ITU-R QUESTION 516-2000 Sky-wave reception in LF MF and HF broadcasting《低频 中频和短波广播中的天波接收》.pdf

1、C:DOCUMENTS AND SETTINGSQGV33745MY DOCUMENTSDOWNLOADSR-QUE-SG06.51-2000-MSW-E.DOC 22.10.03 15.07.10 QUESTION ITU-R 51/6*Sky-wave reception in LF, MF and HF broadcasting (1990-1997-2000) The ITU Radiocommunication Assembly, considering a) that broadcasting services at LF, MF and HF are also provided

2、by sky-wave propagation; b) that to plan a satisfactory service via sky-wave propagation, fading allowances are required to be taken into account, decides that the following Question should be studied 1 What is the nature of the distortion due to the effects of the ionosphere at distances beyond the

3、 ground-wave coverage area? 2 What is the degradation of the subjective quality of the sky-wave signal when received beyond the limit of the ground-wave coverage area, according to the system envisaged and as a function of distance and other possible factors, such as the geographical location of the

4、 transmitter, the frequency, the season of the year and the characteristics of the transmitting antenna? 3 What is the degree of distortion for a given percentage of time that would, after demodulation at the receiver, provide satisfactory sky-wave reception? 4 What is the reduction in distortion, d

5、ue to the effects of the ionosphere, that can be secured by improvements in methods of reception, for example, replacing envelope detectors by other detection devices? 5 What performance improvement in terms of the parameters included in decides 1 to 4 above can be expected by the implementation of

6、digital modulation techniques? further decides 1 that the results of the above studies should be addressed to: update existing Recommendation(s); prepare (a) new Recommendation(s); 2 that the above studies should be completed by the year 2005. _ *This Question should be brought to the attention of Radiocommunication Study Group 3.