1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 1 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU%.%2!,G0G02%#/-%.$!4)/.3G0G0/.G0G04%,%0(/.%37)4#().G0G0!.$G0G03).!,).#,!53%3G0G0!00,)#!“,%G0G04/G0G0)45G134G0G034!.$!2$3934%-3#/%#4)/.G0G0/ the same is valid (in the international exchanges) for the register
2、signal receivers inSystems R1 and R2.2.2.2 An in-band line signal receiver should be protected against disturbing currents (voice currents or possiblynoise), coming from the near end of the circuit, by a buffer amplifier or other arrangement. The arrangement usedshould introduce an appropriate suppl
3、ementary attenuation in such a manner that, at the point where the line signalreceiver is connected, these disturbing currents are of such a level that they cannot:- operate the line signal receiver;- interfere with the reception of signals by operating the guard circuit of the line signal receiver.
4、The additional attenuation introduced should in consequence take account of:a) the relative level n at the point where the signal receiver is connected (this relative level is obtained byassuming a zero relative level at the distant origin of the circuit);b) the minimum permissible signal level at t
5、he input to the signal receiver, for example:-18 + n dBm in the case of System No. 4 (see Recommendation Q.123 3.2.1),-16 + n dBm in the case of System No. 5 (see Recommendation Q. 144 2.4.1);c) the maximum permissible level for disturbing currents (voice currents and switching noise) coming fromthe
6、 near end of the circuit. The maximum level of voice current might be assumed to be, for example, +10 dBm0 in the direction opposite to that of the signals. The nature of the switching noises depends onthe national systems used;d) any attenuation (terminating set and possibly pads) between the point
7、 where the signal receiver isconnected and the point where the near-end disturbing currents are considered;e) a safety margin to give an appreciable reduction of the level of disturbing currents coming from the nearend as defined in c) compared to the minimum level of the signal as defined in b).2.2
8、3 When a register-signal receiver is connected to the circuit, the exchange side of the circuit is disconnectedand hence the receiver is not subject to near-end disturbances.2.2.4 The Recommendations of Volume III concerning international circuits must still be met after the connectionof a signal s
9、ender and a signal receiver and of the switching equipment. In consequence, it is necessary to fix the limitsof input and output impedance, insertion loss, attenuation distortion, non-linear distortion, balance, and crosstalk of linesignal senders and receivers; an example of specification clauses concerning these conditions is given inRecommendation Q.114.
