1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU).4%2.!4)/.!,G0G0!.!,/5%G0G0#!22)%2G0G03934%-3%.%2!,G0G0#(!2!#4%2)34)#3G0G0#/-/.G0G04/G0G0!,!.!,/5%G0G0#!22)%2G1342!.3-)33)/.G0G03934%-3(90/4(%4)#!,G0G02%2) On tropospheric-scatter radio-relay systems (see CCIR
2、 Recommendation 396 4);3) For satellite systems (see CCIR Recommendation 352 5).2 Fascicle III.2 - Rec. G.212Each of these various hypothetical reference circuits has the same total length1)and they are all used in thesame way. They are only a guide for planning carrier systems.These hypothetical re
3、ference circuits allow designers to study through connection between different carriersystems at basic groups, supergroups, etc., as discussed in Recommendation G.211. Moreover, when they contain morethan one pair of channel modulators and demodulators, they also allow the designers to study an inte
4、rnational switchedconnection having the same total length.3 homogeneous sectionF: section homogneS: seccin homogneaA section without diversion or modulation of any channel groups, supergroups, etc., established on the systemwhich is being considered except for those modulations or demodulations defi
5、ned at the ends of the section.All the hypothetical reference circuits defined above consist of homogeneous sections of equal length 6, 9 or12 sections2)as the case may be.It is assumed that at the end of each homogeneous section, the channels, groups, supergroups, etc., areconnected through at rand
6、om.4 psophometric powerF: puissance psophomtriqueS: potencia sofomtricaWhere square law addition (power addition) of noise can be assumed, it has been found convenient forcalculations and design of international circuits to use the idea of psophometric power as defined below:A convenient unit is the
7、 micro-microwatt or picowatt (pW), and this equation can then be given as follows:_1)With the exception of the hypothetical reference circuits for satellite systems and for circuits of 5000 km.2)The number is not specified for the tropospheric-scatter radio-relay systems.Fascicle III.2 - Rec. G.212
8、3References1 CCITT Recommendation 4-MHz valve-type systems on standardized 2.6/9.5-mm coaxial cable pairs, OrangeBook, Vol. III-l, Rec. G.338, ITU, Geneva, 1977.2 CCIR Recommendation Hypothetical reference circuit for radio-relay systems for telephony using frequency-division multiplex with a capaci
9、ty of 12 to 60 telephone channels, Vol. IX, Rec. 391, Dubrovnik, 1986.3 CCIR Recommendation Hypothetical reference circuit for radio-relay systems for telephony using frequency-division multiplex with a capacity of more than 60 telephone channels, Vol. IX, Rec. 392, Dubrovnik, 1986.4 CCIR Recommenda
10、tion Hypothetical reference circuit for trans-horizon radio-relay systems for telephonyusing frequency-division multiplex, Vol. IX, Rec. 396, Dubrovnik, 1986.5 CCIR Recommendation Hypothetical reference circuits for telephony and television in the fixed satelliteservice, Vol. IV, Rec. 352, Dubrovnik, 1986.
