1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 2 G0BISTELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU4%,%2!0(94%,%2!0(G0G042!.3-)33)/.34!.$!2$):%$G0G04%84G0G0(b) that the text should form a short repetitive test message suitable for conducting routine tests on circuits thatinclude code-dependent channel
2、s (International Telegraph Alphabet No. 2) and/or code-independent channels;(c) that it is best to choose a text that can be received directly by start-stop equipment and that also presents asequence of the combinations recognized as those that generally cause the maximum distortion;(d) that the tex
3、t should contain an equal number of unit elements of each binary condition and that it should besuitable for start-stop or isochronous measurement of distortion when used with code-independent transmissionequipment,unanimously declares the view(1) that the text to transmit in the course of tests on
4、telegraph transmission equipment should be as shown inFigure 1/R.51 bis;(2) that when equipment capable of generating the foregoing text is not available, it is acceptable to use thetext given in Recommendation R.51 for testing code-independent systems only.Note 1 Test equipment capable of generatin
5、g the text in Figure 1/R.51 bis should also be capable ofgenerating 1:1, 2:2, 1:6 and 6:1 patterns for testing code-independent systems only (see 2 in Recommendation R.51).Note 2 Start-stop predistortion may be introduced (on an optional basis) to QKS signals by shortening orlengthening the start el
6、ements of alternate characters. The first character of each cycle (combination No. 29, letter-shift)will have a shortened start element. After predistortion is applied, the nominal duration of each character will bemaintained as shown in Figure 1/R.51 bis by means of complementary changes in the stop element lengths.
