摘要:

High-voltage characteristics of concentric radio-frequency cables with polythene dielectric have been studied. These have included determinations of power-frequency breakdown voltage, and the effect of power-frequency stressing on power factor, life with pulse voltages, discharge characteristics measured mainly at power frequencies, and performance with 600-Mc/s radio-frequency pulse operation. The correlation between life on unidirectional pulses and discharge characteristics has been examined, and a comparison has been made between thermal ratings derived by calculation and experimental determinations at a frequency of 600 Mc/s. Finally, tentative voltage ratings based on the experimental work are proposed.

DOI:10.1049/ji-3-2.1947.0034

出版商:IEE    

年代:1947

数据来源: IET

摘要:

The elements of propagation of radio waves are developed from the ordinary theory of transmission lines, familiar to electrical engineers, without any explicit reference to Maxwell's equations. Phenomena such as the Brewster angle, the critical angle, propagation in hollow metal pipes, reflection and transmission by wire netting, etc., are all counterparts of well-known phenomena in the theory of transmission lines. The most powerful instrument for integrating all these phenomena into a single picture is the concept of field impedance. Just as potential difference (measured in volts) divided by current (measured in amperes) leads to the concept of circuit impedance, so electric field (measured in volts/metre) divided by magnetic field (measured in amperes/metre) leads to the concept of field impedance. Widespread use of the concept of field impedance was overdue before the war but has to some extent come into its own during the war.

DOI:10.1049/ji-3-2.1947.0037

出版商:IEE    

年代:1947

数据来源: IET

摘要:

The relative magnitudes of radio-frequency signals are measured by passing the signals through a linear heterodyne frequency-convertor and comparing the magnitudes of the resulting intermediate-frequency signals with those of signals from a standard i.f. generator of known performance. Standard-signal generators are calibrated in this way with respect to relatively large fiducial signals. The standard i.f. generator includes an H11-mode piston attenuator excited through a filter designed to reduce errors due to the transmission of energy in other modes. The signals from the frequency convertor and standard generator are compared by means of a linear amplifier with a square-law output meter, which enables accurate measurements to be made with signals below noise level. Signal ratios up to 90 db can be measured directly with the equipment described; the range of indirect measurement is substantially greater. Signal ratios up to 10 db can be measured to 0.02 db, and greater ratios to within 0.2% of their decibel values. Signals 16 db below noise can be measured to 0.5 db. The method has been used at frequencies between 3 and 3000 Mc/s, and can be used for both lower and higher frequencies.

DOI:10.1049/ji-3-2.1947.0040

出版商:IEE    

年代:1947

数据来源: IET

摘要:

A circuit is described which permits a highly-selective transmission-measuring equipment to be designed to meet a specified accuracy of measurement; it is suggested that ±0.25 db is quite readily obtainable. The basic principles of the method are (a) the direct demodulation of the test signal by means of an identical frequency obtained from an oscillator synchronized to the test tone, (b) discrimination against unwanted line signals obtained by means of low-pass filters, (c) the elimination of the effect of the phase difference between the test and demodulating tones by Barber's two-path method, and (d) the use of an envelope-modulated test signal.

DOI:10.1049/ji-3-2.1947.0041

出版商:IEE    

年代:1947

数据来源: IET

摘要:

A comparison is made of the two main methods of describing the performance of pulse and television amplifiers, namely bandwidth, and speed of build-up of a suddenly-applied signal. It is shown for a variety of circuit arrangements (including asymmetrical circuits) that equal speeds of build-up based on the slope of the build-up curve at half the steady-state amplitude correspond fairly closely to equal bandwidths measured between the points at which the response is 3 db below that at the applied frequency. It is therefore concluded that either of these criteria would be satisfactory in practice, since they are mutually consistent. Other methods of defining the speed of build-up are discussed, and the main inconsistency is shown to be that, for only one or two stages, but not for larger numbers, the use of the maximum slope of the build-up curve gives misleading results.The problems of humps in the attenuation/frequency response and overshoot in the transient response are only briefly discussed, owing to the difficulty of assessing quantitatively their importance as performance criteria. A few other design factors, especially adjacent-channel interference suppression, are briefly considered in relation to the main discussion.

DOI:10.1049/ji-3-2.1947.0043

出版商:IEE    

年代:1947

数据来源: IET