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/ if this is done, Scheme 1 bis ofFigure 2 b) /G.322, is obtained.1.3.3 Systems providing 5 groupsThe frequency spectrum transmitte
2、d to line should be in accordance with Scheme 2 of Figure 2 c)/G.322.Note 1 - Where there is direct interconnection between a system with 5 groups on symmetric pairs and systemswith a smaller number of groups, by agreement between the Administrations concerned, the system with 5 groups,shown in Sche
3、me 2 bis of Figure 2 c)/G.322, may be used.Note 2 - By agreement between the Administrations concerned, the arrangement in Figure 3/G.322 can be usedfor a supergroup on a coaxial cable system which is to be interconnected at basic supergroup frequencies (312-552 kHz)with either a 5-group system on s
4、ymmetric pairs using Scheme 2 bis Figure 2 c)/G.322, or with a 4-group system usingScheme 1 Figure 2 b)/G.322.Supplement No. 8 5 shows a simple way of assembling basic groups B into a supergroup in accordance withone of the schemes shown in Figure 3/G.322 and in Figure 1/G.338 6 and vice versa.1.3.4
5、 Systems providing 2 supergroupsFascicle III.2 - Rec. G.322 3The frequency spectrum transmitted to line should be in accordance with either Scheme 3 or Scheme 4 ofFigure 4/G.322, whichever the Administration decides.Supergroups 1 and 2 are the same as those in coaxial cable carrier systems. Supergro
6、up 1* is the same as thatnormally recommended for 5-group systems on symmetric cable pairs.4 Fascicle III.2 - Rec. G.322Note - By agreement between the Administrations concerned, for five group systems on symmetric cable pairs,instead of supergroup 1*, supergroup 1* may be used Scheme 2 bis, Figure
7、2 c)/G.322, which gives the arrangementshown in Scheme 3 bis of Figure 4/G.322.1.4 Line-regulating pilots1.4.1 Systems providing 1, 2, 3, 4 or 5 groupsEither of the following methods can be used (see Figure 5/G.322).Either of these methods can be chosen by the Administrations concerned and can be us
8、ed without difficulty,provided the pilots are efficiently suppressed at the end of a regulated-line section.a) Systems providing one, two or three groupsb) Systems providing four groupsc) Systems providing five groupsFIGURE 2/G.322Line-frequency allocation for international carrier systems on symmet
9、ric cable pairsFascicle III.2 - Rec. G.322 5a) Arrangement of groups and channels (supergroup 3 has been shown as an example)b) Example of possible positions, in the coaxial line-frequency band of the supergroup corresponding to Scheme 2 bis of Figure 2c)/G.322FIGURE 3/G.322Arrangement of groups in
10、a supergroup, which may be used in coaxialcarrier systems interconnected with systems on symmetric pairsFIGURE 4/G.322Line-frequency allocation for international carrier systemsproviding 2 supergroups on symmetric pair cables6 Fascicle III.2 - Rec. G.322FIGURE 5/G.322Line-regulating pilots for carri
11、er systems on symmetric pairsMethod A1) A pilot at 60 kHz with a power level of -15 dBm0, this frequency being in the gap between groups A andB and it being understood that this pilot would be used for regulation of the line on all regulated-linesections, whatever their length, and also for synchron
12、ization or checking of frequencies.2) Where necessary, and especially for long regulated-line sections, an additional line-regulating pilot 4 kHzabove the maximum frequency transmitted to line and with a power level of -15 dBm0.Note - There are in existence systems with five groups in which this pil
13、ot is only 1 kHz above the maximumfrequency transmitted.The recommendation under 2) above does not apply to systems with a single group.The recommended accuracy for these pilot frequencies is: 1 Hz for the 60-kHz pilot; 3 Hz for auxiliary pilot located 4 kHz above the maximum frequency of the channe
14、l group concerned.Method BTwo pilots situated in the basic group B at 64 kHz and at 104 kHz transmitted with a power level of -17 dBm0.On the high-frequency line, it is possible to have two pilots per 48 kHz of transmitted band and, from amongstthese pilots, 16 kHz and the maximum transmitted freque
15、ncy less 4 kHz are selected.Fascicle III.2 - Rec. G.322 7For systems having two or more groups, a third line-pilot is used, located between the top and bottom pilots,64 kHz is the frequency used in 2-group systems, and 112 kHz in 5-group systems.Note - Method B is hardly compatible with the use of a
16、 supergroup pilot and/or the alternative group pilot104.08 kHz (Table 4/G.232 and Recommendation G.233, 9).1.4.2 System providing 2 supergroupsThe following frequencies and levels are recommended (as shown in Method A of 1.4.1 above): lower pilot: 60 kHz power level of -15 dBm0; upper pilot: 4 kHz a
17、bove the highest transmitted frequency, i.e. at 556 kHz, power level of -15 dBm0.The recommended accuracy for the frequencies of these pilots is as follows: 1 Hz for the 60-kHz pilot; 3 Hz for the 556-kHz pilot.Note - If a supergroup is through-connected from a coaxial-pair system to occupy the posi
18、tion of the uppersupergroup in the band of line frequencies, there can be a residue from a line-regulating pilot or additional measuringfrequency. The recommendations for the through-supergroup equipment (Recommendation G.243) ensure that thisresidue will be sufficiently attenuated to cause no inter
19、ference with the line-regulating pilots or additional measuringfrequencies of another coaxial-pair system when these are sent at a power level of -10 dBm0. So that there will be nointerference with the 120-circuit system line-regulating pilot sent at -15 dBm0, this system should incorporate its owna
20、dditional protection of 5 dB at 556 kHz for a through-connected supergroup.1.5 Matching of repeater and line impedancesIt is desirable to limit the return-current coefficient at the ends of an elementary cable section so that the effectof the reflected near-end crosstalk does not contribute excessiv
21、ely to the total far-end crosstalk.For example, in a cable which has a near-end crosstalk ratio of 56.5 dB and which meets the limit for far-endcrosstalk ratio (direct far-end crosstalk) of at least 69.5 dB (the cable being between impedances equal to itscharacteristic impedance), the contribution o
22、f the reflected near-end crosstalk would be insignificant compared with theeffect of the far-end crosstalk at the maximum frequency transmitted, if the return current coefficients between repeatersand line have the following values.The modulus of the return-current coefficient between the input (or
23、output) impedance of the repeater (in itsnormal operating condition and including line transformers and equalizers) measured between the line terminals at thefrequency f, and the nominal value of the impedance at the frequency f of the cable pair connected to the input (oroutput) of the repeater, sh
24、ould not exceed the value given by the formulae:8 Fascicle III.2 - Rec. G.322Note - The values of the return-current coefficient recommended for systems with 1, 2 or 3 groups would ingeneral be unsatisfactory if they were tolerated on all the sections of a line link; but they have been accepted as l
25、imits fora frontier section because, first, an international circuit will usually comprise only one such frontier interconnection and,second, the matching conditions at such a point may be complicated by the fact that one of the repeaters of this sectionmay not have been specified for the exact type
26、 of cable to which it is connected.2 Special recommendations (formerly Part B)2.1 Systems to be used simultaneously with valve-type systems in the same cablesIn those exceptional cases when some pairs in an elementary cable section are already equipped with valve-typesystems and it is desired to equ
27、ip the free pairs with new transistor systems without changing the existing installations,the new system using transistors must meet the recommendations in 1 above and also the provisions ofRecommendation G.324 7 relating to valve-type systems. However, it may depart from those Recommendationsspecif
28、ying permissible values for amplifier harmonic margin and overload point 8.Note - Recommendation G.323 gives an example of a 60-channel high-gain transistor system.2.2 Low-gain systems2.2.1 Relative level at the output of the repeatersThe relative level per channel, at any frequency, at the output o
29、f each repeater shall be: 11 dBr for systems with 1, 2 or 3 groups; 14 dBr for systems with 4 or 5 groups or 2 supergroups.2.2.2 Monitoring frequenciesIf a monitoring (or fault-locating) frequency is sent over a normally operating system, it may for example be inthe band 560-600 kHz for a 2-supergro
30、up system.Note - Frequencies sent only over a system already withdrawn from service because of a fault can be selectedby each Administration on the national level.2.2.3 Harmonic distortionThe harmonic distortion of a repeater should not exceed a value corresponding to the limits shown in theTable 1/
31、G.322.TABLE 1/G.322a)For definition, see Reference 9.Note - These values are measured for a power of 1 mW applied at a point of zero relative level on any channel.2.2.4 Noise factorThe noise factor of a complete repeater (taking into account noise due to the transistors, the input network andthe lin
32、e-matching network) must not exceed 10 dB.Limits forSystems providing1, 2 or 3 groups 4 or 5 groups 2 supergroups2nd-order harmonic margina)3rd-order harmonic margina)79 dB92 dB82 dB98 dB85 dB104 dBFascicle III.2 - Rec. G.322 92.2.5 Overload pointThe overload point, defined in 6.1 of Recommendation
33、G.223, must be at least 14 dBm for the intermediaterepeaters.Note - For determination of this overload point, account has been taken of a margin of a few decibels for levelvariations due to geographical differences with respect to the theoretical site of a repeater, to temperature variations ofthe c
34、able, to equalization inaccuracies, etc. In stations where this margin is unnecessary, a repeater overload point that isslightly lower may therefore be chosen.2.2.6 Crosstalk ratio between repeaters in the same stationA typical figure for the crosstalk ratio between repeaters in the same station is
35、87 dB. With this figure it ispossible to use repeater stations regardless of the cable-balancing method adopted.Note - If, however, the cable is balanced by elementary sections in the conventional way, a figure of 80 dB isadequate.The figures given above apply to all the equipment at the repeater st
36、ation, from the input transformer to theoutput transformer.2.2.7 Power feedingIn the absence of a special agreement between the Administrations concerned in a power-feeding sectioncrossing a frontier, it is recommended that each Administration power-feed only the repeater stations on its ownterritor
37、y.References1 CCITT Recommendation 4-MHz valve-type systems on standardized 2.6/9.5-mm coaxial cable pairs, OrangeBook, Vol. III-l, Rec. G.338, c), ITU, Geneva, 1977.2 Method of use by the French Administration of the hypothetical reference circuit for carrier systems onsymmetric pairs, CCITT Blue B
38、ook, Vol. III, Part 4, Annex 14, ITU, Geneva, 1965.31 Contribution by the Federal German Administration to the study of noise on carrier systems worked oversymmetric pairs, CCITT Blue Book, Vol. III, Part 4, Annex 15, ITU, Geneva, 1965.4 Calculation of crosstalk noise on symmetric pair systems, CCIT
39、T Blue Book, Vol. III, Part 4, Annex 16, ITU,Geneva, 1965.5 Method proposed by the Belgian Telephone Administration for interconnection between coaxial and symmetricpair systems, Green Book, Vol. III-2, Supplement No. 8, ITU, Geneva, 1973.6 CCITT Recommendation 4-MHz valve-type systems on standardiz
40、ed 2.6/9.5-mm coaxial cable pairs, OrangeBook, Vol. III-1, Rec. G.338, Figure 1/G.338, ITU, Geneva, 1977.7 CCITT Recommendation General characteristics for valve-type systems on symmetric cable pairs, OrangeBook, Vol. III-1, Rec. G.324, ITU, Geneva, 1977.8 Ibid., B.c) and B.d).9 CCITT Definition: nthorder harmonic distortion, Vol. X (Terms and Definitions).
