摘要:

This paper deals with the electrical characteristics of submarine cables designed to transmit carrier frequencies. The sphere of this branch of communication is outlined, and the general principles of operation and cable design are stated.The use of bridge networks to determine the characteristics of short lengths of cable, and of a completed laid cable, is described. Test data obtained during the manufacture of a carrier-frequency cable are given, and predictions made therefrom are compared with the results of impedance and attenuation tests on the laid cable. Alternative methods of measuring average and high attenuations are specified.In view of the probable future extension of this form of communication, recent improvements in materials and their effect on transmission capacity are considered. The chief improvements are in new dielectrics having considerably less leakance than those commonly used in submarine cables, and in magnetic loading material adaptable to the carrier-frequency range.

DOI:10.1049/jiee-1.1933.0117

出版商:IEE    

年代:1933

数据来源: IET

摘要:

Reactive volt-ampere-hour meters of the type which necessitate only standard potential transformers, and where the neutral point is not available, have been known for some years, but have been subject to comparatively large variations in accuracy with change of frequency. They present some advantages over the type which necessitates a special and additional potential transformer to obtain the requisite voltage phase relation, in that a comparatively costly piece of apparatus, viz. the special potential transformer, is eliminated, and, further, the loading of the potential transformer is straightforward, thus simplifying the measurement of ratio and phase angle. In the type of meter described in the paper a method of considerably reducing the accuracy variation with change of frequency is presented. Difficulties in accurate calibration of reactive volt-ampere-hour meters have been experienced in the past. A simple method of accomplishing this result is described in some detail.

DOI:10.1049/jiee-1.1933.0119

出版商:IEE    

年代:1933

数据来源: IET

摘要:

A method of calibrating reactive volt-ampere-hour meters is described, in which an electrometer is used in conjunction with an air-cored mutual inductor. A comparison with another method is described, satisfactory concordance having been obtained.

DOI:10.1049/jiee-1.1933.0120

出版商:IEE    

年代:1933

数据来源: IET

摘要:

In Part I it is pointed out that only a few of the existing 50 radio-telephone links are at present working at anything like full-load capacity. For this reason the chief problem for the engineers on most of the links is one of reducing operating costs. On a few heavily-loaded links, however, the expense of some improvement in circuit performance would be justified. Various means are discussed in outline for dealing with these two problems.In Part II further details of the improvements proposed in Part I are dealt with, and in particular the probable value of the single side-band method in relation to other possible solutions is discussed.(1)Operating costs.—It is found that on an existing typical link, with either light or heavy traffic, the single side-band suppressed-carrier system would be expected to save about 87 per cent of the valve replacement costs, and 90 per cent of the cost of the power.(2)Improved performance.—In the cost estimates of (1) it is shown that changing to single side-band working should be equivalent in. signal/noise ratio to increasing the peak power of the transmitter about 16 times. If this factor is allowed for, by greatly reducing the transmitter size, it is shown that single side-band working should still give circuit improvements in relation to fading, quality, and privacy. The single side-band system eliminates the chief cause of distortion at present, i.e. that due to selective fading-out of the carrier. It should also make workable several well-known privacy schemes at present useless during selective fading, and give rise to a promising new method.A possibly new means of reducing distortion due to intermodulation in Class 3 single side-band amplifiers is referred to.In Part III an attempt is made to answer the following three questions: 6pIs the problem technically possible at all under present commercial conditions?If it seems possible, what is likely to be the best general method—independent stable oscillators at each end, or the use of a pilot signal?Having decided on the most promising general method, what problems will be met in designing practical equipment, and how can we solve these problems?The answer to the first is in the affirmative; single sideband working should be possible in practice, either by separate stable oscillators or by a pilot signal.6pA discussion of the second question results in favour of the pilot method, particularly as it is shown that some sort of pilot is almost indispensable in any case, for controlling the medium-period fading.6pAnswering the third, it is suggested that a single radio frequency corresponding to an audio frequency of about 3.4 kilocycles per sec. would be most suitable, and that this pilot should control the frequency of a local oscillator. It is pointed out that exact synchronizing in the correct phase would in any case be useless at present; while selective fading is still not overcome, the exact signal wave-form can never be reproduced at the receiver, even with perfect carrier synchronism.6pExperiments were carried out by the author on three shortwave links using equipment on the lines suggested in Part III, and the results are given in Part IV. The final tests between Madrid and Paris showed that the expected improvements-over double side-band working, discussed in Part II, were fully obtained. A maximum synchronizing error of 6 cycles per sec. over periods of several hours was found.6pIn Part V it is suggested that—6p(1) A simplified form of the receiver described in Part IV could be used commercially, and would meet requirements for at least the next few years. In this connection a somewhat new form of filter, on the “balanced reaction” principle, is described.6p(2) For the immediate future the principle used in the transmitter should be that of the “side-band balance”, i.e. a method of selecting the side-band in one stage directly at the final high frequency, without relying on filters. This circuit is discussed.6pAssuming selective fading to be absent, it is shown in Part VI that synchronizing at the exact frequency, within predetermined phase limits, is fairly simple. One form of circuit to do this is described.6pA high-quality circuit is explained, giving exact synchronism in phase except during periods of deep fading, when the frequency difference may amount to a few cycles per second.

DOI:10.1049/jiee-1.1933.0122

出版商:IEE    

年代:1933

数据来源: IET

摘要:

In this paper it is shown that, owing to the effect of the ship on the incoming wave, a vertical magnetic field may, through re-radiation, cause errors in the observed bearing taken with a wireless direction-finder. Experiements show that in the case of calibrations carried out with a roof aerial, if the receiving ship is not in line with the roof, errors of 1° or 2° may arise if the roof is not symmetrical. The error, however, decreases rapdily with increasing distance from the transmitter, and also with increasing frequency.The expressions for these errors are then derived mathematically and it is shown that they are closely allied to the ordinary deviation due to “ ship effect”. The error should be most marked in the direction of the electric axis of the ship (that in which the deviation is zero, usually the fore-and-aft line) and non-exitent at right angles to this.The work was carried out in a light cruiser with one of H.M. destroyers as transmitting ship, and this paper has been prepared in H.M. Signal School.

DOI:10.1049/jiee-1.1933.0124

出版商:IEE    

年代:1933

数据来源: IET

摘要:

The paper describes a wireless direction-finder free from ambiguity which has been developed for use in ships as well as on shore. In most forms of direction-finder it is customary to use a figure-of-eight reception characteristic for taking the directipn, and afterwards, by a separate operation, to resolve the. ambiguity. This second operation increases the time required for taking a bearing, and the main advantage of the new system is that the direction and sense are determined by a single operation.The principle involved is a combination of a figure-of- eight reception characteristic with a cardioid under conditions which ensure:—(1) That the minimum of the cardioid is coincident in direction with one zero of the figure-of-eight.(2) That the cardioid e.m.f. is in quadrature with that of the figure-of-eight.These conditions can be fairly easily satisfied for an instrument set up on shore, but special precautions are necessary when it is installed in a metal ship, owing to the effect of various parts of the ship and its rigging on the wireless wave.An analysis is made of the magnetic forces in the wave in the vicinity of a ship and of the e.m.f. induced in the receiver of the instrument, and it is shown that in all cases where direction-finding with simple apparatus is possible in a ship it is also possible to obtain a satisfactory performance from the new instrument. The deviations that would be expected in a typical Service ship with the new instrument are calculated.By suitable arrangements of circuits the deviations that are experienced with the new instrument can be reduced to the same deviations as would be obtained with the equivalent simple direction-finder in the same position; for example, witfr a fixed spaced-aerial instrument all deviations could be removed as in the case of a Bellini—Tosi system. Methods for effecting these corrections in the new system are discussed.Finally, the setting-up of the new instrument in a cruiser is described and an account of trials carried out, the results obtained, and a comparison with expected results, are given.

DOI:10.1049/jiee-1.1933.0125

出版商:IEE    

年代:1933

数据来源: IET

摘要:

The paper describes a wattmeter depending for its action on the use of two thermionic valves and a direct-current measuring instrument. Three forms of instrument are described, the first suitable for measuring the powers used in ordinary power work, and the second and third for measuring the small powers using in communication work.

DOI:10.1049/jiee-1.1933.0128

出版商:IEE    

年代:1933

数据来源: IET

摘要:

A theorem is proved which states that any network with three accessible terminals can be replaced by a star or delta of certain e.m.f.'s and impedances. This is an extension of Kennelly's star-delta theorem, and Thévénin's theorem.The theorem is applied to find the equivalent network of a transformer and a 3-phase alternator (with coupling between windings and unequal e.m.f.'s)The sensitivity of an impedance bridge, in which a 3-winding transformer is used, is also found by the help of the theorem.Finally, the theorem is used to find the errors in voltage measurement due to earth capacitances. An important result which emerges is that, in measurements of attenuation in balanced systems, an unbalance of capacitance that occursafterthe attenuation pad causes an error in the measured voltage which isnotattenuated by the pad. This is in contradiction to accepted theory, but agrees with practice.

DOI:10.1049/jiee-1.1933.0129

出版商:IEE    

年代:1933

数据来源: IET

摘要:

The theory of the static frequency-changer is developed and a number of expressions of a simple character are obtained which enable the performance to be calculated for any loading conditions.It is shown that, knowing the magnetization characteristic of the iron, the maximum attainable output per unit volume of iron for unity-power-factor conditions in the load may be calculated for the ideal transformer from a simple formula.It is found theoretically that if the load is of suitable impedance and leading power factor an output from a given weight of iron is obtainable which is many times that obtainable when the load is of unity power factor. The power factor of the input is also improved.Experimental work, confirming the theoretical work, is described.Finally, design particulars are given of a 550-kW unit, changing from 50 cycles to 150 cycles with an efficiency of 94 per cent and output power factor of 0–53 leading. The input power factor of the unit as designed is 0–38 lagging, but this may be increased by the use of additional capacitative kVA on the higher-frequency side.

DOI:10.1049/jiee-1.1933.0130

出版商:IEE    

年代:1933

数据来源: IET