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1887

Radio and Electronic Engineer

Volume 39, Issue 2, February 1970

Volumes & issues:

Volume 39, Issue 2

February 1970

Automatic test systems
Interconnexion of frequency-division and time-division multiplex transmission systems
  • Author(s): J.E. Flood  and  A.C. Ponder
  • Source: Radio and Electronic Engineer, Volume 39, Issue 2, p. 67 –76
  • DOI:  10.1049/ree.1970.0009
  • Type: Article
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  • p. 67 –76 (10)
    Multichannel transmission systems are of two general types: frequency-division multiplex (f.d.m.) and time-division multiplex (t.d.m.). In order to interconnect a t.d.m. system with an f.d.m. system, it is not necessary to demodulate each channel to audio frequencies. An amplitudemodulated t.d.m. signal can be converted to f.d.m. by gating it to a bank of band-pass filters, each passing one harmonic of the pulse repetition frequency (p.r.f.). The output of these filters are connected to a common path to provide an f.d.m. signal. An f.d.m. signal can be converted to t.d.m. by separating the channels with band-pass filters and sampling the output of each filter with a pulse occupying a different position in the t.d.m. cycle. The sampled outputs are connected to a common path to provide an amplitude-modulated t.d.m. signal. It is necessary, however, for the carrier frequencies of the f.d.m. system to be harmonics of the p.r.f. of the t.d.m. system.It is shown that resonant-transfer can be used to reduce energy losses in the conversion and so eliminate amplifiers. This has been demonstrated experimentally.
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Design for a multi-input binary adder
  • Author(s): D.W. Lewin
  • Source: Radio and Electronic Engineer, Volume 39, Issue 2, p. 77 –80
  • DOI:  10.1049/ree.1970.0010
  • Type: Article
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  • p. 77 –80 (4)
    The need often arises in digital systems for a fast multi-input adder capable of adding together n distinct serial binary numbers. The normal design method is to employ a parallel-series configuration of 2-input synchronous adders. It is shown how the overall speed of a multi-input adder may be enhanced using a 3-input adder stage. A circuit is described using cascaded 2- and 3-input synchronous adders, which may be clocked at 100 ns allowing the addition of six 10-bit binary numbers in lµs.
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Transient behaviour and characteristics of the high-field domain in Gunn-effect diodes
  • Author(s): Akio Sasaki
  • Source: Radio and Electronic Engineer, Volume 39, Issue 2, p. 81 –96
  • DOI:  10.1049/ree.1970.0011
  • Type: Article
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  • p. 81 –96 (16)
    Quasi-linear equations are used to analyse characteristics of a high-field domain in Gunn-effect bulk semiconductors. The analysis shows that the differential mobility appearing in the relaxation time of the large-signal analysis is not the same as that used in the small-signal analysis. It is also shown that an equivalent admittance of domain is represented by a parallel connexion of capacitance and conductance which vary with time in the transient state. The equations for the shape of domain and for the time-constant of the admittance are derived. The width of a high-field domain and the displacement current of diodes are discussed. The maximum value of the domain excess potential in the diode biased at the threshold is given. Numerical examples of characteristics of a high-field domain based on the results of the analysis are presented. It is pointed out that non-linear and parametric operations of Gunn-effect diodes can be interpreted by the use of an expression for admittance of the diode in which the effects of r.f. circuit voltage on the domain are taken into account.
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A sealed-off beryllia tube argon ion laser
  • Author(s): P.C. Conder  and  H. Foster
  • Source: Radio and Electronic Engineer, Volume 39, Issue 2, p. 97 –103
  • DOI:  10.1049/ree.1970.0012
  • Type: Article
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  • p. 97 –103 (7)
    An argon ion laser is described in which the discharge is confined by a beryllia capillary tube. This has enabled the current density in the discharge to be increased to more than 600 A cm−2 with negligible gas cleanup. Sealed-off lasers have been life tested for more than 1000 hours without the need for a gas replenishing system and have shown less than 10% change in output. The total output of 1.5 W can be increased to more than 3 W by the application of a magnetic field. This performance is obtained from a 3 mm bore, 30 cm long plasma tube with an argon pressure of 0.7 torr.
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Coherent light scattering measurements on single and cladded optical glass fibres
  • Author(s): K.C. KAO ; T.W. Davies ; R. Worthington
  • Source: Radio and Electronic Engineer, Volume 39, Issue 2, p. 105 –111
  • DOI:  10.1049/ree.1970.0013
  • Type: Article
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  • p. 105 –111 (7)
    This paper considers the scattering, at normal incidence, of a laser beam by single and cladded optical glass fibres with a view to estimating their radii and refractive indices. For parallel and perpendicular polarizations of the incident light, the scattered intensity was calculated using the wave theory. The scattering pattern from a single fibre was also calculated by geometrical optics. The light scattered by a cladded fibre in air was photographed for fibres of three different overall diameters. A similar experiment was conducted for the fibre immersed in a liquid having a refractive index near to that of the cladding. Matching was achieved by thermal means.In both cases considered, the experimental results were found to be in agreement with theoretical results. For a cladded fibre in air, information about the core could not be obtained but a measurement of the angular fringe spacings and positions enabled the cladding diameter and index to be calculated. For a cladded fibre immersed in an index matching liquid, it was found that a measurement of the angular positions of minimum intensity enabled the core diameter to be calculated.
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Weighing vehicles in motion
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Automatic, on-line calibration of flowmeters
  • Author(s): P. Ridley
  • Source: Radio and Electronic Engineer, Volume 39, Issue 2, p. 113 –119
  • DOI:  10.1049/ree.1970.0017
  • Type: Article
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  • p. 113 –119 (7)
    This paper describes a method of calibrating digital output flowmeters of the turbine meter type whilst the meters are in use. No interruption of the metering process is involved during calibration. In the specific application for which the system was designed, the volumes of batches of refined petroleum products ‘shipped’ in an oil pipeline are metered to an accuracy of 0.05%. Meter calibration cycles are initiated automatically when product types or flow rates change.
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