摘要:

The principles underlying the majority of telemetering systems at present in use, or known to be under development, are considered together with the characteristics of various types of modulation and methods of multiplexing. Various telemetering systems are outlined, together with typical pick-ups. The development of a 6-channel frequency-multiplex f.m./a.m. system, and its application to various problems, is discussed in some detail.

DOI:10.1049/pi-3.1953.0011

出版商:IEE    

年代:1953

数据来源: IET

摘要:

A brief historical review is given of the investigations on the absorption of radio waves made in the United Kingdom since 1935 together with a detailed discussion of the factors which must be considered when making accurate measurements of this phenomenon. An outline of the theory of ionospheric absorption and its application to practical absorption measurements is included. The effects of double refraction, polarization, spatial attenuation, dispersion, ionospheric inhomogeneities and partial reflection, which modify the apparent attenuation of radio waves reflected in the ionosphere, are discussed. The methods used to minimize errors due to these factors are presented in detail. The experimental techniques used in the routine absorption measurements are described fully. The detailed results of the measurements of the absorption of radio waves in the ionosphere, conducted in South-East England during the years 1935 to 1948, are being published separately.

DOI:10.1049/pi-3.1953.0015

出版商:IEE    

年代:1953

数据来源: IET

摘要:

The paper describes the measurement of the change of phase with distance of a 127.5-kc/s wave over a particular inhomogeneous land path and the deduction of the mean velocity.The measuring system made use of transmissions from stations of the English chain of the Decca Navigator System, and the path studied was that between the Lewes (Sussex) and Warwick stations (177 km). With the aid of a mobile phase-measuring equipment the difference between the phase of the signal from one transmitter and that of the signal from the other transmitter was measured with an accuracy of 0.25° at 25 points along the path. From these results and a knowledge of the exact position of the points it was possible to plot a curve showing the deviation of the measured phase from that calculated on the assumption of a velocity equal to that in free space.The mean velocity deduced for the path was 299 230 ± 12 km/sec.An examination was made of the measured change of phase along the path in relation to the profile and geological structure. Although there was no definite evidence of the phase of the wave being affected by the ground contours, the influence of the nature of the soil was very marked. A detailed study of the geological structure was undertaken and the electrical characteristics of each section of the path were assessed. A high velocity over ground of good conductivity and a low velocity over ground of poor conductivity was clearly shown.Comparisons between the measurements and the phase changes derived by a method based on theoretical curves of phase lag over homogeneous ground showed good correlation. They also confirmed the theoretical predictions of a characteristic phase disturbance at the boundary between sections of differing conductivity. It is concluded that this method of phase determination over an inhomogeneous path is one which offers a good approximation to the phase changes actually taking place.

DOI:10.1049/pi-3.1953.0016

出版商:IEE    

年代:1953

数据来源: IET

摘要:

Measurements of the attenuation produced by air-filled drawn waveguide tubing have been made at a frequency of 9375 Mc/s. The theoretical and experimental performances of various waveguide surfaces are compared and discussed. Detailed studies of the roughness of the internal surfaces of certain standard commercial waveguides have been made, to determine the orders of magnitude of the irregularities and to try to set up a correlation between measured and calculated attenuation values. It is concluded that the discrepancies between these values are due solely to surface roughness, and it is doubtful whether further improvements in surface finish over that of present precision-drawn tubes are required for any applications at frequencies near or below 24 000 Mc/s.The effects of small changes in waveguide dimensions on attenuation, together with the problems involved in measuring both the attenuation and d.c. resistivity of a waveguide sample, are considered.

DOI:10.1049/pi-3.1953.0017

出版商:IEE    

年代:1953

数据来源: IET

摘要:

The fluctuation current flowing in a diode is given, in the temperature-limited case, by the well-known formulaI̅f2=2eIΔf. The relation between this and the thermodynamical formulaV̅2=4kTRΔfis considered and an explanation is given of why the thermodynamical approach is of no assistance in the practical space-charge-limited case.

DOI:10.1049/pi-3.1953.0018

出版商:IEE    

年代:1953

数据来源: IET

摘要:

The slotted transmission line has long been used as a standard device for determining impedance. Over the v.h.f. range, however, the constructional difficulties due to the physical length required for the slotted line make it primarily a laboratory instrument. The need for an alternative device of comparable or improved accuracy, capable of giving much more rapid measurements, and sufficiently robust to be used on field tests of aerial arrays, has led to a modified approach.A test section of low-loss coaxial line, which may be as short as one-third of the equivalent slotted line, is fitted with fixed probes to measure the relative voltage amplitudes at three known points. From these ratios the unknown impedance can be found, either analytically or graphically, each ratio defining a circular locus on the Smith chart. The frequency range covered by a line of this type is approximately 3:1; near mid-frequency the present equipment can measure standing-wave ratios up to 5:1, corresponding to resistive loads ranging from 15 to 375 ohms for a line of 75 ohms.An important advantage of the new equipment is that the adjustment of a load to a prescribed value is shown by the simultaneous zero reading of two meters.

DOI:10.1049/pi-3.1953.0019

出版商:IEE    

年代:1953

数据来源: IET

摘要:

The paper deals with the ionospheric propagation of waves of frequencies less than 3 Mc/s and is confined mainly to transmission over medium and long distances (greater than 500 km).The results of investigations on low and very-low frequencies (less than 300 kc/s) are summarized under the headings of field strength, phase and polarization measurement, the effects of ionospheric disturbances, the study of local ionospheric characteristics and theoretical studies. Since our knowledge of medium-frequency propagation was adequately summarized in a report64in 1937, only work done since that date has been considered here. An important item of the recent work is the study of ionospheric cross-modulation.The paper concludes with a summary of our present knowledge of the subject and recommendations for further studies.

DOI:10.1049/pi-3.1953.0020

出版商:IEE    

年代:1953

数据来源: IET

DOI:10.1049/pi-3.1953.0021

出版商:IEE    

年代:1953

数据来源: IET

DOI:10.1049/pi-3.1953.0024

出版商:IEE    

年代:1953

数据来源: IET

DOI:10.1049/pi-3.1953.0025

出版商:IEE    

年代:1953

数据来源: IET