1、INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU J.24 (ex CMTT.474) (02/82 TELEVISION AND SOUND TRANSMISSION MODULATION OF SIGNALS CARRIED BY INTERFERING SIGNALS FROM POWER SUPPLY SOURCES BY SOUND-PROGRAMME CIRCUITS ITU-T Recommendation J.24 (Formerly Recom
2、mendation ITU-R CMTT.474) STD-ITU-T RECMN J-24-ENGL 1782 I qBb259L Ob31757 275 FOREWORD The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the International Telecom- munication Union. The ITU-T is responsible for studying technical, operating and tariff questions and is
3、suing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, established the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on
4、 these topics. ITU-T Recommendation J.24 (formerly Recommendation ITU-R CMTT.474) was elaborated by the former ITU-R Study Group CMTT. See Note 1 below. NOTES 1 As a consequence of a reform process within the International Telecommunication Union (ITU), the CCITT ceased to exist as of 28 February 19
5、93. In its place, the IT Telecommunication Standardization Sector (ITU-T) was created as of 1 March 1993. Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector (ITU-R). Conforming to a joint decision by the World Telecommunication Standardizatio
6、n Conference (Helsinki, March 1993) and the Radiocommunication Assembly (Geneva, November 1993), the ITU-R Study Group CMTT was transferred to ITU-T as Study Group 9, except for the satellite news gathering (SNG) study area which was transferred to ITU-R Study Group 4. 2 telecommunication administra
7、tion and a recognized operating agency. In this Recommendation, the expression ?Administration? is used for conciseness to indicate both a O ITU 1990 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photoc
8、opying and microfilm, without permission in writing from the ITU. STD-ITU-T RECMN J*ZY-ENGL 1782 4Ab255L Ob31758 121 Recommendation 5.24) MODULATION OF SIGNALS CARRIED BY SOUND-PROGRAMME CIRCUITS BY INTERFERING SIGNALS FROM POWER SUPPLY SOURCES (1970; revised 1982) The CCIR UNANIMOUSLY RECOMMENDS th
9、at the ratio of a sine-wave test signal applied to the sound programme circuit to the highest level unwanted side component due to modulation caused by interfering signals from power supply sources should be greater than 45 dB. Note I - This limit is identical to that which is considered tolerable f
10、or other types of transmission (FM Note 2 - This limit applies only where the interfering signals are the usual low order mains frequency harmonics. For Note 3 -For design purposes this limit should be taken as applying to the hypothetical reference circuit of length 2500 km. and AM-VF telegraphy, facsimile transmission, speech, telephone signalling and data transmission). modulation by much higher frequencies a more stringent limit is likely to apply. I) Formerly Recommendation ITU-R CMTT.474. Recommendation 5.24 (02/82) 1
