1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 - TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU-!).4%.!.#% ).4%2.!4)/.!,G0G04%,%0(/.%G0G0#)2#5)433%44).G0G050G0G0!.$G0G0,).).G0G050G0G0!G0G0#)2#5)4&)44%$G0G07)4(G0G0!G0G0#/-0!.$/2)45G134G0G0RecommendationG0G0- (Extract from the “LUEG0“OOK)NOTES1 ITU-T Rec
2、ommendation M.590 was published in Fascicle IV.1 of the Blue Book. This file is an extract fromthe Blue Book. While the presentation and layout of the text might be slightly different from the Blue Book version, thecontents of the file are identical to the Blue Book version and copyright conditions
3、remain unchanged (see below).2 In this Recommendation, the expression “Administration” is used for conciseness to indicate both atelecommunication administration and a recognized operating agency. ITU 1988, 1993All rights reserved. No part of this publication may be reproduced or utilized in any for
4、m or by any means, electronic ormechanical, including photocopying and microfilm, without permission in writing from the ITU.Fascicle IV.1 - Rec. M.590 1Recommendation M.590Fascicle IV.1 - Rec. M.590SETTING UP AND LINING UP A CIRCUIT FITTEDWITH A COMPANDOR1 The compandor should first be tested in ac
5、cordance with the appropriate design information which should bemade available in a suitable form to repeater station staff. In particular, because the unaffected level of a compandor isdefined with reference to an 800 Hz signal, it should be verified for each type of compandor that use of a referen
6、ce testfrequency of 1020 Hz produces the same results as using a reference test frequency of 800 Hz.2 Circuits fitted with compandors should be lined up to achieve the same limits as circuits without compandors.The compandor should be fitted to the circuit only after the circuit without its compando
7、r is considered satisfactory inrespect of loss and loss/frequency response. It should be noted that to achieve the limits for loss/frequency response onthe companded circuit without equalization, it will be necessary for the loss/frequency response of the uncompandedcircuit to be within one half of
8、the circuit limits.3 Measurements of total distortion and idle channel noiseAfter compandors have been fitted, total distortion and idle channel noise measurements should be made. Thetest signal used for the total distortion measurement should be applied at the unaffected level of the compandor.In t
9、he case of a circuit which is fitted with a compandor to subjectively reduce the noise generated within aterrestrial circuit section, the measurements should be noted.In the case of a circuit which is fitted with a compandor to subjectively reduce the noise generated by asatellite circuit section, t
10、he procedure is as follows: For analogue routed circuits1), the noise objectives given in Table 4/M.580 for the appropriate terrestriallength of circuit should be combined with the total distortion objective for the satellite channel2) toproduce a total distortion objective for the whole circuit. Se
11、e Annex A for an example of this calculation. For mixed analogue/digital routed circuits, the total distortion objectives given in Table 5/M.580 for theappropriate terrestrial length of circuit should be combined with the total distortion objective for thesatellite channel2)to produce a total distor
12、tion objective for the whole circuit. See Annex A for anexample of this calculation. If the measured total distortion is higher than the calculated total distortion objective, then a fault shouldbe suspected and action should be taken to locate and remedy any fault where possible. When the total dis
13、tortion measurement has been made and is found to meet the calculated total distortionobjectives, an idle channel noise measurement should be made. The idle channel noise measurement should be compared with the maintenance objective given inTable 4/M.580 for the appropriate length of circuit, taking
14、 into account the note associated with that tablewhich states that the satellite section of the circuit may be considered to have an equivalent length of2500 km. This is a valid consideration provided that the total distortion objective of the satellite channel isnot greater than 30 dBm0p. If the me
15、asured value is higher by 5 dB or more than the noise objective given in Table 4/M.580 or ishigher than 37 dBm0p, whichever is the more stringent requirement, then a fault should be suspectedand action should be taken to locate and remedy any fault where possible.4 A speaking test should be made on
16、the circuit to verify the correct operation of the compandors._1)It should be noted that in the case of mixed analogue/digital circuits, if the unaffected level is other than 10 dBm0 then thisprocedure will produce less accurate results and in this case it should be used as a general guide only.2)Th
17、e total distortion objective for INTELSAT single sideband Standard B satellite channels is 41 dBm0p (FM compandedcircuit).2 Fascicle IV.1 - Rec. M.5905 DesignationsCompanded circuits and groups of circuits which are all companded should be designated in accordance withRecommendation M.140.Note Repea
18、ter station staff should be well instructed as to the subjective effect of errors and the location offaults affecting compandors.ANNEX A(to Recommendation M.590)Total distortion and idle channel noise objectives for circuitswhich are fitted with compandors in order to subjectively reducethe effect o
19、f noise generated on satellite channelsA.1 A distinction is made between:a) circuits which are fitted with compandors to subjectively improve the noise generated by a terrestrialsection, andb) circuits which are fitted with compandors to subjectively improve the noise generated by a satellitesection
20、.This distinction is made because in case a) it is not possible to specify noise or total distortion objectives.However, in case b), the satellite system operator can specify noise objectives for the satellite section. Thus these limitscan be combined with those contained in Recommendation M.580 to
21、calculate an overall limit.A.2 Examples of calculations of total distortion for case b)Example 1Consider an analogue circuit which has a terrestrial length of 1600 km and which is routed via a satellite whichhas a specified idle channel noise objective of 41 dBm0p for analogue channels.From Table 4/
22、M.580, the noise objective for a length of 1600 km is 51 dBm0p.Combining 41 dBm0p and 51 dBm0p gives a total distortion of 40.59 dBm0p.Thus the total distortion objectives should be 41 dBm0p.Example 2Consider a mixed analogue/digital circuit which has a terrestrial length of 1600 km, two analogue/di
23、gitalconversions using 8 bit coding (i.e., 2 QDUs) and which is routed via a satellite which has a specified idle channel noiseobjective of 41 dBm0p for analogue channels.From Table 5/M.580, the total distortion objective for a length of 1600 km is 30 dB or 40 dBm0p.Combining 41 dBm0p and 40 dBm0p g
24、ives a total distortion of 37.46 dBm0p.Thus the total distortion objective should be 37 dBm0p.A.3 Idle channel noise objectives for case b)It is stated in 3 that provided the total distortion objective of the satellite channel is not greater than 30 dBm0p, it is valid to consider that this section o
25、f the circuit has an equivalent length of 2500 km.This statement is justified because the compandor characteristic which is illustrated in Figure A-1/M.590indicates that an idle channel noise of 30 dBm0p generated in a satellite section would be reduced to 50 dBm0p. Thisvalue of noise is that which from Table 4/M.580 is attributed to an equivalent circuit length of 2500 km.Fascicle IV.1 - Rec. M.590 3d01-scFIGURE1/M.590.D01
