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Radio and Electronic Engineer

Issue 7 • Date July 1982

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Displaying Results 1 - 6 of 6
  • Television Systems for DBS

    Page(s): 311 - 313
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (248 KB)  

    First Page of the Article
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  • A reappraisal of h.f. receiver selectivity

    Page(s): 315 - 320
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    H.f. communication receivers have progressed towards a high level of sophistication yet a high percentage of reception failures are still due to limitations within the receiver. This paper considers the role of frequency selectivity for an ideal receiver and proposes a costeffective approach which should noticeably reduce reception failure. View full abstract»

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  • An improved 'piccolo' m.f.s.k. modem for h.f telegraphy

    Page(s): 321 - 330
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1446 KB)  

    The Piccolo system of multi-frequency signalling has been in operation on the h.f. telegraphy network of the UK Foreign and Commonwealth Office for almost 20 years and has proved extremely effective. A new generation equipment has now been designed which is smaller, more reliable and more flexible than previous models, and incorporates a number of parameter changes and additional facilities suggested by experience and more detailed mathematical analysis. It allows operation in the ITA-2 code at 75 or 50 bauds, and in the ITA-5 code at a 110 bauds. The new parameters have enabled the bandwidth to be considerably reduced and the stability required from the reference source to be relaxed. The improved synchronizing system will pull in to synchronism in less than 3 seconds and remain synchronized over long periods of poor or lost signal. Special provision is made for operation on continuous cryptographically-protected data streams. The unit also includes a selective calling system and an optional error indicating code. Four telegraph channels can be frequency division multiplexed into a 2 kHz bandwidth. The availability of the system under poor-signal conditions is a considerable improvement over orthodox binary techniques. View full abstract»

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  • How complex a learning curve model need we use?

    Page(s): 331 - 338
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1058 KB)  

    In using learning curves for management control in a typical industrial environment, we seek to identify a number of patterns in the basic data, each of which is an important source of information to be fed into the decision-making machinery. These patterns may beclassified as follows: (a) A trend-line, which in some `best¿ sense, can be used for predicting future output. This trend-line can be influenced by proper design and planning of the product line. (b) `Normal¿ scatter about the trend-line, which constitutes a natural and acceptable variation, and which can be used for setting upper and lower bounds predicted output. (c) `Abnormal¿ scatter about the trend-line, which results in an unacceptable variation. It indicates an avoidable loss in production which can be traced to an assignable cause and hence eliminated by management control. (d) `Deterministic¿ changes in the trend-line. These may be long or short term, and have an assignable cause. An example of a management-induced cause is a planned change in the size or constitution of the direct labour force. To derive a learning curve model which will cope with these four patterns simultaneously is a complex problem. The author believes there are considerable advantages in selecting the simplest model which is adequate for the purpose of efficient management control of a particular enterprise and will review a procedure for doing so. We are, after all, dealing with huge cost savings if we properly plan this activity. Understanding and implementing a simple model derived on the back of an envelope can be often more profitable for management than a sophisticatedcomputerized model, the significance of which is difficult to grasp. The paper concentrates attention on the time constant model, and its variants, as found appropriate to `industry learning¿. View full abstract»

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  • Book review: The Kingdom of Sand: Essays to Salute a World in Process of being Born

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    Freely Available from IEEE
  • A simple model of longitudinal digital magnetic recording

    Page(s): 339 - 357
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (2162 KB)  

    A two-dimensional theoretical distribution with many of the features observed on a 5000 :1 model is developed and the field external to the medium linking the replay head is shown to be equivalent to the field from a filamentary pole parallel to the medium surface and transverse to the track direction located at the centre of each transition. Each transition is described by s pole strength per unit track width, tand its distance behindthe medium surface, a. Methods for relating and a to the magnetic characteristic and physical dimensions of themedium are developed. Prediction of the replay performance from the theory show good agreement with experimental data. A notation for describing vectorial magnetization in two cartesian dimensions is introduced which automatically enforces the requirement that the divergence of B is zero whilst simultaneously allowing the magnetization of elements within the distribution some independence so that internal divergence of magnetization is described. View full abstract»

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