ITU-T R 4-1988 METHODS FOR THE SEPARATE MEASUREMENTS OF THE DEGREES OF VARIOUS TYPES OF TELEGRAPH DISTORTION《电话与话上电报在同一电缆内的共存》.pdf

1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 2 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU4%,%2!0(94%,%2!0(G0G042!.3-)33)/.-%4(/$3G0G0 amended at Geneva, 1980)For separate measurements of the degrees of characteristic distortion, bias distortion and fortuitous distortionaffecting a telegraph modul

2、ation or restitution, the following is recommended where circuits and voice-frequencytelegraph (VFT) channels are used to carry information employing International Telegraph Alphabet No. 2, withoutregeneration;1 Measure the degree of overall distortion (at the actual mean modulation rate) on text, f

3、or instance the QKS textspecified in Recommendation R.51 bis. Let be the measurement obtained.2 Measure the degree of distortion on reversals at the modulation rate used in the measurement of (1) above.Let 1be the measurement obtained. 1is the sum of the bias and fortuitous distortions.3 By using a

4、compensator fitted to the distortion-measuring equipment, for example a compensating winding onthe distortion meter relay, reduce the degree of distortion reading obtained to its minimum value. Let this figure be .For practical purposes is the fortuitous distortion. 1 is, for practical purposes, the

5、 bias distortion.4 Keep the distortion meter adjusted as for the measurement of . Measure the degree of distortion at the actualmean modulation rate on text (QKS text, for instance). Let be the reading. is, for practical purposes, thecharacteristic distortion.Note 1 This method gives approximate res

6、ults, it is possible that the equation 1+ = may not beexactly satisfied.Note 2 The method can be applied by using either an isochronous distortion-measuring set or a start-stopdistortion-measuring set.Note 3 The fact that the separate measurement of degrees of different types of distortion is said to be possibleand that a method is recommended for such a measurement does not mean that separate measurements of the degrees ofdifferent types of distortion are to be recommended when international routine maintenance measurements are carriedout.