摘要:

Plans have been prepared by the Post Office to enable subscribers to dial their own trunk calls. This is called ‘subscriber trunk dialling’ (s.t.d.).The new service will be opened at Bristol Central Exchange in December, 1958, and will be extended as rapidly as resources permit. By the end of 1961, subscriber trunk dialling is expected to be available in over 100 centres.A national numbering scheme has been prepared, and ultimately a long-distance call from any part of the United Kingdom will be obtained by dialling the national number of the required subscriber. Local numbers will be unaffected.Exchanges have been divided into groups for charging and routing purposes. The charging and routing will be controlled by register-translator equipment (Grace), an electronic form of which will be used for the larger installations.In s.t.d. areas, new methods of charging for calls will be introduced. All calls will be timed, and the unit fee will be reduced to 2d. The existing 3 min minimum charge will not apply to s.t.d. calls. Instead, unit fees will be recorded, each unit paying for a period of time which depends on the distance of the call. Both trunk and local units will be registered on existing subscribers' meters, and a bulked bill will be rendered. Private meters will be rented to subscribers who require them. Accounts will be sent to s.t.d. subscribers quarterly, and the preparation of accounts will be increasingly mechanized. A new coin box has been developed so that trunk calls in s.t.d. areas can also be dialled by coin-box users.

DOI:10.1049/pi-b-2.1959.0268

出版商:IEE    

年代:1959

数据来源: IET

摘要:

The aim of the telephone designer has generally been the attainment of greater sending and receiving sensitivity, so that conversations may be carried on over connections of greater loss. With the telephone sets hitherto available, the sensitivity has not been so high as to give excessively loud reception on short connections. However, recent developments, particularly in the electromagnetic design of telephone receivers, have made available substantial increases in sensitivity, and the new British Post Office subscriber's telephone set (the 700 type) is more sensitive on long lines than its predecessor (the 300 type) by some 4 dB in both sending and receiving directions. This enhanced sensitivity, which is of great advantage in permitting the use of longer or smaller-gauge subscribers' local lines without degradation of performance, is liable if uncontrolled to be an embarrassment on short lines, and, in fact, subjective tests carried out in the field and in the laboratory have established that, on short connections, most subscribers would find this sensitivity too high.The problem is discussed, and it is shown that the best solution is the incorporation in the telephone set of an automatic regulating device which reduces the sending and receiving efficiencies and the sidetone level when the line current is high, while leaving the full sensitivity unimpaired on longer lines. The regulator makes use of the non-linear voltage/current characteristics of selenium-rectifier elements, biased in the forward direction by a control voltage derived from the voltage drop across a metal-filament lamp in series with the line. These elements are used to provide shunt losses on short lines of up to 6 dB on sending and 4 dB on receiving, and also to reduce sidetone.Details are given of the performance of the new Post Office Telephone No. 706 which embodies such a sensitivity control as an integral part of the telephone set. It has as good a performance on a 1-kilohm local line as the 300-type set had on a 660-ohm line; at the other extreme, on very short lines, the sensitivity of the new set is, owing to the action of the regulator, no greater than that of the old set.

DOI:10.1049/pi-b-2.1959.0270

出版商:IEE    

年代:1959

数据来源: IET

摘要:

The steps leading to the development of modern emitters are described and the characteristics and operation of such emitters are discussed.

DOI:10.1049/pi-b-2.1959.0272

出版商:IEE    

年代:1959

数据来源: IET

摘要:

The complex internal current gain, αd, of a diffusion-type germanium transistor has been derived from measurements of the external short-circuit current gain, α, at frequencies up to 20 Mc/s and for emitter currents between 15 μA and 3 mA, by taking account of the effects of the emitter and collector depletion-layer capacitances and the ohmic base resistance. The resulting frequency dependence of αdis that expected from unidimensional diffusion theory. At low emitter currents, the flow of r.f. current in the emitter depletion-layer capacitance causes the cut-off frequency of α to be less than one-third that of αd.

DOI:10.1049/pi-b-2.1959.0275

出版商:IEE    

年代:1959

数据来源: IET

摘要:

The complex internal short-circuit current gain, αd, of a type 2N247 plane alloy-junction germanium transistor has been determined from measurements of the external short-circuit current gain, by taking account of the effects of the emitter and collector depletion-layer capacitances and the ohmic base resistance. Measurements have been made up to 105 Mc/s and over a range of emitter current from 50 μA to 8 mA. It has been found that the loci of αdmay be interpreted in terms of Kroemer's theoretical treatment, which is based on the existence of a uniform drift field across the base. The value of ΔV/kTis found to be 5 at room temperature.

DOI:10.1049/pi-b-2.1959.0276

出版商:IEE    

年代:1959

数据来源: IET

摘要:

Approximate expressions are derived for (a) the critical frequency above which the ideal transistor is unconditionally stable, and (b) the resulting maximum available gain, for the common-emitter configuration. These involve the internal cut-off frequency, the low-frequency emitter input conductance, the ohmic base resistance and the emitter and collector depletion-layer capacitances.

DOI:10.1049/pi-b-2.1959.0277

出版商:IEE    

年代:1959

数据来源: IET

摘要:

The features of existing frequency-modulation techniques are reviewed and compared with those of the feedback method. A practical embodiment of the latter is described, and is considered in some detail.It has very few controls requiring adjustment to secure good performance, either on installation or after valve replacements, and should be particularly suited for use in unattended transmitters.

DOI:10.1049/pi-b-2.1959.0278

出版商:IEE    

年代:1959

数据来源: IET

摘要:

Eddy-current methods of non-destructive testing applied to travelling metal objects on production lines show two advantages over other techniques. These are the comparative ease with which an instrument can be coupled to test objects and the high speed of response, making possible the fast scanning rates required with fast manufacturing process.Experience in recent years has shown that relative motion between test object and measuring head gives results which differ from those of a static system, and may severely limit permissible scanning rates. The paper draws attention to dynamically-induced currents, as causing the speed effect experienced in eddy-current testing. The theoretical arguments advanced have been used to evolve three methods of overcoming the speed effect.

DOI:10.1049/pi-b-2.1959.0279

出版商:IEE    

年代:1959

数据来源: IET

摘要:

Measurements are given of radiation patterns of open-ended rectangular waveguide with conducting flanges attached to the long edges of the aperture. In particular, the considerable effect of different flange lengths and included angles on the E-plane patterns is examined; these measurements are made at three frequencies in order to supplement data, already published, describing measurements made at a single frequency. A suggestion that the E-plane radiation pattern can be approximated by the radiation pattern of a primary source and two secondary sources near the end of the flanges has been substantiated if a suitable obliquity factor is assumed. Some E-plane patterns of flanged H-plane sectoral horns are also given. It is found that there are differences between these patterns and those of similarly flanged waveguide.The effect of flanges on the H-plane patterns of an E-plane sectoral horn is comparatively small, as was expected.

DOI:10.1049/pi-b-2.1959.0280

出版商:IEE    

年代:1959

数据来源: IET

摘要:

The transmission-line analogue technique has been applied to calculate the reactances of a few types of surface which may support surface waves. Experimental methods of estimating the reactances of such surfaces have been discussed, with special reference to the difficulties encountered in practice. Results obtained by theoretical calculations have been found to agree with experimental results within the limits of experimental error and the validity of the assumptions made in the theoretical calculations.

DOI:10.1049/pi-b-2.1959.0281

出版商:IEE    

年代:1959

数据来源: IET