ITU-T G 226-1993 NOISE ON A REAL LINK《实际链路上的噪声》.pdf

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./)3%G0G0/.G0G0!G0G02%!,G0G0,).+)45G134G0G0RecommendationG0G0 (Extract fro

2、m the “LUEG0“OOK)NOTES1 ITU-T Recommendation G.226 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 Book

3、 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 be

4、 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.226 1Recommendation G.226Fascicle III.2 - Rec. G.226NOISE ON A REAL LINK1 Cable systemsIt should be appreciated that

5、designers are usually concerned, not with particular circuits or links, but with plantthat will be used for the establishment of many links. It is not practicable for the CCITT to specify the performance ofevery real link that may be established, or for the designer to contemplate changing his desig

6、n to suit the various lengthsor other conditions on different real links. The CCITT has therefore defined hypothetical reference circuits, so thatdesigners can be sure that, if their particular design of plant is used throughout a real circuit made up in the same way asa hypothetical reference circu

7、it, the performance specified by the CCITT for the hypothetical reference circuit will berealized on that real circuit.A real international link usually has a different make-up from that of the hypothetical reference circuit, andoften includes equipments of different design. For each of these two re

8、asons the performance to be expected from reallinks cannot be deduced uniquely from the Recommendations relative to hypothetical reference circuits.However, on a real homogeneous section it must be expected that the noise power measured at the time ofcommissioning, and with a conventional load as de

9、fined in 2 of Recommendation G.223, will be about the same as thatcalculated taking into account the particular composition of the real homogeneous section and the real parameters as wellas the implications of Recommendation G.222, 2.6. There should be no cause for anxiety unless the measured noisep

10、ower exceeds the calculated power by an appreciable amount, which might indicate a fault somewhere in theequipment. In such a case, every effort should be made to reduce the measured noise power to a value of the same orderas that calculated.2 Radio linksSee CCIR Recommendation 395 1.Reference1 CCIR Recommendation Noise in the radio portion of circuits to be established over real radio-relay links forFDM telephony, Vol. IX, Rec. 395, Dubrovnik, 1986.