1、INTERNATIONAL TELECOMMUNICATION UNION ITU=T G.232 TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU INTERNATIONAL ANALOGUE CARRIER SYSTEMS GENERAL CHARACTERISTICS COMMON TO ALL ANALOGUE CARRIER-TRANSMISSION SYSTEMS 12 - CHANNEL TERMINAL EQUIPMENTS ITU-T Recommendation G.232 (Extract from the Blue Book
2、) COPYRIGHT International Telecommunications Union/ITU TelecommunicationsLicensed by Information Handling ServicesNOTES 1 ITU-T Recommendation G.232 was published in Fascicle 111.2 of the Blue Book. This file is an extract from the Blue Book. While the presentation and layout of the text might be sl
3、ightly different from the Blue Book version, the contents of the file are identical to the Blue Book version and copyright conditions remain unchanged (see below). 2 telecommunication administration and a recognized operating agency. In this Recommendation, the expression “Administration” is used fo
4、r conciseness to indicate both a O ITU 1988,1993 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU. COPYRIGHT International Telecommuni
5、cations Union/ITU TelecommunicationsLicensed by Information Handling ServicesRecommendation G.232 12-CHANNEL TERMINAL EQUIPMENTS (amended at Geneva, 1964; further amended) The CCITT recommends that, except in the particular cases cited in Recommendations G.234 and G.235, channel terminal equipment s
6、hould provide 12 channels in a basic group, with 4-kI-i spaced carrier frequencies, in conformity with the present Recommendation. 1 Attenuation distortion The following three conditions should be satisfied simultaneously: The variation with frequency of the mean of the overall losses of the 12 pair
7、s of channel transmitting and receiving equipments of one terminal equipment should not exceed the limits shown in Graph A of Figure K1.232. For each pair of channel transmitting and receiving equipments of one terminai equipment, the variation of overall loss with frequency should not exceed the li
8、mits shown in Graph B of Figure UG.232. For the transmitting equipment of any channel, the attenuatiodfrequency distortion should not exceed the limits in Graph C of Figure 2/G.232 where: - the fiequencies shown as abscissae are audio frequencies, before modulation, - the ordinates give the limits o
9、f relative power level measured at carrier frequency. Graph A -Limits for the average variation of overall loss of 12 pairs of equipment of one 12-channel terminal equipment CCiR. 4SZW Graph B -Limits for any pair of channel transmitting and receiving equipments FIGURE 1lG.232 Permissible limits for
10、 the variation with frequency of the overall loss of transmittingand receiving equipments of one 12-channel terminal equipment Fascicle 111.2 - G.232 1 COPYRIGHT International Telecommunications Union/ITU TelecommunicationsLicensed by Information Handling ServicesGraph C -Allowable limits for the va
11、riation, as a function of frequency, of the relative power level al the output of the sending equipment of any channel or of the receiving equipment of any channel of a 12-channel terminal For the receiving equipment of any channel, the attenuation/fiequency distortion should not exceed the limits o
12、f this same Graph C where, this time: - the frequencies shown as abscissae are audio frequencies, afier demodulation, the ordinates give the limits of relative power level measured at each frequency, at the audio output terminals. - This last recommendation (under 3) above) is based on the assumptio
13、n that the transmitting and receiving equipments will be treated on an equal footing, and that the overall tolerances will be equally shared between the transmitting and receiving sides. Note - Some Administrations use, for circuits interconnecting international centres of the higher orders, .e. CTl
14、 s and CT2s (international transit centres), channel-translating equipment that gives an improved losdfrequency response by comparison with equipment meeting the above recommendation. (See i.) Such equipment does not incorporate outband signalling. 2 Limits for the response outside the band 300 to 3
15、400 Hz The CCITT recommends that in order to secure the values referred to in Table UG.122 of Recommendation G.122 2, these terminal equipments should show a loss (and not a gain) in relation to the value for 800 Hz at all frequencies below a value fand all frequencies above a value F. For Graph B o
16、f Figure 116.232 the recommended values are the following: y= 200 Hz and F = 3600 Hz The values recommended for Graphs A and C are: Graph A: f = 250 Hz and F = 3600 Hz; Graph C:J= 200 Hz and F = 3600 Hz. 2 Fascicle 111.2 - G.232 COPYRIGHT International Telecommunications Union/ITU Telecommunications
17、Licensed by Information Handling ServicesSTDmITU-T RECMN G.232-ENGL 1993 4862591i 066775b 5T7 Frequency band 400- 500 HZ 500- 600 HZ 600- 1000 HZ 1000- 2600 HZ 2600-3000 HZ 3 Group-delay distortion Group-delay distortion 5 ms 3 ms 1.5 ms 0.5 ms 2.5 ms The group-delay distortion produced by all types
18、 of 4-kHz channel terminal equipment is normally found to be quite acceptable so that no special equalization is needed. To ensure that this remains true for the future, it is recommended that the limits in Table ilG.232 for the groupdelay distortion (relative to the minimum delay) should not be exc
19、eeded by a pair of channel transmitting and receiving equipments of one 12-channel terminal equipment. Group-delay distortion values which are encountered in practice and which are unlikely to be exceeded are 5 ms at 300 Hz and 2.5 ms at 3300 Hz. (This information may be of interest to network desig
20、ners.) TABLE UG.232 4 5 5.1 Stability of virtual camer frequencies See Recommendation G.225. Carrier leak Carrier leakr within the basic group band 60-108 kHz The carrier leaks are measured at the group distribution frame (or an equivalent point). The absolute power level of these leaks, referred to
21、 a point of zero relative level, should be lower than the following values: - - However, if the group is transmitted via open-wire lines over the whole or part of its length, and if it is desired to guard against the risk of conversations over the open-wire line being picked up by an ordinary wirele
22、ss receiver, the carrier leak must be furiher reduced. carrier leak measured on one channel: -26 dBmO; sum of carrier leak powers of the various channels, measured within a group: -20 dBmO. The place and method to be used for the supplementary suppression of carrier leak, when a group on a cable is
23、transferred to an open-wire line, should be agreed to by the Administrations concerned. Fascicle 111.2 - G.232 3 COPYRIGHT International Telecommunications Union/ITU TelecommunicationsLicensed by Information Handling ServicesSTD-ITU-T RECMN G.232-ENGL L993 YBb259L 0667757 433 5.2 Carrier leaks outsi
24、de the basic group band 60-108 wiz Carrier leaks resulting from different methods of modulation (premodulation, pregroup modulation, etc.) may fall outside the frequency band 60-108 kHz and, after group and supergroup modulation, affect adjacent groups and interfere with wideband services. In order
25、to limit such interferences, the power level of any such carrier leak should be lower than -50 dBmO measured at the group distribution frame, or at an equivalent point. Noie - This value is sufficient for many applications (such as wideband data, etc.). In the case of sound- programme transmission a
26、nd 3-kHz spaced channels, etc. in the adjacent group, more stringent limits need to be applied (see Recommendation G.233, 11 and Recommendation G.235, 5). 6 Protection against harmful voltage surges, clicks, etc. Experience has shown that it may be necessary to protect equipment against harmful volt
27、age surges arising, for example, from clicks caused by switching equipment or by low-frequency ringing currents. Some protection against these harmful voltage surges derives from the use by various Administrations of terminations giving a highpass filter effect and having a high loss for frequencies
28、 below 300 Hz, or from limiting devices which are either normally fitted in their carrier systems or which can be inserted in the termination. Other arrangements can also be used. 7 Linearity The curve representing the variation (as a function of power), of the overall loss per channel of a combinat
29、ion of sending and receiving terminal equipments should be within the limits of Figure 3/G.232 (Graph No. 3), the measurements of the output power being made by means of a square law device. I Input pani Iwd FIGURE 3/G.232 Graph No. 3 -Permissible limits for the variation with applied audio power le
30、vel, of the overall loss of the combination of sending and recehing ll-channel terminal equipments. The curve shows the variation of overall loss as a function of the power level applied to the audio input terminals of one channel and referred to the overall loss when the applied power is 1 mW 8 Amp
31、litude limiting The sending equipment of an individual channel, with the addition of a limiter where necessary, must produce the limiting effect defined as follows: for any sine wave signal, at any frequency between 300 and 3400 Hz applied at the input at any level not exceeding 20 however, certain
32、general principles and their application to particular outband systems have been included as a guide for an approach to the problem. Note - Throughout 0 13 and in Annexes A and B it is assumed that the pilots used are, on the one hand, at the frequencies 84.080 and 84.140 Wz, and, on the other hand,
33、 at 41 1.920 and 41 1.860 kHz. If the pilots 104.080 kHz and 547.920 Wz are used, the same provisions apply with the following changes: Channels 1 and 2 are associated with the group pilot at 104.080 kHz just as channels 6 and 7 are associated with the pilot at 84.080 MIZ). The interference frequenc
34、y at 64.080 IrHz in group 5 and channels 11 and i2 are associated with the supergroup pilot at 547.920 kHz just as the interference frequency at 104.080 kHz in group 3 and channels 1 and 2 are associated with the pilot at 41 1.920 kHz). 13.1 Protection and suppression of the group referencepilot In
35、view of the various possibilities of interference indicated in Annex A, it is recommended that the terminal equipment of a 12-channel group should conform to the attenuationlfrequency requirements of Table 3/G.232. Pilot frequency Channel No. TABLE 31G.232 Minimum loss (relative to 8OO-Hz loss) Inte
36、rference frequency in the channel with respect to the camer (3) 3920 -80 3860 -140 Send equipement Receive equipement 20 30 35 20 I Note by the Secretariat - See Recommendations 4.2 1 81 and Q.4 14 9. 1) 8 Fascicle 111.2 - G.232 COPYRIGHT International Telecommunications Union/ITU Telecommunications
37、Licensed by Information Handling ServicesThe required attenuation at the equivalent frequencies of -80 and 3920 Hz or -140 and 3860 Hz may be obtained by a combination of audio filters, HF channel filters and bandstop filters at the discretion of the Administration concerned. It is, however, noted t
38、hat, when there is a nonlinear device (such as a channel modulator operated as a limiter, see 0 8 above) between audio-frequency and HF, filtration on the audio-frequency filters could have a much reduced effect on high-level audio-frequency interference signals compared with the effect on low-level
39、 signals. The relative losses quoted in columns (4) and (5) of Table 3iG.232 are the total effective losses required after the inclusion of a limiter. Channel No. (3) 1 2 1 2 Ail the attenuation values indicated above should be obtained over a band of at least rt 3 Hz relative to the nominal pilot f
40、requency for the pilot at 84.080 kHz and f 5 Hz for the pilot at 84.140 kHz for both send and receive sides. This bandwidth allows for the tolerances on the pilot (Recommendation G.241, 8 3) and for the possible frequency variations on an international circuit (Recommendation G.225,O 1). Minimum att
41、enuation (relating to 800-Hz) Interference frequency in the channel with respect to the carrier Sending Receiving (H4 (B) (dB) (4) (5) (6) 3920 20 40 -80 20 20 3860 20 35 -140 30 20 In addition, on the send side, the attenuation over a band off 25 Hz relative to the nominal frequency of the pilot sh
42、ould be such that the total energy of a white noise signai occupying that bandwidth is attenuated by at least 20 dB (see Annex A), Any unwanted signals falling within this band are liable to be within the passband of the pilot pick-off filter and may cause interference with an automatic gain regulat
43、or, measuring equipment, etc. Pilot frequency 13.2 Protection and suppression, of the supergroup reference pilots Disturbing frequency in group 3 Considerations analogous to those outlined above lead to the recommending of identical values but now applying to channels 1 and 2 of the terminal equipme
44、ns (instead of channels 6 and 7 respectively). However, the total attenuation required may be obtained, at the discretion of the Administration concerned, either in the channel terminal equipment or in the group-translating equipment (using blocking filters either at 104.140 kiiz or 104.080 1Hz in g
45、roup 3 of the group-translating equipment or at 41 1.860 kHz or 41 1.920 IrHz), or as a combination of the two equipments. The precautions to be taken against such interference in the channel equipment have therefore to be determined in relation to the precautions taken in the group equipment (Recom
46、mendation G.233, 9). The total attenuation required is indicated in Table 4iG.232. (kW (1) 41 1.920 41 1.860 (kW (2) 104.080 104.140 Remarks, the same as in Q 12.1 above, relative to the frequency bands in which these values of attenuation are necessary, remain valid in the present case. However, th
47、e attenuation in the sending side, within a band of f 25 Hz relative to the nominal frequency of the supergroup pilot, may with difficulty be obtained at other than voice frequency. Fascicle 111.2 - G.232 9 COPYRIGHT International Telecommunications Union/ITU TelecommunicationsLicensed by Informatio
48、n Handling Services13.3 Mutual interference between pilots and outband signalling In the specification of equipment intended for use with outband signalling, account should be taken of the mutual disturbance between signalling and pilots, and calculation made for each case of the protection necessar
49、y as a function of the parameters of the signalling system, according to the following principles: 13.3.1 Protection ofpilots When the signalling current is interrupted at the different speeds determined by the signalling code, the level of the signalling interference resulting in a band of 25 Hz on either side of the pilot frequency should remain at least 20 dB below the level of the pilot. If the transmission of the signalling current is of very short duration compared with the time constant of the regulator, a higher level of interference could be tolerated. Precautions s
