摘要:

Certain aspects of the failure of constant-luminance operation in bandshared colour-television receivers are reviewed in the light of recent developments in reproducing phosphors and the use of normalising chromaticities other than those specified for the system. Recommendations are made in order that better adherence to constant-luminance operation of colour-television receivers may be obtained under likely conditions of broadcast reception.

DOI:10.1049/piee.1964.0190

出版商:IEE    

年代:1964

数据来源: IET

摘要:

Simple expressions, suitable for design purposes, are deduced for the major aberrations due to the magnetic deflection of the convergent electron beam in a cathode-ray tube. These expressions are confirmed by measurements on a number of saddle and toroidal scanning coils. Conditions are derived for an anastigmatic display.

DOI:10.1049/piee.1964.0191

出版商:IEE    

年代:1964

数据来源: IET

摘要:

The study of third-order astigmatism and curvature of field associated with deflecting coils, described in a companion paper, has been extended to cover more general conditions, including multiple beams and the problem of reconvergence. The analysis has been applied in particular to the performance of the RCA colour yoke and the shadowmask tube and has resulted in a simple yet efficient method of reconvergence which is superior to existing methods in that a single control achieves comparable results, the time taken being drastically reduced.

DOI:10.1049/piee.1964.0192

出版商:IEE    

年代:1964

数据来源: IET

摘要:

The responses of the optical-and optical/electrical-transducer sections of a television camera are theoretically analysed for the case of step-function inputs of variable width. From this analysis it is shown that it is possible to characterise the performance of a television camera by means of an optical ‘pulse-and-bar’ pattern as input to the system, and measuring the pulse/bar height ratio at the system output. A vidicon-camera chain is discussed as a convenient example throughout the analysis, and the results of tests using the above test pattern with such a chain are recorded.

DOI:10.1049/piee.1964.0193

出版商:IEE    

年代:1964

数据来源: IET

摘要:

The receiver is an all-transistor triple superheterodyne with remote selection of 560 channels with spacing of 50kc/s between 108 and 136Mc/s. A novel signal/noise-operated squelch or muting system is incorporated.The introduction of v.h.f. transistors for the first time in an airborne application raised several aspects of circuit design for reliable operation of equipment in the extreme conditions encountered in aircraft.The problem of spurious responses in multiple superheterodynes is discussed with particular reference to the operation and limitations of the semiconductor mixer. Difficulties encountered with operation on simultaneous offset frequency transmissions of the ‘climax’ type are examined. The compromise necessary between mechanical layout for maximum electrical efficiency and ease of maintenance is considered.

DOI:10.1049/piee.1964.0194

出版商:IEE    

年代:1964

数据来源: IET

摘要:

The requirements for frequency and amplitude stabilisation of the transmitter of a c.w. radar are derived, and loop gain and sensitivity values calculated. It is shown that the desired sensitivity characteristics are provided by a microwave discriminator described previously. The principal criteria in the design of a circuit are considered, and the results achieved with this circuit presented. It is shown that, although adequate performance can be achieved in practice, it is inferior to that which would be predicted.

DOI:10.1049/piee.1964.0195

出版商:IEE    

年代:1964

数据来源: IET

摘要:

The ratio known as noise factor, originally used as a measure of performance at microwave frequencies, seems likely to be useful also at higher frequencies; namely in the infrared and optical regions. It seems to be a convenient measure for most terrestrial applications at all frequencies, and for both terrestrial and space applications at the higher frequencies.While, perhaps, most useful for summarising the measured performance of a practical device, examples are given of estimated bounds. Thus, the minimum noise factor of a molecular amplifier rises from unity at low frequencies to 2 at high frequencies; and the minimum noise factor of a photocathode heterodyne mixer may be unity if an unattenuated fluctuation-free local oscillator is used, but it rises to 2 if the local oscillator is attenuated.

DOI:10.1049/piee.1964.0196

出版商:IEE    

年代:1964

数据来源: IET

摘要:

The problem of obtaining a one-sided spectrum by means of a combination of amplitude and phase modulation of a carrier is examined with particular reference to the question of compatibility with the a.m. method of transmission and reception.The spectrum of composite modulation, when the phase modulation is introduced either directly or indirectly, has been analysed for both single-tone and two-tone signals. The analysis indicates that, while it is possible to eliminate one of the two sideband components of a composite modulated wave, new components on the desired side of the carrier appear which have the character of the spectrum caused by single-sideband modulation of a carrier by the squared signal and the squared envelope.Some practical arrangements which enable maintenance of the required relationship between the amplitude- and phase-modulating signals for compatible-single-sideband operation have been described. The experimental results obtained for the different systems indicate that, for modulation by speech-like signals, the undesired radiation under normal conditions of modulation can be kept below 1% of the carrier, and the spectrum of the output is confined, as in single sideband, to the band of modulating frequencies.

DOI:10.1049/piee.1964.0197

出版商:IEE    

年代:1964

数据来源: IET

摘要:

A method is presented for calculating the lowest cutoff wavenumber of a new microwave transmission line, the ‘T septate lunar line’. The T septate lunar line is a modified lunar line formed by two eccentric circular metal tubes; part of the inner metal tube is cut out, and a metal bar is passed through the cutout section to connect the opposing inner surfaces of the two tubes.The wave equation for the boundary-value problem associated with this complex waveguide form can be found by a perturbation method, using a cylindrical co-ordinate system. The cross-section of the T septate lunar line is approximated by introducing a series of steps in the outer guide wall and dividing the cross-section intomfan-shaped regions. The problem is thus reduced to one of a multiple-step waveguide. The solution of themstepped waveguide results in a system of 2mequations containing 2munknowns involving the cutoff wavenumber βcthe order of Bessel functionpithe angular parameter αiand the coefficient ratio parameter η1for the first composite region intersected by the inner metal tube. A successive approximation method is applied to obtain the cutoff wavelength. The calculated value is in close agreement with the experimental value.In the 200–2000Mc/s frequency band, the very compact and light T septate lunar line should find its greatest application in aircraft and space systems.

DOI:10.1049/piee.1964.0198

出版商:IEE    

年代:1964

数据来源: IET

摘要:

Single helical aerials with gains of over 25dB have been constructed, and the measured variation of this gain with axial length is presented. The beamwidth corresponding to this 25dB gain is approximately 5° between half-power points. From separate experiments comparing short helixes of circular, square and triangular section, the latter appears to offer a satisfactory alternative to the conventional forms of construction.

DOI:10.1049/piee.1964.0199

出版商:IEE    

年代:1964

数据来源: IET