摘要:

The a.m. noise spectrum in reflex klystrons is treated experimentally and theoretically. The frequency range of the measurements is 1–100 kc/s from the signal frequencies, which are 4.7 and 9.3 Gc/s. It is shown that the measurement equipment cannot consist of a crystal detector immediately followed by a low-frequency amplifier because the crystal noise up to about 20 kc/s is greater than the klystron noise. To reduce the effect of crystal noise the klystron is frequency modulated and the measurement equipment consists of a crystal diode as first detector, an i.f. amplifier, a vacuum diode as second detector and a selective l.f. amplifier. The measurements show that the noise density is, with great accuracy, constant in the actual range. This agrees with the theory, which is based on a treatment by Knipp. The deviation from Knipp's noise formula is due to the introduction of an inherent synchronizing effect in the noise current. The theory indicates that the noise is approximately constant up to a displacement of 10−4to 10−3from the signal frequency.

DOI:10.1049/pi-b-2.1959.0328

出版商:IEE    

年代:1959

数据来源: IET

摘要:

The paper reviews present-day practice in the design and operation of high-grade microphones used for broadcasting, sound reinforcement, sound recording, acoustical measurements, etc.General requirements, basic operating principles and design details are given for typical microphones of various types. They are classified acoustically into omnidirectional and directional categories for the purposes of discussion and analysis.

DOI:10.1049/pi-b-2.1959.0329

出版商:IEE    

年代:1959

数据来源: IET

摘要:

The paper describes an instrument for direct analogue computation of electron trajectories, a resistance network providing the necessary field data. Constructional details are given, and results for two typical electrostatic lenses are shown and compared with results obtained experimentally. Methods for improving accuracy and speed of operation are outlined.

DOI:10.1049/pi-b-2.1959.0332

出版商:IEE    

年代:1959

数据来源: IET

摘要:

To increase the number of channels available for television broadcasting, it is now becoming increasingly necessary in several countries to utilize the ultra-high-frequency bands (Band IV, 470–585 Mc/s, and Band V, 610–960 Mc/s). The paper considers some of the factors concerning the relatively restricted coverage on ultra-high frequencies and the power requirements of transmitters to offset this disadvantage. This leads to a discussion on the choice of valve types for use in u.h.f. television transmitters. The choice of a high-gain klystron output amplifier for a 10 kW transmitter enables a relatively low-power modulated amplifier to be used in the penultimate stage. The paper describes the fully engineered transmitter installed experimentally at the B.B.C. television transmitting station at Crystal Palace for propagation and television reception tests in the u.h.f. band covering both the 405-line and 625-line television systems.

DOI:10.1049/pi-b-2.1959.0335

出版商:IEE    

年代:1959

数据来源: IET

摘要:

The paper examines the factors involved in the reception of 405-line television signals in the four frequency bands assigned by international agreement to television broadcasting in Europe. After consideration of the receiving-installation characteristics appropriate to the various bands, and the statistical variation of field strength with aerial location over the range of frequencies involved, a basis for the specification of the median field strength defining the nominal limit of the service area of a television station is described.The estimates made, particularly for Bands IV and V, must of necessity be provisional: it may be necessary to modify them when first-hand experience of operation in these Bands becomes available. Despite this limitation, however, it is considered that the figures given provide a useful interim guide for planning purposes.

DOI:10.1049/pi-b-2.1959.0336

出版商:IEE    

年代:1959

数据来源: IET

摘要:

The paper opens with a review of the theoretical studies of coastal deviation which have been made in recent years. It shows that there is close agreement between the various formulae derived for the deviation and that the graphical method used in an earlier paper by two of the present authors produces results which are substantially in agreement with those obtained from the formulae.In an endeavour to obtain experimental confirmation of the theoretical magnitude of the deviation and its variation with distance from the boundary with angle of incidence of the wave front at the boundary, etc., existing data from various sources have been examined. Two new series of measurement on low- and medium-frequency waves have also been made. In both cases the transmitters were located at sea and the directional measurements taken at numerous sites on land. The general conclusion obtained from this experimental investigation was that a deviation due solely to the change in ground conductivity at the boundary and of the magnitude given by theory is small compared with the larger random directional errors which are attributed to ground irregularities, surface obstructions and other causes. The only systematic deviations observed had amplitudes of up to 7° and occurred within a few hundred metres (less than a half-wavelength) of the coast on the seaward side; at such near distances the theoretical formulae are not valid. It is concluded that for many coastal direction-finding stations coastal deviation as such is unimportant.

DOI:10.1049/pi-b-2.1959.0339

出版商:IEE    

年代:1959

数据来源: IET

摘要:

The paper presents briefly the principles underlying the current development of a high-frequency directional aerial system which can be steered in both azimuth and elevation. The system comprises a number of omnidirectional unit aerials whose outputs (in the case of reception) may be brought approximately into phase with each other for any desired combination of frequency and direction by means of direction-control equipment which is basically a high-speed computer. The aerial system provides a number of independent outlets, each of which may be individually steered by the direction-control equipment. An experimental system based on these principles and designed for the reception of high-frequency signals from transmitters at long distances will be described in later papers.The present paper mentions briefly some of the potential advantages of this type of aerial system, e.g. flexibility of design and operation, and notes that the basic principles are applicable to both transmission and reception.

DOI:10.1049/pi-b-2.1959.0340

出版商:IEE    

年代:1959

数据来源: IET

摘要:

Using a published formulation of the equations for the reflection of an electromagnetic wave from a transversely magnetized ferrite block in a rectangular waveguide, a solution in closed form for the integral equation involved is given. A detailed discussion of this solution in a certain range of the gyromagnetic parameter follows. Outside this range the published solutions are shown to be faulty, and the present solution is also unusable, for unknown reasons. A second-order solution is also given, and reasons are advanced for believing that quasi-static approximations are not the cause of the difficulties encountered.

DOI:10.1049/pi-b-2.1959.0341

出版商:IEE    

年代:1959

数据来源: IET