ITU-T G 611-1993 CHARACTERISTICS OF SYMMETRIC CABLE PAIRS FOR ANALOGUE TRANSMISSION《用于模拟传输的对称电缆线对的特性》.pdf

1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU42!.3-)33)/.G0G0-%$)!G0G0#(!2!#4%2)34)#3?#(!2!#4%2)34)#3G0G0/ amended at Geneva, 1980)1 Cable specification - Examples of the electric characteristics of a star-quad cable designed to provide 12,24, 36, 48, 60

2、or 120 carrier telephone channels on each quad pair1.1 Types of cableAdministrations which decide to equip their symmetric pair cable network should, wherever possible, choosethose which conform to the types of cable defined below.New cables laid in the European and North-African international telep

3、hone network include unloadedsymmetric pairs, designed to be used for 12, 24, 36, 48, 60 or 120 carrier telephone channels on each pair. These pairsare laid up in star quads and all unloaded pairs of the same cable are one of the types whose nominal characteristics areshown in Table 1/G.611.It is es

4、sential that a repeater section crossing a frontier should be of a uniform type throughout its length. Whena frontier section is between a large and a small country, the Administration of the larger country should do everythingpossible to use whichever of the three types has been adopted by the smal

5、ler country, so as not to oblige theAdministrations of small countries to use sections of international cable of a different type from that of their nationalcables.Note 1 - Some Administrations, by paying special attention to crosstalk balance and adopting appropriaterepeater spacing, have been able

6、 to set up systems with 2 supergroups, in accordance with Recommendation G.322, onpaper-insulated symmetric pairs conforming with this present specification.Note 2 - It is also possible to set up 2 supergroup systems that conform with Recommendation G.322 on pairs oftype II bis and type III bis. Typ

7、e II bis pairs are insulated by polythene and type III bis pairs by styroflex.TABLE 1/G.611Type I Type II Type IIbisType III Type III bisDiameter of conductors (mm)Effective capacity (nF/km)Characteristic impedance ()to 60 kHzto 120 kHzto 240 kHzto 550 kHzAttenuation per unit length at 10 C in dB/km

8、to 60 kHzto 120 kHzto 240 kHzto 552 kHz0.9331531482.33.11.226.51781741722.02.94.81.2212062032001981.52.13.11.3281701651631.82.74.41.3221961931901881.42.03.02 Fascicle III.3 - Rec. G.6111.2 Regularity of factory lengthsThe regularity may be characterized by one or other of the equivalent methods belo

9、w, the choice of which is leftto the Administrations concerned.1.2.1 Effective capacityThe “effective capacity“ is measured between the two conductors of the pair, all other cable conductors beingconnected together and to the sheath.Ratios of the effective capacityType I cable - The average of the e

10、ffective capacities of all the pairs in any factory length should not differ fromthe nominal value by more than 5%.In any factory length, the difference between any individual value of effective capacity and the average valueobtained for this factory length should not exceed 7.5%; the arithmetic mea

11、n of the magnitudes of these differencesshould not exceed 2.5%.Types II, II bis, III and III bis cables - The average effective capacity of any length should not differ by morethan 3% from the nominal value.In any length, the difference between the effective capacity of any pair and the average capa

12、city for the cablelength should not exceed 5%.1.2.2 Impedance (types II, II bis, III and III bis cables)The real part of the characteristic impedance of any circuit, measured with a frequency of 120 kHz, should notdepart by more than 5% from the mean value of all the pairs of the first manufacturing

13、 batch of each type. This meanvalue should not depart by more than 5% from the nominal value at 120 kHz.The impedance will be measured on the factory lengths using a bridge, the circuits being terminated by animpedance equal to that which is measured by the bridge.1.3 CrosstalkThe quality of the cab

14、le from the point of view of crosstalk may be characterized by one or other of the twoequivalent methods below, the choice of which is left to the Administrations concerned.1.3.1 Direct measurements of crosstalkFor a factory length of 230 metres the crosstalk between any two side circuits should sat

15、isfy the followingconditions:- far-end crosstalk ratio should be greater than 68 dB;- near-end crosstalk attenuation should be greater than 56 dB.For cables to be used with 5 groups or 2 supergroups these values should hold up to 240 kHz; and for cableswith two groups, up to 120 kHz.During these mea

16、surements, the circuits will be terminated by the real part of the nominal impedance for thefrequency considered.For factory lengths greater than 230 metres, the above limits will be reduced byL being the length in metres. Lengths shorter than 230 metres should satisfy the same conditions as a lengt

17、h of230 metres.Fascicle III.3 - Rec. G.611 31.3.2 Capacity unbalance and mutual inductancesAll the capacity unbalance measurements should be made with an alternating current of 800 Hz. The mutualimpedance measurements should be made with an alternating current of 5000 Hz. All the measurements should

18、 be madeat the ambient temperature, without applying corrections; but in case of dispute, the results obtained at 10 C will beconsidered as final. All the conductors, other than those under test, should be connected to the cable sheath.For a factory length of 230 metres the capacity unbalance should

19、 not exceed the values given in Table 2/G.611and the mutual inductances should not exceed the values given in Table 3/G.611. These tables show different values fortype I cables in one column, and for types II, II bis, III and III bis in the other.TABLE 2/G.611Capacity unbalanceNote - The limits show

20、n for the mean values do not apply to cables which have four or less quads.Mean of all readings(ignoring signs)Maximum individualreadingType I Types II, II bis,III and III bisType I Types II, IIbis,III and III bisCapacity unbalance in picofarads:between pairs of the same quadbetween pairs of adjacen

21、t quads in the same layer3310175125606025between pairs in nonadjacent quads in the same layermean value not specifiedbecause all possiblecombinations are notmeasured20 10between pairs in quads in adjacent layersbetween any pair and earth10100510060400254004 Fascicle III.3 - Rec. G.611TABLE 3/G.611Mu

22、tual inductancesMean of all readings(ignoring signs)Maximum individualreadingType ITypes II, II bis,III and III bisType ITypes II, II bis,III and III bisMutual inductances in nanohenrys:between pairs of the same quadbetween pairs of adjacent quads in the same layerbetween pairs in nonadjacent quadsb

23、etween pairs in quads in adjacent layers15010050100125402040600400350600500150150250Note - The limits shown for the mean values do not apply to cables which have four or less quads.For lengths greater than 230 metres, it is necessary to apply the following rules:The average values from pair to pair

24、given in Tables 2/G.611 and 3/G.611 should be multiplied by the squareroot of the ratio between the length in question and 230 metres.All the maximum values, as well as the average values between a pair and earth, should be multiplied by theratio between the length in question and 230 metres.Lengths

25、 shorter than 230 metres should satisfy the same conditions as the length of 230 metres.1.4 Dielectric strengthWhen specially requested, cables will have a construction such that the insulation of any cable length should becapable of withstanding, without breakdown, a potential difference specified

26、in each particular case but not exceeding2000 volts r.m.s., applied for at least 2 seconds between all the conductors, connected together and the earthed sheath.The test can be made with a 50-Hz alternating current. The value of the test voltage should not exceed by more than 10%the peak value of a

27、sinusoidal voltage having the same r.m.s. value.The test can also be carried out using direct current (see 1). In such a case, the limit for the voltage will be1.4 times the r.m.s. value of the voltage when using alternating current1).1.5 Insulation resistanceIn a length of cable, the insulation res

28、istance measured between a conductor and all the other conductorsconnected together, and to the earthed sheath, should not be less than 10 000 M-km, the potential difference usedbeing at least 100 volts and not greater than 500 volts. The reading shall be made after electrification for one minute, t

29、hetemperature being at least 15 C._1)In reference 2, the CCITT does not recommend a formula for general application for tests on mixed dielectrics.However, for tests of telephone cables, the CCITT recommends the use of the factor 1.4 as representative of current commercialpractice.Fascicle III.3 - R

30、ec. G.611 52 Specification of a repeater section2.1 Maximum attenuation in a repeater sectionThe maximum attenuation at the highest frequency transmitted to line of a normal repeater section shall be 41dB for low-gain systems with 1, 2 or 3 groups and 36 dB for low-gain systems with 4 or 5 groups or

31、 2 supergroups.2.2 CrosstalkThe far-end crosstalk ratio between circuits in the same direction, measured on the repeater sections of a carriersystem on unloaded symmetric pairs, terminated at their two ends by impedances equal to their characteristic impedance,should not be less than the values show

32、n below (which allow for the existence of any crosstalk balancing networks).1) For the classical method of balancing, the repeater section far-end crosstalk ratio for low gaintransistorized systems up to 120 channels on type II and III cables (or similar cables) or low-gain 120-channel systems on ty

33、pe II bis or III bis cables should not be less than 69.5 dB.2) When a “balancing section“ comprises several repeater sections, an equivalent result can be obtained fromthe formula 69.5 - 10 logl0n (dB), where n is the number of repeater sections in the balancing section.2.3 Regularity of impedanceTh

34、e impedance of any circuit in a repeater section forming part of a carrier system on unloaded symmetric pairsshould not differ from the nominal value by more than the values shown below: 5% (value measured at 60 kHz) for a repeater section forming part of a 12-channel system; 8% (value measured at 1

35、08 kHz) for a repeater section forming part of a 24-channel system; 8% (value measured at 120 kHz) for a repeater section forming part of a 36- or 48-channel system; 8% (value measured at 240 kHz) for a repeater section forming part of a 60-channel system; 8% (value measured at 552 kHz) for a repeat

36、er section forming part of a 120-channel system.2.4 Dielectric strengthIf it is desired to check the dielectric strength of a repeater section after laying, direct current will be applied tothe cable at a voltage equal to the specified r.m.s. alternating current test voltage for tests on factory len

37、gths (see 1.4above).2.5 Insulation resistanceThe insulation resistance measured at the end of the cable between any one conductor and all the otherconductors bunched and connected to the earthed sheath (excluding internal repeater station wiring) should not be lessthan 10 000 M-km measured at a potential difference of at least 100 volts and not more than 500 volts. The readingshall be made after electrification for one minute.References1 Dielectric strength tests, Blue Book, Vol. III, Part 4, Annex 19, ITU, Geneva, 1965.2 Ibid., 4.