it is only a fraction of that across the plate electrodes; this increases the fineness of adjustment. The micrometer capacitor can be calibrated only by using the cavity as a wavemeter; the capacitance settings were therefore expressed in terms of the corresponding resonance frequencies, and the calculations of power factor then became identical in form with those of the frequency-change method, although the measurements were made at a constant frequency. After applying the appropriate corrections the permittivity can be determined to within ± 1% over most of the range. The high Q-factor of the cavity and the precision of adjustment of the micrometer capacitor make the power-factor determinations highly accurate. For values less than about 0.01 the error is estimated as being less than ± 2 × 10−5 (for measurements on solids). For higher values a superheterodyne receiver incorporating a piston attenuator is used as the detector, and the estimated limits of error for such measurements are ± 5 × 10−4.
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Note on the variations of phase velocity in continuously-wound delay lines at high frequencies
The effect of the Earth's magnetic field on short-wave communication by the ionosphere
  • Author(s): G. Millington
  • Source: Proceedings of the IEE - Part III: Radio and Communication Engineering, Volume 98, Issue 54, p. 314 –319
  • DOI:  10.1049/pi-3.1951.0064
  • Type: Article
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  • p. 314 –319 (6)
    This paper is mainly a re-presentation of the magneto-ionic theory for oblique transmission through the ionosphere with special reference to numerical applications, but it is directed particularly to the problem of using ionospheric knowledge to plan short-wave long-distance communication. The quartic equation of the theory is solved graphically by the intersection of a straight line with a certain curve, and a chart is described for the construction of the latter for various values of the electronic density. By the method of stationary phase, simple expressions are obtained for the differential coefficients of the ray path, including the group time, lateral deviation and specific attenuation. Numerical integration along the ray path for a given density distribution is discussed with special reference to the relation of oblique to vertical transmission. Some preliminary results are given, but no detailed numerical survey is included, as this would more fittingly form the subject of a separate paper.
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Application of the compensation theorem to certain radiation and propagation problems
Nuclear particle and radiation detectors. Part 1: Ion chambers and ion-chamber instruments
A counting-rate meter of high accuracy
An accurate logarithmic counting-rate meter covering a wide range
Nuclear particle and radiation detectors. Part 2: Counters and counting systems
Scintillation counting equipments
The development of end-window Geiger-Müller counter tubes
A survey equipment using low-voltage halogen-quenched Geiger-Müller counters

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