ITU-R P 844-1-1994 Ionospheric Factors Affecting Frequency Sharing in the VHF and UHF Bands (30 MHz-3 GHz)《在VHF和UHF频段内(30MHz-3GHz)影响频率共享的电离层因素》.pdf
《ITU-R P 844-1-1994 Ionospheric Factors Affecting Frequency Sharing in the VHF and UHF Bands (30 MHz-3 GHz)《在VHF和UHF频段内(30MHz-3GHz)影响频率共享的电离层因素》.pdf》由会员分享,可在线阅读,更多相关《ITU-R P 844-1-1994 Ionospheric Factors Affecting Frequency Sharing in the VHF and UHF Bands (30 MHz-3 GHz)《在VHF和UHF频段内(30MHz-3GHz)影响频率共享的电离层因素》.pdf(6页珍藏版)》请在麦多课文档分享上搜索。
1、 Rec. ITU-R P.844-1 1 RECOMMENDATION ITU-R P.844-1*IONOSPHERIC FACTORS AFFECTING FREQUENCY SHARING IN THE VHF AND UHF BANDS (30 MHz-3 GHz) (Question ITU-R 218/3) (1992-1994) Rec. ITU-R PI.844-1 The ITU Radiocommunication Assembly, considering a) that the ionosphere, while primarily responsible for r
2、eflection of radio waves below approximately 30 MHz, is capable of supporting propagation in the VHF (30-300 MHz) band under some conditions, during relatively short periods of time, and in certain areas of the world; b) that propagation mechanisms which exist for relatively short periods of time sh
3、ould be taken into consideration when planning radio systems which share frequencies; c) that frequency sharing is important in the efficient use of the radio spectrum, recommends that the following information be taken into account when planning radio systems which make use of frequency sharing in
4、the VHF and UHF bands (30 MHz-3 GHz). 1. Terrestrial propagation 1.1 Introduction Radio propagation at VHF is mainly controlled by physical objects, such as terrain and ground cover (clutter), and tropospheric factors, principally refraction. However, at VHF, ionospheric propagation over long distan
5、ces can take place with relatively small losses. Such propagation events may be significant in causing interference at VHF, particularly for systems requiring high reliability. 1.2 Summary of potential ionospheric interference mechanisms Table 1 provides a summary of ionospheric propagation mechanis
6、ms which may be significant causes of interference at VHF. Further information on the more important mechanisms is given in the following sections. 1.3 Normal F-region propagation Near the peak of the solar cycle long-distance propagation via the F2 layer can occur for a significant fraction of the
7、time at frequencies above 30 MHz. This effect extends to 70 MHz at low latitudes. Figures 1, 2 and 3 show, for a path length of 4 000 km, values of the MUF exceeded for 1% of hours for three seasons at sunspot maximum. 1.4 Trans-equatorial propagation (TEP) Strong transmission can occur, particularl
8、y during high sunspot years, over long North-South paths spanning the geomagnetic equator. There appear to be two types of trans-equatorial propagation characterized by the times of peak occurrence, fading characteristics and modes of propagation. _ *Radiocommunication Study Group 3 made editorial a
9、mendments to this Recommendation in 2000 in accordance with Resolution ITU-R 44. 2 Rec. ITU-RP.844-1TABLE 1 Main causes of ionospheric interference to stations working at frequencies between 30 and 300 MHz Cause of interference Latitude zone Period of severe interference Approximate highest frequenc
10、y with severe interference (MHz) Approximate frequency above which interference is negligible (MHz) Approximate range of distances affected (km) Principal distinguishing features Regular F-layer reflections Mid Day, equinox and winter, solar-cycle maximum 50 60 E-W paths3 000-6 000 or Occurrence bro
11、adly in accordance with regular-layer morphology Low Afternoon to late evening, solar-cycle maximum 60 70 N-S paths 3 000-10 000 High Night 70 90 500-4 000 Principally during summer months in mid latitudes. Sudden onset and conclusion, beginning later and ending earlier with increase of operating fr
12、equency. Area concerned Sporadic-E reflections Mid Day and evening, summer 60 83-135 (1)relatively small and mobile. Duration minutes or hours. No associated signal enhancements at short range Low Day 60 90 Sporadic-E scatter Low Evening to midnight 60 90 Up to 2 000 (1) For 0.1% of the time during
13、the hours 0800-2300 LT for May to August (111 min total) the following frequencies may be derived from Annex 1 to Recommendation ITU-R P.534 for a distance of 1 800 km and = 30 dB for temperate zone: Region A (Europe and North Africa): 083 MHz Region B (North America): 093 MHz Region C (Asia): 135 M
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