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%-35.7!.4%$G0G0-/$5,!4)/.G0G0!.$0(!3%G0G0*)44%2)45G134G0G0RecommendationG0G0
2、(Extract from the “LUEG0“OOK)NOTES1 ITU-T Recommendation G.229 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 t
3、he 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 rights reserved. No part of this public
4、ation 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 III.2 - Rec. G.229 1Recommendation G.229Fascicle III.2 - Rec. G.229UNWANTED MODULATION AND PHASE JITTER(Geneva, 1972, fu
5、rther amended)1 Unwanted modulation by harmonies of the power supply and other low frequencies1.1 Requirements on carrier transmission systemsTo enable the limit indicated in the Recommendation cited in 1 to be met, it is recommended that a minimumside component attenuation of 45 dB should be obtain
6、ed when a signal is transmitted over a channel having the samecomposition as the 2500 km hypothetical reference circuit for the system concerned.This limit is subdivided as indicated in 1.2 and 1.3 below into allocations to terminal and to line equipment.1.2 Combined effect due to all translating eq
7、uipmentThe combined effect due to all translating equipment on the hypothetical reference circuit should correspond toa minimum side component attenuation of 48 dB.For each translating equipment, send and receive side taken separately, and measured at the signal output, a sidecomponent attenuation o
8、f at least 63 dB should be obtained under normal operating conditions. Under adverse powersupply conditions a minimum of 60 dB should be met. It is expected that then an overall value of 48 dB, indicatedabove, will only rarely be exceeded.Note - The above requirements are derived from the hypothetic
9、al reference circuits for the 4 MHz, 12 MHz and60 MHz systems. The same figures may be applied to other systems provided that their hypothetical reference circuitdoes not differ significantly from those referred to above.1.3 Combined effects due to all line equipmentThe combined effects due to all l
10、ine equipment on the hypothetical reference circuit should correspond to aminimum side component attenuation of 48 dB.Line equipments can be subject to two types of interference which will cause side components on a transmittedsignal:- Effects from power supplies (for example, a residual mains frequ
11、ency ripple may be superimposed on thed.c. power feeding current). These are potentially systematic on the complete length of the circuit.- Effects from voltages caused by induction (for example, from railway traction currents). They are notexpected to occur as systematically as the effects from the
12、 power supplies.The influence caused by power supply ripple should be such that a minimum side component attenuation of 51dB is observed for the combined effect of all line equipment on the hypothetical reference circuit. It is recommended thaton a single power feeding section, the side component at
13、tenuation should not be less than 51 + 10 log k dB, where k isthe number of power feeding sections on the hypothetical reference circuit.Note - Based on the assumptions that some power feeding sections may be powered from battery supplies andthat adverse cumulation over the full length of the hypoth
14、etical reference connection is unlikely, it can be expected thatthe limit of 51 dB will be observed with a high probability.The influence caused by induced voltages should be such that a minimum side component attenuation of 51 dBis observed for the combined effects of all line equipment on the hypo
15、thetical reference circuit. However, voltagescaused by induction vary considerably with time. The effect of a source of induction is very often confined to one powerfeeding section. It seems very unlikely that the induced voltage reaches its maximum value in more than one section atthe same instant.
16、2 Fascicle III.2 - Rec. G.229It is recommended that the r.m.s. value of the longitudinal voltage in a power feeding section caused byinduction under normal operating conditions (excluding short circuits and arcing on railways, etc.) should not exceed150 volts. (This limit has been recommended regard
17、ing safety aspects and is contained in 2. It seems reasonable toadopt the same value for the present purpose.)Calculations indicate that an allowance of 6 dB for the combined effect of several sections under the influenceof induction should cover the majority of likely cases. It is therefore recomme
18、nded that a minimum side componentattenuation of 57 dB should be observed on a power feeding section under the influence of the maximum allowedinduced voltage. It is estimated that then the value of 51 dB on a circuit of 2500 km would only be exceeded in rarecircumstances and infrequently, particula
19、rly in view of the fact that only a fraction of the total length would be exposedto interference by induction.2 Phase jitter due to translating equipmentsFor each translating equipment, send and receive sides taken separately, a phase jitter on a signal should notexceed 1 peak-to-peak when measured
20、on the output of the equipment. The measurement should be of all phase jittercomponents on each side of the signal in the frequency band 20-300 Hz, i.e. equivalent to the frequency band indicatedin Recommendation O.91 3.Note 1 - The above requirement is derived from a consideration of data signals o
21、n a telephone-type circuit overa 2500-km hypothetical reference circuit. Conforming to this requirement will ensure a high probability that the overallphase jitter from this source will not exceed 6 peak-to-peak. This performance will also ensure a high probability thatfor telephone speech transmiss
22、ion the phase jitter will be below the detection threshold of a majority of listeners.Note 2 - In practice it is expected that phase jitter of the magnitude given above will occur only on translatingequipments using high frequency carriers and that correspondingly lower phase jitter will be caused b
23、y translatingequipment using lower frequency carriers.Note 3 - Where the phase jitter is caused mainly by random noise a peak-to-peak/r.m.s. ratio of 10 should beassumed.References1 CCITT Recommendation General performance objectives applicable to all modern international circuits andnational extens
24、ion circuits, Vol. III, Rec. G.151, 7.2 CCITT manual Directives concerning the protection of telecommunication lines against harmful effects fromelectricity lines, Chapter IV, 6, 7 and 71, ITU, Geneva, 1963, 1965, 1974, 1978.3 CCITT Recommendation Essential clauses for an instrument to measure phase jitter on telephone circuits,Vol. IV, Rec. O.91.
