1、STD-ITU-T RECMN J-LOL-ENGL 1990 Li8b259L Ob30L8b 703 INTERNATIONAL TELECOM MUNICATION UN ION ITU=T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU JA01 (ex CMTT.720) (06/90) TELEVISION AND SOUND TRANSMISSION MEASUREMENT METHODS AND TEST PROCEDURES FOR TELETEXT SIGNALS ITU-T Recommendation J.101 (For
2、merly Recommendation ITU-R CMTT.720) STDDITU-T RECMN J*LOL-ENGL 1990 48b2591 Ob30187 biT = FOREWORD The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the International Telecom- munication Union. The IT-T is responsible for studying technical, operating and tariff quest
3、ions and issuing 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 IT-T Study Groups which, in their turn, produce Recommen
4、dations on these topics. ITU-T Recommendation J. 1 O 1 (formerly Recommendation ITU-R CMTT.720) 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
5、28 February 1993. In its place, the ITU Telecommunication Standardization Sector (ITU-T) was created as of i 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 Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector (ITU-R).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
6、 Standardization 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 telecommunica
7、tion administration 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, i
8、ncluding photocopying and microfilm, without permission in writing from the ITU. STD*ITU-T RECMN J-LOI-ENGL 1990 llBb259I Ob30188 58b M Recommendation 5.101) MEASUREMENT METHODS AND TEST PROCEDURES FOR TELETEXT SIGNALS (1990) The CCIR, CONSIDERING that Report 956, Appendix I to Part 1, provides conc
9、eptual definitions to proposed data signal parameters; (a) (b) of special signals resulting from transmission over television circuits; (4 normal teletext lines; (4 analysis of results easier; (e) that Report 969 is intended to identify measurement methods and test procedures for checking the impair
10、ment that operational measurements on teletext signals need no special test signals, because they can be made on the that automatic measurement of teletext signals suits the requirements of operational staff and makes the that the definitions given in this Recommendation may be applicable to other d
11、ata services, UNANIMOUSLY RECOMMENDS, that, when measuring equipment is used to make measurements on teletext signals, the definitions used in quantiQing the parameters should be those given in Annex I. ANNEX I 1. Introduction The need for each of the measurements described in this Recommendation (a
12、nd possibly other measurements) No special test signals are necessary to meet the requirements of this Recommendation. The definitions of parameters were specifically designed to meet the requirements of automatic measuring To reduce the influence of non-linear distortions the signal shall be bandli
13、mited prior to measurement to a Due to the random nature of the teletext signals, the results will exhibit some fluctuation between successive will depend on the type of plant in use and the policy of the administrations. equipment. They are also suitable for manual measurements. frequency between t
14、he upper limit of the television system and the teletext clock frequency. measurements. 2. Definition of terms This section defines terms which are used in 3 3 to define the measurement parameters. Mean value of clock run-in The mean value of clock run-in is defined as the mean level of the clock ru
15、n-in waveform excluding the first 2.1 two bits. 2.2 All-zeros level The all-zeros level is the level resulting from a continuous stream of “zero” pulses. For measuring purposes the all-zeros level is defined as the mean level of the back porch within the nominal duration of the colour burst. Formerl
16、y Recommendation ITU-R CMTT.720. Recommendation 5.101 (06190) 1 - - - STD*ITU-T RECMN J-101-ENGL 1770 YBb2571 Ob30187 Li12 9 - 4 ?7? Basic amplitude f ?O? - 2.3 All-ones level - - -I- Peak-to-peak amplitude - -el- The all-ones level is the level resulting from a continuous stream of ?one? pulses. Fo
17、r measuring purposes the all-ones level is defined as twice the mean value of clock run-in minus the all-zeros level. 2.4 Basic amplitude The basic amplitude is the difference between the all-ones level and the all-zeros level. 2.5 Nominal teletext signal amplitude The nominal teletext signal amplit
18、ude is defined as a fixed percentage of the luminance bar amplitude and represents the ideal binary ?1? amplitude in any teletext system (Fig. 1). If no luminance bar signal is present, the nominal value of the luminance bar signal is used. Note - The luminance bar amplitude is defined in Recommenda
19、tion 569. The relationship of the nominal teletext signal amplitude to the luminance bar amplitude is defined in Recommendation 653. r White level Black level FIGURE 1 - Teietextpammefers 2.6 Timing reference The timing reference for each line is a uniform sequence of timing instants whose timing is
20、 derived only from the clock run-in of that line excluding the first two bits. The timing of these instants is such that they coincide with the average timing of the points where the clock run-in crosses the mean value defined in Q 2.5. 2.7 Sampling instants for decoding margin The sampling instants
21、 for decoding margin are half way between the timing instants defined in 9 2.6. 3. Definition of parameters 3.1 Basic amplitude error This parameter is defined as the difference between the basic amplitude and the nominal teletext signal amplitude expressed as a percentage of the latter. In terms of
22、 abbreviations in Fig. 1 the basic amplitude error is: Error! 2 Recommendation 5.101 (06190) - - STD-ITU-T RECMN J-101-ENGL 1990 9Bb257L Ob30170 L34 3.2 Peak-to-peak amplitude The peak-to-peak amplitude is defined as the sum of basic amplitude zero overshoots and ones overshoots. It is expressed as
23、a percentage of the basic amplitude (see Fig. 1). 3.3 Decoding margin The decoding margin is defined as the difference between the highest “O” bit level and the lowest “1” bit level The difference is expressed as percentage of the basic measured at the sampling instants for a bit error ratio of ampl
24、itude. 3.4 Number of run-in bits This parameter counts the number of the “1” and “O” run-in bits present at the start of the teletext waveform prior to the framing code. The result will be always an even number because a “O” bit follows every “1” run-in bit. The counting starts with the first bit wi
25、th amplitude exceeding the mean value of the clock run-in. 3.5 Data timing In teletext System B the data timing is defined as the time difference between the peak of the penultimate “1” run-in bit and the line time datum (see Report 624). In teletex System A the data timing is defined as the time di
26、fference between the leading edge of the data signal and the line time datum (see Fig. 2). Data timing (teletext System B) Timing reference Ilai (penultimate run-in bit) . . . . . . Line t : run-in code FIGURE 2 - Data timing do2-sc BIBLIOGRAPHY CROLL, M. G. 19771 Ceefax measurement techniques. BBC
27、Research Department Report RD 1977/6. DEAN, A. and HUTT, P.R. September, 19801 NEMESIS -Numerical eye measuring equipment for surveillance of insertion signals. Proc. Eighth International Broadcasting Convention (IBC SO). IEE Conf. Publ. No. 191. CCIR Documents 1986-901: CMTT/34, CMTT/207 (Germany (Federal Republic 00). Recommendation 5.101 (06/90) 3 -
