1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 2 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU4%,%2!0(94%,%2!0(G0G042!.3-)33)/.).4%2“!.$G0G04%,%2!0(9G0G0/6%2/0%.G0G13G07)2%G0G0 G13#(!%,G0G0#!22)%23934%-3)45G134G0G0RecommendationG0G02 (Extract from the “LUEG0“OOK)NOTES1 ITU-T Recommendation R.49 was pu
2、blished in Fascicle VII.1 of the Blue Book. This file is an extract from theBlue Book. While the presentation and layout of the text might be slightly different from the Blue Book version, thecontents of the file are identical to the Blue Book version and copyright conditions remain unchanged (see b
3、elow).2 In this Recommendation, the expression “Administration” is used for conciseness to indicate both atelecommunication administration and a recognized operating agency. ITU 1988, 1993All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, elec
4、tronic ormechanical, including photocopying and microfilm, without permission in writing from the ITU.Fascicle VII.1 - Rec. R.49 1Recommendation R.49Fascicle VII.1 - Rec. R.49INTERBAND TELEGRAPHY OVER OPEN-WIRE 3-CHANNEL CARRIER SYSTEMS(New Delhi, 1960)The CCITT,considering(a) It is considered neces
5、sary to introduce, for international traffic, an open-wire carrier system that usescommon line repeaters for telephone and interband telegraph channels.(b) This is important for some Administrations that desire to have a small number of telegraph channels (up tosix) without having to use a standard
6、voice-frequency telegraph system on one of the telephone circuits, therebyeffecting an economy, as all the telephone circuits are retained entirely for telephone traffic.(c) The arrangement of line frequencies as far as the telephone channels are concerned should be as specifiedin Recommendation G.3
7、61 1.unanimously declares the following view:1 Four interband telegraph channels, for a modulation rate of 50 bauds, can be set up over an open-wire carriersystem by the use of line repeaters common to the telephone channels and the telegraph channels provided that thesystem in question conforms to
8、the Recommendation cited in 2.2 The nominal frequencies of these four telegraph channels are as follows:2.1 Low-frequency direction of transmission:3.22 3.34 3.46 and 3.58 kHz.2.2 High-frequency direction of transmission:a) telephone channels occupying the frequency band 18 and 30 kHz:30.42 30.54 30
9、.66 and 30.78 kHz;b) telephone channels occupying the frequency band 19 and 31 kHz:18.22 18.34 18.46 and 18.58 kHz.3 When in-band signalling is employed on the telephone channels (as opposed to out-band signallng outside the4-kHz bandwidth), it becomes possible to provide two additional telegraph ch
10、annels having the following nominalfrequencies:3.1 Low-frequency direction of transmission:3.70 and 3.82 kHz.3.2 High-frequency direction of transmission:a) telephone channels occupying the frequency band 18 and 30 kHz:30.18 and 30.30 kHz;b) telephone channels occupying the frequency band 19 and 31
11、kHz:18.70 and 18.82 kHz.4 In those cases where, as a result of agreement between the Administrations concerned, the system employs anupper pilot of 17.800 kHz, the following frequencies may be used as alternatives to those specified in 2.2 b) and 3.2 b) above. This alternative arrangement permits, i
12、n certain types of systems, a more economical modulationprocess: 31.42 31.54 31.66 and 31.78 kHz, instead of 18.22 18.34 18.46 and 18.58 kHz, also 31.18 and 31.30kHz instead of 18.70 and 18.82 kHz.2 Fascicle VII.1 - Rec. R.495 This Recommendation applies to amplitude-modulated telegraphy and to freq
13、uency-modulated telegraphy.6 It is not considered desirable to standardize absolutely the power transmitted to the line as this may bedependent upon the conditions on the open-wire route. Under favourable conditions a recommendable value for thepower on each telegraph channel would be 20 dBm0 (refer
14、red to one milliwatt at a point of zero relative level).7 For amplitude modulation the tolerance on the sent frequency will be 6 Hz and for frequency modulation thetolerances given in Recommendation R.35 will apply.8 In tests made on the local end, equipments should meet the distortion conditions de
15、scribed in (2) ofRecommendation R.50 for amplitude modulation, and those described in 13 of Recommendation R.35 for frequencymodulation.9 The correspondence between the significant conditions described in 15 of Recommendation R.31 and 9 ofRecommendation R.35 applies to these channels for interband telegraphy.References1 CCITT Recommendation Systems providing three carrier telephone circuits on a pair of open-wire lines,Rec. G.361.2 Ibid., 2.
