摘要:

The paper discusses the importance of frequency standardization to the telecommunication engineer, and outlines the work which the Post Office has carried out in this field. As published information on the subject is scanty, the historical development of frequency standards is reviewed, a bibliography is included and the factors affecting the design of a standard are briefly analysed. The design, performance and application of the Post Office standard are considered in some detail. In particular, the absolute calibration of the group of crystal-controlled oscillators comprising the standard is discussed, and details are given of equipment designed for the precise intercomparison of the frequencies of the individual oscillators. A specialized form of frequency standard, known as a “quartz clock,” which is now being used by astronomers in addition to the older type of pendulum clock, is briefly described.The methods available for the comparison, both national and international, of frequency standards are analysed, and a résumé of international comparisons reveals the advances achieved in frequency standardization during the past two decades. At present it is considered that the absolute value of the Post Office standard of frequency is known to ±1×10−8. Finally, the development work now being carried out to improve the stability and reliability of the standard is outlined.

DOI:10.1049/ji-3-2.1946.0037

出版商:IEE    

年代:1946

数据来源: IET

DOI:10.1049/ji-3-2.1946.0041

出版商:IEE    

年代:1946

数据来源: IET

摘要:

The paper describes a television system in which sound pulses having a constant height and variable width are inserted in the line synchronizing periods. It is claimed that this method of transmission leads to a simplified receiver and that the programme quality is better in the presence of severe interference. Other advantages are that the frequency band-width for transmission is reduced; the method of receiving sound ensures automatic volume control; the sound pulses provide a fixed reference level for automatic volume control on the vision channel; mutual interference between vision and sound often present on two-channel reception is avoided; reduced transmission band-width simplifies the design of the receiving antenna; mutual coupling between the vision and sound antennae at the transmitter is avoided; and the installation and maintenance costs of the sound transmitter are saved.The frequency range of the system operated in conjunction with the pre-war British transmission would be limited to 5 kc/s.

DOI:10.1049/ji-3-2.1946.0044

出版商:IEE    

年代:1946

数据来源: IET

DOI:10.1049/ji-3-2.1946.0047

出版商:IEE    

年代:1946

数据来源: IET

摘要:

By the process of field-plotting in the cross-section of a uniform transmission line, an orthogonal field pattern of curvilinear squares satisfying the boundary conditions is obtained. IfNvis a number of voltage steps andNfthe number of electrostatic flux lines in this field plot, the characteristic impedance is given byZ= 377Nv/Nf√μ/kwhere μ is the permeability, andKis the permittivity.Applications to coupling and screening are also considered.The use of models in an electrolytic tank for capacitance determination from field plots or direct measurement is discussed, and an axially symmetrical three-dimensional field is plotted. Mention is made of the relaxation process and rubber-sheet methods of field-plotting.

DOI:10.1049/ji-3-2.1946.0048

出版商:IEE    

年代:1946

数据来源: IET

摘要:

The principles used in calculating the temperature rise in cables which are required to transmit radio-frequency power are considered. The theoretical attenuation characteristics and power ratings of a number of standard r.f. cables are set down in graphical form for a wide range of operating frequencies. The ratings are based on a maximum temperature rise of 30 deg C, in an ambient of 55°C, established in a matched line for the steady-state condition. The use of suitable “rating factors” for other operating conditions is proposed. The effect of such operating conditions as the presence of standing waves and the effect of end cooling are briefly considered in relation to the rating of the cables.

DOI:10.1049/ji-3-2.1946.0051

出版商:IEE    

年代:1946

数据来源: IET