1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 . TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU-!).4%.!.#%G0G0/ and ifconsidered useful: 30, 40, 11 000, 12 000 and 15 000 Hz: for a 6.4-kHz circuit: 50, 80, 100, 200, 500, 800, 1000, 2000, 3200, 5000 and 6400 Hz3)The equalizers are adjusted to bring the
2、curve within CCITT limits, which are given above.3.2 Measurement of group-delay distortion 6If necessary, the group-delay distortion/frequency characteristic is plotted for the whole international sound-programme circuit.3.3 Measurement of circuit noiseWhen, after all necessary adjustments, the inte
3、rnational sound-programme circuit meets the CCITTRecommendations, noise measurements are made.These should consist of the weighted noise reading using a meter and network conforming toRecommendation O.41 10 or CCIR Recommendation 468 11 or a combination of these.The noise limits given in the tables
4、of this Recommendation are for circuits of 840 km maximum length. Forlonger circuits appropriate limits may be calculated from the formula given in CCIR Recommendation 605 2.3.4 Measurement of nonlinearity distortionFor circuits routed entirely on audio pairs and not equipped with pre-emphasis equip
5、ment the nonlinearitydistortion is measured at the end of the international sound-programme circuit by sending, for a few seconds, asinusoidal signal at an appropriate frequency in the band to be transmitted at a level of +9 dBm0._3)Administrations are invited to propose measuring frequencies for 5
6、kHz circuits, 7 kHz circuits, and 15 kHz circuits. ISOstandard No. 266 9 should be taken into account.Fascicle IV.3 - Rec. N.21 3For a circuit which includes at least one carrier section no measurement of nonlinearity distortion should bemade. However, if, in very exceptional cases, it should be ess
7、ential, in order to provide service on such a circuit, tocarry out a check of nonlinearity distortion, for example, to locate a fault, the frequency of the sent signal should notexceed 1020 Hz at +9 dBm0 and the period for which the tone is connected should be as short as possible - that is, notmore
8、 than about four seconds. However the best procedure would be to use a suitable automatic measuring equipmentif such is available (see Recommendation O.31 3, 4, 5).The total harmonic-distortion coefficient for the sound-programme hypothetical reference-circuit (2500 km)must not exceed 4% (harmonic m
9、argin 28 dB) at any frequency4)within the transmitted band. For shorter and for lesscomplex circuits, the distortion should be less.Moreover, since end-to-end measurements of nonlinearity distortion on circuits routed on carrier systemsmight give rise to serious disturbance to transmission on other
10、channels, especially if the group is transmitted on atransistorized carrier system, it is permitted to make only local measurements of non-linearity distortion on terminalmodulating and demodulating equipments. For example, a sound-programme circuit modulating and demodulatingequipment could be conn
11、ected back-to-back via a suitable network (and suitable amplifiers if necessary) and themeasurement made on the resulting complete assembly.3.5 Additional mesurementsIn addition to the measurements specified above, the following parameters may be measured at the discretionof the Administrations conc
12、erned. Such measurements may be particularly useful when a faulty condition is suspected.3.5.1 Interference caused by power supply sourcesWhen a sinusoidal test signal is transmitted over a sound-programme circuit at a level of 0 dBmO the level ofthe strongest unwanted modulation component should no
13、t exceed 45 dBmO.3.5.2 Frequency errorThe frequency error introduced by a sound programme circuit must not exceed the following limits:7 kHz, 115 kHz 1 Hz5 kHz, 6.4 kHz, 10 kHz 2 Hz3.6 Application of a simulated sound-programme test signalCCIR Recommendation 571 12 specifies a simulated sound-progra
14、mme test equipment which can be usedfor measuring interference in other channels.3.7 Single tone-interference levelWhere this parameter is concerned, the characteristic of the weighting filter according to CCIRRecommendation 468 11 has to be taken into account by using the correction factor . The la
15、tter, which can bedetermined from Figure 1/N.21 (identical with Figure 1b of CCIR Recommendation 468 11 is to be subtracted fromthe numerical values of the tables. To exclude the effect of random noise, selective measurement is needed._4)The European Broadcasting Union has stated that many of its me
16、mbers have expressed the opinion that for a circuit 1500 kmlong, acceptable limits for nonlinearity distortion would be:40 dB at fundamental frequencies above 100 Hz,34 dB at fundamental frequencies of 100 Hz and below.4 Fascicle IV.3 - Rec. N.21d01-scFIGURE 1/N.21.D013.8 Measurement of stereophonic
17、 pairsThe quality criteria given refer to those of Recommendations O.32 4 and O.33 5. The limits can be easilymeasured with the aid of such equipments. If other measuring means are used, attention is drawn to the fact that thefrequencies of 10, 11.92 and 14 kHz should be avoided because of possible
18、stop filters which may be inserted in thetransmission equipment concerned for reducing carrier leaks.Fascicle IV.3 - Rec. N.21 53.9 Record of resultsThe final measurements made under the above headings when the circuit has been lined up are referencemeasurements and should be carefully recorded.TABL
19、E 1/N.21Limits for the lining-up of 15 kHz sound-programme circuitsItem Parameter Unit Limits1 Insertion gainAdjustement error dB 0.4Variation during 24 h dB 0.40.04 to 0.125 kHzdB + 0.4dB 1.50.125 to 10 kHz dB 0.42 Gain/frequency response 10 to 14 kHzdB + 0.4referred to 0.8 ou 1 kHzdB 1.514 to 15 k
20、HzdB + 0.4dB 2.30.04 kHz ms 373Groupe delay/frequencyresponse referred0.075 kHz ms 16to minimum14 kHz ms 5.415 kHz ms 84 Weighted noiseIdle channel dBq0ps 47Programme-modulated dBq0ps 355 Single tone interference level + dBm0s 756 Disturbing modulation by power supply dB 477 Total harmonic0.04 to 0.
21、125 kHz % 0.8distortion0.125 to 7.5 kHz % 0.46 Fascicle IV.3 - Rec. N.21TABLE 1/N.21 (cont.)Item Parameter Unit Limits8 3rd order difference tone at 0.18 kHz % 0.49 Error in reconstituted frequency Hz 0.80.04 kHz dB 5210 Intelligible crosstalk ratio 0.5 to 5 kHz dB 7615 kHz dB 6211 Error in amplitud
22、e/amplitude response dB 0.40.04 to 0.125 kHz dB 1.112 Difference in gain0.125 to 10 kHz dB 0.6between A and B channels10 to 14 kHz dB 1.1Additionalparameters14 to 15 kHz dB 2.3for stereotransmission0.04 to 0.2 kHz degree 2313 Phase difference0.2 to 4 kHz degree 11between A and B channels14 kHz degre
23、e 2314 to 15 kHz degree 3014 Intelligible crosstalk ratio A/B dB 5215 Crosstalk ratio (intermodulation) A/B dB 62Fascicle IV.3 - Rec. N.21 7TABLE 2/N.21Limits for the lining-up of 10 kHz international sound-programme circuitsItem Parameter Unit Limits1 Insertion gainAdjustment error dB 0,3Variation
24、with time dB 0,30,05 to 0,1 kHzdB + 0,8dB 2,10,1 to 0,2 kHzdB + 0,8dB 1,22Gain/frequency response referredto 0.8 or 1 kHz0.2 to 6 kHz dB 0.86 to 8.5 kHzdB + 0.8dB 1.28.5 to 10 kHzdB + 0.8dB 2.10.05 kHz ms 263Group delay/frequency response referredto minimum0.1 kHz ms 6.610 kHz ms 2.44 Weighted noise
25、 (Idle channel)adBq0ps 445 Single tone interference level + b)dBm0s 756 Disturbing modulation by power supply dB 517 Total harmonic distortion0.05 to 0.1 kHz % 1.40.1 to 10 kHz % 18 3rd order difference tone at 0.18 kHz % 19 Error in reconstituted frequency Hz 0.510 Intelligible crosstalk ratioc)dB
26、8011 Error in amplitude/amplitude response dB 0.2a)For circuits on carrier systems, it is not always possible, in absence of special precautions, to meet these limits (see Annex IIto CCIR Recommendation 504 13).b)Or 20 dB below measured weighted noise level, whichever is higher.c)It is in some cases
27、 difficult or impossible to meet these limits (see 3.8, Note 2, in Annex I to CCIR Recommendation 504 13).8 Fascicle IV.3 - Rec. N.21TABLE 3/N.21Limits for the lining-up of 7 kHz international sound-programme circuitsItem Parameter Unit Limits1 Insertion gainAdjustment error dB 0.3Variation during 2
28、4 h dB 0.30.05 to 0.1 kHzdB + 0.5dB 1.42 Gain/frequency response referred to0.8 or 1 kHz0.1 to 6.4 kHz dB 0.56.4 to kHzdB + 0.5dB 1.40.05 kHz ms 26Group delay/frequency response0.1 kHz ms 6.63 referred to minimum6.4 kHz ms 1.77 kHz ms 3.34 Weighted noiseIdle channel dBq0ps 49Programme-modulated dBq0
29、ps 375 Single tone interference level + dBm0s 796 Disturbing modulation by power supply dB 517 Total harmonic distortion0.1 kHz % 0.78 3rd order difference tone at 0.18 kHz % 0.79 Error in reconstituted frequency Hz 0.50.05 kHz dB 5910 Intelligible crosstalk ratio 0.5 to 3.2 kHz dB 806.4 kHz dB 7311
30、 Error in amplitude/amplitude response dB 0.210 Fascicle IV.3 - Rec. N.21TABLE 5/N.21Limits for the lining-up of 5 kHz international sound-programme circuitsReferences1 CCIR Recommendation Hypothetical reference circuits for sound-programme transmissions, Vol. XII,Rec. 502, ITU, Geneva, 1986.2 CCIR
31、Recommendation Estimation of transmission performance of sound-programme circuits shorter orlonger than the hypothetical reference circuit, Vol. XII, Rec. 605, ITU, Geneva, 1986.3 CCITT Recommendation Automatic measuring equipment for sound-programme circuits, Vol. IV,Rec. O.31.4 CCITT Recommendatio
32、n Automatic measuring equipment for stereophonic pairs of sound-programmecircuits, Vol. IV, Rec. O.32.Item Parameter Unit Limits1 Insertion gainAdjustment error dB 0.3Variation during 24 h dB 0.30.07 to 0.2 kHzdB + 0.5dB 1.42 Gain/frequency response referredto 0.8 or 1 kHz0.2 to 4 kHz dB 0.54 to 5 k
33、HzdB + 0.5dB 1.43 Group delay/frequency response0.07 kHz ms 20referred to minimum5 kHz ms 54 Maximum weighted noise level dBq0ps 375 Single tone interference level + dBm0s 796 Disturbing modulation by power supply dB 517 Total harmonic distortion0.1 kHz % 0.78 3rd order difference tone at 0.18 kHz %
34、 0.79 Error in reconstituted frequency Hz 0.50.07 kHz dB 6310 Intelligible crosstalk ratio 0.5 to 3.2 kHz dB 805 kHz dB 7611 Error in amplitude/amplitude response dB 0.2Fascicle IV.3 - Rec. N.21 115 CCITT Recommendation Automatic equipment for rapidly measuring stereophonic pairs and monophonicsound
35、-programme circuits, links and connections, Vol. IV, Rec. O.33.6 CCIR Report Relative values of sound-programme signal levels established with the VU meter and with apeak-programme meter, Vol. XII, Rep. 820, Geneva, 1986.7 CCITT Recommendation 1020 Hz reference test frequency, Vol. IV, Rec. O.6.8 CC
36、ITT Recommendation Bringing international group, supergroup, etc., links into service, Vol. IV,Rec. M.460.9 ISO Standard No. 266 Acoustics-preferred frequencies for measurements.10 CCITT Recommendation Psophometers (apparatuses for the objective measurements of circuit noise),Vol. IV, Rec. O.41.11 C
37、CIR Recommendation Measurement of audio-frequency noise voltage level in sound broadcasting, Vol. X,Rec. 468, ITU, Geneva, 1986.12 CCIR Recommendation A conventional test signal simulating sound-programme signals for measuringinterference in other channels, Vol. XII, Rec. 571, ITU, Geneva, 1986.13 CCIR Recommendation Performance characteristics of 10 kHz type sound-programme circuits, Vol. XII,Rec. 504, ITU, Geneva, 1982.
