DOI:10.1049/pi-b-1.1958.0233

出版商:IEE    

年代:1958

数据来源: IET

DOI:10.1049/pi-b-1.1958.0234

出版商:IEE    

年代:1958

数据来源: IET

DOI:10.1049/pi-b-1.1958.0235

出版商:IEE    

年代:1958

数据来源: IET

DOI:10.1049/pi-b-1.1958.0236

出版商:IEE    

年代:1958

数据来源: IET

DOI:10.1049/pi-b-1.1958.0237

出版商:IEE    

年代:1958

数据来源: IET

DOI:10.1049/pi-b-1.1958.0238

出版商:IEE    

年代:1958

数据来源: IET

摘要:

Measurements of the absorption of waves travelling between Slough and Inverness (740 km), and reflected once from the E-region during the process, are compared with similar measurements made simultaneously for vertical incidence at Slough. The absorption over the oblique path, calculated by Martyn's absorption theorem from the value obtained at vertical incidence, was found to be much too low. Approximately correct values are obtained from the formula for non-deviative absorption, provided that the lowest-frequency (2 Mc/s) vertical-incidence results are used: otherwise the oblique-incidence value is too high. It is therefore considered tentatively that the absorption measurements which have been made for many years past at 2 Mc/s, using vertical-incidence reflections at Slough, might prove to be a useful guide to the absorption likely to be obtained over other oblique E-region paths during any part of the sunspot cycle, and they have been formulated accordingly. The anomalous variation of absorption which occurs during winter in high latitudes is also considered.The additional transmitter power required, as a consequence of fading, to enable a desired signal level at the receiver input to be exceeded for given percentages of the time is discussed, and a method of calculating losses due to polarization changes brought about by magneto-ionic splitting is indicated.

DOI:10.1049/pi-b-1.1958.0239

出版商:IEE    

年代:1958

数据来源: IET

摘要:

The rapid and slow components of a fading signal are separated by a semi-empirical process in which each component is, in turn, assumed to consist of a steady or specularly reflected component with a random component added. The process is applied to some measurements of the amplitude of first-order reflections from the E-region at vertical and oblique incidence on equivalent frequencies. The standard deviation of the amplitude variation due to rapid fading was found to be greater at vertical than at oblique incidence, but insufficient evidence is yet available to determine whether the variation due to slow fading was also greater.The accuracy of measurement of the smoothed value of field strength is defined as the range of values having a 99% chance of containing the correct value. On this basis, the accuracy of noon absorption, as calculated from a single day's observations at one frequency, has been estimated to be about +4, −12dB at vertical incidence and +4, −11 dB at oblique incidence. These limits are not symmetrically disposed about the mean value, as is conventional in normal statistics, partly because of the effect of the decibel scale, and partly owing to the characteristics of deep fading.

DOI:10.1049/pi-b-1.1958.0240

出版商:IEE    

年代:1958

数据来源: IET

摘要:

Magneto-ionic calculations show that deviative absorption is not necessarily negligible at vertical incidence for waves reflected from the E-region at frequencies considerably below the penetration value. Consequently, the value of absorption calculated by the conventional ‘non-deviative’ formula for a short-wave oblique path from vertical-incidence absorption measurements tends to be too high. Deviative absorption on paths sufficiently oblique is, however, negligible. The calculations also show the effect of the earth's magnetic field on Martyn's absorption theorem to be similar to the effect of losses due to partial reflections: namely to make the absorption in decibels calculated from an oblique path from vertical-incidence measurements too low by a multiplying factor approaching the cosine of the angle of incidence. It is suggested that the absorption to be expected on a radio path might best be calculated by applying the conventional non-deviative formula to measurements made at oblique rather than at vertical incidence.

DOI:10.1049/pi-b-1.1958.0241

出版商:IEE    

年代:1958

数据来源: IET

摘要:

The periodic structure of conducting rods, normally used for Yagi-type aerials, is investigated from the point of view of a guide for surface waves. In a series of resonator experiments it is found that a non-radiating plane surface wave of the HE11-mode may be guided along the structure, and that radiation occurs only from a discontinuity. The guiding effect is found to exist only where the rod lengths are less than λ/2. The structure is thus analogous to a capacitively-loaded transmission line. The propagation coefficients are experimentally determined for structures of different rod length and spacing. These propagation coefficients are used to predict the radiation patterns of Yagi aerials in conjunction with the theory outlined in a previous paper. There is quite good agreement with experimentally-observed radiation patterns of long Yagi aerials. The side-lobe structure is explained by interference with direct radiation from the driven element caused by inefficient launching of the surface wave.

DOI:10.1049/pi-b-1.1958.0242

出版商:IEE    

年代:1958

数据来源: IET