ITU-T R 74-1988 CHOICE OF TYPE OF TELEGRAPH DISTORTION-MEASURING EQUIPMENT《电报畸变测量设备的选择》.pdf

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1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 2 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU4%,%2!0(94%,%2!0(G0G042!.3-)33)/.#(/)#%G0G0/amended at Geneva, 1964 and 1980)The CCITT,in view ofRecommendation R.90,considering(a) that measurements of isochronous distortion made with the text specified in

2、Recommendation R.51 bisshould normally be applied to code-independent telegraph channels;(b) that it may in principle be desirable to measure the distortion of telegraph channels in terms of start-stopdistortion;(c) that all important terminals of voice-frequency telegraph systems are equipped with

3、isochronous distortion-measuring equipment and that their replacement by start-stop instruments would be expensive,unanimously declares the view(1) that, for the maintenance of code-independent telegraph channels, isochronous distortion measuringequipment should normally be used;(2) that Administrat

4、ions may nevertheless, by common consent, use for this purpose start-stop distortionmeasuring equipment,considering also(d) that measurements of the quality of start-stop signals cannot normally be made without start-stop distortionmeasuring equipments;(e) that the planning and establishment of tele

5、graph networks are to be judged in terms of conventional degreesof start-stop distortion, and that degrees of start-stop distortion may also prove to be the best basis for calculations ofthe summation of degrees of distortion and for calculation of conventional start- stop distortion;(f) that, for the maintenace of telegraph channels incorporating code-dependent systems, start-stop testequipment is essential,unanimously declares the view(3) that all international switching and testing centres (ISTCs) should be equipped with start-stop distortion-measuring equipment.