ITU-T G 423-1993 INTERCONNECTION AT THE BASEBAND FREQUENCIES OF FREQUENCY - DIVISION MULTIPLEX RADIO - RELAY SYSTEMS《在频分多路复用无线接力系统的基带频率上互连》.pdf
《ITU-T G 423-1993 INTERCONNECTION AT THE BASEBAND FREQUENCIES OF FREQUENCY - DIVISION MULTIPLEX RADIO - RELAY SYSTEMS《在频分多路复用无线接力系统的基带频率上互连》.pdf》由会员分享,可在线阅读,更多相关《ITU-T G 423-1993 INTERCONNECTION AT THE BASEBAND FREQUENCIES OF FREQUENCY - DIVISION MULTIPLEX RADIO - RELAY SYSTEMS《在频分多路复用无线接力系统的基带频率上互连》.pdf(12页珍藏版)》请在麦多课文档分享上搜索。
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
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