摘要:

For the first time, a radio telescope has been constructed with sufficient directivity for the production of detailed ‘radio pictures’ of the brightness distribution on the solar disc at decimetre wavelengths.The aerial system, which operates at 21 cm wavelength, consists of two long mutually-perpendicular arrays, each made up of 32 paraboloid antennae, 19 ft in diameter, spaced uniformly along a 1 200 ft base-line. The polar diagram of each array is a set of fan-shaped beams, with high resolution in one direction only. A pencil-beam response (with multiple beams) is produced by combining the signals from the two arrays by a phase-switching method. With the dimensions used, these pencil beams are 3' of arc in diameter and about 1° apart. West-east scanning is provided by the earth's rotation, and the north-south position of the beams can be adjusted by a phase-shifting mechanism. A series of parallel profiles across the sun is obtained; these profiles may be combined to give a ‘picture’ of the solar disc.For satisfactory performance, side lobes in the arrays must be kept at a very low level. To achieve this, the current distribution is tapered from the centre to the ends of each array, and very close tolerances are maintained on the phase relationships between the elements. Phase errors due to thermal expansion of the long twin-wire feeder system are avoided by arranging the lines so that all the elements are connected to the receiver through equal lengths of feeder.The design and construction of the instrument are described in detail. The paper concludes with an account of the techniques used in testing and adjusting the arrays.

DOI:10.1049/pi-b-2.1961.0012

出版商:IEE    

年代:1961

数据来源: IET

摘要:

The general outline of the International Civil Aviation Organization specification for an instrument approach system was largely based on equipment developed during the last war. Only minor modifications have been incorporated in the specification since then. The paper states the problem of providing a radio guidance system similar to that in use but with an improved accuracy. It is suggested that the accuracy must be improved by a factor of 3 if the system is to be used for landing and not merely approach.Some parameters required of an instrument landing system localizer are established and a line of attack on the aerial problem is described.

DOI:10.1049/pi-b-2.1961.0013

出版商:IEE    

年代:1961

数据来源: IET

摘要:

The paper is concerned with the provision of satisfactory signals to viewers in the immediate vicinity of the Crystal Palace television station, where an 8-tier aerial is sited in an urban area. The problem was complicated by differences between the halves of the aerial, but a satisfactory performance was ultimately obtained. The only serious discrepancy between theoretical and experimental results could be removed by taking account of reflection at the ground, ignoring the effect of buildings.In order to provide continuity of service in spite of any single breakdown, the halves of the aerial were originally supplied from separate transmitters; this arrangement had to be abandoned, since it proved impossible to provide undistorted signals at receiving points where the contributions from the transmitters were in phase opposition.

DOI:10.1049/pi-b-2.1961.0014

出版商:IEE    

年代:1961

数据来源: IET

摘要:

An investigation is described of the effect of extraneous radio-frequency interference in frequency-modulation multi-channel radio-telephony transmission systems. The noise power ratio in the output telephony baseband due to an r.f. interfering signal is derived theoretically, and comparison is made with measured values. When the practical limitations in the method of measurement are taken into account, it is concluded that the theoretical results are valid.Results of general application in the design of radio systems are derived from the theory, and the analogy, under certain circumstances, with interference due to long-delay echo-signals is discussed.

DOI:10.1049/pi-b-2.1961.0015

出版商:IEE    

年代:1961

数据来源: IET

摘要:

Miniature hollow cathodes, internally coated with conventional oxides, have been studied. As visual inspection revealed, oxide deposits at the narrow orifice edge constricted the flow of electrons, and the initial emission from this edge was then spontaneously destroyed by saturation-caused deactivation, owing to positive-ion action. Large hexagonal crystal growth on the outer nickel body was also observed. While the external field causes the electrons to emerge from the cavity as a laminar flow, the conditions in the cavity change abruptly to a gas discharge with large field, and at this point ion bombardment damages the coating. The emission characteristics suggest a strong temperature dependence of the electron flow to an external collector. Although a current density of 10 amp/cm2at 965°C was obtained where the proximity of the anode worked against early ionization breakdown, a load of 7 amp/cm2at 920° C was maintained in other cases for 800 hours. Modified orifice arrangements showed that optimum emission is obtained with a sharp orifice edge and solid cavity walls, although no difference in emission was detected between a fully and a partly coated cavity. Grid-controlled operation revealed a decrease in transconductance, owing to field shielding and to the receding virtual cathode, while the focusing quality suffered mainly by the added orifice lens.In Section 3 an interpretation of the mechanisms of current flow to an internal and an external anode is attempted. Since the emission characteristics do not reveal the presence of the underlying emission laws in an explicit form, emission is related to an equivalent diode with dynamic perveance. Hollowness in the beam cross-section at higher currents is interpreted as the result of bunching near the orifice edge, localized current saturation, and of a weaker field along the axis.

DOI:10.1049/pi-b-2.1961.0016

出版商:IEE    

年代:1961

数据来源: IET

摘要:

Carbonyl-nickel powder pressed and sintered with alkaline-earth triple carbonates serves as an experimental emitter. The general behaviour of this dispenser-type cathode under the severe field and ion-focusing conditions below closely spaced and apertured electrodes is investigated.Locally confined ionization processes in the alkaline vapour components will develop. The ion-focusing ability of the aperture, particularly if the surface-protecting space charge is removed, enhances evaporation. A spontaneous rise in cathode temperature accompanies this effect, leading to more vapour generation.Deep pit formations will invalidate the advantage believed to exist in a well-determinable surface profile. Negative grid control produces similar ionization effects because of the large centre field below the aperture.The self-sustaining discharge, starting just beyond the saturation bend, will last as long as sufficient alkaline metal is available on the surface. Three discharge peaks were measured with gradually increased anode voltage, indicating the replenishing ability from within the matrix. A faster recovery from the discharge state at higher temperatures is explained by a higher deionization rate, owing to a more intense vaporization of nickel.Under the severe aperturing conditions the cathode is inferior to oxide-coated cathodes and also to dispenser-type cathodes with built-in chemical reaction and vapour controls.

DOI:10.1049/pi-b-2.1961.0017

出版商:IEE    

年代:1961

数据来源: IET

摘要:

A porous layer of magnesium oxide may be used as a cold source of electrons in a vacuum tube, the emission depending upon the maintenance of a positive electric field through the oxide layer. Methods of making and processing cathodes of this type are described, and it is shown that stable emission is obtained only from cathodes in a fully oxidized state. The behaviour of these cathodes under various experimental conditions has been examined with particular reference to voltage and temperature effects.

DOI:10.1049/pi-b-2.1961.0018

出版商:IEE    

年代:1961

数据来源: IET

摘要:

The scope of microwave spectroscopy and its relationship to other branches of spectroscopy are briefly indicated, attention being especially directed to those aspects which are important in the design of spectrometers. The factors determining spectrometer sensitivity are discussed. The basis of molecular modulation is presented with special reference to Stark modulation. A survey is made of the various types of spectrometer and their relative merits are discussed. The application of the method to chemical analysis is considered and indications are given of the directions in which further experimental work is required.

DOI:10.1049/pi-b-2.1961.0019

出版商:IEE    

年代:1961

数据来源: IET

摘要:

If two similar coaxial transmission lines are coupled by sharing a common outer conductor for part of their length, so as to form a 3-conductor line, they constitute a symmetrical directional coupler.In work on coaxial directional couplers at microwave frequencies up to 7 Gc/s, new designs of coupled transmission lines have been developed for use as power monitors and variable attenuators.

DOI:10.1049/pi-b-2.1961.0020

出版商:IEE    

年代:1961

数据来源: IET

摘要:

The paper describes the design and performance of a low-noise electron-beam parametric amplifier of the quadrupole type. This is a transverse-field device in that the electron beam interacts with a radio-frequency field transverse to its direction of motion.Particular attention is directed to the conditions necessary to achieve the lowest overall noise figure of the amplifier. It is shown that these also lead to the broadest amplification bandwidth.The minimum noise figure so far obtained is 1.6 dB at about 200 Mc/s, which corresponds to an amplifier noise temperature of 130° K. This was obtained at an overall gain of 10 dB which required about 2 mW of pump power. The amplification bandwidth was 25 Mc/s. These performance figures compare well with those reported for the original quadrupole amplifier at higher frequencies.

DOI:10.1049/pi-b-2.1961.0021

出版商:IEE    

年代:1961

数据来源: IET