ITU-T G.621-1988 0.7/2.9mm 同轴电缆线对的特性 Characteristics of 0.7/2.9 mm coaxial cable pairs

pdf标准 ITU-T G.621-1988 0.7/2.9mm 同轴电缆线对的特性 Characteristics of 0.7/2.9 mm coaxial cable pairs

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ITU-T G.621-1988 0.7/2.9mm 同轴电缆线对的特性 Characteristics of 0.7/2.9 mm coaxial cable pairs  第 1 页 ITU-T G.621-1988 0.7/2.9mm 同轴电缆线对的特性 Characteristics of 0.7/2.9 mm coaxial cable pairs  第 2 页 ITU-T G.621-1988 0.7/2.9mm 同轴电缆线对的特性 Characteristics of 0.7/2.9 mm coaxial cable pairs  第 3 页 ITU-T G.621-1988 0.7/2.9mm 同轴电缆线对的特性 Characteristics of 0.7/2.9 mm coaxial cable pairs  第 4 页 ITU-T G.621-1988 0.7/2.9mm 同轴电缆线对的特性 Characteristics of 0.7/2.9 mm coaxial cable pairs  第 5 页
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国外分类,ITU,ITU-T(电信标准分局),itu,9mm,同轴,电缆,同轴电缆,特性,characteristics,of,mm,coaxial,cable,pairs

INTERNATIONAL TELECOMMUNICATION UNION )45 4 ' TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU 42!.3-)33)/. -%$)! #(!2!#4%2)34)#3 #(!2!#4%2)34)#3 /&    MM #/!8)!, #!",% 0!)23 )45 4 Recommendation ' (Extract from the "LUE "OOK) NOTES 1 ITU-T Recommendation G.621 was published in Fascicle III.3 of the Blue Book. This file is an extract from the Blue Book. While the presentation and layout of the text might be slightly different from the Blue Book version, the contents of the file are identical to the Blue Book version and copyright conditions remain unchanged (see below). 2 In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. © ITU 1988, 1993 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU. Recommendation G.621 Fascicle III.3 - Rec. G.621 CHARACTERISTICS OF 0.7/2.9 mm COAXIAL CABLE PAIRS (Geneva, 1976; amended at Geneva, 1980) Administrations which decide to use for digital transmissions, and possibly also for particular types of analogue transmission, coaxial pairs smaller than the 1.2/4.4-mm coaxial pair should as far as possible choose pairs complying with the specifications given in this Recommendation. The use of these pairs is defined in Tables 1 and 2 given in the introduction to Subsection 6.2. 1 Pair characteristics 1.1 Electrical characteristics of the coaxial pair 1.1.1 Characteristic impedance The nominal value of the real part of the characteristic impedance at 1 MHz should be 75 Ω. The mean real part of the impedance of a coaxial pair at 1 MHz should not differ from the nominal figure by more than ± 2.5 Ω. Table 1/G.621 shows the general trend of the variation of the impedance as a function of frequency. TABLE 1/G.621 Mean real part of the impedance measured at various frequencies Frequency (MHz) 0.2 1.1.2 75.9 2 75 5 10 20 ∞ 74.2 1 77.7 Impedance (Ω) 0.5 73.4 73 72.8 72.2 Attenuation coefficient The nominal value of the attenuation coefficient, at 10 °C and at 1 MHz, is equal to 8.9 dB/km. Table 2/G.621 shows the general trend of the variation in attenuation coefficient as a function of frequency at the temperature 10 °C. TABLE 2/G.621 Mean values of the attenuation coefficient at various frequencies Frequency (MHz) 0.2 0.5 1 2 5 Attenuation coefficient (dB/km) 4.5 6.5 8.9 12.6 19.8 1.2 10 20 28.0 39.6 Mechanical construction of the coaxial pair The pair has the following constitution: a) nominal diameter of solid-copper wire inner conductor: 0.7 mm; Fascicle III.3 - Rec. G.621 1 b) c) 2.1 outer conductor consisting of a copper tape with a thickness of the order of 0.1 mm, laid lengthwise with overlap1) ; d) 2 nominal internal diameter of outer conductor: 2.9 mm; screen consisting of a steel tape with a thickness of the order of 0.1 mm, laid lengthwise with overlap 1). Cable specification (factory lengths of about 500 m) Characteristic impedance To check that the value given in § 1.1.1 is met, pulse measurements can be made. The mean real part of the impedance at 1 MHz is to be taken as meaning the resistive component of the impedance at 1 MHz of the network with the best balance against the coaxial pair measured. 2.2 Impedance regularity Routine control measurements of impedance regularity are carried out by means of pulse echometers from one or both ends of the factory lengths. The echo curve should be plotted with correction in amplitude and if possible in amplitude and phase. Table 3/G.621 shows the various values to be obtained according to the purpose for which the cable is intended. TABLE 3/G.621 Echometric measurement of factory lengths a) Type of system Digital Medium bit rate (6 to 34 Mbit/s) Bit rate Maximum pulse duration 100 ns 100 % 95 % General provisions 36 dB 39 dB Maximum peak A Mean of 3 maximum peaks B 39 dB Equivalent resistance error Additional optional provisions a) a) It is enough to cheek that one of the two conditions A or B is fulfilled. Note 1 - The percentage figures given in the table relate to all the pairs of a batch of cables submitted for control or delivered at the same time. Note 2 - With the construction techniques used so far, systematic faults do not give rise, in steady-state measurements of regularity return loss, to peaks at frequencies below 60 MHz. For this reason, and taking _______________ 1) A single bimetallic copper-steel-copper tape may also be used to serve as outer conductor and screen. 2 Fascicle III.3 - Rec. G.621 into account the bit rate envisaged, ste

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