摘要:

This paper describes a pulse-code modulator, using junction transistors, designed to provide a 5-digit transmission of a signal having a total bandwidth of 800 c/s. The system described uses the pulse-count method as being the most straightforward way of producing a digital code from an a.c. waveform. A monitor unit is included to decode any required number of digits of the output signal so that system-evaluation tests can be carried out.Temperature tests are also described, the results of which show that the equipment will operate satisfactorily up to a temperature of at least 65° C.

DOI:10.1049/pi-b-2.1959.0115

出版商:IEE    

年代:1959

数据来源: IET

摘要:

The paper discusses the design and engineering details of two types of demodulator equipment which will operate from a p.a.m. system, and could be used, for example, in the field of electronic telephone exchanges. Apart from normal circuit-elements the equipments contain only semiconductor diodes and transistors. The equipments described will provide electrical characteristics conforming to different levels of performance such as might be required for local or trunk routing. They are both designed to operate on a 100-channel system and will provide gain of the signal information of about 40 dB.The effects of variations in device parameters and environmental conditions on electrical performance are considered in some detail, and the results achieved in practice are discussed in relation to the standards of performance likely to be required. Special attention has been paid to the stability of the semiconductor parameters with life, and the effect of this on the long-term performance of the circuits. A preliminary investigation to determine life trends of the type of transistor specified has been undertaken, and the results obtained are presented and discussed.

DOI:10.1049/pi-b-2.1959.0116

出版商:IEE    

年代:1959

数据来源: IET

摘要:

Because equipment using transistors will be introduced into communication networks in which valve equipment is already in use, questions of compatibility will arise. In some cases the performance of transistor equipment will have to conform closely to that of existing valve equipment, whilst, in others, no such restriction will occur. With present transistors this latter case would lead to the use of low signal levels and low-gain amplifiers. With feedback amplifiers employed in carrier systems the effect is to divide the amplifiers into two classes. The first class must operate with high gains and high output powers, whilst the second class is essentially one of low-power amplifiers. Examples of both classes are described, and various features of their design are discussed. These are a high-power amplifier suitable for use on an open-wire line system, a low-power wide-band amplifier for use on a system for pair cables, and a narrow-band feedback amplifier of the type used in pilot control systems.Future developments are briefly discussed.

DOI:10.1049/pi-b-2.1959.0117

出版商:IEE    

年代:1959

数据来源: IET

摘要:

The paper first considers the repeater spacing which produces the minimum noise per channel for a given route length, cable type and repeater-amplifier output power. The optimum spacing is shown to be equivalent to a repeater section of 1-neper loss if the repeater amplifier has a flat gain characteristic. The case where the amplifier gain follows the cable-loss characteristic is also discussed. The relationship between the technical optimum and the best economic spacing is considered: the transistor repeater is shown to permit a closer approach to the technical optimum spacing than is economically possible with a valve repeater. This is because of the lower initial cost of the repeater and its housing and of its lower power consumption. The lower section loss also permits relaxation of the near-end crosstalk requirements for the cable, permitting economies in its construction.The design of transistor repeater amplifiers is discussed, comparing common-base stages in tandem without overall feedback with connections which give considerable current gain but which require overall feedback to obtain the linearity and gain stability required in a repeater. The straightforward common-base connection appears to yield better linearity and stability than the more sophisticated arrangements which give equal gain in a broad-band repeater. If the difficulties in the feedback amplifiers can be overcome, it should be possible to design the amplifier gain to follow the cable loss with consequent improvement in noise performance, whereas it is difficult to produce a common-base amplifier with anything substantially different from a flat gain/frequency characteristic.

DOI:10.1049/pi-b-2.1959.0118

出版商:IEE    

年代:1959

数据来源: IET

摘要:

In recent years there has been increasing interest in the use of digital methods to transmit speech signals over mobile communication networks. The advent of transistors has enabled the necessary equipment to be produced in a cheap and convenient form, combining the advantages of lightness, ease of operation, and low power consumption. The paper illustrates the use of transistors in this field by describing the more interesting design features of a 4-channel 5-digit pulse-code-modulation system employing signal compression and expansion. Consideration is also given to the transistor properties which limit the accuracy of such equipment, and it is shown that an 8-digit system is a practical proposition.

DOI:10.1049/pi-b-2.1959.0119

出版商:IEE    

年代:1959

数据来源: IET

摘要:

Frequency-division-multiplex telephone terminal equipment requires a series of stable carrier-frequency supplies, together with other frequencies for pilot and signalling purposes. The paper surveys the application of transistors to the generation of these supplies, with reference to circuits designed to meet typical requirements.Carrier supplies are usually derived from a single master oscillator and the design of such an oscillator with a long-term frequency stability of better than one part in 106is discussed. Circuits for the derivation of groups of carrier frequencies from the master source are also described. These include harmonic generators and a divider of the regenerative-modulator type.Power levels required at the various carrier frequencies vary from a few milliwatts to several watts for different frequencies and applications. Some of the problems of obtaining stable amplification with transistors at high levels and high frequencies are illustrated by examples of amplifier design for frequencies up to 612kc/s. A particular problem is the supply of pilot signals having an extremely stable amplitude. The design of an effective constant-output amplifier for this purpose is described.

DOI:10.1049/pi-b-2.1959.0120

出版商:IEE    

年代:1959

数据来源: IET

摘要:

A compandor for use on telephone speech circuits, which has a compression/expansion ratio of 2, and which gives a subjective improvement in signal/noise ratio of about 25 dB, is described. Junction transistors are used as variable-loss elements, control-current rectifiers and for temperature compensation, as well as for amplification. Use is made of the properties of the base-emitter junction of the transistor to achieve a closer approximation to the desired compression/expansion characteristic, over a wider range of signal levels than has been possible in the past, without the need for special selection or matching of the variable-loss circuit elements. A small number of compandors has been made and tested in the laboratory, and the performance of a typical unit is described.

DOI:10.1049/pi-b-2.1959.0121

出版商:IEE    

年代:1959

数据来源: IET

摘要:

The sending and receiving of voice-frequency signals over telephone circuits is well established as a practice with thermionic-valve receivers. Transistor receivers would reduce the steady drain on the exchange power supply. Capital cost and reliability in service have yet to be determined.The paper outlines the technical requirement of v.f. receivers, compares the design features of valves and transistors, and uses an experimental design of transistor receiver to illustrate the problems involved.

DOI:10.1049/pi-b-2.1959.0122

出版商:IEE    

年代:1959

数据来源: IET

摘要:

The knowledge required of an operator for manual or machine sorting is considerable. The code translator, which has been in use at the Head Post Office in Southampton since March, 1958, provides method of reducing the memory required of a machine operator. The translator employs a matrix of 5×26 rectangularB/Hloop cores to translate a five (or less) alphabet character code, which has been derived from the address on the envelope, into one of 144 possible output signals. The maximum capacity of the translator at present in service is about 4000 five-character codes.

DOI:10.1049/pi-b-2.1959.0124

出版商:IEE    

年代:1959

数据来源: IET

摘要:

A transistor-driven magnetic-core store which has a capacity of 4096 words, each of 37 bits, has been developed for a large transistorized computing system. The paper describes a system in which the drive currents are generated in a central generator, and address selection is achieved by transistor gating circuits. A typical store cycle—reading followed immediately by writing—requires 12 microsec with random access.

DOI:10.1049/pi-b-2.1959.0125

出版商:IEE    

年代:1959

数据来源: IET