摘要:

Two degenerate parametric amplifiers for the frequency of 3100 Mc/s are described. The first is a single-resonator type with a bandwidth of 140 Mc/s, a gain of 19 dB and an excess noise temperature of 84°K. The second uses an additional resonant circuit to increase the bandwidth to over 300 Mc/s, but the excess noise temperature is also increased to 180° K owing to additional losses. The gain and bandwidth of the amplifiers are near optimum.

DOI:10.1049/piee.1963.0185

出版商:IEE    

年代:1963

数据来源: IET

摘要:

A comparison of theory and experiment has been made for a negative-resistance three-frequency parametric amplifier incorporating a single varactor diode, operating in the h.f. band. The effect of diode series loss resistance has been simulated simply by connecting resistors in series with the diode. Good agreement between theory and experiment, in relation to gain, bandwidth and noise figure, has been obtained when the direct current flowing through the diode is negligible. Effects associated with a significant direct current have been investigated.

DOI:10.1049/piee.1963.0186

出版商:IEE    

年代:1963

数据来源: IET

摘要:

A review is given of the capacitance and elastance approaches to the solution of the equations of circuits incorporating varactor diodes. An attempt has been made to set down a framework within which the approximations made in any particular analysis can be assessed.

DOI:10.1049/piee.1963.0187

出版商:IEE    

年代:1963

数据来源: IET

摘要:

Consideration is given to the problem of correcting for the effects of the attenuation/ and phase/frequency distortion of a coaxial-cable pair on the transmission of video waveforms. A method of designing correcting networks is described which uses an adjustable waveform corrector to provide the component values for a fixed network whose design tolerances are arranged to give the minimum waveform distortion. Using this method, the design of waveform correctors for use with coaxial cable becomes a rapid and straightforward operation.

DOI:10.1049/piee.1963.0188

出版商:IEE    

年代:1963

数据来源: IET

摘要:

A description is given of a video transmission system capable of transmitting 625-line monochrome television signals with very low distortion on coaxial-pair cable over distances of up to 25 miles, possibly extensible to more than 50 miles. Because power for intermediate repeaters is not fed over the coaxial-pair cables, the use of the system may be restricted under some circumstances.Special techniques are used for the reduction of hum and low-frequency interference and for the waveform correction of the coaxial-pair cable. The system is designed on a waveform basis with the minimum reference to steady-state characteristics.

DOI:10.1049/piee.1963.0189

出版商:IEE    

年代:1963

数据来源: IET

摘要:

The Secam colour television system has many parameters in common with the N.T.S.C. system, but the constraints imposed on the reproduction of both large-area colour and colour transitions by the practical limitations on amplitude and frequency excursions are different. After discussing the parameters of the Secam system which have been assumed throughout the paper, the relationship between the chromaticity of the transmitted colour and the modulation of the subcarrier is considered and compared with the relationship which exists for the N.T.S.C. system. In particular, the effect of luminance level on the gamut of reproducible chromaticities is examined, and it is shown that the frequency limitations on the deviation of the Secam subcarrier are not important in so far as they might be expected to limit the practical colour gamut. The chrominance resolution of the system is discussed, and the use of an asymmetric passband for the colour subcarrier is suggested. The effects on the colour picture of some types of signal defect are mentioned.

DOI:10.1049/piee.1963.0190

出版商:IEE    

年代:1963

数据来源: IET

摘要:

The basic principles involved in reading the charge image which is stored on the insulating surface of the target in a camera tube are discussed. The relative importance of various sources of noise is investigated, choice of optimum frequency response depends on the detailed

DOI:10.1049/piee.1963.0191

出版商:IEE    

年代:1963

数据来源: IET

摘要:

The paper gives an account of an investigation, both theoretical and experimental, of angular-dependent EH11modes in a circular corrugated waveguide. The investigation was undertaken because oscillation in a mode of this type has been shown to be the cause of pulse-shortening or beam blow-up troubles occurring in electron linear accelerators under certain high-beam-current conditions.It is shown that the dispersion characteristics can represent either forward waves or backward waves dependent on the dimensional parameters, and under certain conditions there can be a changeover from one to the other within the pass-band. There are marked similarities between these results and those found theoretically by other workers, for hybrid modes in a circular waveguide containing a coaxial dielectric rod.The measurements also include the distribution of magnetic and electric fields in the axial region, using perturbation techniques. Series impedance values (relating fundamental electric field intensity to power flow) are derived, and are comparable with the theoretical results. They confirm that in a linear accelerator an EH11oscillation need only build up to a power level of the order of kilowatts to account for the disruptive effect on the beam observed during pulse shortening.

DOI:10.1049/piee.1963.0192

出版商:IEE    

年代:1963

数据来源: IET

摘要:

The application of wideband technique to h.f. transmitters is described. The particular band dealt with is 2–27.5 Mc/s, but the findings are not restricted to this band. The general principles of wideband power amplification are discussed, followed by a description of, and results obtained with, a 1 kW wideband amplifier which uses a modified distributed-amplifier technique. This not only permits better utilization of valves, but the amplifier is also less sensitive to varying output-load conditions. The amplifier may be used on a number of frequencies simultaneously. The use of wideband stages in conjunction with tunable stages in very-high-power transmitters is advantageous.The retuning of drives for a frequency change is avoided by the wideband mixer, which accepts an intelligence signal at 3.1 Mc/s and a frequency-determining signal, giving an output at the desired radiated frequency. Wideband transformers use ferrite cores, and introduce very small power loss. Transformers with a power rating of 40 kW are in use.The availability of wideband equipment simplifies the operation of transmitting stations. An arrangement particularly suitable for ground stations in air communication is described as an example of one of the many ways in which wideband equipment can be used.

DOI:10.1049/piee.1963.0193

出版商:IEE    

年代:1963

数据来源: IET

摘要:

The operating costs of a transmitting station can be substantially reduced if the equipment is automatically tuned and all services are directly controlled from a central point. This is due to the reduction of operating staff covering three shifts, and to the saving in ‘off the air’ time made possible by rapid change of frequency.The paper describes a range of transmitters with output powers up to 85kW which have completely automatic control of tuning, coupling and gain. The transmitters are of the linear-amplifier type, and hence are suitable for all forms of service used in h.f. communication, when associated with the appropriate signal source. In particular, the paper describes the automatic control system of the transmitter.Various aspects of performance are discussed, including the design requirements for low distortion and for the reduction of spurious and harmonic emissions.If the saving in operating costs is to be fully realized, a high standard of reliability is necessary. The types of components used are described. They include variable vacuum capacitors, variable inductors, silicon rectifiers and vapour-cooled valves.

DOI:10.1049/piee.1963.0194

出版商:IEE    

年代:1963

数据来源: IET