1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 - TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU-!).4%.!.#%G0 ).4%2.!4)/.!,G0G04%,%0(/.%G0G0#)2#5)43-%4(/$3G0G0 at frequencies of 400, 1020 and 2800 Hz, when measurements are made at more than one frequency.Measurements may be made at additional frequencie
2、s if required.Whenever automatic level recorders or display sets are available at the ends of the circuit, the measurementsshould be made with this equipment at all frequencies over the range of interest.1.2 Noise measurementsThe psophometric noise power as indicated by a CCITT psophometer should be
3、 measured in both directions oftransmission. It would be useful to make this measurement at the same time as the measurement of overall loss.1.3 Signalling tests1.3.1 Manually operated circuitsThe power of the voice-frequency signalling current, in its normal operating condition, should be measured
4、atthe same time as the overall loss at several frequencies is measured.If n is the relative power level at the point of measurement, the measured absolute power level of the signallingcurrent transmitted at 500/20-Hz interrupted signalling current should fall within the following limits:(n 3) 1/2 dB
5、assuming that the signalling units used conform to the specifications of the Series Q Recommendations.The operation of the voice-frequency signalling receivers is tested as an in-station test.For information, the operating limits of the signalling receiver are as follows:If n is the relative power l
6、evel at the point of connection in the circuit where the receiver is connected, it willoperate reliably when the absolute power level N of the signalling current at the input of the receiver falls within thefollowing limits:8.5 + n N + 2.5 + n dB.1.3.2 Semi-automatic or automatic circuitsSee Recomme
7、ndation M.732.1.4 RecordsAll the results of measurements and tests should be recorded by the control and sub-control stations concerned._1)For further information about the choice of the signal frequency, refer to Recommendation O.6 1.2 Fascicle IV.1 - Rec. M.6202 Use of automatic transmission measu
8、ring and signalling testing equipment ATME No. 2See Recommendation O.22 2.2.1 Transmission measurementsWhen ATME No. 2 is available for the routine maintenance of automatic and semi-automatic internationalcircuits, it should be used to make the following measurements: overall loss at 1020 Hz or at 4
9、00, 1020 and 2800 Hz, as required; psophometric noise power level.The test frequencies for overall loss measurements should be at a level of 10 dBm0.2.2 Signalling testsThe signalling functions involved in the setting-up and clearing down of a connection between the directingand responding equipment
10、s will be checked during each test call. In addition, ATME No. 2 should be used to make thefollowing line signalling tests: forward transfer (where provided), clear back, re-answer, busy flash.Note It is inappropriate to perform a signalling test using a Type B ATME No. 2 responder on SignallingSyst
11、em No. 6 speech circuits.2.3 Test of echo control devicesEcho control devices may be tested using an appropriate test system such as that specifies as an option inRecommendation O.22 2. If a test system is not available, then subjective test calls may be used. However it should benoted that these te
12、st calls will not quantitatively assess echo control device performance 3.3 Corrective action3.1 Readjustment of overall lossWhen, during a routine measurement, the overall loss at 1020 Hz is not equal to its nominal value, theprocedure below should be followed.Deviations of less than 1 dB from nomi
13、nal shall be deemed not to require adjustment. If measurements at aterminal station reveal a deviation from the nominal value of 1.0 dB up to and including 2.5 dB, adjustment to asnear the nominal value as possible should be made at the terminal station and if practical at any intermediate stationin
14、volved. Where it is appropriate and practical to do so, adjustment shall be made on the group or supergroup links inaccordance with Recommendation M.530. If the deviation from nominal exceeds 2.5 dB a fault should be suspectedwhich should be sought and cleared. If no fault is found, readjustment sho
15、uld be carried out at the intermediate andterminal stations as necessary, with particular attention to alignment of the group and supergroup link or links that maybe involved.3.2 Measurements at more than one frequencyWhen measurements are made at more than one frequency, a check should be made to e
16、nsure that the valuesobtained are within the limits permitted (see Tables 1/M.580, 2/M.580 and 3/M.580). If they are not, appropriate stepsshould be taken.3.3 Noise measurementsIt should be noted that any substantial deterioration in performance from the original line-up value may serveto indicate a
17、 fault. Comparison should also be made to noise measurements on circuits of identical or similar constitutionto help locate a possible fault.Fascicle IV.1 - Rec. M.620 34 Other measurements without recommended periodicitya) Systematic subjective testing, see Recommendation M.731;b) Measurement of si
18、gnal-to-crosstalk ratio between go and return channels. The measured signal-to-crosstalk ratio should not be less than 43 dB;c) Frequency errors arising from frequency translation. The difference between the sent and received audiofrequencies should not exceed 2 Hz. See Recommendation O.111 4 for a
19、method of measuring thiserror.References1 CCITT Recommendation 1020 Hz reference test frequency, Vol. IV, Rec. O.6.2 CCITT Recommendation CCITT automatic transmission measuring and signalling testing equipment ATMENo. 2, Vol. IV, Rec. O.22.3 Rapid verification test for echo control devices, Vol. IV, Supplement No. 2.11.4 CCITT Recommendation Frequency shift measuring equipment for use on carrier channels, Vol. IV,Rec. O.111.
