摘要:

A description is given of a method of measuring the effective deionization time in thyratrons, i.e the time that must elapse, after arc current has ceased, before the grid regains control. In this method, voltage is applied to the anode at a known rate and at any desired interval after the passage of an arc-current pulse. The duration of the pulse, a few microseconds, is negligible compared with the deionization times being measured. The interval before the anode voltage is reapplied is reduced until the loss of grid control indicates that insufficient time has been allowed for deionization. A study of the decay of ionization, by observations of the ion current to the negatively charged grid, shows that grid control may be regained before deionization is quite complete.The method is illustrated by the results of comparative tests showing the variation of deionization time with changes in grid design, and in the nature and the pressure of the gas or vapour filling.

DOI:10.1049/pi-3.1949.0058

出版商:IEE    

年代:1949

数据来源: IET

摘要:

The paper gives methods for calculating the transient performance of the low-pass filter. It is shown that the currentImin the termination of anm-section filter whose critical frequency is ωc/(2π) is given byIm=1/ωc∫ωct0g(λ)E(ωct−λ)dλwhereE(ωct) is the voltage applied to the filter att=0, andg(ωct) is the response of the filter to a unit impulse. Results are given in the cases for whichg(λ) can be calculated, which include filters terminated in a resistance of □(L/C), and short- and open-circuits (in this last case the voltage across the open-circuit is found). The method also gives solutions for the uniformly dissipative filter with these terminations. For all these casesg(λ) is expressed in terms of the repeated integrals of Bessel functions, andImcan be found in terms of these functions by, at most, one numerical integration of the above equation. These solutions prove very suitable for numerical computation, especially at the start of the transient.The method has been applied to work out in detail the transient performance of 3-, 4-, and 5-section filters terminated in a resistance of □(L/C). The concept of delay time, based on a treatment using “ideal” filters or “smooth” lines, is examined and shown to be very approximate. It is pointed out that the solutions obtained can be interpreted in terms of waves propagated to and fro through the filter, but that this is an approximate conception, for the “wave” starts to arrive immediately any voltage is applied.

DOI:10.1049/pi-3.1949.0061

出版商:IEE    

年代:1949

数据来源: IET

摘要:

This critical review of the specification and measurement of polarization errors in Adcock-type direction-finders was prepared in 1944. The respective merits of the “standard-wave error” introduced by Barfield, and the “pick-up ratio” for wanted and unwanted fields suggested by several other workers, are examined. It is concluded and recommended that the former is to be used for Adcock direction-finders erected not higher than about ¼λ above ground, while the latter is appropriate for more elevated systems. Comparison of direction-finders falling into different categories can only be carried out if a complete specification of polarization error performance over all relevant angles of incidence is available.The problems involved in using a relatively nearby test transmitter are discussed. For frequencies above about 3 Mc/s it is shown that a suitable local radiator consists of a rotatable closed loop used at moderate elevations, and at distances not less than a wavelength. The effects of loop size are discussed, and it is shown that adequately large loops are practicable; for example, for frequencies in the range 3–30 Mc/s, a loop up to about 5 ft in diameter may be used, providing the distance is not less than 100 m. For frequencies below about 2–3 Mc/s it is suggested that the “local-injection” method due to Barfield may be more practicable than a radiation method.It is pointed out that the performance of a direction-finder is in general intimately bound up with the electrical properties of the site on which it is erected.

DOI:10.1049/pi-3.1949.0062

出版商:IEE    

年代:1949

数据来源: IET

摘要:

The paper deals with special types of power transformers for electrical equipments. Climatic and altitude problems are examined in so far as they affect transformers. Transformer design and constructional features are presented with a view to obtaining the smallest possible transformer for a given rating. It is suggested that high-grade magnetic materials should be used for the cores, and that high-temperature insulating materials, such as the silicone products, be used to replace organic insulating materials. A design for a 500-VA 1 600-c/s transformer is given in the Appendix.

DOI:10.1049/pi-3.1949.0064

出版商:IEE    

年代:1949

数据来源: IET

摘要:

The Q-meter (or magnification factor meter) has become the recognized instrument for all kinds of r.f. impedance measurement. The resonant measuring circuit which forms the basis of such instruments may be excited from the oscillator source in different ways. In this paper, instruments have been classified into low-impedance and high-impedance injection types, according to the systems employed. The low-impedance resistance injection type has proved very satisfactory for use at frequencies below about 20 Mc/s. The various causes of error have been analysed and the difficulties of design for accuracy at the higher frequencies outlined. An instrument based on a novel principle of high-impedance injection has been developed, and it is possible to extend the range of accurate measurement to the region of 150 Mc/s. Slightly different technique is necessary when using the new principle, and illustrations of the use for various classes of measurement are given.A section of the paper is devoted to the definition ofQand the relationship between the quantities obtained on differing bases clarified. It is shown that the definitions ofQby frequency selectivity, by decrement, or by relation between energy storage and mean rate of dissipation are equivalent in the general case of a resonant system at a simple resonance. The essential difference between Q-value and magnification factor, as measured by a Q-meter, is discussed in detail.

DOI:10.1049/pi-3.1949.0069

出版商:IEE    

年代:1949

数据来源: IET

摘要:

The relative merit of the display of radio bearings and sense by aural-null and twin-channel cathode-ray goniometers has been examined as a function of various characteristics of the signal. The visual method of bearing display has been shown to be superior in nearly all respects except for its relative ineffectiveness in operating at very low signal/noise ratios. It has been shown quantitatively that this disadvantage is slight and could be overcome by a suitable narrowing of the receiver bandwidth. The advantage of the visual method is specially pronounced when the signal received includes an appreciable phase-quadrature component. Similar conclusions have been reached regarding the performance of the associated methods of sense display.

DOI:10.1049/pi-3.1949.0073

出版商:IEE    

年代:1949

数据来源: IET

摘要:

The paper summarizes theoretical and practical investigations into the cause and properties of site errors at metre wavelengths. Attention is mainly directed to Adcock-type aerial systems; but other classes of instrument are considered in an Appendix. A criterion is there suggested to express the susceptibility of a direction-finder to site error, and is applied to well-known instrumental types.With some simplifying assumptions, the variations in error with azimuth and elevation angle due to “point”, “linear” and “sheet” type reflecting obstacles are examined. Certain properties of error charts which may be useful in locating the sources of error on a site are discussed. Errors introduced by randomly dispersed obstacles are considered from a statistical viewpoint.The theoretical and practical difficulties encountered in calibrating a site are discussed, the limitations of correction processes involving the use of previously measured error data being pointed out.Practical techniques available for locating the effective reflecting obstacles on a site are described, and examples of their application are given. Methods for suppressing unwanted reflections are considered.The work has led to a better understanding of site error phenomena at metre wavelengths, but further experimental work, linked with theoretical studies, is necessary.

DOI:10.1049/pi-3.1949.0074

出版商:IEE    

年代:1949

数据来源: IET

摘要:

The paper describes an experimental determination of the usefulness and limitations of elementary theory in estimating the fields scattered by metal wires and sheets, treated as passive scattering-elements. The results are of interest in assessing errors due to obstacles on a direction-finding site. Formulae are derived for the scattered fields, using the transmission-line theory for wires and diffraction theory for sheets.A method is described for the measurement of scattered fields and the results of measurements on various wires and sheets, at a frequency of 600 Mc/s (50 cm), are shown to be in substantial agreement with the elementary theory. The measured amplitudes of the resonance peaks which occur in the field scattered by a wire as the length of the wire is varied are, however, much smaller than would be expected, except for wires less than two wavelengths long.The results indicate that for wires of the order of 1-mm diameter resonance effects at a frequency of 600 Mc/s are small if the length of the wire is more than about five wavelengths. This conclusion is probably true for a wide range of wire diameters and frequencies. Resonance effects in sheets may be neglected if the dimension of the sheet normal to the electric vector is greater than a wavelength.It is concluded that scattered fields may be computed from elementary theory to the accuracy normally required in direction-finding work.

DOI:10.1049/pi-3.1949.0075

出版商:IEE    

年代:1949

数据来源: IET

摘要:

The electro-mechanical analogies between inductances and capacitances in lumped circuits on one hand, and masses and springs on the other hand, are commonly known, and have been found extremely useful in many different ways. In the paper the analogies are considered for distributed elements, the detailed relations being shown between the electromagnetic fields in cavities, waveguides, etc. (with or without discontinuities) and the mechanical vibrations of elastic sheets having similar boundaries. The conclusions reached are quite general, and apply to plane sections of these electromagnetic fields, having any conducting boundaries, and with either TE or TM modes. The equivalent lumped circuits, whereby such fields may be represented to any degree of accuracy desired, are considered and illustrated by experimental examples. It is shown that these circuits result from applying the method of relaxation to the distributed-field calculation.It is shown that, although two different sets of electro-mechanical analogies are commonly applied to circuits of one dimension (such as transmission lines and filters), only one of these sets is at all applicable to distributed systems, namely that in which velocity corresponds to voltage (or ξ-vector), and force corresponds to current (or magneticH-vector). This latter analogy is strictly true for steady-state or transient conditions. Again, mass corresponds to capacitance (or to κ) and elastic constant to inverse inductance (or to 1/μ).The possible applications of such analogies, apart from their aiding in the understanding of electromagnetic field problems, fall into two classes. In the first, elastic membranes are stretched over frames of suitable shape, and a study of their vibration patterns may assist in the design of microwave components, such as valve anode blocks, resonators, guides with discontinuities such as diaphragms or slots, etc. In the second, the development of the lumped equivalent circuits, which are essentially two-dimensional circuits, is a contribution to the general study of periodic structures. The selectivity and impedance properties of these lumped circuits are examined in relation to the properties of conventional constant-kfilter structures.

DOI:10.1049/pi-3.1949.0078

出版商:IEE    

年代:1949

数据来源: IET