1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 - TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU-!).4%.!.#% ).4%2.!4)/.!,G0G04%,%0(/.%G0G0#)2#5)432/54).%G0G0,).%G0G0-%!352%-%.43G0G04/G0G0“%-!$%G0G0/.G0G04(%G0G0,).%G0G02%0%!4%23G0G0/ measurements of relative level at the output of the repeaters (when mea
2、suring overall loss on the completecircuit, in the frontier stations and wherever else such measurements are considered necessary); measurements of circuit stability and test for determining singing points (with 2-wire repeaters).The measurement of stability is obtained from the definition of stabil
3、ity of the circuit considered: = q (q1+ q2)/2q being the mean of the nominal overall loss of the circuit in each of the two directions of transmission under normalworking conditions and q1and q2being the singing points measured for the two directions of transmission respectively.In order to measure
4、these singing points in the case of a 2-wire circuit, singing is started by increasing,step-by-step and simultaneously for the two directions of transmission, the gains of one or of several repeaters(preferably those in the middle of the circuits because they are usually in the most critical positio
5、n from the point of viewof singing). Having done this, without touching the adjustment which has been obtained, the transmission in the reversedirection is suppressed and the overall loss of the circuit at 1020 Hz is measured for the forward direction oftransmission; this is the singing point q1abov
6、e. Next the transmission in the first direction is suppressed and the overallloss of the circuit at 1020 Hz is measured for the reverse direction of transmission: this is the singing point q2above.When the circuit is composed of 2-wire and 4-wire sections, or carrier sections, the method of measurementgiven for 2-wire circuits is valid.This stability should be determined with the ends of the circuit open-circuited; when there are high-impedancerelays permanently connected across the line during a call, these relays may remain during stability tests.
