1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 * TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU4%,%6)3)/.G0G0!.$G0G03/5.$G0G042!.3-)33)/.!G0G0#/.6%.4)/.!,G0G04%34G0G03).!,3)-5,!4).G0G03/5.$G0G13G002/2!-%G0G03).!,3(b) that the interference depends on the total loading of the FDM system;(c) that the inte
2、rference in a channel can be measured as a noticeable deterioration of the signal-to-noise ratio;(d) that for setting realistic performance limits of interference, a conventional test signal imitating the sound-programme channel loading is desirable,unanimously recommendsthat for simulating sound-pr
3、ogramme signals a conventional test signal with the following parameters should beused:(1) a uniform spectrum energizing signal covering the frequency band up to at least 15 kHz shall be shapedaccording to the nominal insertion loss/frequency shown in Table 1/J.19 and Figure 1/J.19;(2) the conventio
4、nal test signal can be produced from a Gaussian white noise generator associated with ashaping network conforming with Figure 2/J.19;_1)This Recommendation corresponds to CCIR Recommendation 571.2)For the definitions of absolute power, relative power and noise levels, see CCIR Recommendation 5742 Fa
5、scicle III.6 - Rec. J.19(3) the total test signal power applied to a sound-programme circuit under test shall be cyclically changed inlevel according to Table 2/J.19.Note This Recommendation is derived from studies given in Report 497.TABLE 1/J.19Frequency(Hz)Relative insertion-loss(dB)Tolerance( dB
6、)31.563100(122)2004008001 0002 0003 1504 0005 0006 3007 1008 0009 00010 00012 50014 00016 00020 00031 50010.93.40.4(0.0)1.55.78.79.210.613.015.718.822.524.626.628.630.434.336.338.642.550.40.50.30.2(0)0.20.30.30.30.50.50.50.50.50.50.50.51.01.01.01.01.01.0Fascicle III.6 - Rec. J.19 3TABLE 2/J.19Step L
7、evelTime for whichsignal is applied1 4 dBm0s 4 s2 + 3 dBm0s 2 s3 no signal 2 sANNEX A(to Recommendation J.19)Study Group XV of the CCITT had put some questions as regards CCIR Recommendation 571 and the CMTThas worked out their answers. As those questions and the answers may be helpful for anyone wh
8、o applies theconventional test signal for carrying out measurements of any kind, they are given below:Questiona) For the measurement of crosstalk from a sound-programme circuit to a telephone circuit, could the signaldescribed in CCIR Recommendation 571 be used, considering the different bandwidth a
9、nd possiblefrequency shift?Reply: The intelligible crosstalk ratio is based on selective measurements in the telephone circuit when thesinusoidal signals are transmitted in the sound-programme circuit within the frequency range of 0.3 to3.4 kHz. In Recommendation J.21 a minimum ratio of 65 dB is def
10、ined. The unintelligible crosstalk ratio should be ascertained by measuring the increase of noise in the telephonecircuit by loading the disturbing sound-programme with the simulated test signal defined in CCIRRecommendation 571. As for this increase no tolerable values are recommended up to now, th
11、e CMTTproposes such values based on a maximum noise contribution produced by interference of 65 dBm0p.Depending on the basic noise level in the telephone circuit the following increased values can be tolerated:TABLE A-1/J.19Basic noise level (dBm0p) 75 70 65 60 55 50Tolerable increase of noise level
12、 (dB) 10.4 6.2 3 1.2 0.4 0.1Questionb) What is the equivalent value for 65 dB ratio (given in Recommendations J.21, J.22 and J.23) usingsinusoidal tones, when measuring with. the recommended new test signal?Reply:The answer to this question is included in the proposal for the measurement of the rati
13、o for the totalcrosstalk caused by intermodulation given in the answer to Question a).4 Fascicle III.6 - Rec. J.19Questionc) Can the signal defined in Table 2/J.19, from the point of view of the mean loading it would impose ontransmission systems and in the light of Recommendations N.12 and N.13, be
14、 regarded as acceptable forunrestricted use over complete sound-programme circuits of any constitution?Reply:The conventional test signal simulating sound-programme signals defined in CCIRRecommendation 571/Recommendation J.19 in all aspects can be regarded as acceptable for unrestricteduse over sound-programme circuits of any constitution.
