1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU).4%2.!4)/.!,G0G0!.!,/5%G0G0#!22)%2G0G03934%-3%.%2!,G0G0#(!2!#4%2)34)#3G0G0#/-/.G0G04/G0G0!,!.!,/5%G0G0#!22)%2G1342!.3-)33)/.G0G03934%-3#/.6%.4)/.!,G0G04%,%0(/.%G0G03).!,)45G134G0G0RecommendationG0G0 (Extract f
2、rom the “LUEG0“OOK)NOTES1 ITU-T Recommendation G.227 was published in Fascicle III.2 of the Blue Book. This file is an extract fromthe Blue 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 Bo
3、ok 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 rights reserved. No part of this publication may
4、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 III.2 - Rec. G.227 1Recommendation G.227Fascicle III.2 - Rec. G.227CONVENTIONAL TELEPHONE SIGNAL(Geneva, 1964; amended at Mar del
5、Plata, 1968)1 PrincipleFor the calculation or measurement of crosstalk noise between adjacent channels and, generally speaking, whenit is desired to simulate the speech currents transmitted by a telephone channel1), the CCITT recommends that aconventional telephone signal be used, the main character
6、istic of which is a shaping network as a function of thefrequency.This network is defined by the following transfer coefficient as a function of the frequency:FIGURE 1/G.227The response curve of the network is shown in Figure 2/G.227, and an example of the design is given inFigure 3/G.227 with relev
7、ant values._1)Care is needed in applying this conventional signal to simulate speech loading, since the statistics of aGaussian noise signal and of real speech are different. A speech-simulating generator for loading purposes is given in1.2 Fascicle III.2 - Rec. G.227FIGURE 2/G.227Relative response
8、curve of the shaping network of the conventional telephone signal generatorFIGURE 3/G.227Shaping network of the conventional telephone signal generatorFascicle III.2 - Rec. G.227 32 Example of network designThe network is made up of three bridged T sections with a constant characteristic impedance e
9、qual to R0ohms.Figure 3/G.227 represents the network and indicates the values of the various components normalized to R0.A tolerance of 1% can be allowed on the value of each component.Note - If 1, 2, 3are the “composite“ transfer coefficients of sections 1, 2 and 3 respectively, we have:The minimum
10、 composite loss2)of the complete network lies in the vicinity of 600 Hz and equals a0 2.9 dB forthis example.The curve in Figure 2/G.227 represents, as a function of frequency, the composite loss2)of the network inFigure 3/G.227 relative to the minimum loss a0.3 Signal at the network inputThe networ
11、k may be energized either by a uniform-spectrum random noise signal or by a closely spacedharmonic series. In the latter case, the following precautions are necessary:1) Spacing of the harmonics should not exceed 50 Hz.2) The measuring instrument must have an adequate integrating time with respect t
12、o the fundamental periodof the harmonic series. Types of CCITT instruments in general use, such as the psophometer, are believedto be satisfactory in this respect.3) The peak/r.m.s. ratio of the signal should not exceed 3.5. This requirement may be achieved, in the case ofa particular generator, by
13、means of an associated phase-changing network.4) The energizing signals (uniform-spectrum random noise and harmonic series) could lead to differentresults for subjective, e.g. aural assessments at the receiving end, and such measurements should not,therefore, involve the use of the conventional tele
14、phone signal generator. That apparatus would be usedsolely for objective measurements, in which a psophometer served as measuring instrument.Reference1 CCITT - Question 5/C, Annex 2, Green Book, Vol. III, ITU, Geneva, 1973._2)Composite loss equals the insertion loss in this particular case since the source and the load impedances are equal.
