摘要:

The paper demonstrates that the intensity variation in a magnetic tape passing through a recording gap forms part of a series of unclosed and markedly asymmetrical hysteresis loops. The effect of asymmetry is investigated theoretically and shown to give distinctive properties to the recording and distortion characteristics of unbiased recording. The gap length of the recording head is critical under these conditions and leads to the occurrence of maxima and minima of recorded level and distortion at specific wavelengths. These properties are confirmed by experiment, and the mechanism of recording employing h.f. bias is examined in the light of the findings. It is shown that the number of bias cycles normally available during the time a tape element is in the recording gap is insufficient for hysteresis symmetry to be attained. Various predictions are made concerning the transitions which may be expected in the recording and distortion characteristics as the h.f. bias field is increased from zero to saturation value. These transitions have been demonstrated experimentally, and it is shown that adequate h.f. bias eliminates the asymmetry of the a.f. intensity variation. A symmetrical variation of a.f. intensity results in the recording and distortion characteristics normally observed. The effect of a bias-leakage field outside the recording gap is discussed briefly with reference to the coercivity of the tape material.

DOI:10.1049/pi-3.1952.0030

出版商:IEE    

年代:1952

数据来源: IET

摘要:

The paper discusses the design of an equipment for the continuous recording of the very small r.f. noise powers received from the sun and the galaxy.It is first shown how a noise power can be described in terms of an equivalent temperature, and how cable attenuation affects the noise power measured at the end of an aerial feeder. The fundamentals of the measurement of noise power are considered; it is shown that the minimum detectable power is determined by the receiver noise and by the ratio of input and output bandwidths of the receiver. The practical difficulties inherent in the measurement have been overcome by the design of a self-balancing equipment in which a locally generated noise power is continuously adjusted to equality with the incoming power.A description of such an equipment is given; the design of the r.f. switch, the local noise source, the receiver and the control circuits for the noise source are considered in some detail.The performance of the equipment is analysed in terms of its accuracy, its response to a step function of input and the fluctuations of its output indication. Experimental determinations of the performance are found to compare reasonably well with theory.

DOI:10.1049/pi-3.1952.0033

出版商:IEE    

年代:1952

数据来源: IET

摘要:

An attempt has been made to integrate all information which might lead to a fuller understanding of the physico-chemical processes occurring on and in getter materials. Both original research results and published work from other sources are included.The characteristics of getters are defined and correlations between them are derived. Methods for measuring the characteristics are described and values of these for different getters and gases are given. Two main mechanisms of the gettering process are distinguished, namely contact gettering and discharge gettering, of which the latter, on account of the higher gettering rates attainable, is found to be of chief importance for the production of very high vacua. The processes contributing to discharge gettering are investigated in detail, and an attempt is made to determine the parts played by adsorption, diffusion and chemical reaction in different systems of getters and gases. The efficiency of flash getters is compared with that of coating getters, particularly thorium. It is found that gases like oxygen and carbon dioxide are taken up irreversibly during discharge gettering with thorium. The pressures attainable in valves using flash and coating getters are measured, and the influence of some parameters such as baking time on the pump or pressure during sealing-off is investigated.

DOI:10.1049/pi-3.1952.0034

出版商:IEE    

年代:1952

数据来源: IET

DOI:10.1049/pi-3.1952.0040

出版商:IEE    

年代:1952

数据来源: IET

DOI:10.1049/pi-3.1952.0041

出版商:IEE    

年代:1952

数据来源: IET

DOI:10.1049/pi-3.1952.0042

出版商:IEE    

年代:1952

数据来源: IET

DOI:10.1049/pi-3.1952.0043

出版商:IEE    

年代:1952

数据来源: IET

DOI:10.1049/pi-3.1952.0044

出版商:IEE    

年代:1952

数据来源: IET

DOI:10.1049/pi-3.1952.0045

出版商:IEE    

年代:1952

数据来源: IET