摘要:

The design and construction of a system suitable for measuring a.m. and f.m. noise spectra from low-power, low-noise oscillators and nonlinear amplifiers is described. A radiometer technique is used to provide enhanced sensitivity, and the design factors and sources of error are considered in some detail. The system has a sensitivity equivalent to a noise temperature of 10°K in a bandwidth of 150kHz over much of its range, and is capable of measuring noise powers with a relative accuracy of 6–10% and an absolute accuracy of 15% over a sideband range of ±1 to 140MHz. The a.m.-plus-background and f.m.-plus-background components can be separated with an accuracy of some 5–10%.

DOI:10.1049/piee.1968.0113

出版商:IEE    

年代:1968

数据来源: IET

摘要:

The scattered field when a plane wave is incident on a slotted perfectly conducting sphere is obtained by superposition of the scattered field from an unslotted sphere and the radiation field from the slot on the sphere. The slot is a finite, thin circumferential slot backed by a cavity which is characterised by an admittance. The induced voltage is represented by a sinusoidal distribution. The amplitude of the induced voltage is then related, in the combined problem, to the incident field by expressing it in terms of the radiating and load admittance of the slot. Expressions for the radiation admittance and the scattered fields are derived. Positions of slots with respect to the orientation of the incident plane wave which give rise to maximum or minimum scattering are discussed. Various special cases, such as the half-circumferential slot and the full-circumferential slot, are also derived.

DOI:10.1049/piee.1968.0114

出版商:IEE    

年代:1968

数据来源: IET

摘要:

Surface fields are calculated for a source-excited flat-strip antenna in free space by modifying a variationalimpedance formulation. The exciting fields are related by an integral to the antenna current, and approximate current distributions correspond to nonvanishing tangential-electric-field components on the metallic antenna surface. Current distributions consisting of sine and shifted cosine waves violate the edge conditions and excite strong tangential electric fields near the ends of the conducting antenna surface. These field singularities are avoided by making the antenna current decay in proportion to the square root of the distance from the antenna edge. The more accurate current distributions produce smaller surface fields on the antenna, and it is possible to distinguish the more accurate current distribution even in cases where the variationally determined antenna impedances differ insignificantly. The calculated current distributions and impedances are compared with experimental data and with results of iterative calculations.

DOI:10.1049/piee.1968.0115

出版商:IEE    

年代:1968

数据来源: IET

摘要:

The present trend in satellite communication systems is towards large geostationary satellites which are accurately maintained on station. A fixed, offset, spherical reflector with a mechanically steered line feed is proposed as an economic design for a ground-station aerial. The distribution of electric field along the axis of the reflector is calculated for the case of an incident circularly polarised wave, and it is shown that the optimum distribution for a transmitting feed follows closely the axial field in the receiving case. Because of the asymmetry of the system, an entirely numerical technique has been developed, using a digital computer to calculate the axial field. A similar technique is used to compute the performance of an aerial using an offset spherical reflector and a line feed of crossed current elements. The aerial is shown to have a high theoretical efficiency (81%), with low spillover and a good sidelobe structure. The limitation of bandwidth with this type of feed is discussed, and proposals are made for an improved, design of line feed.

DOI:10.1049/piee.1968.0116

出版商:IEE    

年代:1968

数据来源: IET

摘要:

An account of experiments demonstrating Moon relay communication at 800bit/s is given. Formulas and graphs are presented which enable the error probabilities for 2-level or more f.s.k. (frequency-shift keying) combined with frequency diversity to be calculated. Comparison is made between the calculated and experimental results. These are in good agreement.

DOI:10.1049/piee.1968.0117

出版商:IEE    

年代:1968

数据来源: IET

摘要:

The propagation behaviour is described of a number of periodically loaded circular waveguide structures containing either dielectric or axially magnetised ferrimagnetic material. The structures include the disc-loaded axial rod and tube. Dispersion characteristics are theoretically determined and the dependence of the lower and upper cutoff frequencies upon various structural and material parameters is studied. For the ferrite structure, two passbands are observed for each mode, one occurring below ferrimagnetic resonance, the other occurring above resonance. The centre frequency of the passband can be varied by changing the strength of the axial applied magnetic field. Experimental dispersion characteristics are shown for both dielectric and ferrite structures, and these are found to agree well with those predicted theoretically.

DOI:10.1049/piee.1968.0118

出版商:IEE    

年代:1968

数据来源: IET

摘要:

Probabilistic transitional processes in the three basic types of regenerative switching circuit are considered by the use of finite Markov chain theory. For the bistable and monostable configurations, the transition probabilities are related to the probabilistic nature of the input signal. The distribution function for resolving times is investigated and is used to derive an expression for the expected switching frequency. Race phenomena are considered, and an equation is derived relating the probability of input-pulse coincidence to the set and reset input-pulse lengths. Finally, an expression for the reliability of a regenerative switching circuit in the transitional state is formulated which takes into account the probability of both gradual and instantaneous failures.

DOI:10.1049/piee.1968.0119

出版商:IEE    

年代:1968

数据来源: IET

摘要:

The constant challenge in power technology is to increase output and, at the same time, to reduce both the capital cost and the running cost of the plant installed, thus keeping the cost of energy to the consumer as low as possible. An unremitting effort has been necessary to provide transport facilities for the larger units which have been developed, and, indeed, throughout the whole period of the development, progress has very much depended on the increase in the size and weight of the units that could be moved from works to sites. By the early 1960s the load-carrying capacity was stretched to the limit, and new methods of carrying had to be devised if further development of plant was not to be restricted. The paper describes the novel methods of sea and land transport which have been developed to enable larger, single units of plant to be delivered to power-station and substation sites than has heretofore been possible in Britain or, with very few exceptions, in any other country in the world. The new facilities will enable major savings to be made in construction and operating costs of new power installations and will enable manufacturers to improve their competitive position in the export market by being able to build the largest units more economically than heretofore. The characteristics of the two special ships now in operation are outlined, the philosophy of design and alternative solutions are examined, and the reasons are given for evolving the type selected. The development of the air-cushion equipment now in use for attachment to road transporters to reduce the stress on highways and bridges is described, and its advantages are set out. The development of a prototype vehicle for off-the-road use over ground such as pasture and plough land to aid access and minimise damage during construction of electricity-transmission works is also set out. The paper concludes with a description of the development of a prototype multiple-wheel assisted-lift road transporter for heavy plant as a possible alternative to the air-cushion equipment under certain conditions.

DOI:10.1049/piee.1968.0121

出版商:IEE    

年代:1968

数据来源: IET

摘要:

An analysis is developed for induction motors having any number of asymmetrical primary windings and any symmetrical or asymmetrical power supply, with any symmetrical or asymmetrical impedances connected to the motor terminals, provided that symmetrical polyphase secondary windings are utilised. The basis of the analysis is the transformation of the asymmetrical primary windings to their equivalent tapped-quadrature windings, which has the advantage of facilitating the application of 2-phase rotating-field theory to the asymmetrical machine. All the parameters involved in the generalised analysis can be calculated from the design details of the motor, and its validity is demonstrated by the performance prediction of the shaded-pole type of single-phase motor.

DOI:10.1049/piee.1968.0122

出版商:IEE    

年代:1968

数据来源: IET

摘要:

It is shown that a single reluctance-machine rotor can be made to operate in magnetic fields with differing numbers of poles. A general theory of performance for machines withppairs of segments andMpmagnetic pole pairs is developed. This theory is fully supported by the results of measured performances (a) for a range of rotors at one pole number and (b) for a single rotor operated in stator fields havingM= 1, 2, 3 and 4. Performance figures are predicted for machines with pole numbers in the ratio 2:4:6:8, and it is shown that, at each pole number, rotor proportions can be chosen so as to give power outputs equal to those that would be achieved with normal single-speed reluctance machines. The associated power factors and efficiencies are also good. Further, for the great majority of all the possible speedcombinations, substantially the same levels of performance can be maintained. It is concluded that individual studies of designs for particular speed combinations and load duties are justified and would result in industrially acceptable multispeed reluctance machines.

DOI:10.1049/piee.1968.0123

出版商:IEE    

年代:1968

数据来源: IET