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Proceedings of the IEE - Part B: Radio and Electronic Engineering

Issue 10 • Date July 1956

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Displaying Results 1 - 25 of 29
  • The calibration of inductance standards at radio frequencies

    Page(s): 429 - 438
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1550 KB)  

    The precision with which standards of inductance can be measured and used at radio frequencies is limited, not only by the ordinary uncertainties of experimental technique, but also by the fact that the standards are necessarily circuit elements with terminations, while inductance is primarily a characteristic of complete circuits. The procedure followed at the National Physical Laboratory when the highest possible precision is required is described in both its experimental and theoretical aspects. The precise relation between the familiar equivalent network for a coil and the basic definitions is indicated, and practical details are given for the resonance method of measurement that has been adopted as standard practice for all work of this kind. It is successfully operated at all frequencies from the audio range, where it overlaps the bridge methods employed as standard practice in the lower ranges of frequency, to values little short of those of self-resonance of the coils. In the overlapping region the bridge and resonance methods agree to about 1 part in 104 and with suitable elaboration the resonance method gives about the same accuracy for coils of any value between 1 H and 10 ¿H at any frequency within their working ranges, the limit for the smaller coils being about 4 Mc/s. With coils of the order of 1 ¿H measured values may show a standard deviation as small as 0.0001 ¿H, but from the general considerations outlined in the paper limits closer than 0.0005 ¿H will seldom be significant in any work with lumped circuits. View full abstract»

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  • Nickel-chromium-aluminium-copper resistance wire

    Page(s): 439 - 447
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    A review is given of the principal materials used for the construction of resistance standards. The difficulty of producing manganin and constantan commercially with the requisite small value of temperature coefficient at room temperature makes attractive the newer alloys, whose temperature coefficients can be controlled by simple heat treatment. One of these alloys, having the additional advantage of a resistivity three times that of manganin, has been studied at the National Physical Laboratory. It is composed of nickel, chromium, aluminium and copper and is known commercially as Evanohm. When the temperature coefficient, at a given temperature, has been reduced to zero by heat treatment, the curvature of the resistance/temperature characteristic is only one-tenth that of manganin. The stability of resistors constructed of this material has been investigated and has been generally found to be of the order of a few parts in 105 per year. The investigations are continuing and it is hoped that better figures may be obtained for well-aged standards. The stability is not adversely affected¿and may be improved¿by operation at temperatures up to 120°C. Above 140°C there is usually an increase of resistance, but even at 400°C this increase is not rapid. Operation above 400°C is not recommended even for low-accuracy resistors. Further advantages of the material are a low thermal e.m.f. to copper, high mechanical strength and high ductility. The disadvantages are the necessity of hard soldering and the susceptibility of the resistance to change due to cold working, including vibration. The resistance standards under investigation for long-term stability are five 1-ohm standards, and one standard of each of the following values: 1 000 ohms, 100 000 ohms, 1 megohm and 10 megohms. An additional 100 000-ohm standard of an alternative design has recently been constructed. View full abstract»

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  • An on-off servo mechanism with predicted change-over

    Page(s): 449 - 460
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    For a relay-controlled servo mechanism represented by an nth-order differential equation it is shown that one change-over and one only, at a unique time, is necessary to bring error and error rate to zero in the least possible time. Previous workers have used the sign of a non-linear function to control change-over, but such methods are suitable only for simple second-order systems with step inputs. To satisfy the need of a technique capable of wider application, e.g. random inputs, prediction of switching by means of a high-speed repetitive analogue computer has been demonstrated with a model experiment. Such a scheme has been shown to be practicable; its use is not limited to simple systems. In the specific example of a 10 kW control system the responses are compared of the on-off control using predicted change-over to those obtained (by simulation) of an orthodox servo mechanism, a linear but saturating servo. The optimized on-off control is always better for all amplitudes of step, ramp and parabolic function inputs, and on the average the same performance would be obtained with both systems using only about half the torque with the on-off control. View full abstract»

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  • The dual-input describing function and its use in the analysis of non-linear feedback systems

    Page(s): 463 - 473
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1328 KB)  

    A new method is presented for the frequency-response analysis of non-linear elements. This involves evaluating the gain of one of the frequency components in passing through the non-linear element when the input to the element consists of two sinusoidal waves of differing amplitudes, phases and frequencies. A cubic characteristic is analysed fully as an example. The paper describes the use of this method for analysing four different types of problem arising in feedback systems containing one simple-type amplitude non-linearity. The method can be considered as an extension of the describing-function technique with a correspondingly wider field of application. View full abstract»

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  • The effect upon pulse response of delay variation at low and middle frequencies

    Page(s): 475 - 478
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    Calculations are given for the magnitude and form of the distortion introduced into a square wave by a network or system which exhibits uniform transmission except for increasing (or decreasing) phase delay in the low-mid-frequency region. The fractional peak distortion is found to be equal to twice the area under the curve relating Tn to frequency, where Tn is the delay relative to that at high frequencies. The waveform of the distortion is given for several simple shapes of curve for Tn. This distortion is especially characteristic of vestigial-sideband systems, and occurs in television as a `pre-shoot¿ before a transition and as a smear (in principle equal, but opposite, to the pre-shoot) after it. View full abstract»

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  • An electronic machine for statistical particle analysis

    Page(s): 479 - 484
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    A system is described for associating and collecting the intercepts of individual particles in a particle scanning system, where the information is presented as a function of the scanning voltages. A series of stores is used to segregate the intercepts, each store having its own memory system and provision for re-use on completion of the scanning of the particle with which it is associated; the stores can thus be used many times during a single frame scan. A method of adding the intercepts of each particle to obtain a measure of the area of the particle is described, but this must be regarded as only one of the possibilities of extracting information from the series of intercepts collected. View full abstract»

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  • A ferrite microwave modulator employing feedback

    Page(s): 485 - 490
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    The amplitude modulation of microwaves produced by the magnetization of ferrites is non-linear and suffers from hysteresis. Hence, square-wave modulation is the only function in which the distortions are not objectionable. The paper describes a feedback method of applying the modulation signal, providing a linearity substantially that of the feedback crystal used to detect the modulated microwave signal, and reducing the effect of hysteresis by an amount approximating the feedback loop gain. Pure sine-wave modulation is achieved at low frequencies, in which the second-harmonic sidebands are more than 45 dB below the fundamental. Linear modulation, by sawtooth and square waveforms, is also achieved, in which the modulation envelope faithfully reproduces the applied signal. The employment of ferrite microwave modulators in engineering applications will involve techniques which are already standard for lower frequencies with conventional components, and the paper establishes the feasibility of using the powerful method of envelope feedback to control them. View full abstract»

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  • Wide-band noise sources using cylindrical gas-discharge tubes in two-conductor lines

    Page(s): 491 - 496
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (885 KB)  

    The provision of wide-band noise sources for the decimetre wavelength region is important for many radio applications. Anoise signal of suitable power level for most purposes is obtained when the plasma region of a gaseous discharge is matched to a transmission line. Examination of the properties of a discharge plasma shows that a noise source with an output which is constant over several octaves can be obtained by matching a cylindrical discharge tube directly to a two-conductor line. Such matching can be achieved by using conductor pairs of various shapes. The factors which affect the operation of the matching element are considered, and a practical design procedure is outlined. These noise sources are simpler to construct and of better performance than those used previously at decimetre wavelengths. View full abstract»

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  • The application of transistors to the trigger, ratemeter and power-supply circuits of radiation monitors

    Page(s): 497 - 504
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    The paper outlines the general requirements and the conditions of use of radiation monitors employed in ¿- and ß-ray survey in connection with geological prospecting. In such instruments, it has been usual to employ either filament valves or cold-cathode valves in amplifier and trigger circuits, and vibrators, filament-valve oscillators or high-voltage battery stacks in the power supplies. Arguments leading to the transistor as the preferable component in all cases are given, and typical transistor circuits are discussed in some detail. Both point-contact and junction transistors are discussed, and the superiority of the junction-type circuits for this type of application is demonstrated. View full abstract»

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  • A point-contact transistor scaling circuit with 0.4 microsec resolution

    Page(s): 505 - 509
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (634 KB)  

    There is a wide choice of scaling devices which will operate at maximum counting rates up to several hundred kilocycles per second, but for counting rates in the region of megacycles per second, the choice is limited almost entirely to special thermionic scaling devices or circuits using thermionic valves. Such circuits tend to be rather complex and have a relatively high power consumption. The paper describes some scaling circuits using transistors which will resolve 0.4 microsec and hence count at a maximum rate of 2.5 Mc/s. The transistors are the normal point-contact type, and the circuits are simple, they have wide tolerances and are economical in power consumption. Features which contribute to the short resolving time are the prevention of bottoming of collector potential and the absence of capacitors. A typical scale-of-10 circuit uses seven transistors, seven pulse transformers and 14 crystal diodes. View full abstract»

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  • A junction-transistor scaling circuit with 2 microsec resolution

    Page(s): 510 - 515
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (790 KB)  

    When junction transistors are used in conventional scaling circuits the maximum speed of operation is limited by the associated circuit, mainly owing to the use of capacitors, which require time to charge and discharge. The limiting speed of a transistor itself, which depends on the switch-on and switch-off times of current, is generally several times higher than this, but cannot be taken advantage of owing to the associated circuit. The basic binary scaling circuit described in the paper overcomes this difficulty by dispensing with capacitors, a differentiating transformer being used instead for coupling. In this way the speed of the circuit depends only on transistor characteristics. With currently-available low-frequency junction transistors (fco¿¿500 kc/s) the circuit is capable of reliably resolving 2 microsec. The basic binary scaler is readily adapted to the formation of a scale-of-5 circuit using three binary stages. When this is preceded by another binary scaler, the result is a scale-of-10 circuit with the same resolving capabilities as the original binary circuit. The circuits have wide tolerances and are insensitive to transistor variations. A complete scale-of-10 circuit uses eight transistors, ten diodes and five transformers. View full abstract»

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  • Frequency-modulation radar for use in the mercantile marine

    Page(s): 519 - 523
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    The principles of f.m. radar are outlined and a comparison is made between pulse and f.m. techniques, particularly with respect to the requirements of the merchant service. It is concluded that multi-gate f.m. radars are too complex for this application and methods are outlined for overcoming the inherently low scanning rate of single sweeping-gate systems. Equipment is described which has an aerial beamwidth of 1.7° and a rotation rate of 10 r.p.m. with a fractional range resolution of 1/30. The future of f.m. radar for mercantile marine use is critically examined, the conclusion being that it will be most useful where very-short-range high-resolution pictures are required. Before such equipment is economically available further developments in transmitting valves must take place. View full abstract»

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  • Change of phase with distance of a low-frequency ground wave propagated across a coast-line

    Page(s): 527 - 534
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    Observations of the change of phase with distance have been made on a frequency of 127.5 kc/s along a number of paths radiating from a transmitter near Lewes and crossing the south coast between Pevensey and Littlehampton. The nature of the ground adjacent to the coast, the angle of crossing the coast-line and the lengths of the land and sea sections covered varied from path to path; the greatest distance covered out to sea was 22 km. Measurements were also made over paths at right angles to the radials, and the phase changes in the area off Worthing, where the paths were tangential to the coast, were examined in detail. The results confirm the existence of a phase-recovery effect which, as theoretical considerations have shown, should be experienced by a wave passing from low-conductivity ground to sea water and which was indicated by previous measurements over geological boundaries on land. The detail of the measurements at sea shows also that, in addition to this general behaviour of the phase, there are superimposed systematic variations whose magnitudes decay from about 4° of phase near the coast to a negligible amount at 6¿ out to sea and on some paths are comparable to the recovery. A very marked phase disturbance within ¿/2 of the coast on the landward side is also evident; it is similar to that previously observed over geological boundaries on land. View full abstract»

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  • The deviation of low-frequency ground waves at a coast-line

    Page(s): 535 - 541
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (884 KB)  

    After consideration of the methods which have been suggested for computing the deviation of ground waves at a coast-line, the phenomenon is re-examined in the light of recent experimental and theoretical work on the phase disturbances at such a boundary. It is shown that the deviation may be calculated from the rate of change of phase with distance along the path of propagation. The changes in this rate which occur at the boundary give rise to a considerable increase in the magnitude of the deviation as the receiving point is brought within a few wavelengths of that boundary. This increase near the coast seems to provide an explanation of the unexpectedly large deviations previously observed at medium frequencies. A series of simultaneous measurements of the phase change and the deviation at 127 kc/s along a number of paths crossing the south coast of England are described. Although general agreement between the measured deviations and those derived from the phase curves was obtained on some paths, there were appreciable discrepancies on others. These discrepancies are attributed to the irregularities in the phase surface which were evident over the area and which the method of derivation did not take into account. View full abstract»

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  • The propagation of a radio atmospheric

    Page(s): 542 - 546
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (508 KB)  

    On the assumption that the space between the earth and the ionosphere acts as a waveguide, the mechanism of propagation of an atmospheric has been considered from the viewpoint of plane-wave reflections. The pulse at the origin has been assumed to be rectangular and of duration 100 microsec. It has been possible to give a physical picture of the mechanism and to explain the oscillatory waveform of distant atmospherics. View full abstract»

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