摘要:

In a class-B push-pull amplifier having balanced transformers, evenorder harmonic distortion can be caused by differences in the characteristics of the two transistors. By considering the voltage gain of the two halves of the amplifier it is possible to obtain general expressions from which distortion caused by any particular characteristic can be calculated.The paper is primarily concerned with audio-frequency amplification. It is necessary to consider harmonics outside this range because of the possibility of their giving rise to intermodulation products in the a.f. range.The parameters giving rise to distortion can be divided into the frequency-independent and frequency-dependent types.With regard to the frequency-independent parameters, the only significant factors are the current gain factor, the variation of basecollector current gain factor with emitter current and the extrinsic base resistance. In the case of the frequency-dependent parameters, which, in general, only become important at the higher audio frequencies, the significant factors are the collector capacitance, the variation of current gain with frequency and the carrier-storage effect. In order to obtain low distortion, some matching of transistor characteristics is necessary. Methods are described whereby this can be achieved by fairly simple measurements.Most of the work described in the paper is based on a low-power junction-type transistor. However, the methods used are quite general, and therefore applicable to other types of transistors.

DOI:10.1049/pi-c.1957.0048

出版商:IEE    

年代:1957

数据来源: IET

摘要:

A highly accurate expression for the Q-factor of a direct-coupled filter is derived which is analogous to that for an associated quarterwave-coupled filter. Existing theories usually consider filters of either the maximally-flat or the Cheby̅shev type, and it is shown directly, by transmission-line methods, that these are special cases of a generalized symmetrical filter. Design formulae are given for the bandwidth, pass-band tolerance, and the attenuation in the rejection band both for quarter-wave-coupled and direct-coupled generalized filters.

DOI:10.1049/pi-c.1957.0049

出版商:IEE    

年代:1957

数据来源: IET

摘要:

The effects of an irregularity of characteristic impedance in a transmission line are displayed graphically on a transmission-line circle diagram. This presentation shows qualitatively the major factors which determine the changes in voltage standing-wave ratio and phase produced by a single irregularity or by a large number of irregularities distributed along the line. This analysis is not limited to matched transmission lines as are the statistical methods. The resonance of a disc-spaced transmission line at super-high-frequency is considered. The method developed by Cotte for the determination of impedance variation along a transmission line by harmonic analysis of the distribution of irregularities is discussed in terms of the graphical approach, and a possible simplification to the experimental method is suggested.

DOI:10.1049/pi-c.1957.0050

出版商:IEE    

年代:1957

数据来源: IET

摘要:

An approximate method is given for evaluating the maximum field strength between charged circular cylinders whose axes are either parallel or perpendicular. The approximate formula is compared with exact results and shows an error of less than ½% for a separation of one diameter. If the error in the approximate formula for crossed cylinders is of the same order, then the difference between the results for the crossed and parallel cases is significantly greater than this error.

DOI:10.1049/pi-c.1957.0051

出版商:IEE    

年代:1957

数据来源: IET

摘要:

The paper presents a detailed theoretical treatment of the beyondhorizon radio scatter propagation problem. The form for the spectral density of refractive-index fluctuation, assumed to be the same as that of velocity fluctuation, is derived from the universal equilibrium theory of turbulence. It is used to predict the spectral densities and magnitudes of brightness fluctuation and angular deflection fluctuation for light from a stellar source, and of field-strength fluctuation for line-of-sight radio propagation. These predictions are compared with experimental data, and support is thereby obtained for the theoretical form of the refractive-index fluctuation spectrum. The height variation of the intensity of the refractive-index fluctuations is derived from the experimental data. There follows a detailed treatment of the beyondhorizon case of radio scatter propagation, including a full analysis of the influence of the geometry of the scattering volume on the received field-strength. It is shown that the form of the scattering crosssection implied in the results is compatible with those obtained in different treatments, based on idealized assumptions.

DOI:10.1049/pi-c.1957.0052

出版商:IEE    

年代:1957

数据来源: IET

摘要:

The paper describes an instrument termed the ‘vibration wattmeter’ which consists of a cavity in which is suspended a thin metal rod mounted on a fine glass spindle with a quartz fibre suspension. The rod is free to execute torsional oscillations in the horizontal plane.The oscillating system receives periodic impulses from the interaction between the metal rod and the electromagnetic field within the cavity, and by the automatic switching of the microwave source a steady amplitude of mechanical oscillations can be maintained. The amplitude of these oscillations is measured by means of a small mirror attached to the spindle and a lamp-and-scale arrangement.The relationship between the power delivered to the cavity and the amplitude of the mechanical oscillations can be found theoretically, and with knowledge of the specific couple of the quartz fibre suspension and of the damping factor of the mechanical system, measurements of power can be made.The instrument measures microwave power with an error estimated as not exceeding ±2%. The measurement is absolute, since the calibration depends only on measurements of mass, length and time.

DOI:10.1049/pi-c.1957.0053

出版商:IEE    

年代:1957

数据来源: IET

摘要:

A single earthed dielectric slab cannot propagate both polarizations of surface waves with equal velocities, so a more complex structure such as a double-layer slab is needed. The nature of surface waves on 2-layer earthed-slab structures is studied quantitatively, and conditions are derived that allow for equal velocities of both polarizations; a situation that will allow a wave of arbitrary or circular polarization to propagate. The upper slab must have a greater dielectric constant, and the square of the inverse velocity ratio (of the surface wave compared with free space) is constrained to lie in a range only slightly greater than that between the two dielectric constants. Extensive numerical data for the design of these arbitrary polarization structures are included.

DOI:10.1049/pi-c.1957.0054

出版商:IEE    

年代:1957

数据来源: IET

摘要:

The paper gives an extension of results on the launching efficiency of surface waves obtained in a previous paper.In particular, a study is made of the effect on the launching efficiency curves of varying the ratiok1/k, which is a measure of the surface reactance of the guiding surface.

DOI:10.1049/pi-c.1957.0055

出版商:IEE    

年代:1957

数据来源: IET

摘要:

Increased intermodulation distortion in frequency-modulation frequency-division multiplex trunk radio systems will be generated under fading conditions when the fade is due to the presence of one or more echoes. The distortion level is not simply related to the fading depth, but depends in a rather complicated way on the parameters of the echoes responsible for the fade. As a guide for future experimental work, theoretical investigation has been made of the nature of this dependence, both for single-echo and for multi-echo fading. In the latter case, a simple formula has been developed for the worst intermodulation distortion due to a system of echoes of given amplitudes and delay times. Numerical results are given for a particular 22.5 dB fade whose echo structure was derived experimentally.2It is concluded that nothing can be deduced from measurements of fading depth alone about the magnitude of intermodulation distortion associated with fades generated by cancelling echoes. Measurements are required either of the parameters of the echoes or, directly, of the distortion.

DOI:10.1049/pi-c.1957.0056

出版商:IEE    

年代:1957

数据来源: IET

摘要:

Designed initially for use with a method for television band compression by variable-velocity scanning, the performance limitations of a magnetic scanner with negative feedback from a novel source are presented: also, some of the many applications of such a scanner are briefly reviewed.The justification of the presentation relies mainly on the mathematical analysis: however, measurements of current waveforms confirm that the influence of non-linearities and other factors which have been explicitly ignored in the derivation of this analysis is negligible in practice.Consideration is given to the practical application of the results, and it is shown that satisfactory operation can easily be obtained for repetitive scanning rates up to 104per second with a maximum displacement error (during a change of velocity) of no more than 0.2%.

DOI:10.1049/pi-c.1957.0057

出版商:IEE    

年代:1957

数据来源: IET