1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 * TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU4%,%6)3)/.G0G0!.$G0G03/5.$G0G042!.3-)33)/.0%2(b) that quality requirements for the hypothetical reference circuit are established for analogue soundprogrammes;(c) that advantage should be taken of the technic
2、al evolution made possible by the introduction of digitaltechniques, particularly for mixed analogue and digital circuits,recommendsthat, with due regard to the application constraints, equipment for new circuits shall meet the requirements laidout below.1 ApplicationThe Recommendation applies to ho
3、mogeneous analogue or mixed analogue-and-digital circuits.The requirements below apply to the hypothetical reference circuit (HRC) defined in Recommendation J.11.For estimation of the performance of circuits shorter or longer than the HRC, see CCIR Recommendation 605.Note 1 For all-digital circuits
4、a separate Recommendation might be envisaged after further study.Note 2 For further work, CCIR Report 496 may be consulted. This Report also draws attention to certaindifferences between CCIR and OIRT Recommendations.2 Interface characteristics2.1 Test conditionsWhen circuit performance is to be mea
5、sured, the system output shall be terminated by a balanced test load,nominally 600 resistive.2.2 ImpedanceSystem input impedance 600 , balanced5)System output impedance, provisionally Low, balanced_1)This Recommendation corresponds to CCIR Recommendation 503. CCIR has agreed, at its XVIth Plenary As
6、sembly,Dubrovnik, 1986, that CCIR Recommendation 504-2 will not be published in the next CCIR book.2)For the definition of absolute power, relative power and noise levels, see CCIR Recommendation 574.3)Sound-programme circuits of the 5 kHz type are widely used in North America.4)6.4 khz-type narrow
7、bandwidth sound-programme circuits are still being used in some countries.5)The tolerance, permitted reactance and degree of unbalance need further study.2 Fascicle III.6 - Rec. J.23The open-circuit output level shall not decrease more than 0.3 dB within the nominal frequency range, if theoutput is
8、terminated by the specified test load.The reactive part of the source impedance must be restricted to 100 max. (provisional value) within thenominal frequency range.2.3 LevelsInput maximum programme level + 9 dBm0sInsertion gain (1 kHz at 12 dBm0) 0 dBAdjustment error, within 0.5 dBVariation over 24
9、 hours not to exceed 0.5 dBRelative level (see Recommendation J.14) + 6 dBrsIf the broadcast organizations wish to have closer tolerances, it is necessary for the receiving broadcastingorganizations to insert additional trimming attenuators.3 Overall performance3.1 Common parameters3.1.1 Gain/freque
10、ncy responseReference frequency 1 kHz (nominal value)The response shall be measured at 12 dBm0sThe gain/frequency response is given in Table 1 /J.23.If broadcasting organizations wish to have closer tolerances, it is necessary for the receiving broadcastingorganization to insert additional equalizer
11、s.TABLE 1/J.23Frequency(kHz)Response(dB)0.05 f 3.2Slope 6 dB/octave74Slope 6 dB/octave3.1.8.2 The near-end and far-end cross-talk attenuations between a sound-programme circuit (disturbing circuit) and atelephone circuit (disturbed circuit) shall be at least 65 dB.Note 1 It is understood that this v
12、alue is defined between the relative levels applicable to telephone circuits.(Administrations are invited to submit contributions on methods for measuring this parameter.)Note 2 The attention of Administrations is drawn to the fact that it is in some cases difficult or impossible tomeet these limits
13、. This may occur when unscreened pairs are used for a long audio-frequency circuit (e.g. about 1000km or longer), or in certain carrier systems on symmetric pair cables, or at low frequencies (e.g. below about 100 kHz)on certain coaxial cable carrier systems. If sub-standard performance is to be avo
14、ided, such systems or parts of systemsmust not be used for setting up programme channels.Note 3 When 4000 pW0p or more noise is continuously present in the telephone channel (this may be thecase in satellite systems, for example), a reduced cross-talk ratio of 58 dB between a sound-programme circuit
15、 and atelephone circuit is acceptable.Note 4 The attention of Administrations is drawn to the fact that, because of cross-talk which may occur interminal modulating and line equipment, special precautions may have to be taken to meet the above cross-talk limitsbetween two sound-programme circuits, s
16、imultaneously occupying the go and return channels respectively, of a carriersystem (the most economical arrangement) because in those circumstances they occupy the same position in the line-frequency band (see Recommendation J.18).Note 5 The value indicated is based on the assumption that sine wave
17、 test signals are used. The use of the testsignal as described in Recommendation J.19 is under study.Note 6 The effect of cross-talk from a sound-programme circuit into a telephone circuit is not a question ofsecrecy, but rather of subjective disturbance by an interfering signal whose character is n
18、oticeably different fromrandom noise or babble.The frequency offset adopted for some sound-programme equipment allows a reduction of cross-talk from atelephone circuit into a sound-programme circuit. However, in the reverse direction, this reduction of cross-talkremains only for speech material but
19、is practically ineffective for music material.3.1.9 Amplitude linearityWhen a 1 kHz input signal is stepped from 6 dBm0s to + 6 dBm0s, or vice versa, the output level shallchange accordingly by 12 0.5 dB.3.2 Additional parameters for stereophonic programme transmissionNot applicable, this section co
20、ncerns 15 kHz type sound-programme circuits (see Recommendation T.21).6 Fascicle III.6 - Rec. J.233.3 Additional requirements for digital systems3.3.1 If a test signal is harmonically related to the sampling frequency, measuring difficulties may arise. In this casethe nominal 1 kHz test signal must
21、be offset. The Recommendation O.33 recommends 1020 Hz.3.3.2 Unbalance of the limitation levelThe difference between those levels which lead to a limitation of the positive or negative half-wave of the testsignal shall not exceed 1 dB.3.3.3 Intermodulation with the sampling signalIntermodulation prod
22、ucts (fd) caused by non-linearities may occur in the sound-channel when the samplingsignal signal (fo) is combined with the inband audio signals (fi) or out-of-band interfering signals (fa).3.3.3.1Inband intermodulationThe following combination rule applies: fd= fo nfi.Only values with n = 2 or 3 ar
23、e of importance.The level difference between a 0 dBm0s signal (fi) and the intermodulation products (fd) shall not be less than40 dB.A restriction to the fi / fdvalues in Table 6/J.23 is sufficient.TABLE 6/J.23n = 2 n = 3fi (kHz)573 5fd (kHz)627 13.3.3.2Out-of-band intermodulationThe following combi
24、nation rule applies: fd= nfo fa.Only values with n = 1 or 2 are of importance.The level difference between a 0 dBm0s signal (fa) and the intermodulation products (fd) shall not be less than60 dB.A restriction to the fa / fdvalues in Table 7/J.23 is sufficient.TABLE 7/J.23n = 1 n = 2fa (kHz)15 17 31 33fd (kHz)1Fascicle III.6 - Rec. J.23 73.3.4 Further parametersCharacteristics for bit errors, clicks, jitters, etc., are under study. (See Study Programme 18A/CMTT and CCIRReport 647.)BibliographyCCIR Document 1978-1982: CMTT/68 (OIRT).
