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1887

Radio and Electronic Engineer

Volume 37, Issue 1, January 1969

Volumes & issues:

Volume 37, Issue 1

January 1969

Experiences in tropospheric scatter propagation experiments
The changing years
Correction: The Sixth Clerk Maxwell Memorial Lecture: Spatial communications
The use of a radio frequency transformer to increase the sensitivity of a radio frequency admittance bridge
  • Author(s): I.L. Freeston
  • Source: Radio and Electronic Engineer, Volume 37, Issue 1, p. 5 –10
  • DOI:  10.1049/ree.1969.0003
  • Type: Article
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  • p. 5 –10 (6)
    This paper describes a technique by which the sensitivity of a radio-frequency admittance bridge was increased by using an r.f. transformer, in order to measure small changes of admittance. The bridge measured the admittance of the primary circuit with the unknown admittance connected across the secondary, the nominal value of the secondary to primary turns ratio being √2. Using this method, measurements at frequencies between 5 and 30 MHz were made of the admittance of a plane capacitor of about 1 pF capacitance, to an accuracy of about 2%, and of changes in this admittance to less than 4%. The system was calibrated by a least-squares method, which also enabled the standard errors in the calibration to be evaluated. The results of measurements made on the plane capacitor in vacuum are presented, and the advantages and limitations of the method are discussed.
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A theoretical appraisal of the quenched multiple domain mode in GaAs microwave diodes
  • Author(s): R.I. Harrison ; S.P. Denker ; H. Berger
  • Source: Radio and Electronic Engineer, Volume 37, Issue 1, p. 11 –15
  • DOI:  10.1049/ree.1969.0004
  • Type: Article
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  • p. 11 –15 (5)
    Quenched multiple domain (q.m.d.) mode oscillations in bulk GaAs have been analysed to obtain the relationships between efficiency, fundamental-frequency power output, fundamental-frequency negative resistance, and d.c. bias voltage. It is found that this highly efficient mode does not have the limitations of transit-time devices and consequently has a frequency-independent power × impedance product. The results demonstrate that q.m.d. oscillators designed with multiple-tuned circuits can operate at twice the efficiency of those operated in single-tuned circuits.
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The design, construction and performance of thick film cermet trimming potentiometers
  • Author(s): B.S. Methven
  • Source: Radio and Electronic Engineer, Volume 37, Issue 1, p. 17 –21
  • DOI:  10.1049/ree.1969.0006
  • Type: Article
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  • p. 17 –21 (5)
    The cermet trimming potentiometer is a miniature light-weight control having an extremely rugged construction. The nature of the resistive element provides an inherent freedom from catastrophic failure and offers a wide range of possible ohmic values. The design and its influence on some of the more fundamental properties of this control is discussed. The effects of both electrical and environmental stresses liab1e to be imposed in practice are given in some detail. This form of control is shown to have a number of advantages over the more conventional wirewound device, some of which can play an important role in present-day high-speed, high-reliability electronic circuits.
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Zero quiescent current monostable multivibrator
  • Author(s): C.F. Ho
  • Source: Radio and Electronic Engineer, Volume 37, Issue 1, p. 22 –24
  • DOI:  10.1049/ree.1969.0007
  • Type: Article
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  • p. 22 –24 (3)
    A simple monostable multivibrator circuit using a complementary pair of transistors is described. In comparison with the conventional configuration, this circuit has such features that it would need no standing power and a smaller number of components. The commonemitter current amplification factor, hfe, of the transistors may be made as the overriding factor for the pulse width control and thus, enables a small combination of C-R to be used for long time-delay. However, the sensitivity of the pulse width on the transistor current amplification factor, hfe, may be reduced, if desired, in the improved circuit.
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Active and passive components for attachment to thick film circuits
Control: past, present and future
  • Author(s): H.H. Rosenbrock
  • Source: Radio and Electronic Engineer, Volume 37, Issue 1, p. 30 –32
  • DOI:  10.1049/ree.1969.0009
  • Type: Article
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  • p. 30 –32 (3)
    Automatic control developed historically as a necessary consequence of replacing human or animal power by wind and water power and later by steam power. Its beginnings were empirical, but an important contribution to the theory was made by Clerk Maxwell, and later the development of feedback amplifiers led to intensive theoretical work in the U.S.A. By 1945 a well-developed and highly successful theory was available, and wide applications have been made.In more recent times, theoretical effort has been concentrated on problems of guidance, using the calculus of variations. The incentive here was to solve aerospace problems, but there have been some applications to industrial problems. This theory seems to have a narrower range of applications than the earlier work.The development of the digital computer has placed in the hands of engineers a tool of unrivalled flexibility and power for the control of processes. By contrast, our theory is at present unable to exploit this power with full effect. The most promising field for control theory and application in the next five to ten years seems to be the application of computer control to all types of industry, and the development of the corresponding theory.
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The impact of pulse code modulation on the telecommunication network
  • Author(s): K.W. Cattermole
  • Source: Radio and Electronic Engineer, Volume 37, Issue 1, p. 33 –46
  • DOI:  10.1049/ree.1969.0010
  • Type: Article
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  • p. 33 –46 (14)
    The basic processes of transmission and switching are cheaper for multiplex digital signals than for their voice-frequency equivalents, and introduce little or no impairment of the message. Conversion between analogue and digital signals introduces much of the cost and almost all of the impairment in a p.c.m. communication system. The long-term plan for a telephone administration should therefore be to introduce an integrated digital network in which only a minimum number of conversions and reconversions is required: ideally only one per connection. Transmission between exchanges should use multiplex p.c.m. and switching of concentrated traffic should be digital (either analogue or electromechanical). A planned transition from present practices towards a digital network is possible, because the partial use of p.c.m. is technically and economically beneficial provided that the applications be carefully chosen. Junction transmission, trunk transmission, tandem switching, group selection in terminal exchanges and integration over limited areas are considered. A digital network whose main traffic is telephony can also carry other messages such as telegraph and data.
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A communication network for real-time computer systems
  • Author(s): D.W. Davies
  • Source: Radio and Electronic Engineer, Volume 37, Issue 1, p. 47 –51
  • DOI:  10.1049/ree.1969.0011
  • Type: Article
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  • p. 47 –51 (5)
    Digital communication between computers and their users has until now been provided by exploiting the telephone network to carry digital data because of the wide coverage of the telephone network and the high capital cost of establishing any new, generally-available telecommunication service. In the long run it is expected that a specialized digital communication network will be required, designed around the requirements of computer services which interact in ‘real-time’ with their remote users. The system design of the proposed new network is outlined and some estimates of performance are given.
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Points from a discussion on communication systems
Thick films in automotive equipment
  • Author(s): R.W. Nolan
  • Source: Radio and Electronic Engineer, Volume 37, Issue 1, p. 53 –56
  • DOI:  10.1049/ree.1969.0013
  • Type: Article
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  • p. 53 –56 (4)
    The problems facing the manufacture of microelectronic equipment for motor vehicles are outlined. These arise from the physical and electrical environments, the power levels to be controlled which result in high currents, a need for very low saturation voltages, low thermal resistances and efficient heat sinks. These items are then considered with reference to a hybrid integrated circuit alternator voltage regulator, and the design employed to develop an economic unit is discussed. The methods include the use of a printed and fired thick film circuit, with dice-mounted directly to the circuit. The assembly is encapsulated into a combined heat sink and cover. Manufacturing costs are discussed in relationship to those of equivalent electromechanical and discrete component assemblies.
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A fast binary to logarithmic analogue converter
  • Author(s): J.A. Ladd
  • Source: Radio and Electronic Engineer, Volume 37, Issue 1, p. 57 –64
  • DOI:  10.1049/ree.1969.0014
  • Type: Article
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  • p. 57 –64 (8)
    The paper describes a circuit configuration which produces an output proportional to the logarithm of binary numbers presented at its input. The circuit is designed to process the first six significant digits only and can deal with binary numbers up to 220–1.The maximum output settling time, to within ½% of the final output level, is about 2 μs. The resolution of the circuit is limited by the number of digits taken; in the unit described it varies from one part in 32 to one part in 64 depending on the value of the binary number. This uncertainty amounts to a maximum of 0.22% of full-scale deflection. Other inaccuracies are small compared with the resolution errors. The circuit employs digital switching and uses linear components only. No devices with special characteristics are required.
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