1、CCITT FASCICLE IV*& * 486259L 0505364 2 References CCIT Recommendation Protection against the effects of faulty transmission on groups and circuits, Vol. VI, Rec. 4.33. CCIT Recommendation 1020 Hz test reference frequency, Vol. IV, Rec. 0.6. CCITT Supplement Crossfalk test device for carrier-transmi
2、ssion systems on coaxial systems, Vol. IV, Supplement No. 3.6. CCIT Recommendation Assumptions for the calculation of noise on hypothetical reference circuits for telephony, Vol. III, Rec. G.223. CCIT Recommendation Characteristics of group links for the fransmission of wide-spectrum signals, Vol. I
3、II, Rec. H.14. CCITT Recommendation Use of leased group and supergroup links for wide-spectrum signal transmission (data, facsimile, etc.), Vol. IV, Rec. M.900. CCIT Recommendation Setting up and lining up an international leased group link for wide-spectrum signal transmission, Vol. IV, Rec. M.910.
4、 Recommendation M.470 SETTING UP AND LINING UP ANALOGUE CHANNELS FOR INTERNATIONAL TELECOMMUNiCATION SERVICES 1 Check of channel-translating equipment The translating equipment, before it is connected to the ends of the link, must be checked and adjusted to ensure that it meets CCIT Recommendations
5、and the other relevant specifications. The check should include a general visual inspection and vibration tests, if applicable. This is of particular importance if the equipment has remained unused since acceptance tests were carried out after installation. 2 Setting up and lining up the analogue ch
6、annels 2.1 Measurement and adjustment of levels After the group link has been set up, and the channel-translating equipment at each end of the group link has been connected and checked, the channels are adjusted as follows. An 1020 Hz test) signal is sent over each channel in turn at a level of - 10
7、 dBmO. At the transmitting end, the channel-translating equipment is adjusted so that the sideband level on each channel at its output is as near to nominal as possible. At the receiving end, the channel-translating equipment should then be adjusted to bring the received level on each channel as nea
8、r as possible to its nominal value. 2.2 Checking the analogue channel performance Channel performance measurements are only required when the need is indicated during circuit line-up. On such occasions the parameters to be checked will depend on the particular difficulty experienced during circuit l
9、ine-up. 3 Check level of line signalling In the case of groups which are intended to be used for telephone circuits employing Signalling System R2, the checks of signalling level stipulated in the Specifications of Signalling System R2 should be made 2. For other signalling systems, the check of sig
10、nalling level should be carried out at the circuit line-up stage (see Recommendation M.580, 6 8). References CCIT Recommendation 1020 Hz reference test frequency, Vol. IV, Rec. 0.6. CCIT Recommendations Speczjkations of Signalling System R2, Vol. VI, Recs. 4.400 to 4.490. i 2 1 For further information about the choice of the test signal frequency, refer to Recommendation 0.6 l. 7 - 7 7 Fascicle IV.l - Rec. M.470 285
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