1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 . TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU-!).4%.!.#%G0G0/&G0G0).4%2.!4)/.!,3/5.$G0G13G002/2!-%G0G0!.$G0G04%,%6)3)/.42!.3-)33)/.G0G0#)2#5)43%33%.4)!,G0G042!.3-)33)/.G0G00%2&/2-!.#%/“*%#4)6%3G0G0&/2G0G0).4%2.!4)/.!,3/5.$G0G13G002/2!-%G0G0#%.42%3G0G0 )
2、30#G9)45G134G0G0RecommendationG0G0. (Extract from the “LUEG0“OOK)NOTES1 ITU-T Recommendation N.11 was published in Fascicle IV.3 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, theconte
3、nts of the file are identical to the Blue Book version and copyright conditions remain unchanged (see below).2 In this Recommendation, the expression “Administration” is used for conciseness to indicate both atelecommunication administration and a recognized operating agency. ITU 1988, 1993All right
4、s reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic ormechanical, including photocopying and microfilm, without permission in writing from the ITU.Fascicle IV.3 - Rec. N.11 1Recommendation N.11Fascicle IV.3 - Rec. N.11ESSENTIAL TRANSMISSION P
5、ERFORMANCE OBJECTIVES FORINTERNATIONAL SOUND-PROGRAMME CENTRES (ISPC)1 Transmission level at interconnection pointsLevels at interconnection points must be such that a signal level of 0 dBm0 on the incoming circuit gives riseto a signal level of 0 dBm0 on the outgoing circuit. A nominal relative lev
6、el of +6 dBr is recommended atinterconnection points (see also Figure 3/J.13 1 and Recommendation J.14, 1 2).2 Balance with respect to earthThe balance with respect to earth (measured by the method defined in 3) of nominally balanced apparatusshould be at least 60 dB in order to give an adequate sup
7、pression against longitudinal interference induced by powersupplies, alarm circuits, etc.3 Access pointsThere should be a well-defined circuit access point associated with the input to a sound-programme circuit atwhich the transmission test levels at all frequencies over the band are nominally the s
8、ame. This access point may be theinterconnection point or separated therefrom by distortion-free loss or gain. A well-defined circuit access point shouldalso be associated with the output of a sound-programme circuit.The nominal relative level at each access point will be chosen by each Administrati
9、on, bearing in mind thedynamic range of their testing and transmission apparatus.Measurements on a sound-programme circuit should be made between such circuit access points.Administrations may also find it convenient to arrange for sound-programme circuit sections to be equippedwith similar access p
10、oints. International sound-programme circuit sections which can be connected to a variety of othercircuit sections should always be equipped with such access points.4 Interconnection of sound-programme circuits4.1 Constant voltage techniqueIf the modulus of the output impedance of any source is not
11、greater than one hundredth of the modulus of thelowest impedance that can be connected to it (bearing in mind that it is possible to connect two or more loads inparallel) then the change in level due to change of load will be negligibly small (less than 0.1 dB approximately).4.2 Impedance matching t
12、echniqueIf the return loss versus the nominal design resistance of the measuring instruments of the impedancepresented by incoming and outgoing circuits to the points where they are interconnected is at least 26 dB over the range50 Hz to 10 or 15 kHz, the error due to mismatch will be insignificant,
13、 assuming that the impedance of testingapparatus has at least 30-dB return loss versus the nominal design resistance, which can be, for example, 600 ohmsnon-reactive.4.3 Digital techniqueThe interconnection of digital sound-programme circuits will be made by preference with the aid of a digitalinter
14、face presenting the following characteristics: plesiochronous or synchronous operation bit rate of 384 kbit/s, 1544 kbit/s or 2048 kbit/s 384 kbit/s to carry either one 15 kHz or two 7 kHz sound-programme signals.Interface for other bit rates, namely to provide for 15 kHz monophonic and stereophonic
15、 circuits with linearcoding and for 7 kHz monophonic sound-programme circuits with companded coding are the subject of further study.2 Fascicle IV.3 - Rec. N.11References1 CCITT Recommendation Definitions for international sound-programme circuits, Vol. III, Rec. J.13.2 CCITT Recommendation Relative levels and impedances on an international sound-programme connection,Vol. III, Rec. J.14.3 CCITT Recommendation Transmission aspects of unbalance about earth Vol. III, Rec. G.117.
