1、CCIR VOLUME*VI 90 = 4855232 0501072 8 42 Rec. 684 RECOMMENDATION 684 PREDICTION OF FIELD STRENGTH AT FREQUENCIES BELOW ABOUT 500 kHz (Study Programme 3 1 D/6) (1990) The CCIR, CONSIDERING (a) that there is a need to give guidance to engineers for the planning of radio services in the frequency band
2、below about 500 kHz; (6) that methods developed for the estimation of field strength at frequencies below about 500 kHz are described in Reports 265 and 895, while, on the other hand, different methods which have been developed for the frequency band 150-1705 kHz are described in Report 575, RECOGNI
3、ZING that the methods contained in these Reports still need to be verified on a world-wide basis, since they have been largely based on observations in ITU Region 1, UNANIMOUSLY RECOMMENDS that the methods of Report 265 (the wave-hop method) and of Report 895 (the waveguide-mode method) be adopted f
4、or use in the estimation of field strength at frequencies below about 500 kHz, keeping in mind some of the limitations highlighted in Annex I. ANNEX I APPLICATION OF THE METHODS OF FIELD-STRENGTH PREDICTION AT FREQUENCIES BELOW 500 kHz The waveguide-mode method described in Report 895 shall be used
5、to predict field strengths at frequencies up to about 60 kHz, using the value 0.3/74 for the ionospheric parameter /H for daytime paths, until additional results taking into account the variations with location, season, solar activity and frequency can be obtained. A more detailed model, which is a
6、function of frequency and latitude, is given in the Report for night-time paths. Since the lower boundary of the waveguide is the Earth, a ground conductivity map of the world (e.g. Report 717) needs to be a part of any programme developed for global application. The ground conductivity map currentl
7、y used for VLF and LF is one that is largely based on geological information. The wave-hop method of Report 265 shall be used at frequencies between about 60 and 500 kHz. The results of this method are in good agreement with those of Recommendation 435 in the overlapping frequency band. When using t
8、his method, account needs to be taken of ground-wave propagation (Recommendation 368), and due allowance taken of the vertical plane antenna factor, using the information in Reports 265 and 575. - COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling Services
