摘要:

The paper surveys the main features which determine the characteristics and life of thyratrons in the light of direct experiment and of field experience. These include electron emission from the cathode, ionization and current build-up, grid control, the current-carrying capacity of the valve, the decay of ionization at the end of conduction, and the provision of suitable operating conditions.Emphasis is laid on factors which, while not immediately affecting electrical performance, may determine valve life; one example is positive-ion bombardment, which may cause damage to the cathode.The control characteristics of different types of grid are discussed; particular reference is made to the pentode design, a recent development enabling heavy currents to be controlled from high-impedance grid circuits.The arc voltage drop varies considerably with filling pressure and with current value, abrupt changes being associated with modifications in the form of the discharge. If the current-carrying capacity of the arc path is exceeded, the arc, if it cannot transfer to an alternative path, may suddenly go out, giving rise to generally undesirable high-voltage surges.A method of studying de-ionization time is described, and results are given showing this time as a function of the gas and its pressure. The characteristics of various gas and vapour fillings are discussed. A non-uniform pressure distribution in mercury-vapour valves assists rapid starting.

DOI:10.1049/pi-3.1949.0081

出版商:IEE    

年代:1949

数据来源: IET

摘要:

The paper gives the results of room-temperature measurements on ceramic (polycrystalline) specimens of magnesium, calcium, strontium and barium titanates at frequencies of 1.5 and 9450 Mc/s (3.18 cm), and on barium titanate at 24000 Mc/s (1.25 cm). It is found that the latter material is unique among this series in showing a considerable fall in permittivity, and a large increase in the loss tangent, at the higher frequencies, compared with the behaviour at 1.5 Mc/s. Variable temperature measurements on barium titanate show that the crystallo-graphic change which is known to occur around 120°C, the Curie point of the material, affects the permittivity at 9450 and 1.5 Mc/s in an analogous manner.Room-temperature measurements at the same frequencies on a range of barium-strontium titanate compositions are also described, and attention is drawn to the composition 56% BaTiO3: 44% SrTiO3, having a permittivity of 760 and loss tangent of 0.02 at 9450 Mc/s and 20°C, as likely to be of value in microwave work.The difficulties associated with the measurement of high-permittivity values at centimetre wavelengths are discussed, and a full description is given of the three methods developed for different parts of the investigation.

DOI:10.1049/pi-3.1949.0085

出版商:IEE    

年代:1949

数据来源: IET

摘要:

A brief account is given of some experiments on the generation of plasma electron oscillations by the discharge from a hot filament through ionized mercury vapour, argon and other gases at low pressures. These are produced both with bare metal cathodes and oxide-coated cathodes. The vacuum wavelengths of the electromagnetic waves produced have ranged from 5 cm to 2 m. Using bare cathodes, they have been detected both below the saturation current and on the saturation section of the tube characteristic. Using oxide-coated cathodes, they have been detected over wide sections of the tube characteristic. Data are given for the variation of wavelength and intensity with operating conditions for some tubes, and with position of an exploring electrode in the tube and on the outside of the tube wall. Under favourable conditions 1% of the anode power can be converted into energy of oscillation in an external circuit coupled with the tube. The observations are in the main consistent with the existence of restricted regions of oscillating plasma, in traversing which the primary electron beams undergo velocity modulation. Suggestions are made as to how the oscillations may be confined within a tube.

DOI:10.1049/pi-3.1949.0086

出版商:IEE    

年代:1949

数据来源: IET

摘要:

A direct indication of distance to known geographical points has long been a requirement for aerial navigation. The system described in this paper consists of an airborne light-weight radar set which works in conjunction with a responder beacon on the ground. The aircraft radar transmitter sends out a stream of pulses which are returned on a slightly different radio frequency by the ground beacon. Automatic circuits in the aircraft set measure the interval between the outgoing and corresponding return pulses and present the information to the pilot on a meter calibrated in miles.The paper describes the design of the airborne set and the results obtained in airline trials of engineered equipment used on an air route.

DOI:10.1049/pi-3.1949.0087

出版商:IEE    

年代:1949

数据来源: IET

摘要:

The first extensive application of the high-speed motor uniselector was in the mechanization of a system for handling long-distance telephone traffic in an overseas installation completed in 1940–41. Further development in this field was suspended during the war, although considerable use was made of the switch in equipment associated with the Air Defence of Great Britain. Since the war, the British Post Office has standardized the motor uniselector for trunk switching in the United Kingdom and, in addition, its use overseas, both in trunk and local systems, is rapidly extending.The paper describes the latest forms of the switch, those features of its design which ensure reliability and low maintenance costs, the facilities afforded by it, and the technique associated with its application in telephone switching and similar systems. A description is also given of the newly developed digit switch used with the motor uniselector.The standard circuit elements used in the control of the switch are dealt with, and an outline is given of its application as the basis of a mechanized trunk switching system and a local switching system. Reference is also made to its use in various miscellaneous applications.Attention is directed to the fact that the design of the switch and of the systems incorporating it is the logical outcome of a scientific study of the requirements to be met, not merely a re-development of traditional apparatus and arrangements.

DOI:10.1049/pi-3.1949.0088

出版商:IEE    

年代:1949

数据来源: IET

摘要:

A simple method of modulator analysis is given which enables the performance of a modulator with frequency-selective terminations to be determined so long as these terminations are resistive, zero or infinite at all significant frequencies. Most of the cases likely to be useful or unavoidable in practice have been worked out for the ring, Cowan (shunt-type) and series modulators, and the optimum terminating resistances (assumed equal) and minimum insertion losses have been tabulated in terms of the rectifier ratio and geometric mean resistance.

DOI:10.1049/pi-3.1949.0091

出版商:IEE    

年代:1949

数据来源: IET

摘要:

This paper describes two types of impedance bridge, one for measuring “unbalanced” and the other for measuring “balanced” impedances to earth.The frequency range is approximately ± 20% of the working midfrequency, and the bridges here described operate at a mid-frequency of 50–250 Mc/s.

DOI:10.1049/pi-3.1949.0092

出版商:IEE    

年代:1949

数据来源: IET

摘要:

Existing theoretical and experimental knowledge is surveyed. The pioneer theory of Bailey and Martyn is restated in a form which relates it more closely to standard ionosphere theory. The experimental results are summarized in a form which enables the magnitude of the cross-modulation effect to be deduced approximately for any pair of stations. The way in which observations of cross-modulation can be used in ionospheric research is outlined.

DOI:10.1049/pi-3.1949.0093

出版商:IEE    

年代:1949

数据来源: IET

摘要:

A radio method for the measurement of winds in the ionosphere is described. A pulse transmitter working on about 4 Mc/s is used in conjunction with three receivers placed at the corners of a right-angled triangle, and separated by distances of the order of 100 m. A simultaneous record is made of the fading of a single radio pulse reflected from the ionosphere and received at the three receivers. If a steady wind is blowing in a non-turbulent ionosphere the three fading records are displaced in time and the velocity and direction of the wind can be deduced. Many of the records obtained are sufficiently simple for reliable deductions to be made.The results of 82 determinations of winds by the use of local pulse transmitters are presented in Figs. 7, 8 and 9 in the form of histograms. The most frequent velocity is found to be of the order of 50 m/sec in a direction towards north-west, but there are clear indications that this velocity varies throughout the day, probably with a semi-diurnal period. The results are compared with previous measurements made by other methods.Measurements have also been made in which a distant pulsed transmitter has been used in conjunction with the same arrangement of receiving aerials. In all the experiments care was taken to avoid the misleading conclusions which may be drawn when “polarization fading” occurs owing to the simultaneous presence of two magnetoionic components in the reflected pulse.

DOI:10.1049/pi-3.1949.0094

出版商:IEE    

年代:1949

数据来源: IET

摘要:

Part 1 of the paper gave an account of the measurement of the velocity of propagation of centimetre waves over a sea path at low level, and concluded that the velocity is 186,217±16 miles/sec. Part 2 gives the results of experimental flights observed from two Oboe ground stations in order to measure the velocity of propagation as a function of height above the earth. The results indicate higher velocities than those previously calculated. The most probable values for the mean velocity of propagation between ground and aircraft at 10,000, 20,000 and 30,000 ft are 186,233, 186,246 and 186,256 miles/sec respectively, the metric equivalents being 299,713, 299,733 and 299,750 km/sec respectively.

DOI:10.1049/pi-3.1949.0095

出版商:IEE    

年代:1949

数据来源: IET