摘要:

The paper reviews the development of resistors as unitary components for use in telecommunication equipment, leading up to the latest forms of “high-stability” film resistors. Sections 1 and 2 contain brief résumés of the historical development and of the construction and properties of eight different types, whose individual characteristics determine to a large extent the particular uses for which they are most suited. Section 3 is a review of the development of the “cracked-carbon” type, often referred to as “high-stability” resistors to differentiate them from the other carbon and composition forms which are liable to have a wider range of spasmodic variations of resistance due to ageing or to ambient conditions. Sections 3 and 4 deal further with the manufacture and the main electrical and high-frequency properties of such resistors.An extensive Bibliography enables additional data on various aspects of resistor construction, uses and properties to be obtained.

DOI:10.1049/pi-3.1949.0036

出版商:IEE    

年代:1949

数据来源: IET

摘要:

Part 1 of the paper is concerned with the theory of a.c. bridges in which the ratio arms consist of tightly-coupled inductors, and refers particularly to bridges in which two sets of such ratio arms are used together in order to obtain very large ratios between the unknown and standard impedances. Reference is made to the important property of inductively-coupled ratio arms which enables the direct impedance between two points to be measured independently, within limits, of any impedances connected between a third point and the two terminals of the impedance being measured. The logical development of bridges with two such ratio arms follows. The material in Part 1 of the paper is the original work of the late A.D. Blumlein, B.Sc.(Eng.), Associate Member, and the present authors have used verbatim a considerable portion of a hitherto unpublished memorandum written by him in January, 1941.Part 2 of the paper describes Blumlein's application of the principles described to a general-purpose mutual-admittance bridge for the measurement of capacitance and resistance. This has a wide range of impedance measurement, and the facility of being able, in many circumstances, to measure componentsin situwhen it is difficult or impossible to isolate them from other components of a circuit.

DOI:10.1049/pi-3.1949.0040

出版商:IEE    

年代:1949

数据来源: IET

摘要:

A height indicator for aircraft is described in which a change in capacitance with altitude is measured at an audio frequency. The capacitance change is indicated on a meter, which is calibrated in feet. Two insulated metal electrodes are mounted on the aircraft, and the direct capacitance between them is measured. This capacitance is affected by the earth, which behaves as a conducting sheet, and the variations can be used to determine the altitude of the aircraft. The changes in capacitance are minute, and measurement is made difficult by the presence in the system of other and much larger capacitances. The difficulties can be overcome by using the double-ratio a.c. bridge described in the associated paper, and the sensitivity can be made sufficient to enable capacitance changes of 1 μμμF to be detected. AS the altitude of the aircraft increases, the capacitance changes caused by the earth become ever smaller, and are eventually obscured by changes arising from other causes. The method is, therefore, suitable only for measuring low altitudes; but, within its range, it is capable of some accuracy.

DOI:10.1049/pi-3.1949.0041

出版商:IEE    

年代:1949

数据来源: IET

摘要:

“Signal imitation” is the term used in telephony to describe the operation by speech currents of voice-frequency signalling equipment. There are means by which signal imitation can be reduced to any desired extent, and eliminated where necessary, at some sacrifice of simplicity of the equipment and of signalling speed. The paper is concerned with analysing the means of reducing signal imitation so that a judicious choice of signals may be made. It is based largely on work undertaken in connection with the standardization by the C.C.I.F. (Comité Consultatif International Téléphonique) of a voice-frequency signalling system for international telephone circuits.The work was primarily directed towards discovering the signalling frequencies least liable to signal imitation. It was found that these frequencies depended on the origin of the speech currents, commercial microphones and telephone circuits giving results very different from high-quality recordings. The effect of language is small compared with that of other variables. Mainly on the evidence of these results, recommendations were made by the 8th C.R. of the C.C.I.F. to use frequencies between 2000 and 2500 c/s for international signalling in Europe.The work was then extended to collect data on the influence on signal imitation of factors other than frequency and language.

DOI:10.1049/pi-3.1949.0049

出版商:IEE    

年代:1949

数据来源: IET

摘要:

A general method for the calibration of milliwattmeters operating in the centimetric-wave region is described. Results of measurements at 3000 Mc/s on a thermistor bridge milliwattmeter are given and it is shown that within the present limits of experimental error (estimated as±4%) this instrument gives true power indications. The powers indicated by other forms of milliwattmeter, for equal power inputs, have been determined and the results are summarized. It is concluded that a number of different instruments may be relied upon to indicate true power withing reasonably small limits of error.

DOI:10.1049/pi-3.1949.0051

出版商:IEE    

年代:1949

数据来源: IET

摘要:

The Multiple-Track Range is a short-distance radio navigational aid similar in principle to Gee and Loran. The paper describes equipment that was built for experimental purposes and given operational trials on a regular air route. The results of the trials and the accuracy are discussed.

DOI:10.1049/pi-3.1949.0054

出版商:IEE    

年代:1949

数据来源: IET

摘要:

The paper describes an instrument which was developed for monitoring continuously the spectrum of a 10-cm naval radar transmitter. The unit consists of a hybrid H011coaxial mode cavity, which can be mechanically tuned over a ± 8 Mc/s frequency range at any predetermined point in the 10-cm band. The spectrum so obtained is displayed on a cathode-ray tube. The accuracy of frequency measurement with the components used is about ± ¼ Mc/s. The paper describes apparatus which would not necessarily be used in future equipments.

DOI:10.1049/pi-3.1949.0056

出版商:IEE    

年代:1949

数据来源: IET