摘要:

The paper describes a series of measurements on solutions of sodium chloride in distilled water over the frequency ranges 0.95-13 and 690-4 320 Mc/s. The results are discussed in terms of the Debye-Falkenhagen theory of electrolytes and of the available data on the absorption band exhibited by water in the region of 10 000 Mc/s (wavelength 3 cm). A comparison is made with the published results on the electrical properties of sea-water—for frequencies up to 10 Mc/s—and deductions are made as to its probable behaviour at very high frequencies.

DOI:10.1049/ji-3-2.1946.0011

出版商:IEE    

年代:1946

数据来源: IET

摘要:

This paper discusses a fundamental problem involved in the theory of multi-channel transmission. In modern carrier telephone systems a number of channels pass through common line amplifiers. The loading of these amplifiers therefore fluctuates in accordance with the sum of the speech voltages applied to the individual speech channels in the carrier group, and the maximum loading depends upon whether there can be a simultaneous occurrence of peak values in all the speech channels. In general, this is an extremely rare occurrence. As an alternative to providing speech circuits, some of the channels may, however, be sub-divided to provide voice-frequency telegraph channels, the speech being then replaced by a number of single-frequency tones. When the telegraph channels are idle, these tones are continuous and the maximum loading of any common amplifier may be increased thereby. Some modern automatic signalling systems also use continuous tones or long periods of tone for the transmission of signals, so that possible overloading of the amplifiers must again be considered. It becomes important, therefore, to be able to determine the probabilities associated with the combination of sinusoidal signals from a number of different channels, and in particular the probabilities that the instantaneous value and the length of the resultant vector will exceed certain limits. The instantaneous value of the resulting signal is, of course, the sum of the values in all the combined channels. Under suitable conditions the peaks of the instantaneous value trace out an envelope for the resulting signal, and the probabilities associated with this envelope are, in general, the same as those associated with the resultant vector.The paper discusses theoretically the probabilities associated with the instantaneous value and the length of the resultant vector obtained by combiningncosine oscillations of equal amplitude and random phase relationship. It is mainly concerned with very small values ofn(=2, 3, 4… 12), and gives, for the first time, a complete set of curves showing the probabilities of the instantaneous value and the length of the resultant vector exceeding any given limits.For large values ofnone aspect of the problem has been discussed by Rayleigh, and solutions for very large values ofnhave been given by Landon and more recently by Rice in connection with fluctuation noise. For the small values ofndiscussed here no solution has hitherto been given, but the empirical combination of speech-voltage distributions for a small number of channels has been studied in the Post Office Engineering Research Station and has been discussed in application to the design of apparatus by a number of authors. The mathematical theory used to derive the results is given in Section 6. It is hoped that this Section will be of general interest, because the underlying theories are of fundamental importance and may be capable of application to other physical problems, as, for example, when the amplitudes as well as the phases of the combined oscillations are random. While some of the formulae used are not original, as the list of references shows, they are, for convenience, collated here from the scattered memoirs in which they appear and which contain much other mathematical material extraneous to the present subject.

DOI:10.1049/ji-3-2.1946.0012

出版商:IEE    

年代:1946

数据来源: IET

摘要:

The paper deals with the various factors in broadcast receiver design which are of particular importance when band-spread tuning is employed, stress being laid throughout on the practical aspects. The first two Sections deal briefly with the way in which this method was developed to meet the need for easier tuning on short-wave bands, and with the various methods employed to achieve it. The general design of the pre-selector and oscillator circuits is then discussed in some detail. The basic circuit for band-spread tuning by variable capacitance is analysed, and formulae are developed for calculating the elements of the capacitance network. From these, graphical methods of solution are developed and illustrated. The use of temperature-compensating condensers, and various methods of circuit trimming, are also discussed. In conclusion, it is shown that there scope for considerable divergence in design to suit the various price ranges of receivers, and that, although the best methods, as usual, cost more, the simpler methods can, by careful design, be made reasonably good. There is, however, the risk that poor design and excessive cheapening might cause the system to fall into disrepute.

DOI:10.1049/ji-3-2.1946.0013

出版商:IEE    

年代:1946

数据来源: IET

摘要:

The paper deals with the technique of radio measurements evolved as a necessary aid to the development of decimetre- and centimetre-wave valves, circuits and equipment, and surveys some of the methods applicable in this wide field. It commences with a review of the circuit theory of coaxial and wave-guide transmission lines, followed by a short section on high-frequency oscillators.Succeeding sections deal with the measurement of the fundamental quantities of frequency, power, impedance and voltage. Heterodyne methods of frequency measurement, and coaxial and resonant cavity wavemeters, are described. The design of bolometer and calorimeter circuits is discussed for powers between 1 microwatt and several hundred watts. Measurements of reflection coefficient and Q-factors are included in the section on impedance.The concluding sections deal with derived measurements: receiver sensitivity, aerials and field strength. A standard of receiver sensitivity is established, based on thermal noise voltage, and the design of suitable signal generators and sensitivity measuring equipment is discussed. The section on aerials comprises measurements of polar diagram, gain and impedance. Finally, equipment for the absolute measurement of field strength at centimetre wavelengths is outlined.

DOI:10.1049/ji-3-2.1946.0014

出版商:IEE    

年代:1946

数据来源: IET

DOI:10.1049/ji-3-2.1946.0019

出版商:IEE    

年代:1946

数据来源: IET

DOI:10.1049/ji-3-2.1946.0020

出版商:IEE    

年代:1946

数据来源: IET

DOI:10.1049/ji-3-2.1946.0021

出版商:IEE    

年代:1946

数据来源: IET