1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU).4%2.!4)/.!,G0G0!.!,/5%G0G0#!22)%2G0G03934%-3%.%2!,G0G0#(!2!#4%2)34)#3G0G0/2) at a junction point between a radio-relay system and a short cable extension (see 3 below). A cableextension is regarded as “short“
2、 if it does not require its own line-regulating system.The pre-emphasis characteristics at the output of cable system repeaters have not been fully standardized bythe CCITT. Moreover, line transmission in a repeater section of a system has various special features due, for example,to the presence of
3、 various pilots and to the power feeding of the repeaters. Further, points R and T defined inRecommendation G.213 may be very near to each other, or they may be linked by several kilometres of cable.For these reasons, it is unnecessary to provide a direct interconnection of a telephony radio-relay l
4、ink witheither a symmetric cable pair or coaxial cable for a telephone system, such that the input and output levels of the relaylink correspond exactly to the normal levels at the input and output of a repeater in the cable system. It is preferable tomake the interconnection at a point in the telep
5、hone equipment where the level is independent of the frequency.Consequently, interconnection with multiplex telephone equipment in the baseband of a radio-relay link (which inaccordance with CCIR Recommendation 381 2 is always considered to be at one end of the line-regulating section ona radio-rela
6、y link) should always be effected in a main repeater station3). Interconnection with another system whethercable or radio-relay link will be effected in this station between points T and T defined in Recommendation G.213.2 Baseband frequency limits, impedance and relative power levelsCCIR Recommenda
7、tion 380 1 includes a table which shows preferred values given by the CCIR for thefollowing:- baseband frequency limits;- nominal baseband impedance;- input and output relative power levels at the radio equipment (R and R);together with an annex on definitions which corresponds to CCITT Recommendati
8、on G.213._1)Brought up to date by the Secretariat after the Plenary Assembly of Mar del Plata, 1968.2)Similarly to the corresponding CCIR Recommendations, this Recommendation applies to line-of-sight andnear line-of-sight radio-relay systems and also to tropospheric scatter systems of the capacities
9、 concerned.3)Described in 3.18 of Recommendation G.211.2 Fascicle III.2 - Rec. G.423Table 1/G.423 shows the frequency arrangements, corresponding to the baseband frequency limits in CCIRRecommendation 380 1, recommended by the CCITT for radio-relay systems that may be interconnected withmetallic lin
10、es. These frequency arrangements are produced by CCITT standardized frequency-translating equipmentsfor cable systems.Figures 1/G.423 to 10/G.423 show diagrams of the frequency arrangement for the radio-relay baseband,recommended for purposes of interconnection with coaxial cable systems.Note 1 - Al
11、l the diagrams in Figures 1/G.423 to 10/G.423 show the line pilots, the mastergroup pilots, thesupermastergroup pilots, the 15-supergroup assembly pilots and the additional measuring frequencies which may be inthe band transmitted (see 3).Note 2 - The meaning of the symbols used in these Figures is
12、given at the beginning of this fascicle.Note 3 - Some of the diagrams in the figures of other Recommendations also apply to radio-relay links (seeTable 1/G.423).3 Regulated-line sections - line-regulating and other pilotsIn CCIR Recommendation 381 2, the following pilots are recommended for the regu
13、lation of radio-relaylinks:1) a continuity pilot outside the “total bandwidth“ shown in Table 1/G.423;2) a line-regulating pilot with a frequency of 308 kHz (or 60 kHz, depending on the radio-link capacity),and a level of -10 dBm0;3) when required, an upper line-regulating pilot of frequency and lev
14、el in accordance with CCITTRecommendations for the relevant cable systems.3.1 Pilot-blocking at an interconnection pointThe CCITT makes the following general recommendations to the CCIR: in all cases, the level of the continuitypilot of a radio-relay system should be reduced so that it is not greate
15、r than -50 dBm0 at an interconnection point with asystem on a metallic line.This interconnection point normally occurs at the limits of two regulated-line sections, one of them being on ametallic line and the other on a radio-relay system. This being so, at the interconnection point the following co
16、nditionsshould be observed:1) the level of any line-regulating pilot on the metallic line should be reduced so that it is not greater than -50 dBm0, unless otherwise agreed by the Administrations concerned;2) the absolute power level of any regulating pilot of the radio-relay link should be reduced
17、so that it isbelow - 50 dBm04);3) any other pilot or additional measuring frequency of the metallic line system that is within the “totalbandwidth“ defined in Table 1/G.423 will be freely transmitted over the radio-relay system.A radio-relay system may be extended by short cable sections that form p
18、art of the same regulated-linesection: there may then be overall transmission of the pilot on that regulated-line section._4)In the case of low-capacity systems (up to 120 channels) a line-regulating pilot of 60 kHz with a level of -10dBm0 may be used; in this case the suppression level should confo
19、rm with the provisions of the CCITT(Recommendation G.243 and Recommendation G.322, 1.4). The level of the line-regulating pilot established by theCCITT for lines differs according to whether it concerns coaxial cables or symmetric pairs (-10 dBm0 for coaxialcables and -15 dBm0 for symmetric pair sys
20、tems).Fascicle III.2 - Rec. G.423 34 Limits for residues of signals outside the basebandThe CCITT makes the following recommendations to the CCIR for residues of signals outside the basebandfrequency limits:4.1 In the absence of any special agreement between Administrations, the level of any pilot o
21、r supervisory signaltransmitted outside the baseband of a radio-relay system at a frequency not specified by the CCIR should be reduced,within the radio equipment, to -50 dBm0 at point R.Similarly, in the absence of special agreements between Administrations, the levels of all pilots or supervisorys
22、ignals sent over the cable system outside the baseband of the radio-relay link should be reduced, within the equipmentof the cable system, to -50 dBm0 at point T.4.2 If a radio-relay system service channel, adjacent to a telephone channel in the baseband, uses the levels,frequency allocation and sig
23、nalling levels corresponding to those which would be recommended by the CCITT for anordinary telephone channel in the same position in the frequency spectrum, the channel filters are sufficient to avoidthe risk of crosstalk interference.4.3 If the condition referred to in 4.2 above is not met, an ad
24、ditional filter may be necessary and must beprovided in the radio equipment.4.4 The frequencies mentioned in 4.1 and 4.2 above must be sufficiently distant from the baseband to ensurethat the filters (or other appropriate devices) required to eliminate them do not cause attenuation distortion in the
25、passband to exceed the recommended values.4.5 To avoid overloading the cable system, the level of any signal transmitted beyond point R outside thebaseband must be kept down to -20 dBm0. Moreover, the level of the total power of the residues of such signals(including noise and intermodulation produc
26、ts) must be kept down to -17 dBm0.5 Other requirements intended to ensure satisfactory transmission performance5.1 Return lossThis characteristic is of great importance for carrier cable systems, which comprise a number of fairlyregularly spaced repeaters. It is felt that, in the case of radio-relay
27、 systems, the cable sections linking the radioequipment to the multiplex equipment are generally fairly short and of unequal lengths, so that there is little fear ofsystematic undulation of the attenuation/frequency characteristic.That being so, it is recommended that at interconnection points T and
28、 T the return loss, in relation to thenominal impedance, should be at least 20 dB throughout the frequency band occupied by the telephone channels. Themain purpose of this recommendation is to facilitate measurements and maintenance and to ensure some protectionagainst the random reflections which o
29、ccur at various points between the equipment and the cable sections; it takes intoaccount the value of 24 dB for the return loss at R and R recommended by the CCIR 4.Note - The attention of the CCIR is drawn to the fact that, if the cables joining the radio equipment to themultiplex equipment in the
30、 intermediate stations are long enough (for example 1 to 2 km) and not equipped withamplifiers, systematic reflection effects may occur. These special cases must be studied in accordance with theprinciples established by the CCITT (see Recommendation G.214); they do not seem to justify a generalreco
31、mmendation.4 Fascicle III.2 - Rec. G.4235.2 Attenuation/frequency distortionAccording to the Recommendation cited in 5, the levels measured at the frontier on a high-frequency cableline section must not deviate at any frequency by more than 2 dB from the nominal values, whatever the pre-emphasis cha
32、racteristic used. At point T, for a cable system, one can expect to find variations of the same order inrelation to a flat characteristic.No value is fixed for the radio-relay links in the Recommendation cited in 6. The CCIR has recommended7 the same tolerance of 2 dB at the points R and R.5.3 Varia
33、tion of loss with timeThe CCITT is studying the results that can be obtained on cable line-regulating sections, taking into accountRecommendations M.530 8 and G.333. When this study is complete, it will be possible to point out to the CCIR thata similar recommendation would be desirable for radio-re
34、lay links.Fascicle III.2 - Rec. G.423 5TABLE 1/G.423Frequency arrangements within the baseband of radio-relay links, which are recommendedin the case of interconnection with systems on metallic linesCapacityof radio-relaysystemRecommendedalternativeDiagramLimits of bandoccupiedPilots or frequenciesw
35、hich maybe transmitteda)(kHz)Totalbandwidthb)(maximumnumberof telephonechannels)arrangementsof telephonechannelsin figure by telephonechannels(kHz)below(4)above(4)(kHz)1234 5 624 2 G c)2 G d)2a)/G.3221/G.327 312-1086-108 or 12-120-12-1086-108 or 12-12060SG 1 2c)/G.322 12-252 - - 12-252SG 1 4/G.322 6
36、0-300 - - 60-300120SG 1 and 2 4/G.322 12-552 - - 12-552SG 1 and 2 4/G.322 60-552 - - 60-5523005 SG 1a)/G.341 60-1300 - 13641 MG e)1b)/G.341 64-1296 60 136460-136460010 SG 1/G.423 60-2540 - 26042 MG e)2/G.423 64-2660 - 279260-2792900 3 MG or 1 SMG f)3/G.423 316-4188 300, 308 4287960 16 SG 4/G.423 60-
37、4028 - 409260-42871260 g)21 SG21 SG4 MGPlan 1h)Plan 2Plan 360-563660-5564316-5564-30856805608560860-568015 SG +3 MG 5/G.423 312-82041800 15 SG + 15 SG i)6/G.423 312-8120300, 3088248 300-82486 MG or 2 SMG 7/G.423 316-820415 SG + 6 MG 8/G.423 312-12 388270015 SG+15 SG+15 SG i)9/G.423 312-12 336300, 30
38、812 435 300-12 4359 MG or 3 SMG 10/G.423 316-12 388G = group SG = supergroup MG = mastergroup SMG = supermastergroup6 Fascicle III.2 - Rec. G.423a) See 3 of the present Recommendation and Recommendation G.322, 1.4.b) This is the bandwidth occupied by the telephone channels, the associated pilots and
39、 reference frequencies, excluding thecontinuity pilots of the radio-relay system.e) For 12-channel radio-relay systems, either of the groups A (12-60 kHz) or B (60-108 kHz) recommended by the CCITT may beaccommodated in the band 12-108 kHz.d) In these variants, there are certain restrictions on the
40、use of noise measurement channels or continuous pilot channelsrecommended by the CCIR.e) This frequency arrangement is obtained from the basic mastergroup by modulating with multiples of the supergroup carriers.f) The special case of 600 channels comprising two mastergroups in the band 316-2868 kHz
41、(Figure 3/G.423) is regarded as apartially equipped 960-channel system.g) According to CCIR Recommendation 380 1, other limits of the band occupied by telephone channels may be used byagreement between the Administrations concerned.h) Figure 1/G.344.i) For the use of 15-supergroup assemblies, see Re
42、commendation G.211.FIGURE 1/G.423FIGURE 2/G.423Fascicle III.2 - Rec. G.423 7FIGURE 3/G.423FIGURE 4/G.4238 Fascicle III.2 - Rec. G.423 Fascicle III.2 - Rec. G.423 9Note - For pilots and additional measuring frequencies transmitted in the frequency band of telephone channels,see Recommendation G.332.F
43、IGURE 9/G.423FIGURE 10/G.42310 Fascicle III.2 - Rec. G.423References1 CCIR Recommendation Interconnection at baseband frequencies of radio-relay systems for telephony usingfrequency-division multiplex, Vol. IX, Rec. 380, Dubrovnik, 1986.2 CCIR Recommendation Conditions relating to line regulating an
44、d other pilots and to limits for the residues ofsignals outside the baseband in the interconnection of radio-relay and line systems for telephony, Vol. IX,Rec. 381, Dubrovnik, 1986.3 CCITT Recommendation Valve-type systems offering 12 telephone carrier circuits on a symmetric cable pair(12 + 12) sys
45、tems, Orange Book, Vol. III-1, Rec. G.327, Figure 1/G.327, ITU, Geneva, 1977.4 CCIR Recommendation Interconnection at baseband frequencies of radio-relay systems for telephony usingfrequency-division multiplex, Vol. IX, Rec. 380, 3, Dubrovnik, 1986.51 CCITT Recommendation Bringing a new internationa
46、l carrier system into service, Vol. IV, Fascicle IV.1,Rec. M.450, 2.2 and 2.3.6 Ibid., 2.1.7 CCIR Recommendation Interconnection at baseband frequencies of radio-relay systems for telephony usingfrequency-division multiplex, Vol. IX, Rec. 380, Note 7, Dubrovnik, 1986.8 CCITT Recommendation Readjustment to the nominal value of an international group, supergroup, etc., link,Vol. IV, Rec. M.530.
