.rs .\" Troff code generated by TPS Convert from ITU Original Files .\" Not Copyright ( c) 1991 .\" .\" Assumes tbl, eqn, MS macros, and lots of luck. .TA 1c 2c 3c 4c 5c 6c 7c 8c .ds CH .ds CF .EQ delim @@ .EN .nr LL 40.5P .nr ll 40.5P .nr HM 3P .nr FM 6P .nr PO 4P .nr PD 9p .po 4P .rs \v | 5i' .sp 2P .LP \fBRecommendation\ G.322\fR .RT .sp 2P .ce 1000 \fBGENERAL\ CHARACTERISTICS\ RECOMMENDED\ FOR\ \fR \fBSYSTEMS\ ON\fR .EF '% Fascicle\ III.2\ \(em\ Rec.\ G.322'' .OF '''Fascicle\ III.2\ \(em\ Rec.\ G.322 %' .ce 0 .sp 1P .ce 1000 \fBSYMMETRIC\ PAIR\ CABLES\fR .ce 0 .sp 1P .PP This Recommendation applies to systems using types of cable so far recommended by the CCITT (see Recommendation\ G.611) and providing 1, 2, 3, 4\ or 5\ groups or 2\ supergroups. .sp 1P .RT .sp 2P .LP \fB1\fR \fBGeneral recommendations\fR .sp 1P .RT .sp 1P .LP 1.1 \fIHypothetical reference circuits\fR \v'3p' .sp 9p .RT .PP 1.1.1 The hypothetical reference circuit on symmetric pairs is 2500\ km long, and is set up on a symmetric pair carrier system. For each direction of transmission, it has a total of: .LP Where systems provide 1, 2, 3 or 4 groups, it is possible to have a smaller number of modulations, but this does not detract from the usefulness of the idea of a hypothetical reference circuit on symmetric pairs. .FE \(em three pairs of channel modulators and demodulators, .LP \(em six pairs of group modulators and demodulators, .LP \(em six pairs of supergroup modulators and demodulators . .PP Figure\ 1/G.322 shows a diagram of the hypothetical reference circuit on symmetric pairs. It will be seen that there is a total of 15\ modulations and 15\ demodulations for each direction of transmission supposing that each modulation or demodulation is effected by a single stage . .LP .rs .sp 10P .ad r \fBFigure 1/G.322, p.\fR .sp 1P .RT .ad b .RT .PP This hypothetical reference circuit consists of 6\ homogeneous sections of equal length (see Recommendation\ G.212). .PP The number of pairs in the cable is assumed to be the same in all sections. .PP The hypothetical reference circuit on symmetric pairs thus defined is used for systems providing 1, 2, 3, 4\ or 5\ groups. .RT .PP 1.1.2 The composition of the hypothetical reference circuit for a 10\(hygroup (2\(hysupergroup) carrier system should be the same as that of the hypothetical reference circuit for a 16\(hysupergroup coaxial cable system (see\ [1]). .sp 9p .RT .sp 1P .LP 1.2 \fIDesign objectives for\fR \fIcircuit noise\fR .sp 9p .RT .PP The objectives mentioned in Recommendation\ G.222 are applicable to hypothetical reference circuits in the circumstances indicated in Recommendation\ G.223. .PP In practice, it is sufficient to check by calculation that, for every telephone channel as defined by the hypothetical reference circuit on symmetric pairs, the mean psophometric power at the end of the channel referred to a point of zero relative level does not exceed 10 | 00\ pW0p during any period of one hour. .bp .PP The subdivision of the total noise between: .RT .LP \(em basic noise, .LP \(em intermodulation noise, .LP \(em noise due to crosstalk, .LP is left entirely to the designer of the system, within the limits of 2500\ pW0p for the terminal equipment and 7500\ pW0p for the line. .PP \fINote\fR \ \(em\ In planning a carrier system on symmetric pairs, calculation of the noise due to crosstalk could be carried out by the methods described in [2], [3] and\ [4]. .sp 2P .LP 1.3 \fILine\(hyfrequency spectrum\fR .sp 1P .RT .sp 1P .LP 1.3.1 \fISystems providing 1, 2 or 3\ groups\fR .sp 9p .RT .PP The line\(hyfrequency spectrum should be in accordance with the scheme shown in Figure\ 2 | fIa)\fR /G.322. .RT .sp 1P .LP 1.3.2 \fISystems providing 4\ groups\fR .sp 9p .RT .PP The frequency spectrum transmitted to line should be in accordance with Scheme\ 1 of Figure\ 2 | fIb)\fR /G.322. .PP \fINote\fR \ \(em\ By agreement between the Administrations concerned, it is possible to omit one group of supergroup\ 1* shown in Scheme\ 2 of Figure\ 2 | fIc)\fR /G.322, for systems with five groups; if this is done, Scheme\ 1 | fIbis\fR of Figure\ 2 | fIb)\fR /G.322, is obtained. .RT .sp 1P .LP 1.3.3 \fISystems providing 5\ groups\fR .sp 9p .RT .PP The frequency spectrum transmitted to line should be in accordance with Scheme\ 2 of Figure\ 2 | fIc)\fR /G.322. .PP \fINote\ 1\fR \ \(em\ Where there is direct interconnection between a system with 5\ groups on symmetric pairs and systems with a smaller number of groups, by agreement between the Administrations concerned, the system with 5\ groups, shown in Scheme\ 2 | fIbis\fR of Figure\ 2 | fIc)\fR /G.322, may be used. .PP \fINote\ 2\fR \ \(em\ By agreement between the Administrations concerned, the arrangement in Figure\ 3/G.322 can be used for a supergroup on a coaxial cable system which is to be interconnected at basic supergroup frequencies (312\(hy552\ kHz) with either a 5\(hygroup system on symmetric pairs using Scheme\ 2 | fIbis\fR [Figure\ 2 | fIc)\fR /G.322], or with a 4\(hygroup system using Scheme\ 1 [Figure\ 2 | fIb)\fR /G.322]. .PP Supplement No. 8 [5] shows a simple way of assembling basic groups\ B into a supergroup in accordance with one of the schemes shown in Figure\ 3/G.322 and in Figure\ 1/G.338\ [6] and vice versa. .RT .sp 1P .LP 1.3.4 \fISystems providing 2 supergroups\fR .sp 9p .RT .PP The frequency spectrum transmitted to line should be in accordance with either Scheme\ 3 or Scheme\ 4 of Figure\ 4/G.322, whichever the Administration decides. .PP Supergroups\ 1 and 2 are the same as those in coaxial cable carrier systems. Supergroup\ 1* is the same as that normally recommended for 5\(hygroup systems on symmetric cable pairs. .PP \fINote\fR \ \(em\ 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 | fIbis\fR , Figure\ 2 | fIc)\fR /G.322], which gives the arrangement shown in Scheme\ 3 | fIbis\fR of Figure\ 4/G.322. .RT .sp 2P .LP 1.4 \fILine\(hyregulating pilots\fR .sp 1P .RT .sp 1P .LP 1.4.1 \fISystems providing 1, 2, 3, 4 or 5 groups\fR .sp 9p .RT .PP Either of the following methods can be used (see Figure\ 5/G.322). .PP Either of these methods can be chosen by the Administrations concerned and can be used without difficulty, provided the pilots are efficiently suppressed at the end of a regulated\(hyline section. .bp .RT .LP .rs .sp 47P .ad r \fBFigure 2/G.322, p.\fR .sp 1P .RT .ad b .RT .LP .bp .LP .rs .sp 26P .ad r \fBFigure 3/G.322, p.\fR .sp 1P .RT .ad b .RT .LP .rs .sp 22P .ad r \fBFigure 4/G.322, p.\fR .sp 1P .RT .ad b .RT .LP .bp .LP .rs .sp 33P .ad r \fBFigure 5/G.322, p.\fR .sp 1P .RT .ad b .RT .sp 1P .LP \fIMethod\ A\fR \v'4p' .sp 9p .RT .LP 1) A pilot at 60\ kHz with a power level of \(em15\ dBm0, this frequency being in the gap between groups\ A and\ B and it being understood that this pilot would be used for regulation of the line on all regulated\(hyline sections, whatever their length, and also for synchronization or checking of frequencies. .LP 2) Where necessary, and especially for long regulated\(hyline sections, an additional line\(hyregulating pilot 4\ kHz above the maximum frequency transmitted to line and with a power level of \(em15\ dBm0. .LP \fINote\fR \ \(em\ There are in existence systems with five groups in which this pilot is only 1\ kHz above the maximum frequency transmitted. .LP The recommendation under \(sc\ 2) above does not apply to systems with a single group. .LP The recommended accuracy for these pilot frequencies is: .LP \(+- | \ Hz for the 60\(hykHz pilot; .LP \(+- | \ Hz for auxiliary pilot located 4\ kHz above the maximum frequency of the channel group concerned. .bp .LP .sp 1P .LP \fIMethod\ B\fR \v'4p' .sp 9p .RT .LP Two pilots situated in the basic group\ B at 64\ kHz and at 104\ kHz transmitted with a power level of \(em17\ dBm0. .LP On the high\(hyfrequency line, it is possible to have two pilots per 48\ kHz of transmitted band and, from amongst these pilots, 16\ kHz and the maximum transmitted frequency less 4\ kHz are selected. .LP For systems having two or more groups, a third line\(hypilot is used, located between the top and bottom pilots, 64\ kHz is the frequency used in 2\(hygroup systems, and 112\ kHz in 5\(hygroup systems. .LP \fINote\fR \ \(em\ Method B is hardly compatible with the use of a supergroup pilot and/or the alternative group pilot 104.08\ kHz (Table\ 4/G.232 and Recommendation\ G.233, \(sc\ 9). .sp 1P .LP 1.4.2 \fISystem providing 2 supergroups\fR .sp 9p .RT .PP The following frequencies and levels are recommended (as shown in Method\ A of \(sc\ 1.4.1 above): .RT .LP \(em lower\ pilot: 60\ kHz power level of \(em15\ dBm0; .LP \(em upper\ pilot: 4\ kHz above the highest transmitted frequency, i.e. at 556\ kHz, power level of \(em15\ dBm0. .PP The recommended accuracy for the frequencies of these pilots is as follows: .LP \(+- | \ Hz\ for\ the\ 60\(hykHz\ pilot; .LP \(+- | \ Hz\ for\ the\ 556\(hykHz\ pilot. .PP \fINote\fR \ \(em\ If a supergroup is through\(hyconnected from a coaxial\(hypair system to occupy the position of the upper supergroup in the band of line frequencies, there can be a residue from a line\(hyregulating pilot or additional measuring frequency. The recommendations for the through\(hysupergroup equipment (Recommendation\ G.243) ensure that this residue will be sufficiently attenuated to cause no interference with the line\(hyregulating pilots or additional measuring frequencies of another coaxial\(hypair system when these are sent at a power level of \(em10\ dBm0. So that there will be no interference with the 120\(hycircuit system line\(hyregulating pilot sent at \(em15\ dBm0, this system should incorporate its own additional protection of 5\ dB at 556\ kHz for a through\(hyconnected supergroup. .sp 1P .LP 1.5 \fIMatching of repeater and line impedances\fR .sp 9p .RT .PP It is desirable to limit the return\(hycurrent coefficient at the ends of an elementary cable section so that the effect of the reflected near\(hyend crosstalk does not contribute excessively to the total far\(hyend crosstalk. .PP For example, in a cable which has a near\(hyend crosstalk ratio of 56.5\ dB and which meets the limit for far\(hyend crosstalk ratio (direct far\(hyend crosstalk) of at least 69.5\ dB (the cable being between impedances equal .PP to its characteristic impedance), the contribution of the reflected near\(hyend crosstalk would be insignificant compared with the effect of the far\(hyend crosstalk at the maximum frequency transmitted, if the return current coefficients between repeaters and line have the following values. .PP The modulus of the return\(hycurrent coefficient between the input (or output) impedance of the repeater (in its normal operating condition and including line transformers and equalizers) measured between the line terminals at the frequency\ \fIf\fR , and the nominal value of the impedance at the frequency\ \fIf\fR of the cable pair connected to the input (or output) of the repeater, should not exceed the value given by the formulae: \v'6p' .RT .LP 0.15 @ sqrt { { \fIf\fR~\d\fImax.\fR~\u } over { fIf\fR } } @ or 0.25 for systems with 1, 2 and 3 groups; .LP .sp 1 0.08 @ sqrt { { \fIf\fR~\d\fImax.\fR~\u } over { fIf\fR } } @ or 0.10 for systems with 4 and 5 groups or systems with 2 supergroups on paper\(hyinsulated cables (types II and III in Recommendation\ G.611); .LP .sp 1 0.10 @ sqrt { { \fIf\fR~\d\fImax.\fR~\u } over { fIf\fR } } @ or 0.17 for systems with 5 groups or systems with 2 supergrops on polythene or styroflex\(hyinsulated cables (types II | fIbis\fR and III | fIbis\fR in Recommendation\ G.611). .bp .PP \fINote\fR \ \(em\ The values of the return\(hycurrent coefficient recommended for systems with 1, 2 or 3\ groups would in general be unsatisfactory if they were tolerated on all the sections of a line link; but they have been accepted as limits for a 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 section may not have been specified for the exact type of cable to which it is connected. .sp 2P .LP \fB2\fR \fBSpecial recommendations\fR (formerly Part B) .sp 1P .RT .sp 1P .LP 2.1 \fISystems to be used simultaneously with valve\(hytype systems\fR \fIin the same cables\fR .sp 9p .RT .LP .PP In those exceptional cases when some pairs in an elementary cable section are already equipped with valve\(hytype systems and it is desired to equip the free pairs with new transistor systems without changing the existing installations, the new system using transistors must meet the recommendations in \(sc\ 1 above and also the provisions of Recommendation\ G.324\ [7] relating to valve\(hytype systems. However, it may depart from those Recommendations specifying permissible values for amplifier harmonic margin and overload point\ [8]. .PP \fINote\fR \ \(em\ Recommendation G.323 gives an example of a 60\(hychannel high\(hygain transistor system. .RT .sp 2P .LP 2.2 \fILow\(hygain systems\fR .sp 1P .RT .sp 1P .LP 2.2.1 \fIRelative level at the output of the repeaters\fR .sp 9p .RT .PP The relative level per channel, at any frequency, at the output of each repeater shall be: .RT .LP \(em11\ dBr for systems with 1, 2 or 3\ groups; .LP \(em14\ dBr for systems with 4 or 5\ groups or 2\ supergroups. .LP .sp 1P .LP 2.2.2 \fIMonitoring frequencies\fR .sp 9p .RT .PP If a monitoring (or fault\(hylocating) frequency is sent over a normally operating system, it may for example be in the band 560\(hy600\ kHz for a 2\(hysupergroup system. .PP \fINote\fR \ \(em\ Frequencies sent only over a system already withdrawn from service because of a fault can be selected by each Administration on the national level. .RT .sp 1P .LP 2.2.3 \fIHarmonic distortion\fR .sp 9p .RT .PP The harmonic distortion of a repeater should not exceed a value corresponding to the limits shown in the Table\ 1/G.322. .RT .LP .rs .sp 12P .ad r \fBTable 1/G.322 T1.322, p.\fR .sp 1P .RT .ad b .RT .sp 1P .LP 2.2.4 \fINoise factor\fR .sp 9p .RT .PP The noise factor of a complete repeater (taking into account noise due to the transistors, the input network and the line\(hymatching network) must not exceed 10\ dB. .bp .RT .LP .sp 1P .LP 2.2.5 \fIOverload point\fR .sp 9p .RT .PP The overload point, defined in \(sc 6.1 of Recommendation\ G.223, must be at least 14\ dBm for the intermediate repeaters. .PP \fINote\fR \ \(em\ For determination of this overload point, account has been taken of a margin of a few decibels for level variations due to geographical differences with respect to the theoretical site of a repeater, to temperature variations of the cable, to equalization inaccuracies,\ etc. In stations where this margin is unnecessary, a repeater overload point that is slightly lower may therefore be chosen. .RT .sp 1P .LP 2.2.6 \fICrosstalk ratio between repeaters in the same station\fR .sp 9p .RT .PP A typical figure for the crosstalk ratio between repeaters in the same station is 87\ dB. With this figure it is possible to use repeater stations regardless of the cable\(hybalancing method adopted. .PP \fINote\fR \ \(em\ If, however, the cable is balanced by elementary sections in the conventional way, a figure of 80\ dB is adequate. .PP The figures given above apply to all the equipment at the repeater station, from the input transformer to the output transformer. .RT .LP .sp 1P .LP 2.2.7 \fIPower feeding\fR .sp 9p .RT .PP In the absence of a special agreement between the Administrations concerned in a power\(hyfeeding section crossing a frontier, it is recommended that each Administration power\(hyfeed only the repeater stations on its own territory. .RT .sp 2P .LP \fBReferences\fR .sp 1P .RT .LP [1] CCITT Recommendation \fI4\(hyMHz valve\(hytype systems on standardized\fR \fI2.6/9.5\(hymm coaxial cable pairs\fR , Orange Book, Vol.\ III\(hy1, Rec.\ G.338,\ c), ITU, Geneva,\ 1977. .LP [2] \fIMethod of use by the French Administration of the hypothetical\fR \fIreference circuit for carrier systems on symmetric pairs\fR , CCITT Blue Book, Vol.\ III, Part\ 4, Annex\ 14, ITU, Geneva,\ 1965. .LP [3] \fIContribution by the Federal German Administration to the study of\fR \fInoise on carrier systems worked over symmetric pairs\fR , CCITT Blue Book, Vol.\ III, Part\ 4, Annex\ 15, ITU, Geneva, 1965. .LP [4] \fICalculation of crosstalk noise on symmetric pair systems\fR , CCITT Blue Book, Vol.\ III, Part\ 4, Annex\ 16, ITU, Geneva, 1965. .LP [5] \fIMethod proposed by the Belgian Telephone Administration for\fR \fIinterconnection between coaxial and symmetric pair systems\fR , Green Book, Vol.\ III\(hy2, Supplement No.\ 8, ITU, Geneva, 1973. .LP [6] CCITT Recommendation \fI4\(hyMHz valve\(hytype systems on standardized\fR \fI2.6/9.5\(hymm coaxial cable pairs\fR , Orange Book, Vol.\ III\(hy1, Rec.\ G.338, Figure\ 1/G.338, ITU, Geneva, 1977. .LP [7] CCITT Recommendation \fIGeneral characteristics for valve\(hytype systems\fR \fIon symmetric cable pairs\fR , Orange Book, Vol.\ III\(hy1, Rec.\ G.324, ITU, Geneva,\ 1977. .LP [8] \fIIbid.\fR , B.c) and B.d). .LP [9] CCITT Definition: \fIn\fR , Vol. X (Terms and Definitions). .LP .sp 2P .LP \fBRecommendation\ G.323\fR .RT .sp 2P .sp 1P .ce 1000 \fBA\ TYPICAL\ TRANSISTORIZED\ SYSTEM\ ON\ SYMMETRIC\ CABLE\ PAIRS\fR .EF '% Fascicle\ III.2\ \(em\ Rec.\ G.323'' .OF '''Fascicle\ III.2\ \(em\ Rec.\ G.323 %' .ce 0 .sp 1P .PP This Recommendation defines a typical 60\(hychannel system installed on symmetric pairs in cable (differing for the two directions of transmission) which comply with Recommendation\ G.611 and equipped with transistorized high gain amplifiers. This system should meet the requirements of Recommendation\ G.322. It must not be considered as recommended by CCITT in preference to other systems which would also meet the requirements of Recommendation\ G.322. It has been specified because it can be used simultaneously with 60\(hychannel valve\(hytype systems in the same cables. .bp .sp 1P .RT .PP The main features are given below: .LP .sp 2P .LP \fB1\fR \fBFrequencies transmitted to line: 12\(hy252 kHz\fR .sp 1P .RT .sp 2P .LP \fB2\fR \fBTransmission levels\fR \v'3p' .sp 1P .RT .ad r \(em without\ pre\(hyemphasis \(em5\ dBr \(em with\ pre\(hyemphasis at\ \ 12\ kHz,\ \ \(em11\ dBr at\ 252\ kHz,\ \ \ \(em1\ dBr .ad b .RT .sp 2P .LP \fB3\fR \fBLine\(hypilot frequencies\fR \v'3p' .sp 1P .RT .ad r \(em for amplification regulation independent of frequency 248 kHz \(em for linear regulation with frequency \ 16 kHz \(em for supplementary regulation (curvilinear) 112 kHz .ad b .RT .LP .sp 2P .LP \fB4\fR \fBRepeater station amplification\fR .sp 1P .RT .ad r (with average regulator positions of the automatic amplification regulation) 50\ \(+- | dB .ad b .RT .sp 2P .LP \fB5\fR \fBLimits of the automatic amplification regulation\fR \v'3p' .sp 1P .RT .LP a) in unattended repeater stations with gain depending on the soil temperature at\ \ 12\ kHz,\ \ \(+- | .1 dB at\ 252\ kHz,\ \ \(+- | .1 dB b) in pilot\(hyregulated stations: .ad r \(em for amplification regulation independent of frequency 248\ kHz, | \ \ \(+- | dB \(em for linear regulation with frequency \ 16\ kHz,\ \ \(+- | .5 dB \(em for supplementary regulation (curvilinear) 112\ kHz, | \ \ \(+- | \ dB .ad b .RT .ad r \fB6\fR \fBAbsolute thermal noise level at the repeater\fR \fBinput in the 248\(hy252\ kHz spectrum\fR \(em132 dBm .sp 1P .RT .ad b .RT .LP .sp 2P .LP \fB7\fR \fBNonlinearity attenuation of the repeaters for a\fR \fBfundamental wave power level of 0 dBm\fR \fBat the output\fR \v'3p' .sp 1P .RT .ad r \(em for the second harmonic higher than \ 87 dB \(em for the third harmonic higher than 109 dB .ad b .RT .ad r \fB8\fR \fBReflection coefficient modulus\fR \fBat the\fR \fBrepeater input and output in relation to the \fBcharacteristic impedance of the cable\fR less than the lower of the two values: \v'6p' .sp 1P .RT .ad b .RT .ad r 0.1 @ sqrt { { \fIf\fR~\d\fImax.\fR~\u } over { fIf\fR } } @ or 0.2 .ad b .RT .ad r .sp 1 \fB9\fR \fBAbsolute overload point\fR \fBof the amplifiers\fR higher than\ 23 dBm .sp 1P .RT .ad b .RT .sp 2P .LP \fB10\fR \fBSignal\(hyto\(hycrosstalk ratio\fR \fB between the two\fR \fBtransmission directions in the station with 52\ dB gain at\fR \fB252\ kHz\fR \v'3p' .sp 1P .RT .ad r \(em for 100% combinations greater than 87\ dB \(em for 75% combinations greater than 95\ dB .ad b .RT .sp 2P .LP \fB11\fR \fBPower feeding\fR .sp 1P .RT .PP Up to 12\ unattended repeater stations are placed between the attended repeater stations. Direct current power is fed to six stations on each side of the attended repeater station by an earth\(hywire system, the repeaters of a system on the power\(hyfeed section being inserted in series in a power circuit. .PP If the induced outside voltages are more than 75\ volts, the supply can be 2\(hywire without earth return and the number of unattended repeater stations on the section between the two attended repeater stations should not exceed\ six. The maximum power\(hyfeed is\ 500\ volts. .bp .PP As far as the effect of induced voltages, raising of the earth potential in the neighbourhood of electric installations, and surges due to lightning is concerned, see K\(hyseries Recommendations. .RT .LP .sp 2P .LP \fB12\fR \fBRemote control of repeaters\fR .sp 1P .RT .PP In this system the efficiency of the repeater is checked from the amplification and nonlinearity attenuation in the frequency combination of 2\fIf\fR\d1\u\ \(em\ \fIf\fR\d2\u. \v'6p' .RT .sp 2P .LP \fBRecommendation\ G.324\fR .RT .sp 2P .ce 1000 \fBGENERAL\ CHARACTERISTICS\ FOR\ \fR \fBVALVE\(hyTYPE\ SYSTEMS\fR .EF '% Fascicle\ III.2\ \(em\ Rec.\ G.324'' .OF '''Fascicle\ III.2\ \(em\ Rec.\ G.324 %' .ce 0 .sp 1P .ce 1000 \fBON\ SYMMETRIC\ CABLE\ PAIRS\fR .ce 0 .sp 1P .ce 1000 (For the text of this Recommendation, see Vol. III .sp 9p .RT .ce 0 .sp 1P .ce 1000 of the \fIOrange Book\fR , Geneva, 1976.) \v'6p' .ce 0 .sp 1P .sp 2P .LP \fBRecommendation\ G.325\fR .RT .sp 2P .ce 1000 \fBGENERAL\ CHARACTERISTICS\ RECOMMENDED\ FOR\ \fR \fBSYSTEMS\fR .EF '% Fascicle\ III.2\ \(em\ Rec.\ G.325'' .OF '''Fascicle\ III.2\ \(em\ Rec.\ G.325 %' .ce 0 .ce 1000 \fBPROVIDING\ 12\ TELEPHONE\ CARRIER\ CIRCUITS\ ON\ A\fR .ce 0 .sp 1P .ce 1000 \fBSYMMETRIC\ CABLE\ PAIR\ [(12\ +\ 12)\ SYSTEMS]\fR .ce 0 .sp 1P .PP Systems of the (12\ +\ 12) type on symmetric pair in cable are used for carrier working either on old deloaded cables or on cables specially constructed for the purpose (without a second cable being required). These systems may be used in regional or local relations, or in long\(hydistance relations, trunk or international. .sp 1P .RT .LP .PP This Recommendation applies to systems for long\(hydistance relations making use of the kinds of cable at present recommended by the CCITT (see Recommendation\ G.611) and to multiple\(hytwin quad cables with conductors of 0.9\ mm diameter, with an effective capacitance of 35 to 40\ nF/km or other kinds of deloaded cables of equivalent quality. For systems used for local or regional relations, some clauses of the present Recommendation may be made less stringent. .sp 2P .LP \fB1\fR \fBFrequency spectrum transmitted to line\fR .sp 1P .RT .PP The CCITT recommends that the line\(hyfrequency spectrum should be in accordance with Scheme\ 1 or\ 2 of Figure\ 1/G.325. .RT .LP .rs .sp 16P .ad r \fBFigure 1/G.325, p.\fR .sp 1P .RT .ad b .RT .LP .bp .PP Administrations concerned in setting up such an international system should agree to use either one or the other of the two schemes. .sp 2P .LP \fB2\fR \fBLine\(hyregulating pilots\fR .sp 1P .RT .PP The following frequencies are recommended: .RT .LP \(em with Scheme\ 1:\ 60\ kHz and 72\ kHz; .LP \(em with Scheme\ 2:\ 54\ kHz and 60\ kHz. .PP The recommended accuracy is \(+- | \ Hz for the 60\(hykHz pilot. The frequency tolerance for other pilots will be decided by agreement between the Administrations concerned. .PP All these pilots should be transmitted at power level of \(em15\ dBm0. .RT .sp 2P .LP \fB3\fR \fBHypothetical reference circuit for (12\ +\ 12) symmetric\(hypair system\fR .sp 1P .RT .PP This is 2500\ kilometres long, and for each direction of transmission comprises a total of: .RT .LP \(em three channel translation pairs; .LP \(em nine special translation pairs translating a basic group into the band transmitted to line, and vice versa. .PP This circuit is carried on a (12\ +\ 12) symmetric\(hypair system in cable, with pairs assumed to be of conductors of 0.9\(hymm diameter, with an effective capacitance of 35 to 40\ nF/km. .PP Figure\ 2/G.325 shows one of the three identical parts of which this hypothetical reference circuit is made up. All in all, it has 18\ homogeneous sections, each 140\ kilometres long. .RT .LP .rs .sp 18P .ad r \fBFigure 2/G.325, p.\fR .sp 1P .RT .ad b .RT .PP \fINote\ 1\fR \ \(em\ There are only half as many translation pairs as there are homogeneous sections, because one of the two bands transmitted to line corresponds to a basic group (see Figure\ 2/G.325). .PP \fINote\ 2\fR \ \(em\ With systems using frequency\(hyfrogging in the repeaters, the appropriate modulators form part of the high\(hyfrequency line. .RT .sp 2P .LP \fB4\fR \fBDesign objectives for\fR \fBcircuit noise\fR .sp 1P .RT .PP The objectives set forth in Recommendation\ G.222 apply to the hypothetical reference circuit for symmetric\(hypair (12\ +\ 12) systems, in the circumstances described in Recommendation\ G.223. .PP In practice, it will suffice to check by calculation that the mean psophometric power at the end of every telephone channel as defined by the hypothetical reference circuit, at zero relative level, does not exceed 10 | 00\ pW0p during any hour. .bp .PP Provisonally, it is recommended that this overall limit be apportioned between the total noise components as follows: .RT .ad r \(em line noise (including noise due to special translation equipment) 9000\ pW0p \(em noise due to channel translating equipment 1000\ pW0p .ad b .RT .PP Apportionment of total noise inherent in the system among: .LP \(em basic noise, .LP \(em intermodulation noise, .LP \(em noise due to crosstalk, .LP is left entirely to the discretion of the carrier system designer, up to 1000\ pW0p for channel translating equipment and 9000\ pW0p for the line. .PP \fINote\fR \ \(em\ In accordance with all recommendations on cable systems in the Series\ G Recommendations, the design objective as regards noise power does not take into consideration noise from external sources; it is assumed that this is negligible compared with the figure of 10 | 00\ pW0p. .PP With regard to real circuits, Administrations must take whatever steps are required in each individual case to ensure that clicks arising on audio\(hyfrequency pairs in the same cable as a (12\ +\ 12) system and transmitted by crosstalk do not create excessive noise on the circuits of that system which may be used for international communications. .RT .sp 2P .LP \fB5\fR \fBError on the reconstituted frequency\fR .sp 1P .RT .PP The difference between a frequency sent at the origin of a homogeneous section 140\ km long (see \(sc\ 3 above and Figure\ 2/G.325) and the frequency received at the end of that section, should not exceed a figure provisionally fixed at 0.3\ Hz; this figure is the same whether there is frequency\(hyfrogging in the intermediate repeaters or not. .RT .LP .sp 2P .LP \fB6\fR \fBDirect line interconnection\fR .sp 1P .RT .PP When Administrations desire the direct line interconnection of two systems (with, of course, the same allocation of line\(hytransmitted frequencies) it is recommended that each of these systems should meet the following requirements on the interconnection section (except where agreed otherwise between the Administrations concerned): .RT .LP These values apply to low\(hygain systems. They are not valid for high\(hygain systems, i.e.\ for systems whose gain is substantially above 30\ dB. .FE 1) Relative level per channel, at all frequencies, at the output of the frontier repeaters: \(em15\ dBr . .LP 2) Attenuation of the frontier elementary cable section at the highest frequency transmitted to line: 25\ dB . .LP \fINote\fR \ \(em\ For composite cables, agreement should be reached between the two Administrations concerned to fix the attenuation of the frontier section in such a way that the repeaters of the symmetric pairs and those of the coaxial cables can be housed in the same frontier stations. .LP 3) Matching of the impedances of the frontier repeaters and the line. The modulus of the return\(hycurrent coefficient between the input (or output) impedance of a repeater and the characteristic impedance of the line should not exceed the lower of the two values: \v'6p' .sp 1P .ce 1000 0.15 @ sqrt { { \fIf\fR~\d\fImax.\fR~\u } over { fIf\fR } } @ or 0.25 .ce 0 .sp 1P .LP .sp 2 .bp .sp 2P .LP \fB7\fR \fBInterconnection in a main station\fR .sp 1P .RT .PP If such interconnection is necessary, either for operating reasons or because the two systems to be interconnected use different allocations of frequencies transmitted to line, one of the following procedures may be followed: .RT .LP 1) interconnection at a group distribution frame, with use of the basic group, levels and impedance applied normally by the Administration to which the frame belongs; .LP 2) direct interconnection between the two systems. If they use different allocations of frequencies transmitted to line, the two Administrations concerned shall reach agreement on which of them shall install the necessary demodulators (the line of separation between the two types of equipment will then be CC` or DD` on Figure\ 3/G.325). .LP .rs .sp 30P .ad r \fBFigure 3/G.325, p.\fR .sp 1P .RT .ad b .RT .PP In the absence of such an agreement, each incoming system must comprise equipment required for the outgoing system, in each direction of transmission (the separating line in Figure\ 3/G.325 would then be the oblique DC`). .PP Unless there is a specific agreement, the relative power level will be \(em36\ dBr at sending (input of each system\ \(em\ points\ C` and\ D in the case of Figure\ 3/G.325). The points considered do not correspond to points\ \fIT\fR and\ \fIT\fR ` defined in Recommendation\ G.213. In particular, a translating equipment of any type cannot be connected to it without precautionary measures (see the levels indicated in the Table\ 1/G.233). .PP By agreement between Administrations, interconnection can be effected as indicated in Figure\ 4/G.325, a method whereby it is possible to replace three modulators by one. .bp .RT .LP .rs .sp 38P .ad r \fBFigure 4/G.325, p.\fR .sp 1P .RT .ad b .RT .sp 2P .LP \fB8\fR \fBEssential clauses for a model specification\fR .sp 1P .RT .PP See Recommendation G.326. .RT .sp 2P .LP \fBRecommendation\ G.326\fR .RT .sp 2P .sp 1P .ce 1000 \fBTYPICAL\ SYSTEMS\ ON\ SYMMETRIC\ CABLE\ PAIRS\ [(12\ +\ 12)\ SYSTEMS]\fR .EF '% Fascicle\ III.2\ \(em\ Rec.\ G.326'' .OF '''Fascicle\ III.2\ \(em\ Rec.\ G.326 %' .ce 0 .sp 1P .PP This Recommendation defines typical systems using one symmetric cable pair for the two directions of transmission. These systems must meet the requirements set forth in Recommendation\ G.325. They have been defined for the benefit of Administrations which do not themselves study specifications for the supply of cables and equipment. They must not be considered as .sp 1P .RT .LP recommended by the CCITT in preference to other systems which would also meet the requirements of Recommendation\ G.325. Administrations and manufacturers which contemplate designing such systems are asked to adhere, as far as possible, to the characteristics of one of the typical systems defined below. .bp .PP The following abbreviations will be used: .LP \(em A: low\(hygain systems; .LP \(em B: high\(hygain systems without frequency\(hyfrogging; .LP \(em C: high\(hygain systems with frequency\(hyfrogging in each line repeater. .sp 2P .LP \fB1\fR \fBGeneral characteristics\fR .sp 1P .RT .sp 1P .LP 1.1 \fIRelative levels\fR .sp 9p .RT .PP Crosstalk restricts the gain of low\(hygain systems to about 30\ dB. Furthermore, the exact length of an elementary cable section is often determined with respect to a loading step. The result is a maximum attenuation of about 27\ to 30\ dB, for an elementary cable section and a repeater output level of \(em10\ to \(em13\ dBr, at least in the upper frequency band transmitted to line. .PP In high\(hygain systems, frequency\(hyfrogging is in general use, with or without pre\(hyemphasis; in this case, the siting of the loading coils has no effect on the placing of repeaters. Typical values are: 56\ to 60\ dB, attenuation for an elementary cable section and either 0\ dBr or +7\ dBr as the repeater output level for systems without frequency\(hyfrogging, or with frequency\(hyfrogging but without pre\(hyemphasis. Other values are applicable for systems with frequency\(hyfrogging and with pre\(hyemphasis. .RT .sp 1P .LP 1.2 \fIMatching of repeater and line impedances\fR .sp 9p .RT .PP The same values are applied in a normal section as those recommended for a frontier section in Recommendation\ G.325, \(sc\ 6. .RT .sp 2P .LP \fB2\fR \fBCharacteristics of \fR \fBrepeaters\fR .sp 1P .RT .sp 1P .LP 2.1 \fINonlinear distortion\fR .sp 9p .RT .PP The harmonic margin and intermodulation products are not less than the figures in Table\ 1/G.326. .RT .LP .rs .sp 18P .ad r \fBTable 1/G.326 T1.326, p.\fR .sp 1P .RT .ad b .RT .LP .bp .sp 1P .LP 2.2 \fINoise factor\fR .sp 9p .RT .PP The noise factor of a complete repeater (including the equalizers or other passive networks, if any) should not exceed 10\ dB at the highest frequencies transmitted. .PP \fINote\fR \ \(em\ In low\(hygain systems, this figure is not critical and may be exceeded. .RT .sp 1P .LP 2.3 \fIOverload point\fR .sp 9p .RT .PP See \(sc 6 of Recommendation G.223. .RT .sp 1P .LP 2.4 \fICrosstalk ratio repeaters in the same station\fR .sp 9p .RT .PP The crosstalk ratio between repeaters in the same station should not be less than: .RT .LP a) 82\ dB in type\ A systems, .LP b) 80\ dB in type\ B and C systems. .PP These values are valid for all the equipment at the repeater station, from the input transformer to the output transformer. .LP .sp 2P .LP \fB3\fR \fBTypes of cable used\fR (formerly Part\ C) .sp 1P .RT .PP (12\ +\ 12) systems can be established: .RT .LP 1) on deloaded old cables, or .LP 2) on new cables, comprising quads reserved for high\(hyfrequency operation. .PP The equipments defined in this Recommendation may be used on both types of cable, but when they are used on deloaded old cables there are other conditions which should be met, apart from those indicated in this Recommendation. In particular, if the disturbance caused by other pairs in the same cable is too great, the noise objectives in Recommendation\ G.325, \(sc\ 4, cannot be achieved. .sp 2P .LP \fBReference\fR .sp 1P .RT .LP [1] CCITT Definition: \fIn\fR , Vol.\ X, (Terms and Definitions). \v'2P' .sp 2P .LP \fBRecommendation\ G.327\fR .RT .sp 2P .ce 1000 \fBVALVE\(hyTYPE\ SYSTEMS\ OFFERING\ 12\ CARRIER\ TELEPHONE\ CIRCUITS\fR .EF '% Fascicle\ III.2\ \(em\ Rec.\ G.327'' .OF '''Fascicle\ III.2\ \(em\ Rec.\ G.327 %' .ce 0 .sp 1P .ce 1000 \fBON\ A\ SYMMETRIC\ CABLE\ PAIR\ [(12\ +\ 12)\ SYSTEMS]\fR .ce 0 .sp 1P .ce 1000 (For the text of this Recommendation, see Vol.\ III .sp 9p .RT .ce 0 .sp 1P .ce 1000 of the Orange Book, Geneva,\ 1976.) .ce 0 .sp 1P .IP \fB3.3\ \ \fR \fBCarrier systems on 2.6/9.5 mm coaxial cable pairs\fR .sp 1P .RT .PP The Recommendations of this sub\(hysection relate to systems established on 2.6/9.5\ mm coaxial cable pairs in conformity with Recommendation\ G.623. The following Table gives a list of these systems with a summary of their characteristics. .bp .sp 1P .RT .ce \fBH.T. [T1.327]\fR .ce TABLE\ 1/G.327 .ps 9 .vs 11 .nr VS 11 .nr PS 9 .TS center box; lw(36p) | lw(35p) | lw(29p) | lw(35p) | lw(29p) | lw(35p) | lw(29p) . .TE .nr PS 9 .RT .ad r \fBTable 1/G.327 [T1.327] + REMARQUES, p.\fR .sp 1P .RT .ad b .RT .sp 2P .LP \fBRecommendation\ G.332\fR .RT .sp 2P .sp 1P .ce 1000 \fB12 MHz\ SYSTEMS\ ON\ STANDARDIZED\ 2.6/9.5 mm\ COAXIAL\ CABLE\ PAIRS\fR .EF '% Fascicle\ III.2\ \(em\ Rec.\ G.332'' .OF '''Fascicle\ III.2\ \(em\ Rec.\ G.332 %' .ce 0 .sp 1P .ce 1000 \fI(Mar del Plata, 1968; amended at Geneva,\ 1980)\fR .sp 9p .RT .ce 0 .sp 1P .PP This Recommendation defines a coaxial cable system providing 2700 telephony channels in the frequency band 0.3\ MHz to about 12.4\ MHz which, according to the provisions of Recommendation\ J.73\ [1], can alternatively be used to provide 1200 telephone channels in the frequency band 0.3\ MHz to about 5.6\ MHz and one TV\(hychannel in the band of about 6\ MHz to 12.3\ MHz for the transmission of a vestigial sideband television signal with an effectively transmitted video\(hyfrequency band up to 5.5\ MHz. The repeaters should be spaced at about 4.5\ km. .sp 1P .RT .LP .sp 2P .LP \fB1\fR \fBArrangement of line frequencies for telephony\fR .sp 1P .RT .PP The arrangement of the line frequencies for telephony shall conform to Plans\ 1A, 1B or\ 2 described below. Plan\ 1A is to be preferred to Plan\ 1B. In international relations between countries using different modulation procedures (see Recommendation\ G.211) and in the absence of any special arrangement between the Administrations concerned including, if necessary, the Administrations of transit countries, Plans\ 1 are to be preferred to Plan\ 2. .RT .sp 1P .LP 1.1 \fIFrequency arrangement of Plan\ 1A\fR .sp 9p .RT .PP Plan\ 1A uses the first modulation procedure described in Recommendation\ G.211. .PP The telephone channels should first be assembled into basic supermastergroups. Three supermastergroups are transmitted to line in accordance with the frequency arrangement of Figure\ 1/G.332. .PP In this figure the virtual carrier frequencies of the two lower supermastergroups are shown. .bp .RT .sp 2P .LP 1.2 \fIFrequency arrangement of Plan\ 1B\fR .sp 1P .RT .LP .sp 1P .LP \fIFrequencies below 4287\ kHz\fR .sp 9p .RT .PP For frequencies below 4287\ kHz, Plan\ 1B uses the second modulation procedure described in Recommendation\ G.211. .PP The telephone channels should first be assembled into supergroups. Fifteen supergroups are transmitted to line in accordance with the frequency arrangement of Figure\ 2/G.332 (frequencies below 4287\ kHz). These fifteen supergroups comprise the basic 15\(hysupergroup assembly\ (No.\ 1) described in Recommendation\ G.233; the carrier frequencies are shown in that Recommendation. Figure\ 3/G.332 gives further details of the frequency arrangement below 4287\ kHz. .RT .sp 1P .LP \fIFrequencies above 4287\ kHz\fR .sp 9p .RT .PP For frequencies above 4287\ kHz, Plan\ 1B uses the first modulation procedure described in Recommendation\ G.211. .PP For frequencies above\ 4287\ kHz, the frequency arrangement of Figure\ 2/G.332 is identical with that of Figure\ 1/G.332. .RT .LP .rs .sp 15P .ad r \fBFigure 1/G.332, p.\fR .sp 1P .RT .ad b .RT .LP .rs .sp 10P .ad r \fBFigure 2/G.332, p.\fR .sp 1P .RT .ad b .RT .LP .rs .sp 7P .ad r \fBFigure 3/G.332, p.\fR .sp 1P .RT .ad b .RT .LP .bp .sp 1P .LP 1.3 \fIFrequency arrangement of Plan\ 2\fR .sp 9p .RT .PP This plan uses the second modulation procedure described in Recommendation\ G.211. .PP The telephone channels should be assembled into basic (No.\ 1) 15\(hysupergroup assemblies. Three 15\(hysupergroup assemblies are transmitted to line in accordance with the frequency arrangement shown in Figure\ 4/G.332. In this figure, the virtual carrier frequencies of 15\(hysupergroup assemblies Nos.\ 2 and\ 3 are shown. .RT .LP .sp 2P .LP \fB2\fR \fBPilots\fR \fBand additional measuring frequencies\fR .sp 1P .RT .sp 1P .LP 2.1 \fILine\(hyregulating pilots\fR .sp 9p .RT .PP The CCITT recommends that 12 | 35\ kHz be used for the main line\(hyregulating pilot. .PP In any regulated\(hyline section crossing a frontier, it is recommended that in both directions of transmission the Administration on the sending side should permanently transmit one or two auxiliary line\(hyregulating pilots at 308\ and/or 4287\ kHz, at the choice and request of the Administration on the receiving side so as to provide for additional regulation, for example. .PP The frequency accuracy recommended for the pilots is \(+- | \ \(mu\ 10\uD\dlF261\u5\d. .PP The power level of the main and auxiliary line\(hyregulating pilots should be adjusted at the point of injection to have a value of \(em10\ dBm0. The harmonics of the 308\ and 4287\ kHz pilot should each have a level not higher than \(em70\ dBm0. .PP Equipment should be designed in such a way that these pilots may be blocked at the end of a regulated\(hyline section, so that their level shall be at least 40\ dB below that of the pilots used on other sections. .RT .LP .rs .sp 25P .ad r \fBFigure 4/G.332, p.\fR .sp 1P .RT .ad b .RT .LP .bp .PP The following tolerances for the level of these pilots are recommended: .LP 1) The design of equipment should be such as to allow the error in the level of any pilot as transmitted, due to finite level adjustment steps, to be kept within \(+- | .1\ dB. .LP 2) The change in output level of the pilot generator with time (which is a factor included in equipment specifications) must not exceed \(+- | .3\ dB during the interval between two maintenance adjustments, e.g.\ in one month. .LP 3) To reduce pilot level variations with time, it is advisable to have a device to give an alarm when the variation at the generator output exceeds \(+- | .5\ dB, the zero of the warning device being aligned as accurately as possible with the lining\(hyup level of the transmitted pilot. .LP .PP The attention of Administrations is drawn to the difficulty which could result from an appreciable reduction in the absolute power level of the pilot sent to line; such a reduction is liable to cause \*Qnear singing\*U, resulting from the operation of the automatic gain\(hycontrol amplifiers. It would be desirable to make arrangements for overcoming this difficulty if it should arise. .PP \fINote\fR \ \(em\ When pre\(hyemphasis and de\(hyemphasis is applied on the line link, it is necessary to define the line pilot level with reference to a point, possibly hypothetical, at the input to or output from the line, at which the relative levels of all telephone channels are equal over the whole of the line\(hyfrequency band. When a part of the line\(hyfrequency band is to be used to provide a television channel, different pre\(hyemphasis and de\(hyemphasis networks may be required but this will not affect the definition of line pilot levels. Figures\ 5/G.332 and\ 6/G.332 show two hypothetical arrangements for the purpose of this definition. .RT .sp 1P .LP 2.2 \fIFrequency comparison pilots\fR .sp 9p .RT .LP .PP Administrations wishing to make an international frequency comparison shall choose the frequency\ 300, 808\ or 1552\ kHz for this purpose, when it is impossible to use 308\ or 1800\ kHz. International comparison of national standards is relatively rare. During a specified period of time, it will always be possible to use for such comparisons one of the frequencies mentioned above, even though it may normally be used as an additional measuring frequency. .RT .LP .rs .sp 20P .ad r \fBFigure 5/G.332, p.\fR .sp 1P .RT .ad b .RT .LP .bp .LP .rs .sp 21P .ad r \fBFigure 6/G.332, p.\fR .sp 1P .RT .ad b .RT .PP A frequency of 300\ kHz can be used for national comparisons when Administrations do not wish to use the 308\ kHz pilot for this purpose. In this case, it is recommended that the 300\ kHz be transmitted at a power level of \(em10\ dBm0. The harmonics of the frequency comparison pilots should each have a level not higher than \(em70\ dBm0. .LP .sp 1P .LP 2.3 \fIAdditional measuring frequencies\fR .sp 9p .RT .PP If the frequency allocation without mastergroups is used at frequencies below 4\ MHz (Figures\ 3/G.332 and\ 4/G.332), the following frequencies \fImay\fR be used for additional measuring frequencies: .RT .ce 1000 560,\ 808,\ 1056,\ 1304,\ 1552,\ 1800,\ 2048,\ 2296, .ce 0 .sp 1P .ce 1000 2544,\ 2792,\ 3040,\ 3288,\ 3536\ and\ 3784\ kHz. .ce 0 .sp 1P .PP Any Administration using 12\(hyMHz working on a line crossing a frontier should, at the request of any other Administration concerned, transmit or measure the measuring frequencies appearing in the following preferred list: .sp 1P .ce 1000 560,\ 808,\ 1304,\ 1800,\ 2296,\ 2792\ and\ 3536\ kHz. .ce 0 .sp 1P .PP Administrations should likewise transmit or measure, at the request of corresponding Administrations, any measuring frequency which may be used in other circumstances, namely: .LP \(em at frequencies below 4\ MHz, if frequency allocation with mastergroups indicated in Plan\ 1A (Figure\ 1/G.332) is used: .LP .sp 1P .ce 1000 560,\ 808,\ 1304,\ 1592\ and\ 2912\ kHz; .ce 0 .sp 1P .LP \(em at frequencies above 4\ MHz, if Plan\ 1A (Figure\ 1/G.332) or\ 1B (Figure\ 2/G.332) is used: .sp 1P .ce 1000 5608,\ 6928,\ 8248 .FS A frequency of 8248\ kHz can be used as a radio\(hyrelay link line\(hyregulating pilot. In such a case, the precautions shown in Recommendation\ G.423 should be applied. .FE ,\ 8472,\ 9792\ and\ 11 | 12\ kHz. .ce 0 .sp 1P .PP Plan\ 2 (Figure\ 4/G.332) is used under the conditions described in Recommendation\ G.211 for the application of the second modulation process, the additional frequencies above 4\ MHz are: .LP 5392,\ 7128,\ 8248,\ 8472,\ 8864,\ 9608\ and\ 11 | 44\ kHz. .bp .sp 1P .ce 1000 .ce 0 .sp 1P .PP All these frequencies are recapitulated in Table\ 1/G.332. .LP .rs .sp 22P .ad r \fBTable 1/G.332 T1.332, p.\fR .sp 1P .RT .ad b .RT .PP The absolute frequency variation of additional measuring frequencies below 4\ MHz should never be outside limits of \(+- | 0\ Hz from their nominal value. For frequencies above 4\ MHz, the relative frequency variation referred to the nominal value should never exceed \(+- | \ \(mu\ 10\uD\dlF261\u5\d. .PP The power level .FS The Note of \(sc\ 2.1 still applies. .FE of the additional measuring frequencies should be adjusted at the point of injection to have a value of \(em10\ dBm0. The harmonics of additional measuring frequencies below 6\ MHz should each have a level at this point not higher than \(em70\ dBm0. .PP The additional measuring frequencies should not be permanently transmitted. They will only be transmitted for as long as is necessary for actual measurement purposes. .PP Arrangements should be made in equipment for the 12\(hyMHz system, so that the 308\(hykHz line\(hyregulating pilot is protected from disturbances from a pilot or additional measuring frequency of the same frequency coming from a 4\(hyMHz system when this protection is not already provided by the equipment of the 4\(hyMHz system. .PP \fINote\fR \ \(em\ Some Administrations use new manual or automatic methods of equalizing attenuation distortion, e.g.\ equalizers based on the Cosine function, using frequencies which do not appear in the list of additional measuring frequencies recommended by the CCITT. .PP Obviously, no additional measuring frequency which might leave the national network should be sent at the same frequency as one of the pilots recommended by the CCITT. .RT .sp 2P .LP \fB3\fR \fBHypothetical reference circuit\fR .sp 1P .RT .PP This hypothetical reference circuit is 2500\ km long and is divided into nine sections of 280\ km each. The three line frequency arrangement plans recommended in \(sc\ 1 require modulation stages of different number to carry a voice signal in the line frequency position. This is bound to affect the constitution of the hypothetical reference circuit. In these circumstances, the CCITT recommends the hypothetical reference circuits represented in Figures\ 7/G.332 and\ 8/G.332. .bp .RT .sp 1P .LP 3.1 \fIHypothetical reference circuit for the Plans 1A and 1B frequency\fR \fIallocations\fR .FS In the case of plan 1B, this hypothetical reference circuit is not valid for the frequency band\ 312\(hy4028\ kHz. .FE .sp 9p .RT .LP .PP This is shown in Figure 7/G.332. It has, for each direction of transmission, a total of: .RT .LP \(em two pairs of channel modulators, each pair including translation from the audio\(hyfrequency band to the basic group and vice versa; .LP \(em three pairs of group modulators, each pair including translation from the basic group to the basic supergroup and vice versa; .LP \(em five pairs of supergroup modulators, each pair including translation from the basic supergroup to the the basic mastergroup and vice versa; .LP \(em seven pairs of mastergroup modulators, each pair including translation from the basic mastergroup to the basic supermastergroup and vice versa; .LP \(em nine pairs of mastergroup modulators, each pair including translation from the basic mastergroup to the frequency band transmitted on the coaxial cable and vice versa. .LP .rs .sp 10P .ad r \fBFigure 7/G.332, p.\fR .sp 1P .RT .ad b .RT .sp 1P .LP 3.2 \fIHypothetical reference circuit for the Plan 2 frequency allocation\fR .sp 9p .RT .PP This is shown in Figure 8/G.332. It has, for each direction of transmission, a total of: .RT .LP \(em two pairs of channel modulators, each pair including translation from the audio\(hyfrequency band to the basic group and vice versa; .LP \(em three pairs of group modulators, each pair including translation from the basic group to the basic supergroup and vice versa; .LP \(em six pairs of supergroup modulators, each pair including translation from the basic supergroup to the the basic 15\(hysupergroup assembly and vice versa; .LP \(em nine pairs of 15\(hysupergroup modulators, each pair including translation from the basic 15\(hysupergroup assembly to the frequency band transmitted on the coaxial cable and vice versa. .LP .rs .sp 10P .ad r \fBFigure 8/G.332, p.\fR .sp 1P .RT .ad b .RT .LP .bp .sp 2P .LP \fB4\fR \fBDesign objectives for\fR \fBcircuit noise\fR .sp 1P .RT .PP The objectives given in Recommendation\ G.222 are applicable to the hypothetical reference circuit for 12\(hyMHz systems on coaxial cable, in the circumstances indicated in Recommendation\ G.223. .PP In practice, it is sufficient to check for each telephone channel as defined by the hypothetical reference circuit, that the mean psophometric power at the end of the channel referred to a zero relative level point does not exceed 10 | 00\ pW0p during any period of one hour. .PP The subdivision of the total noise between basic noise and intermodulation noise is left entirely to the designer of the system, within the limits of 2500\ pW0p for the terminal equipment and 7500\ pW0p for the line. .RT .sp 2P .LP \fB5\fR \fBMatching of the impedance of a coaxial pair and the impedances\fR \fBof the repeaters\fR .sp 1P .RT .LP \fIZ\fR\d\fIL\fR\u is the characteristic impedance of the line (for any frequency\ \fIf\fR effectively transmitted), this impedance being the ordinate for the frequency\ \fIf\fR of a smooth curve, agreed by the Administrations concerned as being representative of the average impedance/frequency characteristic of the type of coaxial cable concerned; .LP \fIZ\fR\d\fIR\fR\u is the worst value of the input impedance (for the frequency\ \fIf\fR ) of the equipment of a repeater station, as seen from the line (see Figure\ 9/G.332); .LP Z\fI\d\fIE\fR\u is the worst value of the output impedance (for the frequency\ \fIf\fR ) of the equipment of a repeater station, as seen from the line; .LP \fIA\fR \ = \fIal\fR the total image attenuation (at the frequency\ \fIf\fR ) of the line between two adjacent repeater stations, \fIa\fR \ being the average attenuation of the coaxial cable per unit length and\ \fIl\fR the average length between two adjacent repeater stations. .LP .rs .sp 9P .ad r \fBFigure 9/G.332, p.\fR .sp 1P .RT .ad b .RT .PP Then the factor\ \fIN\fR is defined by the formula: \v'6p' .sp 1P .ce 1000 \fIN\fR = 2 \fIA\fR + 20 log \d10 \u @ left | { fIZ~\dE\u\fR~+~\fIZ~\dL\u\fR } over { fIZ~\dE\u\fR~\(em~\fIZ~\dL\u\fR } right | @ + 20 log \d10 \u @ left | { fIZ~\dL\u\fR~+~\fIZ~\dR\u\fR } over { fIZ~\dL\u\fR~\(em~\fIZ~\dR\u\fR } right | @ \ \ (dB) .ce 0 .sp 1P .PP .sp 1 The present Recommendation refers only to 12\(hyMHz systems on 2.6/9.5\(hymm coaxial pairs having repeaters with a nominal spacing of about 4.5\ km. .PP The sum\ \fIN\fR of the three terms defined above must in this case be equal to at least 48\ dB at 300\ kHz and to at least 55\ dB at all frequencies above 800\ kHz. Between 300\ and 800\ kHz the permissible limit in decibels varies linearly with the frequency. .PP \fINote\fR \ \(em\ The CCITT has defined the permissible limits for\ \fIN\fR , as a sum of the three terms (see the above formula). It is recommended that Administrations concerned with a coaxial cable section crossing a frontier should agree on permissible values in this particular case for each of these three terms to meet the above condition, that is to say, agree on the use of as good a match as possible or of a methodical mismatch at the ends of the repeater section. .bp .RT .sp 2P .LP \fB6\fR \fBRelative levels and interconnection in a frontier section\fR .sp 1P .RT .sp 1P .LP 6.1 \fIInterconnection in a frontier section\fR .sp 9p .RT .PP In an elementary cable section which crosses a frontier, the relative level at the input of the cable section (output of the repeater equipment) should be equal to \(em13\ dBr at 12 | 35\ kHz. .PP \fINote\ 1\fR \ \(em\ This recommendation is based on the assumption that the attenuation in the frontier section is approximately 37\ to 38\ dB. This should be taken into consideration in determining the actual length of the frontier section. .PP \fINote\ 2\fR \ \(em\ When the pre\(hyemphasis curves of the two systems are different, Recommendation\ G.352 should be applied. .RT .LP .sp 1P .LP 6.2 \fIRelative levels in any elementary cable section\fR .sp 9p .RT .PP It has not been possible to standardize a single value. .RT .sp 1P .LP 6.3 \fIPre\(hyemphasis\fR .sp 9p .RT .PP From the information supplied by various Administrations, the pre\(hyemphasis generally lies between\ 9 and\ 12\ dB. .RT .sp 2P .LP \fB7\fR \fBPower\(hyfeeding and alarm systems\fR .sp 1P .RT .sp 1P .LP 7.1 \fIPower feeding across a frontier\fR .sp 9p .RT .sp 1P .LP 7.2 \fIPower\(hyfeeding systems\fR .sp 9p .RT .PP The text of Recommendation\ G.341, \(sc\(sc\ 7.1 and 7.2, applicable to all 1.2/4.4\(hymm pair systems, still applies for 12\(hyMHz transistor systems on 2.6/9.5\(hymm pairs. .RT .sp 1P .LP 7.3 \fISupervision and alarms in a frontier section\fR (see Annex\ A) .sp 9p .RT .sp 2P .LP \fB8\fR \fBUse of\fR \fB12 MHz systems for television transmission\fR .sp 1P .RT .sp 1P .LP 8.1 \fIGeneral\fR .sp 9p .RT .PP This \(sc summarizes all the additional conditions recommended for the transmission of television on a 12\ MHz system. The characteristics of the television signal are discussed in Recommendation\ J.73\ [1]. .RT .LP .sp 1P .LP 8.2 \fICircuit noise\fR .sp 9p .RT .PP When a 12 MHZ system is used for a television transmission on the basis of a hypothetical reference circuit 2500\ km in length, the mean value of the thermal line noise should not exceed 1\ pW0p/km. Experience has shown that a mean value of 1.5\ pW0p/km for the total line noise is sufficient when the noise is measured in normal telephony conditions. .RT .sp 1P .LP 8.3 \fIMatching of repeater and line impedance\fR .sp 9p .RT .PP For the transmission of a television programme, it is recommended that number \fIN\fR defined in \(sc\ 5 of the present Recommendation should be at least 70\ dB in the band occupied by the television signal. .RT .sp 1P .LP 8.4 \fIArrangement of frequencies transmitted in line\fR .sp 9p .RT .PP The 12 MHz system provides a television channel and 1200 telephone channels. Figure\ 10/G.332 shows the frequency arrangement recommended for television transmission. The television channel is capable of transmitting the signals of all television systems defined by the CCIR with a video bandwidth not exceeding\ 5.5\ MHz. .bp .RT .LP .rs .sp 29P .ad r \fBFigure 10/G.332, p.\fR .sp 1P .RT .ad b .RT .ce 1000 ANNEX\ A .ce 0 .ce 1000 (to Recommendation G.332) .sp 9p .RT .ce 0 .ce 1000 \fBFrequencies used for supervision or fault location\fR .sp 1P .RT .ce 0 .PP The frequencies or frequency bands used in various countries for supervising or for locating faults are given in Table\ A\(hy1/G.332 for information. .sp 1P .RT .ce \fBH.T. [T2.332]\fR .ce TABLE\ A\(hy1/G.332 .ps 9 .vs 11 .nr VS 11 .nr PS 9 .TS center box; cw(60p) | cw(102p) . Country Band (kHz) _ .T& lw(60p) | lw(102p) . Belgium { 280 and 12 | 00 and 170 to 210 for regulation } .T& lw(60p) | lw(102p) . Japan 13 | 00 to 13 | 80 .T& lw(60p) | lw(102p) . France 12 | 00 to 12 | 00 .T& lw(60p) | lw(102p) . Netherlands { 280 and 170 to 210 for regulation } .T& lw(60p) | lw(102p) . F.R. of Germany 269 and (13 | 00 \(+- | 5) .T& lw(60p) | lw(102p) . United Kingdom 13 | 00 + 12,5 .T& lw(60p) | lw(102p) . Sweden 12 | 00 to 13 | 00 _ .TE .nr PS 9 .RT .ad r \fBTable A\(hy1/G.332 [T2.332], p.\fR .sp 1P .RT .ad b .RT .LP .bp .PP \fINote\fR \ \(em\ A fault\(hytracing system was used by the Chile Telephone Company using direct currents transmitted over interstitial pairs of the cable, which obviates any risk of interference with the systems mentioned above. .sp 2P .LP \fBReference\fR .sp 1P .RT .LP [1] CCITT Recommendation \fIUse of a 12\(hyMHz system for the simultaneous\fR \fItransmission of telephony and television\fR , Vol.\ III, Rec.\ J.73. \v'6p' .LP .sp 2P .LP \fBRecommendation\ G.333\fR .RT .sp 2P .sp 1P .ce 1000 \fB60\ MHz\ SYSTEMS\ ON\ STANDARDIZED\ 2.6/9.5\ mm\ COAXIAL\ CABLE\ PAIRS\fR .EF '% Fascicle\ III.2\ \(em\ Rec.\ G.333'' .OF '''Fascicle\ III.2\ \(em\ Rec.\ G.333 %' .ce 0 .sp 1P .LP \fBIntroduction\fR .sp 1P .RT .PP This Recommendation defines a coaxial cable pair system providing 10 | 00 telephone channels in the frequency band of approximately 4\ to 60\ MHz. The system may be used for the transmission of six television signals without any telephone signal or for a mixed transmission of telephone and television signals. The nominal repeater spacing is approximately 1.5\ km and can be obtained by dividing the repeater spacing of 12\ MHz systems by three. .RT .LP .sp 2P .LP \fB1\fR \fBLine frequencies\fR .sp 1P .RT .PP The allocation of line frequencies for telephony should be in conformity with one of the two plans given below. .RT .sp 1P .LP 1.1 \fIPlan\ 1\ \(em\ Line\(hyfrequency allocation and modulation stages for\fR \fI60\(hyMHz systems\fR (Figure\ 1/G.333) .sp 9p .RT .LP .rs .sp 17P .ad r \fBFigure 1/G.333, p.\fR .sp 1P .RT .ad b .RT .PP In this plan, the basic block for interconnection is the supermastergroup of 8516\ to 12 | 88\ kHz recommended by the CCITT in Recommendation\ G.211. It thus contains the three mastergroups constituting the basic supermastergroup, but the same frequency band could contain a 15\(hysupergroup assembly (see Plan\ 2). .bp .PP All modulation and demodulation between the basic supermastergroup and the line\(hyfrequency band is carried out in one modulation step. The carrier frequencies for this modulation are shown in Figure\ 1/G.333. They are all low multiples of 440\ kHz, or multiples of 2200\ kHz. These two fundamental frequencies are both closely related to frequencies normally used in the 12\(hyMHz systems. .PP The extraction of blocks directly from the line\(hyfrequency band can be carried out individually for the four lowest supermastergroups. Higher supermastergroups can only be extracted in the form of an assembly of four supermastergroups. This method is chosen to save frequency bandwidth. .PP The two lowest supermastergroups are identical with supermastergroups Nos.\ 2 and\ 3 shown in Figure\ 1/G.332. .RT .sp 1P .LP 1.2 \fIPlan\ 2\ \(em\ Line\(hyfrequency allocation and modulation stages for\fR \fI60\(hyMHz systems\fR (Figure\ 2/G.333) .sp 9p .RT .LP .rs .sp 17P .ad r \fBFigure 2/G.333, p.\fR .sp 1P .RT .ad b .RT .PP According to Plan\ 2, eleven assemblies of 15\ supergroups are translated into the frequency band 8620\ to 12 | 36\ kHz which lies within the frequency band of the basic supermastergroup. .PP The 15\(hysupergroup assemblies transmitted to line and numbered\ 3 to\ 13, are obtained in the same way as the corresponding supermastergroups of Plan\ 1 above. The assembly of 15\ supergroups numbered\ 2 is obtained by modulation of a 15\(hysupergroup assembly in the band 312\(hy4028\ kHz, the carrier frequency being 68\ \(mu\ 124\ =\ 8432\ kHz. .PP The facilities for extracting blocks directly from the basic\(hyfrequency band are identical to those of Plan\ 1. .PP The two lowest 15\(hysupergroup assemblies are identical with the second and third 15\(hysupergroup assemblies in Figure\ 4/G.332. .PP \fINote\fR \ \(em\ It is understood that Plan\ 1 would be chosen in those countries whose national networks are based upon the use of basic mastergroup and supermastergroups, whereas Plan\ 2 could be adopted in those countries whose national networks are based on the use of supergroup assemblies only. .PP \fR In international connections between countries using the same plan in their national networks, i.e.\ both using Plan\ 1 or both using Plan\ 2, the plan common to these two countries would naturally be used. .PP However, in international connections between countries which use different plans in their national networks and in the absence of any special agreement between the interested Administrations, including Administrations of transit countries, use of Plan\ 1 is recommended. .bp .RT .sp 2P .LP \fB2\fR \fBPilots\fR \fBand additional measuring frequencies\fR .sp 1P .RT .sp 1P .LP 2.1 \fILine\(hyregulating pilots\fR .sp 9p .RT .PP The CCITT recommends that 61 | 60\ kHz should be used for the main line\(hyregulating pilot on all regulated\(hyline sections crossing a frontier. The main line\(hyregulating pilot is used for automatic temperature correction of the cable attenuation. .PP In any regulated\(hyline section crossing a frontier, it is recommended that in both directions of transmission the Administration on the transmitting side should permanently transmit so as to provide, for example, for additional regulation, one or more auxiliary line\(hyregulating pilots chosen by the Administration on the receiving side from the following list: .RT .LP .sp 1P .ce 1000 4287\ kHz,\ 12 | 35\ kHz,\ 22 | 72\ kHz\ and\ 40 | 20\ kHz. .ce 0 .sp 1P .PP The power level of these pilots should be regulated, at the output of the transmit amplifier, to a nominal value of \(em10\ dBm0. The harmonics of the 4287, 12 | 35, 22 | 72\ kHz pilots should each have a level not higher than \(em70\ dBm0. .PP The frequency stability recommended for pilots is better than \(+- | \ \(mu\ 10\uD\dlF261\u5\d. .PP The tolerances for this level are the same as those given in Recommendation\ G.332, \(sc\ 2.1. .RT .sp 1P .LP 2.2 \fIFrequency comparison pilots\fR .sp 9p .RT .PP Since international comparison of frequencies is rarely carried out, the CCITT recommends that Administrations choose one of the following two frequencies: .RT .LP \(em 4200\ kHz, which is a multiple of 300\ kHz and a neighbouring value of 4400\ kHz, .LP \(em 8316\ kHz (27\ \(mu\ 308\ kHz) which can easily be included in the free intervals of the two frequency arrangements proposed (Figures\ 1/G.333 and\ 2/G.333). .PP It is recommended that this pilot be transmitted at a power level of \(em10\ dBm0. The harmonics of the frequency comparison pilots should each have a level not higher than \(em70\ dBm0. .sp 1P .LP 2.3 \fIAdditional measuring frequencies\fR .sp 9p .RT .PP Frequencies that may be used as additional measuring frequencies are given in Table\ 1/G.333. .PP The power level of these additional measuring pilots should be adjusted at the output of the transmit amplifier, to obtain a nominal value of the line pilot of \(em10\ dBm0. The harmonics of additional measuring frequencies below 30\ MHz should each have a level at this point not higher than \(em70\ dBm0. .PP The frequency stability recommended is better than \(+- | \ \(mu\ 10\uD\dlF261\u5\d. .PP The additional measuring pilots should not be permanently transmitted. They will be transmitted only for as long as is necessary for actual measurement purposes. This does not apply when the frequency is used as a line pilot. .RT .sp 1P .LP 2.4 \fIBand reserved for monitoring and fault\(hytracing signals\fR .sp 9p .RT .PP These signals should be below the 4200\ kHz frequencies comparison pilot. .RT .sp 2P .LP \fB3\fR \fBHypothetical reference circuit\fR .sp 1P .RT .sp 1P .LP 3.1 \fIGeneral considerations\fR .sp 9p .RT .PP The reference circuit has to reflect what is expected to be the practical application of the system. The spacing of main stations is the same as in earlier systems, e.g.\ the 12 MHz system. A length of 2500\ km, divided into 9\ sections each of 280\ km with a total of 10\ main stations, has therefore been adopted. .bp .RT .sp 1P .LP 3.2 \fIModulation\fR .sp 9p .RT .PP With either of the line\(hyfrequency allocations recommended in\ \(sc\ 1\ above, five modulation stages are generally needed to place a particular channel in its position in the line\(hyfrequency band. .PP On the above basis, the hypothetical reference circuits shown in Figures\ 3/G.333 and 4/G.333 are recommended by the CCITT. .RT .sp 1P .LP 3.3 \fIDirect through\(hyconnection at line frequencies\fR .sp 9p .RT .PP It was agreed that direct through\(hyconnection was envisaged not for points intermediate between the main stations as defined above, but rather at these stations themselves so that demodulation would be avoided. While this would be an advantage from the point of view of the amount of modulation equipment, it would involve more severe requirements on line equipment. .RT .LP .sp 1 .rs .sp 39P .ad r \fBTable 1/G.333 T1.333, p.\fR .sp 1P .RT .ad b .RT .LP .bp .LP .rs .sp 24P .ad r \fBFigure 3/G.333, p.\fR .sp 1P .RT .ad b .RT .LP .rs .sp 20P .ad r \fBFigure 4/G.333, p.\fR .sp 1P .RT .ad b .RT .LP .bp .PP It has, however, been found possible to use restricted through\(hyconnection at main repeater stations with equipment designed to meet the normal noise objectives defined in connection with a hypothetical reference circuit for the 60\(hyMHz system on coaxial pairs (see Figure\ 3/G.333) without incurring a noise penalty. .PP The necessary restrictions are as follows: .RT .LP 1) The frequency band containing supermastergroups\ 6 to\ 9 inclusive may be directly through\(hyconnected over a total length which must not exceed 830\ km, but the adjacent frequency bands in the sections concerned must be homogeneous sections which are not abnormally long. .LP 2) It is in principle also possible to use direct through\(hyconnection for the frequency band containing supermastergroups 2\(hy5\ inclusive provided that the adjacent frequency bands containing supermastergroups\ 6\(hy9 and\ 10\(hy13 are transmitted on normal length homogeneous sections. In practice it may be necessary to restrict the through\(hyconnection to supermastergroups which have a sufficiently low impedance mismatch effect (\(sc\ 7) to permit the extension without excessive accumulation of attenuation roll effect. .sp 2P .LP \fB4\fR \fBCircuit noise\fR .sp 1P .RT .PP It is recommended that the system be designed on the basis of Recommendation\ G.222, i.e.\ in such a way as to obtain a mean psophometric power of about\ 3\ pW per\ km of line, on the worst telephone channel having the same composition as the 2500\(hykm hypothetical reference circuit. .RT .sp 2P .LP \fB5\fR \fBMatching of repeater impedances and line impedance\fR .sp 1P .RT .PP A value of 65\ dB is recommended for the magnitude\ \fIN\fR defined in Recommendation\ G.332, \(sc\ 5. .RT .sp 2P .LP \fB6\fR \fBInterconnection\fR .sp 1P .RT .PP \fILevels in a main station\fR | see Recommendation\ G.213) .PP When one part of the frequency band is transmitted without demodulation, the same value of \(em33\ dBr is recommended at the output of the direct through\(hyconnection filter. .PP The level at the repeater output on the highest channel should be \(em19\ \(+-\ 1\ dBr. .PP \fINote\fR \ \(em\ Values for pre\(hyemphasis ranging from 7 to 10\ dB are commonly used. .RT .sp 2P .LP \fB7\fR \fBPower\(hyfeeding and alarm systems\fR .sp 1P .RT .sp 1P .LP 7.1 \fIPower feeding across a frontier\fR .sp 9p .RT .PP In the absence of a special agreement between the Administrations concerned with a power\(hyfeeding section crossing a frontier, it is recommended that each Administration power\(hyfeed only those repeater stations in its own country. Many Administrations used looped power\(hyfeeding on the two sides of a power\(hyfeeding station, half of each of the sections between this station and the adjacent power stations being so fed; they can close the loop at their frontier stations. Agreements will be necessary if, for example, the frontier is very far from the mid\(hypoint between the two nearest feeding stations, or if the Administrations concerned use looped power\(hyfeeding on the entire section between two feeding stations. .PP If repeater stations in a country are fed from another country, special precautions will be required to protect the staff working on the cables. .RT .sp 1P .LP 7.2 \fIRemote power\(hyfeeding systems\fR .sp 9p .RT .PP Although CCITT does not recommend the use of a specific remote power\(hyfeeding system for the 60\(hyMHz coaxial line system, in practice only the constant current d.c. feeding via the inner conductors of the two coaxial pairs of a system is used. .PP The 60\(hyMHz coaxial cable system may be subject to induced voltages and currents caused by lightning, power lines, railways, etc. .PP Precautions must be taken to protect the staff from any possible danger arising from the normal operating voltages and remote power\(hyfeed currents as well as from the induced voltages and currents. .bp .PP Many national Administrations have issued detailed rules and regulations for the protection of persons. It is obligatory in most cases to meet these rules and regulations. In addition the CCITT Directives\ [2] give guidance on these problems. .PP Precautions are also needed for the protection of the equipment against induced voltages and currents. The equipment should therefore be designed in such a way that it passes the tests specified in Recommendation\ K.17\ [3]. .RT .sp 1P .LP 7.3 \fISupervision and alarms in a frontier section\fR .sp 9p .RT .PP This should be governed by agreement between the Administrations concerned. In particular, it is necessary at the points of interconnection between two systems that if frequencies are used for monitoring or for locating faults, they be attenuated to a level of \(em50\ dBm0 on the receiving sides to prevent any disturbance to similar frequencies used in the system farther down the line. .PP \fINote\fR \ \(em\ Frequencies sent only over a system already withdrawn from service because of a fault may be selected by each Administration on the national level. .RT .sp 2P .LP \fB8\fR \fBUse of\fR \fB60\(hyMHz systems for television transmission\fR .sp 1P .RT .sp 1P .LP 8.1 \fIGeneral remarks\fR .sp 9p .RT .PP In \(sc\ 8 all additional requirements are summarized which are recommended in the case of television transmission on the 60\(hyMHz system. The characteristics of the television signal in the first intermediate frequency allocation (transmit side conditions) are dealt with in Recommendation\ J.77\ [4]. .RT .sp 1P .LP 8.2 \fICiruit noise\fR .sp 9p .RT .PP If the 60\(hyMHz system is used for television transmission on the basis of a hypothetical reference circuit (HRC) of a length of 2500\ km, the mean value of the thermal noise of the line should not exceed 1\ pW0p/km. Experience has shown that a mean value of 1.5\ pW0p/km total noise of the line is sufficient when measured according to normal telephone conditions. In making through\(hyconnections between homogeneous sections of an HRC, different transmission bands may be used. As different transmission bands give different distributions of basic noise and intermodulation noise, it seems justified to assign noise limits which are average values within the whole transmission band, i.e.,\ among the five measuring channels recommended in Recommendation\ G.228. .RT .LP .sp 1P .LP 8.3 \fIMatching of repeater impedances and line impedance\fR .sp 9p .RT .PP For television programme transmission a value of at least 72\ dB for the magnitude \fIN\fR , defined in Recommendation\ G.332, \(sc\ 5, has been agreed to in the band occupied by television signals. .RT .sp 1P .LP 8.4 \fINumber, nature and position of\fR \fIline television channels\fR .sp 9p .RT .PP Television signals may be transmitted without any other wanted signals or simultaneously with telephone channels. In the first case, there are six television channels. In the case of mixed transmission, the attention of Administrations is drawn to the fact that, if there are more than two television channels, harmful interference may occur between the two types of signal, especially interference to telephony from television. This clause is therefore limited to cases where the number of channels is less than or equal to two. .PP Whether or not the 60 MHz system is allocated wholly or partially to television, television channels are capable of transmitting the signals of all television systems defined by the CCIR having a video bandwidth not exceeding 6\ MHz. .PP When a 60 MHz system is used entirely for television, it can provide six television channels, arranged in three pairs each of which extends over the bandwidth of four supermastergroups. The line\(hyfrequency allocation is shown in Figure\ 5/G.333. .PP When transmission is mixed, a distinction should be made according to whether the number of television channels is two or one. .bp .PP If there are two, the use of channels 3 and 4 is recommended. .PP In the case of a single television channel, there are two possibilities: .RT .LP \(em first alternative: channel 3 or channel 4, the choice being immaterial; .LP \(em second alternative: channel 1. .PP The first alternative has the advantage of low group delay distortion and is suitable for long links. The second allows the use of simple modulation equipment, if modulation method No.\ 2 is applied (see Note\ 1 below). On the other hand, it has the disadvantage of a higher group delay distortion, requiring the use of correctors whose complexity increases with the length of exceeds a certain limit. .PP \fINote\ 1\fR \ \(em\ Two recommended modulating methods are shown in Annex\ A. .PP \fINote\ 2\fR \ \(em\ A television channel\(hypair pilot can be provided at the mean of the carrier frequencies of each television channel pair, i.e.\ 12 | 60\ kHz (4\ \(mu\ 3190\ kHz), 31900\ kHz (10\ \(mu\ 3190\ kHz) and 51 | 40\ kHz (16\ \(mu\ 3190\ kHz). It is recommended that these pilots be transmitted at a power level of \(em10\ dBm0. The harmonics of the pilot 12 | 60\ kHz should have a level of not higher than\ \(em70\ dBm0; the level of the harmonics of the other pilots should not exceed \(em50\ dBm0. .RT .LP .rs .sp 19P .ad r \fBFigure 5/G.333, p.\fR .sp 1P .RT .ad b .RT .sp 1P .LP 8.5 \fIPilots and additional measuring frequencies\fR .sp 9p .RT .PP Those pilots and additional measuring frequencies (mentioned in\ \(sc\ 2), falling in gaps between TV\ channels, can be used. \v'2P' .RT .ce 1000 ANNEX\ A .ce 0 .ce 1000 (to Recommendation\ G.333) .sp 9p .RT .ce 0 .ce 1000 \fBModulation methods for television transmission | fR \fBon the 60\(hyMHz system\fR .sp 1P .RT .ce 0 .PP Two recommended modulating methods are shown in Figure\ A\(hy1/G.333 and Figure A\(hy2/G.333 respectively. The modulation methods are compatible with those of the 18\(hyMHz system (see Annex\ A to Recommendation\ G.334). .bp .sp 1P .RT .LP .rs .sp 26P .ad r \fBFigure A\(hy1/G.333, p.\fR .sp 1P .RT .ad b .RT .LP .rs .sp 22P .ad r \fBFigure A\(hy2/G.333, p.\fR .sp 1P .RT .ad b .RT .LP .bp .sp 2P .LP \fBReferences\fR .sp 1P .RT .LP [1] CCITT Recommendation \fIRoutine maintenance measurements to be made\fR \fIon regulated line sections\fR , Vol.\ IV, Rec.\ M.500. .LP [2] CCITT manual \fIDirectives concerning the protection of telecommunication\fR \fIlines against harmful effects from electricity lines\fR , ITU, Geneva,\ 1963, 1965, 1974\ and\ 1978. .LP [3] CCITT Recommendation \fITests on power\(hyfed repeaters using solid state\fR \fIdevices in order to check the arrangements for protection from\fR \fIexternal interference\fR , Vol.\ IX, Rec.\ K.17. .LP [4] CCITT Recommendation \fICharacteristics of the television signals\fR transmitted over 18\(hyMHz and 60\(hyMHz systems\fR , Vol.\ III, Rec.\ J.77. \v'6p' .LP .sp 2P .LP \fBRecommendation\ G.334\fR .RT .sp 2P .sp 1P .ce 1000 \fB18\ MHz\ SYSTEMS\ ON\ STANDARDIZED\ 2.6/9.5\ mm\ COAXIAL\ CABLE\ PAIRS\fR .EF '% Fascicle\ III.2\ \(em\ Rec.\ G.334'' .OF '''Fascicle\ III.2\ \(em\ Rec.\ G.334 %' .ce 0 .sp 1P .ce 1000 \fI(Geneva, 1980)\fR .sp 9p .RT .ce 0 .sp 1P .LP \fBIntroduction\fR .sp 1P .RT .PP Amplifier design technique has made it possible to provide a usable band of about 18\ MHz while still keeping the repeater spacing of about 4.5\ km as defined in Recommendation\ G.332; the CCITT has therefore defined an 18\ MHz system which offers a transmitting capacity of 3600 telephone channels in the case of pure telephone application. Alternatively, the system may be used for the transmission of up to two TV channels or one TV signal plus 1800 telephone channels. Another possibility is that the bandwidth above 12 | 35\ kHz could be used for the provision of an 8448\ kbit/s digital path. .RT .LP .sp 2P .LP \fB1\fR \fBArrangement of line frequencies for telephony\fR .sp 1P .RT .PP The arrangement of line frequencies most suitable for the network of a particular Administration depends to a high degree on the organization of this network with respect to the interconnection with and through connection to the other systems existing in this network. On the other hand, it is very desirable to limit the number of different frequency plans for the 18\ MHz system. .PP The CCITT therefore recommends that in any case one of the following three plans should be applied. However, in international connections between countries which use different modulation procedures (see Recommendation\ G.211) and in the absence of any special arrangements between the interested Administrations including, if necessary, the Administrations of transit countries, Plan\ 1 is to be preferred. .RT .sp 1P .LP 1.1 \fIFrequency arrangement of Plan 1\fR .sp 9p .RT .PP Plan\ 1 uses the first modulation procedure described in Recommendation\ G.211. .PP The telephone channels should first be assembled into basic supermastergroups. The four supermastergroups are transmitted to line in accordance with the frequency arrangement of Figure\ 1/G.334. .PP \fINote\fR \ \(em\ The arrangement of the supermastergroups No.\ 1, 2 and\ 3 is the same as in Plan\ 1A of the 12\(hyMHz system (Recommendation\ G.332) and supermastergroup No.\ 4 corresponds to its arrangement in Plan\ 1 of the 60\(hyMHz system (Recommendation\ G.333). .RT .sp 1P .LP 1.2\fR \fIFrequency arrangement of Plan 2\fR .sp 9p .RT .PP This Plan uses the second modulation procedure described in Recommendation\ G.211. .PP The telephone channels should first be assembled into basic (No.\ 1) 15\(hysupergroup assemblies. Four 15\(hysupergroup assemblies are transmitted to line in accordance with the frequency arrangement shown in Figure\ 2/G.334. .PP \fINote\fR \ \(em\ The arrangement of the 15\(hysupergroup assemblies Nos.\ 1, 2 and\ 3 is the same as in Plan\ 2 of the 12\(hyMHz system (Recommendation\ G.332). .bp .RT .LP .rs .sp 20P .ad r \fBFigure 1/G.334, p.\fR .sp 1P .RT .ad b .RT .LP .rs .sp 18P .ad r \fBFigure 2/G.334, p.\fR .sp 1P .RT .ad b .RT .sp 1P .LP 1.3 \fIFrequency arrangement of Plan 3\fR .sp 9p .RT .PP This Plan uses the first modulation procedure described in Recommendation\ G.211, but adds a further intermediate frequency position. .PP The telephone channels should first be assembled into basic supermastergroups. The four supermastergroups are then translated into the position of the supermastergroups Nos.\ 6\(hy9 as in Plan\ 1 of the 60\(hyMHz system (Recommendation\ G.333). .bp .PP By translating with an additional 40 | 80 kHz carrier frequency, these supermastergroups are transmitted to line in accordance with the frequency arrangement of Figure\ 3/G.334. .PP \fINote\ 1\fR \ \(em\ This arrangement is best suited to those networks which need frequent direct through\(hyconnections between the 18\(hyMHz and 60\(hyMHz systems. It therefore makes use of a wider frequency band for through\(hyconnection than the basic supermastergroup. The arrangement is also suitable for the interconnection of 18\(hyMHz systems and for the interconnection between 18\(hyMHz systems and 60\(hyMHz systems via the basic supermastergroup 8516\(hy12 | 88\ kHz, because the relatively large frequency space between the supermastergroups permits the use of simpler through supermastergroup filters. .PP \fINote\ 2\fR \ \(em\ This arrangement can handle also 15\(hysupergroup assemblies by bringing them first into the frequency band of the basic supermastergroup (15\(hysupergroup assembly No.\ 3). .RT .LP .rs .sp 20P .ad r \fBFigure 3/G.334, p.\fR .sp 1P .RT .ad b .RT .sp 2P .LP \fB2\fR \fBPilots\fR \fBand additional measuring frequencies\fR .sp 1P .RT .sp 1P .LP 2.1 \fILine\(hyregulating pilots\fR .sp 9p .RT .PP It is recommended that 18 | 80\ kHz be used for the main line regulating pilot .FS 18 | 80\ kHz is a multiple of 308\ kHz (60\ \(mu\ 308) and of 440\ kHz (42\ \(mu\ 440). .FE . .PP In any regulated\(hyline section crossing a frontier, it is recommended that in both directions of transmission the Administration on the sending side should, if requested, permanently transmit an auxiliary line\(hyregulating pilot at 308\ kHz to provide facilities for additional regulation, for example. .PP For Frequency Plans\ 1 and\ 2 as defined under \(sc\ 1 above, 4287\ kHz and/or 12 | 35\ kHz may be used as additional auxiliary line\(hyregulating pilots on request of the Administration on the receiving side. .RT .LP .sp 1 .bp .PP The frequency accuracy recommended for the pilots is \(+- | \ \(mu\ 10\uD\dlF261\u5\d. .PP The power level of the main and auxiliary line\(hyregulating pilots should be adjusted at the point of injection to have a value of \(em10\ dBm0. The harmonics of the 308\ kHz and 4287\ kHz pilots should each have a level not greater than \(em70\ dBm0. .PP Equipment should be designed in such a way that these pilots may be blocked at the end of a regulated\(hyline section, so that their level shall be at least 40\ dB below that of the pilots used on other sections. .PP The following tolerances for the level of these pilots are recommended: .RT .LP .PP 2.1.1 The design of equipment should be such as to allow the error in the level of any pilot as transmitted, due to finite level adjustment steps, to be kept within \(+- | .1\ dB. .sp 9p .RT .PP 2.1.2 The change in output level of the pilot generator with time (which is a factor included in equipment specifications) must not exceed \(+-\ 0.3 | B during the interval between two maintenance adjustments, e.g.\ in one month. .PP 2.1.3 To reduce pilot level variations with time, it is advisable to have a device to give an alarm when the variation at the generator output exceeds \(+- | .5\ dB, the zero of the warning device being aligned as accurately as possible with the lining\(hyup level of the transmitted pilot. .sp 1P .LP 2.2 \fIFrequency comparison pilots\fR .sp 9p .RT .PP Administrations wishing to make an international frequency comparison shall choose the frequency 300, 308 or (for Plans\ 1 and 2 only) 4200\ kHz for this purpose. International comparison of national standards is relatively rare. During a specified period of time, it will always be possible to use for such comparisons one of the frequencies mentioned above, even though it may normally be used for other purposes. .PP It is recommended that the frequency comparison pilot be transmitted at a power level of \(em10\ dBm0. The harmonics of the frequency comparison pilots should each have a level not higher than \(em70\ dBm0. .RT .sp 1P .LP 2.3 \fIAdditional measuring frequencies\fR .sp 9p .RT .PP Frequencies that may be used as additional measuring frequencies are given in Table\ 1/G.334. .PP The absolute frequency variation of additional measuring frequencies below 4\ MHz should never be outside limits of \(+- | 0\ Hz from their nominal value. For frequencies above 4\ MHz, the relative frequency variation referred to the nominal value should never exceed \(+- | \ \(mu\ 10\uD\dlF261\u5\d. .PP The power level of the additional measuring frequencies should be adjusted at the point of injection to have a value of \(em10\ dBm0. The harmonics of the additional measure frequencies below 9\ MHz should each have a level not higher than \(em70\ dBm0 as transmitted to the line. The additional measuring frequencies should not be permanently transmitted. They will only be transmitted for as long as is necessary for actual measurement purposes. .PP Arrangements should be made in equipment for the 12\(hyMHz system, so that the 308\ kHz line\(hyregulating pilot is protected from disturbances from a pilot or additional measuring frequency of the same frequency coming from a 4\(hyMHz system when this protection is not already provided by the equipment of the 4\(hyMHz system. .PP \fINote\fR \ \(em\ Some Administrations use new manual or automatic methods of equalizing attenuation distortion, e.g.\ equalizers based on the Cosine function, using frequencies which do not appear in the list of additional measuring frequencies recommended by the CCITT. .PP Obviously no additional measuring frequency which might leave the national network should be sent at the same frequency as one of the pilots recommended by the CCITT. .bp .RT .ce \fBH.T. [T1.334]\fR .ce TABLE\ 1/G.334 .ps 9 .vs 11 .nr VS 11 .nr PS 9 .TS center box; cw(54p) | cw(42p) sw(42p) | cw(42p) , ^ | c | c | ^ . Frequency plan 1 (kHz) Frequency plan 2 Frequency plan 3 (kHz) (see Note 1) (kHz) (see Note 2) (kHz) _ .T& lw(54p) | cw(42p) | lw(42p) | cw(42p) . \ \ | 60 \ \ | 52 .T& lw(54p) | cw(42p) | cw(42p) | cw(42p) . \ \ | 08 1 | 56 .T& lw(54p) | cw(42p) | cw(42p) | cw(42p) . \ 1 | 04 1 | 52 .T& cw(54p) | cw(42p) | cw(42p) | cw(42p) . \ 1 | 92 \ 1 | 00 2 | 48 \ 1 | 72 .T& cw(54p) | cw(42p) | cw(42p) | cw(42p) . \ 2 | 96 2 | 44 .T& cw(54p) | cw(42p) | cw(42p) | cw(42p) . \ 2 | 12 \ 2 | 92 3 | 40 .T& cw(54p) | cw(42p) | cw(42p) | cw(42p) . 3 | 88 \ 3 | 92 .T& cw(54p) | cw(42p) | cw(42p) | cw(42p) . \ 3 | 36 3 | 84 \ 4 | 58 .T& cw(54p) | cw(42p) | cw(42p) | cw(42p) . \ 5 | 08 \ 5 | 92 \ 6 | 72 .T& cw(54p) | cw(42p) | cw(42p) | cw(42p) . \ 6 | 28 \ 7 | 28 \ 7 | 92 .T& cw(54p) | cw(42p) | cw(42p) | cw(42p) . \ 8 | 48 (see Note 3) \ 8 | 48 .T& cw(54p) | cw(42p) | cw(42p) | cw(42p) . \ 8 | 72 \ 8 | 72 .T& cw(54p) | cw(42p) | cw(42p) | cw(42p) . \ 8 | 64 \ 9 | 58 .T& cw(54p) | cw(42p) | cw(42p) | cw(42p) . \ 9 | 92 \ 9 | 08 10 | 72 .T& cw(54p) | cw(42p) | cw(42p) | cw(42p) . 11 | 12 11 | 44 .T& lw(54p) | lw(84p) . .T& lw(54p) | cw(84p) | cw(42p) . 12 | 76 11 | 92 .T& cw(54p) | cw(84p) | cw(42p) . 12 | 78 13 | 52 13 | 58 .T& cw(54p) | cw(84p) | cw(42p) . 14 | 08 14 | 40 15 | 72 .T& cw(54p) | cw(84p) | cw(42p) . 15 | 28 16 | 76 16 | 92 .TE .LP \fINote\ 1\fR \ \(em\ Additional measuring frequencies to be sent or measured on request. .LP \fINote\ 2\fR \ \(em\ Other additional measuring frequencies which can be sent. .LP \fINote\ 3\fR \ \(em\ A frequency of 8248 kHz can be used as a radio\(hyrelay link line\(hyregulating pilot. In such a case, the precautions shown in Recommendation\ G.423 should be applied. .nr PS 9 .RT .ad r \fBTable 1/G.334 [T1.334], p.\fR .sp 1P .RT .ad b .RT .sp 2P .LP \fB3\fR \fBHypothetical reference circuit\fR .sp 1P .RT .sp 1P .LP 3.1 \fIGeneral considerations\fR .sp 9p .RT .PP The hypothetical reference circuit is 2500 km long and is divided into nine homogeneous sections of 280\ km each. .RT .sp 1P .LP 3.2 \fIModulation\fR .sp 9p .RT .PP The three line\(hyfrequency allocations recommended in \(sc\ 1 above need different numbers of modulating stages to bring an audio signal into the line\(hyfrequency position. This has to be reflected in the constitution of the hypothetical reference circuit. .PP On the above basis, the hypothetical reference circuits, as shown in Figure\ 4/G.334 and Figure\ 5/G.334, are recommended by the CCITT. .RT .LP .rs .sp 8P .ad r \fBFigure 4/G.334, p.\fR .sp 1P .RT .ad b .RT .LP .bp .LP .rs .sp 8P .ad r \fBFigure 5/G.334, p.\fR .sp 1P .RT .ad b .RT .sp 1P .LP 3.2.1 \fIHypothetical reference circuit for the Plan 1 frequency\fR \fIallocation\fR .sp 9p .RT .PP This is shown in Figure 4/G.334. It has, for each direction of transmission, a total of: .RT .LP \(em two pairs of channel modulators, each pair including translation from the audio\(hyfrequency band to the basic group and vice versa; .LP \(em three pairs of group modulators, each pair including translation from the basic group to the basic supergroup and vice versa; .LP \(em five pairs of supergroup modulators, each pair including translation from the basic supergroup to the basic mastergroup and vice versa; .LP \(em seven pairs of mastergroup modulators, each pair including translation from basic mastergroup to the basic supermastergroup and vice versa; .LP \(em nine pairs of supermastergroup modulators, each pair including translation from basic supermastergroup to the frequency band transmitted on the coaxial cable and vice versa. .sp 1P .LP 3.2.2 \fIHypothetical reference circuit for the Plan 2 frequency\fR \fIallocation\fR .sp 9p .RT .PP This is shown in Figure 5/G.334. It has, for each direction of transmission, a total of: .RT .LP \(em two pairs of channel modulators, each pair including translation from the audio\(hyfrequency band to the basic group and vice versa; .LP \(em three pairs of group modulators, each pair including translation from the basic group to the basic supergroup and vice versa; .LP \(em six pairs of supergroup modulators, each pair including translation from the basic supergroup to the basic 15\(hysupergroup assembly and vice versa; .LP \(em nine pairs of 15\(hysupergroup assembly modulators, each pair including translation from the basic 15\(hysupergroup assembly to the frequency band transmitted on the coaxial cable and vice versa. .sp 1P .LP 3.2.3 \fIHypothetical reference circuit for the Plan 3 frequency\fR \fIallocation\fR .sp 9p .RT .PP This is shown in Figure 4/G.334. It differs from that for Plan 1 only by the fact that the supermastergroup modulators consist of two translating stages. .RT .sp 2P .LP \fB4\fR \fBCircuit noise\fR .sp 1P .RT .PP In accordance with Recommendation G.222 the system is to be designed in such a way as to obtain a mean psophometric noise power of 3\ pW0p per km of line or less as a design objective for the worst telephone channel in the 2500\(hykm hypothetical reference circuit as defined under \(sc\ 3 above. .RT .sp 2P .LP \fB5\fR \fBMatching of repeater and line impedances\fR .sp 1P .RT .PP The present Recommendation refers only to 18\(hyMHz systems on 2.6/9.5\(hymm coaxial pairs in which the nominal spacing between repeaters is approximately 4.5\ km. .PP The sum \fIN\fR of the three terms defined as in G.332, \(sc\ 5 must in this case be equal to at least 48\ dB at 300\ kHz and to at least 55\ dB at all frequencies above 800\ kHz. Between 300 and 800\ kHz the permissible limit in decibels varies linearly with the frequency. .bp .RT .sp 2P .LP \fB6\fR \fBRelative levels\fR .sp 1P .RT .PP Levels in the main station (see Recommendation G.213). .PP When one part of the frequency band is transmitted without demodulation, the same value of \(em33\ dBr is recommended at the output of the direct through\(hyconnection filter. .RT .sp 2P .LP \fB7\fR \fBPower feeding\fR .sp 1P .RT .PP Recommendation G.341, \(sc\(sc 7.1 and 7.2, applies. .RT .sp 2P .LP \fB8\fR \fBMonitoring and fault tracing bands\fR .sp 1P .RT .PP Frequency bands for monitoring and fault tracing signals should be situated below 300\ kHz and/or above 18 | 80\ kHz, that is, leaving a clear band for traffic signals. .RT .sp 2P .LP \fB9\fR \fBUse of\fR \fB18\(hyMHz systems for television transmission\fR .sp 1P .RT .sp 1P .LP 9.1 \fIGeneral remarks\fR .sp 9p .RT .PP In \(sc 9 all additional requirements are summarized which are recommended in the case of television transmission on the 18\(hyMHz system. The characteristics of the television signal in the first intermediate frequency allocation (transmit side conditions) are dealt with in Recommendation\ J.77\ [1]. .RT .sp 1P .LP 9.2 \fICircuit noise\fR .sp 9p .RT .PP If the 18\(hyMHz system is used for television transmission on the basis of a hypothetical reference circuit of a length of 2500\ km, the mean value of the thermal noise of the line should not exceed 1\ pW0p/km. Experience has shown that a mean value of 1.5\ pW0p/km total noise of the line is sufficient when measured according to normal telephone conditions. .RT .sp 1P .LP 9.3 \fIMatching of repeater impedances and line impedance\fR .sp 9p .RT .PP For television programme transmission a value of at least 70 dB for the magnitude\ \fIN\fR , defined in Recommendation\ G.332 \(sc\ 5, is recommended in the band occupied by television signals. .RT .sp 2P .LP 9.4 \fILine\(hyfrequency allocation of the television channels\fR .sp 1P .RT .sp 1P .LP 9.4.1 \fITV transmission only\fR .sp 9p .RT .PP The 18\(hyMHz system can provide two television channels. The line\(hyfrequency allocation is shown in Figure\ 6/G.334. The television channels are capable of transmitting the signals of all television systems defined by the CCIR having a video bandwidth not exceeding 6\ MHz. .PP \fINote\ 1\fR \ \(em\ Two recommended modulating methods are shown in Annex\ A. .PP \fINote\ 2\fR \ \(em\ A television channel\(hypair pilot can be provided at the mean of the two carrier frequencies, i.e.\ 9570\ kHz (3\ \(mu\ 3190\ kHz). It is recommended that this pilot be transmitted at a power level of \(em10\ dBm0. The harmonics should have a level of not higher than\ \(em50\ dBm0. .RT .LP .rs .sp 9P .ad r \fBFigure 6/G.334, p.\fR .sp 1P .RT .ad b .RT .LP .bp .sp 1P .LP 9.4.2 \fIMixed telephone\(hytelevision transmission\fR .sp 9p .RT .PP One television channel and a maximum of two 900\(hychannel groups can be provided. Two line\(hyfrequency allocations are possible: .RT .LP a) the upper television channel 2* of Figure 6/G.334; .LP b) the lowest television channel (TV channel No.\ 1) of the 60\(hyMHz television line\(hyfrequency allocation of Figure\ 4/G.333. .PP \fINote\ 1\fR \ \(em\ The modulation methods for a) and b) conform to the first modulation steps of Figure\ A\(hy1/G.334 and Figure A\(hy2/G.334 respectively in Annex\ A. .sp 1P .LP 9.5 \fIPilots and additional measuring frequencies\fR .sp 9p .RT .PP Pilots and additional measuring frequencies (mentioned in \(sc 2), outside the television channels can be used. \v'2P' .RT .LP .ce 1000 ANNEX\ A .ce 0 .ce 1000 (to Recommendation G.334) .sp 9p .RT .ce 0 .ce 1000 \fBModulation methods for television transmission\fR \fBon the 18\(hyMHz system\fR .sp 1P .RT .ce 0 .PP Two recommended modulating methods are shown in Figure A\(hy1/G.334 and Figure\ A\(hy2/G.334 respectively. The modulation methods are compatible with those of the 60\(hyMHz system (see Annex\ A to Recommendation\ G.333). .sp 1P .RT .LP .rs .sp 27P .ad r \fBFigure A\(hy1/G.334, p.\fR .sp 1P .RT .ad b .RT .LP .bp .LP .rs .sp 28P .ad r \fBFigure A\(hy2/G.334, p.\fR .sp 1P .RT .ad b .RT .sp 2P .LP \fBReference\fR .sp 1P .RT .LP [1] CCITT Recommendation \fICharacteristics of the television signals\fR \fItransmitted over 18\(hyMHz and 60\(hyMHz systems\fR , Vol.\ III, Rec.\ J.77. \v'6p' .LP .sp 2P .LP \fBRecommendation\ G.337\fR .RT .sp 2P .sp 1P .ce 1000 \fBGENERAL\ CHARACTERISTICS\ OF\ \fR \fBSYSTEMS\ ON | fR \fB2.6/9.5\ mm\ COAXIAL\ CABLE\ PAIRS\fR .EF '% Fascicle\ III.2\ \(em\ Rec.\ G.337'' .OF '''Fascicle\ III.2\ \(em\ Rec.\ G.337 %' .ce 0 .sp 1P .ce 1000 (For the text of this Recommendation, see Vol. III .sp 9p .RT .ce 0 .sp 1P .ce 1000 of the \fIOrange Book\fR , Geneva, 1976) \v'6p' .ce 0 .sp 1P .sp 2P .LP \fBRecommendation\ G.338\fR .RT .sp 2P .sp 1P .ce 1000 \fB4\ MHz\ VALVE\(hyTYPE\ SYSTEMS\ ON\ STANDARDIZED | fR \fB2.6/9.5\ mm\ COAXIAL\ CABLE\ PAIRS\fR .EF '% Fascicle\ III.2\ \(em\ Rec.\ G.338'' .OF '''Fascicle\ III.2\ \(em\ Rec.\ G.338 %' .ce 0 .sp 1P .ce 1000 (For the text of this Recommendation, see Vol. III .sp 9p .RT .ce 0 .sp 1P .ce 1000 of the \fIOrange Book\fR , Geneva, 1976) .ce 0 .sp 1P .LP .bp