摘要:

After an Introduction in Part (1), Part (2) of the paper presents a study of the relations between the attenuation and phase characteristics of 4-terminal networks and their response to an impulse of infinitely short duration applied to the input terminals. It is shown that a rigid relationship exists between the characteristics of 4-terminal networks and their impulse response. In particular:—(a) If the phase-shift produced by the network is proportional to frequency, the impulse response is even;(b) If the phase-shift produced by the network is 90° at all frequencies, the impulse response is odd.From this theoretical analysis is developed, in Part (3), a method of obtaining any desired impulse response by means of a circuit containing a multiple-section artificial line. The response is obtained by effecting appropriate amplitude reflections at the end of each section, these reflections being produced by means of small variable condensers.An experimental circuit is described enabling characteristics identical with those of any network to be obtained in a few minutes.A practical example is given of the design of a low-pass filter with linear phase-shift, as used in television circuits.The paper concludes with the practical consideration of filters having a phase-shift of 90° at all frequencies. It is shown that with the type of circuit described, practical designs are possible for:—(a) High-pass filters whose characteristics are satisfactory up to frequencies as high as 10 to 20 times the cut-off frequency;(b) Band-pass filters, if the band width is not too narrow;(c) Low-pass filters, if the frequencies to be transmitted are not too low.

DOI:10.1049/ji-3-1.1943.0030

出版商:IEE    

年代:1943

数据来源: IET

摘要:

This paper describes a frequency synthesizer which enables any frequency that is harmonically related to a sub-multiple of a standard frequency to be generated by means of a decade system involving a synthesis process. The adjacent harmonic interference is substantially independent of the order of the harmonic and can be extremely small.The paper is divided into two Parts. The limitations of the present technique as applied to frequency measurements and the means of overcoming them are given in Part 1, while Part 2 outlines the principles of the frequency synthesizer and gives a detailed description of a typical example with some applications of its uses as a source.

DOI:10.1049/ji-3-1.1943.0031

出版商:IEE    

年代:1943

数据来源: IET

摘要:

In B.S. 800 “Permissible Limits of Radio Interference” a certain degree of control of interference at the source is specified and in this paper an estimate is attempted of the probable reduction in the interference due to domestic sources which might be expected if B.S. 800 were applied. To this end a calculation is first made of the distribution among listeners of the susceptibility to interference based upon available statistics of the effective heights of aerials and of the magnitude of the coupling between aerial terminals and source of interference. This enables a calculation to be made for any coupling of the probability of interference to a given broadcast field when the distribution of intensity among interfering sources is known.The nature of the distribution of interfering voltages within a given type of appliance is studied and different types are compared. The statistical basis of the method of limitation adopted in B.S. 800 is explained and its implications in practice are considered. From this estimates are made of the distributions of the intensity of interference among domestic sources before and after suppression. From the formulae previously established it is then possible to calculate the ratio of the probability of interference after the application of B.S. 800 to that before, which gives the reduction of interference to be expected and also a relative estimate of the degree of protection afforded to the listener.The result discloses that a not unfavourable situation is provided by the British Standard in question, and although directions for the further reduction of interference at the source are suggested it is shown that substantial further amelioration would involve reduction of the susceptibility to interference of some receiving installations. This would mean some degree of standardization of such installations, the advantages of which are demonstrated.

DOI:10.1049/ji-3-1.1943.0033

出版商:IEE    

年代:1943

数据来源: IET