摘要:

An account is given of measurements which have been made of the variation of attenuation with frequency in a number of concentric-line filters. It is shown that the results are in rough agreement with formulae derived from transmission-line theory, though discrepancies arising from end-effects are by no means negligible. It is also shown that, for nearly all practical purposes, the cut-off frequency of a filter can be calculated from simple lumped-circuit theory.Constructional details are given for a number of low-pass and for one high-pass filter, and an appendix is included, giving Messrs. Proctor and Sloane's derivation of the transmission-line theory.

DOI:10.1049/ji-3a-1.1946.0225

出版商:IEE    

年代:1946

数据来源: IET

摘要:

Experimental results are described which serve to emphasize the importance of taking certain precautions when attempting to use crystal rectifiers in measurement work. Particular attention is drawn to the effect of the r.f. circuit impedance on the apparent rectification law and to that of temperature on the rectification sensitivity. The main conclusion drawn is that if crystal rectifiers are to be used in measurements in which their rectification law is in any way involved, considerable care must be taken to ensure correct working conditions. In this connection certain general recommendations are made.

DOI:10.1049/ji-3a-1.1946.0226

出版商:IEE    

年代:1946

数据来源: IET

摘要:

A method of comparing the noise factor of radio receivers is described. This factor is the ratio of the signal/noise ratio in a resistive source at room temperature before connection to the receiver, to that existing in the receiver output. It is assumed that the noise in the source is thermal, i.e. that no extraneous noise pick-up is present.The measurement is made by using a dummy aerial as a source, and raising its temperature until a measurable increase in noise output is obtained. The noise factor can then be deduced from the increase in noise output and the temperature of the dummy aerial.The method has been used at frequencies up to 1 200 Mc/s.The paper includes some practical details of measurement, and experimental results obtained at frequencies of 45, 200 and 600 Mc/s.

DOI:10.1049/ji-3a-1.1946.0227

出版商:IEE    

年代:1946

数据来源: IET

摘要:

This paper describes an instrument capable of giving a picture of the frequency-response curves of amplifiers whose pass bands are enclosed in the bands 5–35 and 38–82 Mc/s, the accuracy of such pictures being ± 0.3 db on the low range, and ± 0.2 db on the high range. The frequency is given to ± 200 kc/s. Any band-width between about 1 Mc/s and the full extent of either band can be satisfactorily displayed.Various methods of obtaining a suitably-modulated measuring signal are discussed, together with the design problems encountered in making the instrument described.

DOI:10.1049/ji-3a-1.1946.0228

出版商:IEE    

年代:1946

数据来源: IET

摘要:

The paper describes a portable equipment for the measurement of the field strength of pulse and continuous-wave signals in the frequency bands 20–30 and 40–650 Mc/s (wavelengths 10–15 and 0.46–7.5 m). The equipment consists essentially of a receiver, in which are incorporated calibrated signal-frequency and intermediate-frequency attenuators and an output meter, and a cathode-ray output-indicator unit. The field strength is measured by adjustment of the attenuators for a standard output, which for pulse signals is read on the cathode-ray tube and for continuous-wave signals on the meter. A half-wave dipole aerial is used, and the initial calibration of the standard output in terms of the field strength at the aerial is carried out by a radiation method. The noise voltage of the first circuit of the intermediate-frequency amplifier is used as the reference voltage for setting up the gain of that amplifier, and an internal oscillator supplies the reference voltage for setting the gain of the indicator unit.The minimum measurable field strength varies with frequency between 3 and 500 μV/m on short pulse (< 2 microsec) signals, and between 1.5 and 250 μV/m on long-pulse and continuous-wave signals. The maximum field strengths which can be measured are 140 db above these minimum values. The accuracy of relative measurements on any one frequency is within ± 0.5 db, and that of absolute measurements is within ± 2 db. Within these limits of accuracy the measurements are independent of pulse width for values greater than 0.5 microsec. The recurrence frequency range is 25–100 000 c/s.Various types of field-strength measurement which have been made with the equipment are described, and they illustrate its wide range of application.

DOI:10.1049/ji-3a-1.1946.0229

出版商:IEE    

年代:1946

数据来源: IET