1、INTERNATIONAL TELECOMMUNICATION UNIONITU-T R.35 bisTELECOMMUNICATIONSTANDARDIZATION SECTOROF ITUTELEGRAPHYTELEGRAPH TRANSMISSION50-BAUD WIDEBAND VFT SYSTEMSITU-T Recommendation R.35 bis(Extract from the Blue Book)NOTES1 ITU-T Recommendation R.35 bis was published in Fascicle VII.1 of the Blue Book.
2、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 version and copyright conditions remain unchanged (see below).2 In this Recommendation, the expressi
3、on “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 reproduced or utilized in any form or by any means, electronic ormechanical, including photocopying
4、and microfilm, without permission in writing from the ITU.Fascicle VII.1 - Rec. R.35 bis 1Recommendation R.35 bisFascicle VII.1 - Rec. R.35 bis50-BAUD WIDEBAND VFT SYSTEMS(Geneva, 1964)The CCITT,considering(a) that Voice-frequency telegraph (VFT) systems standardized by the CCITT for 50-baud channel
5、s aredescribed in Recommendations R.31 (for amplitude modulation) and R.35 (for frequency modulation). Systems thatcomply with these Recommendations are those normally recommended by the CCITT. However, it may sometimes beadvisable to use a VFT system for a speed of 50 bauds in which the channels ha
6、ve wider spacing than in systemscomplying with Recommendations R.31 and R.35,(b) that the use of channels with a spacing of more than 120 Hz for a modulation rate of 50 bauds offers certainadvantages in the following cases:i) on links with not much traffic (which it is not intended to increase to mo
7、re than 12 channels for a long timeto come);ii) on links where channels are required to have less distortion than on channels established in accordance withRecommendations R.31 and R.35;iii) as far as maintenance is concerned, wideband equipment requires less attention,(c) that in particular, if tel
8、ephone-type circuits carrying VFT systems are unstable, the use of widebandchannels together with frequency modulation is recommended,(d) Moreover that, if systems are standardized so that only one modulation method is used, the cost ofequipment should be lower.unanimously declares the viewthat when
9、 Administrations agree to set up a 50-baud VFT system with spacing of more than 120 Hz, the VFTequipment should have the following characteristics:1) VFT systems for wideband 50-baud channels should be homogeneous systems using frequency modulationonly;2) equipment in conformity with Recommendation R.37 is recommended for this purpose.
