1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU).4%2.!4)/.!,G0G0!.!,/5%G0G0#!22)%2G0G03934%-3).$)6)$5!,G0G0#(!2!#4%2)34)#3G0G0/ the dotted lines w, x, y and z showthe possible locations of the actual frontier. The correcting networks shown between repeater
2、points II and III aredesigned in conjunction with the cable length between II and III to compensate for the differences in level and pre-emphasis of systems A and B. The correcting networks may be mounted in the repeater boxes at II or at III or may bemounted one in each box. Alternatively, they cou
3、ld be mounted in a separate box between II and III. The distancebetween II and III will normally be less than the repeater spacing of system A or system B and could in the limit bezero, with the repeater boxes II and III adjacent to one another, the frontier would then be at w or z.Interconnection o
4、f two systems can be established by this method, using only passive interconnectingnetworks, if the following condition is met: the repeater input level at any frequency of one system is lower than theoutput level of the other system at the same frequency, by a small amount (say 1 dB) to allow for t
5、he loss of theinterconnecting circuit.The repeaters of type A could be fed with power and supervised from the nearest power-feeding station incountry A and similarly for type B repeaters. If the frontier were located at x or y, neither of the power-feeding andsupervisory systems need cross the bound
6、ary.With this method all repeaters could be of standard types and the output and pilot levels could be normal.Special correcting networks would be required.Fascicle III.2 - Rec. G.352 3ANNEX B(to Recommendation G.352)An alternative method to that given in Annex A is shown in Figure B-1/G.352, in whi
7、ch the ordinary length ofrepeater spacing with the nominal loss a is maintained in the frontier cable section. The nominal relative sending levelof system I is nIand that of system II is nII. The difference of the relative levels is defined as the differential pre-emphasis:pre= n1- nIIIt shall be as
8、sumed that preis positive over the whole transmission band and that at the highest transmitted frequency,the sending levels of the two systems are almost equal. For the adaptation of the relative levels between system I andsystem II it is necessary to introduce an additional passive correction netwo
9、rk prein the direction I II and anadditional active correction network -prein the direction II I.For reasons associated with the size of the repeater housing and power supply, it may be desirable to avoidadditional amplification in the frontier section, which usually has underground repeaters with a
10、 remote power supply.There is no great drawback in using the pre-emphasis of the foreign incoming system up to the following attendedrepeater station and to accommodate only in this station the requisite gain for transformation of the pre-emphasis. In theattended repeater station, there will be no s
11、pecial difficulty in getting the necessary space and current for the additionalequipment. The requisite gain in the direction II I (for - pre) and in the direction I II (because of a possible basicloss in the prenetwork) is supplied by additional amplifiers which are usually already provided for in
12、attendedstations, to compensate for the basic attenuation of precision equalizers.As indicated in Figure B-1/G.352 it may be well to use differential pre-emphasis for both directions in thesame repeater station, for example on that side of the frontier where there is the system using the smallest pr
13、e-emphasis(higher sending relative level). If we assume as is shown in Figure B-1/G.352 that this is system I, the few undergroundrepeaters of system I between the frontier and the attended repeater station will (in lower channels) be operated withthe lower level of system II and will affect the overall noise performance of the whole system less critically than if thesituation were reversed, such that system II were operated at a higher level.
