1、ITU-T RECMN*O*33 95 48b259L 0600692 BL7 INTERNATIONAL TELECOMM UN KATION UN ION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU 0.33 (07/95) SPECIFICATIONS FOR MEASURING EQUIPMENT AUTOMATIC EQUIPMENT FOR RAPIDLY MEASURING STEREOPHONIC PAIRS AND CIRCUITS, LINKS AND CONNECTIONS MONOPHONIC SOUND-
2、PROGRAMME ITU-T Recommendation 0.33 (Previously “CCIlT Recommendation”) FOREWORD The ITU-T (Telecommunication Standardization Sector) is a permanent organ of the International Telecommunication Union (ITU). The ITU-T is responsible for studying technical, operating and tariff questions and issuing R
3、ecommen- dations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, establishes the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on thes
4、e topics. The approval of Recommendations by the Members of the ITU-T is covered by the procedure laid down in WTSC Resolution No. 1 (Helsinki, March 1-12, 1993). ITU-T Recommendation 0.33 was revised by ITU-T Study Group 4 (1993-1996) and was approved under the WTSC Resolution No. 1 procedure on th
5、e 27th of July 1995. NOTE In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. O ITU 1995 All rights reserved. No part of this publication may be reproduced or utilized in any form or by
6、 any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the IT. ITU-T RECMN*0*33 95 48b259L Ob00694 69T CONTENTS General . Basic design . 2.1 Start/source/program identification 2.2 Modes of operation . Design and construction . Parameters 4.1 R
7、eceived level (insertion gain) . 4.2 Frequency/attenuation distortion (frequency response) 4.3 Distortion 4.4 Signai-to-noise ratio 4.5 Compandor linearity . 4.6 Expanded noise . Stereo parameters . 5.1 Interchannel difference in gain and phase 5.2 Interchannel crosstalk and circuit transposition Eq
8、uipment characteristics - Sending unit Equipment characteristics - Receiving unit . 7.1 Input impedance: 20 kohms . 7.2 Minimum accuracy and range . Operating equipment Annex A . Measurement sequence for monophonic sound-programme circuits Annex B . Measurement sequence for stereophonic pairs of sou
9、nd-programme circuits Annex C . Measurement sequence for medium band sound-programme circuits Annex D . Measurement sequence for narrow-band (telephone type) circuits Annex E . Measurement sequence for narrow-band (telephone-type) circuits used for sound-programme transmissions which are fitted with
10、 compandors . Annex F . Measurement sequence for the CMTT three-levei test signals (without station announcement) for the alignment of international sound-programme connections References . Page 1 1 2 2 3 3 3 3 3 4 4 4 4 4 4 5 5 5 5 5 6 7 8 9 10 11 12 Recommendation 0.33 (07/95) 1 . 486259L 0600695
11、526 m Recommendation 0.33 AUTOMATIC EQUIPMENT FOR RAPIDLY MEASURING STEREOPHONIC LINKS AND CONNECTIONS PAIRS AND MONOPHONIC SOUND-PROGRAMME CIRCUITS, (Malaga-Torremolinos, 1984; amended at Melbourne, 1988; revised in 1995) 1 General An automatic measuring equipment for sound-programme circuits must
12、be capable of rapidly measuring ail relevant parameters necessary for checking the quality of such circuits. The parameters to be measured and the facilities that must be offered by the equipment are outlined in this Recommendation but neither the measurement method nor the processing of the results
13、 are specified in detail. Manufacturers are thus free to adopt any appropriate design that will fulfil the requirements of this Recommendation. However, it is evident that it would be advantageous to control the measurement sequence by stored programs. The use of different measuring sequences, each
14、suited to the requirements of individual users and individual applications should be possible. It should be noted that the equipment will meet the requirements of Recommendations N.12 i and N.13 2. However, measurement of every parameter specified in Recommendations N.10 3, N.21 4 and N.23 5 is not
15、possible, e.g. group delayl-equency response. 2 Basic design The equipment shall consist of either two units, send and receive, or a combined sending and receiving unit of modular construction permitting a send-only or receive-only facility. The measurement results should be made available by a dire
16、ct display via a storage mechanism to permit a long-term display of any measured parameter. The results of the measurements are not only to permit an immediate decision by the staff in the field, but also to provide the basis for later exact evaluation by the responsible transmission engineer. It is
17、 preferred that the results be available also as a 110- and 300-baud ISO-7 bit serial data output 6 at a standard RS 232-C 7 interface, selectable between 110 and 300 bauds, or optionally, at a Standard IEEE 488/IEC 625 8 interface. In each case, the parameters measured must be clearly identified an
18、d the source code given (see 2.1). The equipment must be capable of measuring at least the following parameters: a) received level (insertion gain); b) frequency/attenuation distortion (frequency response); c) harmonic distortion (non-linear distortion); d) e) compandor linearity; 0 signal-to-noise
19、ratio unweighted, and weighted in accordance with CCIR Recommendation 468 9; programme modulated noise and expanded noise. These parameters are further defined in clause 4. In addition, the equipment must be capable of measuring in channels A and B at least the following parameters: g) h) interchann
20、el difference in gain and phase; interchannel crosstalk and circuit transposition, The stereo parameters are further defined in clause 5. The physical design should preferably be such that this capability is provided by user conversion of the monophonic equipment by the addition of appropriate plug-
21、in units and, possibly, minor internal wiring changes, .,i“ Recommendation 0.33 (07/95) 1 ITU-T RECMN*O.33 95 486259L Ob00696 4b2 The equipment will be required to send audio test signals at amplitudes consistent with that required at the users test point. Since the nominal working levels vary from
22、broadcasting organization to broadcasting organization, and from PTT Administration to Administration, it is not desirable to specify absolute levels. “TEST level has therefore been defined as the level 9 dB below the maximum permitted level at the point at which the measurement is made. TEST level
23、corresponds to an absolute value of O dBmO when measured at a point of zero relative level (O dBr) lo. Manufacturers of automatic measurement equipment should therefore choose to make TEST level equal to a convenient level (e.g. O dBmO). At this fixed level, the send frequency amplitudes in the prog
24、ramme measurement sequences will conform to the definitions for permitted maximum level (+9 dBmOs), alignment level (O dBmOs) and measuring level (-12 dBmOs) given in Recommendation N. 15 1 i. Switching should be provided so that TEST level may be set to 4 dB, O dB. or -3 dB with respect to 0.775 V
25、r.m.s. This switch must be protected, particularly for absolute values greater than O dBm0, against unintentional operation, e.g. by mounting it inside the instrument. Consideration should also be given to providing -20 dB with respect to 0.775 V r.m.s. 2.1 Starsourcdprogram identification The measu
26、rement sequence will be chosen to suit the requirements of individual applications. Defined measurement programs are annexed to this Recommendation. The sequence of operations of the measurement program together with the associated time units are shown. The sequence of audio test signals is to be pr
27、eceded by a start/source/program identification signal which will: - - - instruct the receiving unit to start the measurement sequence; identify the source of the test signals; indicate which of the stored measurement programs is to be used, The start/source/program identification signal using the I
28、SO-7 6 code with one even parity bit and two stop bits, is to be sent by frequency-shift keying with a mark frequency of 1650 Hz and a space frequency of 1850 Hz, at a transmission rate of 110 bauds. The message structure of the identification signai is formed by the following order of characters: -
29、 - - Special signalling (one character); - - Start of heading (character “SOH”); Source identification (four alphanumeric characters); Start of text (character “STX); Measurement program identification (two numeric characters 00-99); - End of text (character “EW). The mark frequency shall be transmi
30、tted for at least 18 ms (two bits) before the start bit of the SOH character. The end of the second stop bit of the ETX character defines the start of the measurement sequence. The start/source/program identification signal shall be set at 12 dB below TEST level. 2.2 Modes of operation It shall be p
31、ossible to operate the equipment in automatic or manual modes. 2.2.1 Automatic mode In the automatic mode, the sending unit shall cycle once through a complete programmed test sequence on receipt of a start signal given either by a push-button on the sending unit or by the momentary closing of a rem
32、ote pair of contacts. The receiver shall, on receipt of the identification signal from the sending unit, cycle once through the complete programmed measurement sequence, storing and/or printing the results for subsequent examination. 2 Recommendation 0.33 (07/95) 2.2.2 Manual mode 2.2.2.1 Sending un
33、it In the manual mode, it shall be possible to cycle the sending unit through the measuring sequence to any chosen test element, upon which the appropriate test signal will be sent continuously. This mode should thus permit the sending unit to operate with manual measuring equipment. It shall also b
34、e possible to manually adjust the output signal to any frequency within the range 40 to 15 O00 Hz to a resolution of better than 5 Hz. The output shall be adjustable within the range -12 dB to +15 dB with respect to 0.775 V r.m.s. with a resolution of 0.2 dB. The instrument shall indicatethe output
35、frequency and level. A flashing warning light shall operate when the output level exceeds 0.775 V r.m.s. 2.2.2.2 Receiving unit In the manual mode, it shall be possible to cycle the receiving unit through the measuring sequence to any chosen parameter measurement to permit the instrument to be used
36、with manual sending equipment. It would be advantageous to display the frequency of the incoming signal. 2.2.3 Remote control Both the sending and receiving units should optionally offer the possibility of remote control. This could be either the RS 232-C 7 or EEE 488/IEC 625 8 interface. 3 Design a
37、nd construction It should be noted that the group delay encountered on long circuits may lead to measurement error, particularly at low frequencies. The design of measurement circuits should therefore be such that measurements are made only after sufficient time has been allowed for the received wav
38、eform to stabilize. In general, the design and construction of the equipment shall conform to national and international provisions, especially in relation to safety requirements and protection against electric shock 12. 4 Parameters 4.1 Received level (insertion gain) 1020 Hz is sent at TEST level;
39、 the received level shall be measured and the result expressed in dB with reference to TEST level. 4.2 Frequency/attenuation distortion (frequency response) The received level shall be measured at a number of discrete frequencies. These frequencies are defined in the individual measurement program.
40、The sending level shall be 12 dB below TEST level. The results shall be displayed in dB relative to the received level at 1020 Hz sent at 12 dB below TEST level. It is not considered acceptable to use the level received from the parameter in 4.1. 4.3 Distortion Total harmonic distortion shall be mea
41、sured at 60 Hz and 1020 Hz. Second harmonic distortion, k2, shall be measured at 1020 Hz. Third harmonic distortion, k3, shall be measured at 60 Hz. The sending level shall be 9 dB above TEST level. The receiving instrument shall give an r.m.s. indication of the harmonic content and the results shal
42、l be expressed in dB with respect to the received levels of the fundamentals. In order to avoid overload of carrier-frequency transmission systems, the sending of test frequencies at the maximum permitted level should be strictly in accordance with the prescriptions of Recommendation N.21 4. Program
43、s which include distortion measurements should therefore limit the duration of transmission to a single time interval (1 s) and a pause of at least one interval must be allowed when successive distortion measurements are to be made. Recommendation 0.33 (07/95) 3 It shall be possible to insert the te
44、st cycle, the measurement of non-linearity distortion by either duplication of the stored programmes with and without this measurement or by the use of a non-locking switch. NOTE -The frequency of 1020 Hz has been chosen to avoid using a sub-multiple of a digital sampling rate. 4.4 Signal-to-noise r
45、atio The sending unit shall suitably terminate the input to the circuit under test and the receiving unit shall measure the highest quasi-peak value, either weighted or unweighted, over a period of eight seconds, consistent with CCIR Recommendation 468 9. The results shall be given in dB with respec
46、t to the received TEST level at 1020 Hz or at maximum permitted level (+9 dBmO). Selection of the weighted or unweighted characteristic and the level reference shall be made by a manually operated switch on the receiving unit. The switch shall be protected against unintentional operation and its pos
47、ition shall be indicated in the results. The normal position will correspond to the weighted characteristic. 4.5 Compandor linearity 820 Hz tone is sent during three consecutive time intervals, at +6 dB, -6 dB and +6 dB with respect to TEST level. The receiving unit shall indicate the levels as rece
48、ived. 4.6 Expanded noise The time interval used for the measurement of distortion at 60 Hz may also be used for the measurement of expanded noise. A high-pass filter (fo I400 Hz, and I 60 dB/60 Hz) is used to eliminate second and third order harmonics. The remaining noise will be measured, either we
49、ighted or unweighted, with a quasi-peak response. 5 Stereo parameters 5.1 Interchannel difference in gain and phase When the stereo modules are used, the equipment shall measure simultaneously the difference in phase and level between the signals present at its two inputs A and B. Measurements shall be made at all frequencies specified for the measurement of frequency/attenuation distortion. The instrument shall preferably indicate the polarity of the error. The results shall be expressed in dB and degrees, taking the A channel as reference.
