nominal diameter of solid\(hycopper wire inner conductor: 0.7\ mm;
.LP
b)
nominal internal diameter of outer conductor: 2.9\ mm;
.bp
.LP
A single bimetallic copper\(hysteel\(hycopper tape may also be used
to serve as outer conductor and screen.
.FE
c)
outer conductor consisting of a copper tape with a thickness of the order
of 0.1\ mm, laid lengthwise with overlap
;
.LP
d)
screen consisting of a steel tape with a thickness of the
order of 0.1\ mm, laid lengthwise with overlap
.
.sp 2P
.LP
\fB2\fR \fBCable specification\fR (factory lengths of about 500\ m)
.sp 1P
.RT
.sp 1P
.LP
2.1
\fICharacteristic impedance\fR
.sp 9p
.RT
.PP
To check that the value given in \(sc\ 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.
.RT
.sp 1P
.LP
2.2
\fIImpedance regularity\fR
.sp 9p
.RT
.PP
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.
.PP
Table 3/G.621 shows the various values to be obtained according to the
purpose for which the cable is intended.
.RT
.ce
\fBH.T. [T3.621]\fR
.ce
TABLE\ 3/G.621
.ce
\fBEchometric measurement of factory lengths\fR
.ce
| ua\d\u)\d
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
lw(156p) | cw(36p) .
Type of system Digital
_
.T&
lw(156p) | cw(36p) .
Bit rate {
Medium bit rate
(6 to 34 Mbit/s)
}
_
.T&
lw(156p) | cw(36p) .
Maximum pulse duration 100 ns
_
.T&
lw(84p) | cw(36p) | cw(36p) | cw(36p) , ^ | ^ | c | c.
General provisions Maximum peak 100% \ 36 dB
\ 95% \ 39 dB
_
.T&
lw(84p) | cw(12p) | lw(60p) | cw(36p) , ^ | c | l | l.
{
Additional optional provisions | ua\d\u)\d
} A Mean of 3 maximum peaks \ 39 dB
B {
Equivalent resistance error
}
.TE
.LP
\ua\d\u)\d
It is enough to check that one of the two conditions A or B is
fulfilled.
.LP
\fINote\ 1\fR
\ \(em\ 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.
.LP
\fINote\ 2\fR
\ \(em\ With the construction techniques used so far, systematic faults do not give rise, in steady\(hystate measurements of regularity return loss, to
peaks at frequencies below 60 MHz. For this reason, and taking into account the bit rate envisaged, steady\(hystate measurements of regularity return loss
do not seem necessary. For other types of construction which might be used in future, supervision of the regularity return loss might be wise; in such cases, the value should be 20 dB from 4 to 60 MHz.
.nr PS 9
.RT
.ad r
\fBTable 3/G.621 [T3.621], p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
2.3
\fIAttenuation coefficient\fR
.sp 9p
.RT
.PP
The attenuation of pairs should be such as to allow compliance with the
provisions of \(sc\ 3.3 below
.FS
At this stage of manufacture, attenuation
measurements are merely prototype measurements.
.FE
.
.bp
.RT
.sp 1P
.LP
2.4
\fINear\(hyend crosstalk attenuation\fR
.sp 9p
.RT
.PP
The near\(hyend crosstalk attenuation between coaxial pairs used for different
transmission directions, measured in the frequency band 0.5\(hy20\ MHz
on factory lengths, must be above 135\ dB for 100% of measurements.
.RT
.sp 1P
.LP
2.5
\fIDielectric strength\fR
.sp 9p
.RT
.PP
The pair should withstand an a.c. voltage of 1000\ r.m.s. at 50\ Hz (or
a d.c. voltage of 1500\ volts) applied for at least 1 minute between the
centre and the outer conductor.
.PP
If in normal service the outer conductors of the coaxial pairs are not
to be earthed, a dielectric strength test must be carried out between the
outer conductors and the earthed metal sheath. For this test, an a.c. voltage
of at least 2000\ volts r.m.s. at 50\ Hz or a d.c. voltage of not less
than 3000\ V will be applied.
.RT
.sp 1P
.LP
2.6
\fIInsulation resistance\fR
.sp 9p
.RT
.PP
The insulation resistance between the centre and outer conductors of the
coaxial pair, measured with a perfectly steady voltage of between\ 100
and 500\ V, should not be less than 10 | 00\ M\(*Q\(hykm after electrification
for one minute at a temperature not lower than 15 | (deC. The measurement
of the insulation resistance should be made after the dielectric strength
test. This measurement should be made on every factory length.
It is enough to check that one of the three conditions A, B or C
is fulfilled.
.LP
\fINote\ 1\fR
\ \(em\ Notes 1 and 2 to Table 3/G.622 still hold good. However, for 0.06 to 1.3 MHz analogue systems, the provisions of column 0.06 to 6 MHz apply, but the pulse duration may attain 400 ns for elementary cable sections longer than
4\ km.
.LP
\fINote\ 2\fR
\ \(em\ Measurements using sine\(hywave signals on elementary cable sections are unnecessary unless there are serious grounds for believing that systematic
irregularities may have been introduced during the laying or installation of the cable. In such cases, the measurement results should not be less than 20\ dB.
.nr PS 9
.RT
.ad r
\fBTableau 6/G.622 [T6.622], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.sp 2
.ce
\fBH.T. [T7.622]\fR
.ce
TABLE\ 7/G.622
.ce
\fBMinimum far\(hyend crosstalk ratio between two 1.2/4.4 mm coaxial pairs\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(60p) | cw(60p) sw(60p) , ^ | c | c.
Length of the section (km) {
Far\(hyend crosstalk ratio (dB)
}
Without phase inversion {
With phase inversion
at repeaters
}
_
.T&
cw(60p) | cw(60p) | cw(60p) .
8 87 \(em
.T&
cw(60p) | cw(60p) | cw(60p) .
6 89 80
.T&
cw(60p) | cw(60p) | cw(60p) .
4 93 \(em
.T&
cw(60p) | cw(60p) | cw(60p) .
3 95 83
.T&
cw(60p) | cw(60p) | cw(60p) .
2 99 \(em
_
.TE
.nr PS 9
.RT
.ad r
\fBTABLEAU 7/G.622 [T7.622], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.PP
There is no need to specify a near\(hyend crosstalk ratio when the
former limits are chosen for the far\(hyend crosstalk ratio.
.PP
When phase inversion is used, the near\(hyend crosstalk ratio for pairs
transmitting in opposite directions must be at least 84\ dB for a section
about 6\ km long, and 87\ dB for a section about 3\ km long.
.PP
\fINote\fR \ \(em\ These limits enable a far\(hyend crosstalk ratio of
65\ dB to be obtained on the worst homogenous 280\(hykm section, assuming
that for the
frequencies in question only far\(hyend crosstalk due to the cable is to be
considered
.FS
In practice it is possible to forget the influence of line
.PP
equipment on intelligible crosstalk, but this is only true for low frequencies
of the band (less than 300\ kHz).
.FE
. It is assumed that the variation in the minimum far\(hyend crosstalk
ratio as a function of the distance approximately
follows a 20\ dB/decade law for distances below a limit distance\ \fIL\fR\d1\uand
a 10\ dB/decade law for distances above\ \fIL\fR\d1\u. The values depend
on a number of factors, mainly the system used, the type of cable and the
considered frequency. A value of 30\ km appears suitable in most cases,
although values of\ \fIL\fR\d1\uranging from a few kilometers to 30\ kilometers
have
been observed in practice, ensuring the consistency of the limits in
Table\ 7/G.622 with the 65\ dB limit on a 280\ km section.
.RT
.sp 1P
.LP
3.5
\fIDielectric strength\fR
.sp 9p
.RT
.PP
The pair must withstand a d.c. voltage of at least 1000\ V applied during
at least one minute between the inner and the outer conductors.
.PP
In addition, a test of dielectric strength between the coaxial pair
and earth shall be made as described in \(sc\ 2.5, using a d.c. voltage
of at least 2000\ V applied for one minute.
.PP
\fINote\fR \ \(em\ The recommended test voltages take account of the normal
safety margins applied in the various countries. Polythene insulation,
however, might reasonably withstand considerably higher test voltages.
In any case, some other dielectric might conceivably be used in the future.
.RT
.sp 1P
.LP
3.6
\fIInsulation resistance\fR
.sp 9p
.RT
.PP
The insulation resistance between the centre and outer conductors of the
coaxial pair, measured with a perfectly steady voltage of between\ 100
and\ 500\ V, should not be less than 5000\ M\(*Q\(hykm after electrification
for one
minute. The measurement of the insulation resistance should be made after
the dielectric strength test. This measurement should be made on every
elementary cable section.
.RT
.ce 1000
ANNEX\ A
.ce 0
.ce 1000
(to Recommendation G.622)
.sp 9p
.RT
.ce 0
.ce 1000
\fBExamples of attenuation coefficient measured or specified in some
countries\fR
.sp 1P
.RT
.ce 0
.ce 1000
(Values given as an indication)
.sp 9p
.RT
.ce 0
.ce
\fBH.T. [T8.622]\fR
.ce
TABLE\ A\(hy1/G.622
.ce
\fBValues measured on a type of pair whose outer conductor is
lw(78p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) , ^ | c | l | l | l | l.
Mean power return coefficient \fIL\fR \( = 250 m 41 dB 35 dB 28 dB \fIL\fR > 500 m
40 dB
.TE
.LP
\fINotes to Tables 3/G.623 and 4/G.623\fR
.LP
\ua\d\u)\d
If investigations or definition studies show that measurements
with shorter pulse durations are required, the duration of 2 ns will be
adopted.
.LP
\ub\d\u)\d
Provided that no more than one value between 48\(hy54 dB is
encountered on one and the same coaxial pair of an elementary cable section.
.LP
\uc\d\u)\d
It is enough to check that one of the two conditions A or B is
fulfilled.
.LP
\ud\d\u)\d
The provisions for 4\(hy70 MHz analogue systems are certainly
adequate. However, much lower values have also been proposed. Agreement should be reached on the values to be specified and the frequency band to be explored (4\(hy100\ MHz or 62\(hy500\ MHz).
.nr PS 9
.RT
.ad r
\fBTable 4/G.623 + notes [T4.623], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.sp 15
.bp
.sp 1P
.LP
2.3
\fIAttenuation coefficient\fR
.sp 9p
.RT
.PP
At this stage of manufacture, attenuation and crosstalk measurements are
merely prototype measurements.
.FE
.
The attenuation of pairs should be such as to allow of compliance with
the provisions of \(sc\ 3.3 below
.
.PP
If reference is made to the length measured along a generation of the cable
sheath, the linear attenuation coefficient should be multiplied by the
take\(hyup factor, the values of which are given as an indication in
Table\ 5/G.623.
.RT
.LP
.sp 1
.ce
\fBH.T. [T5.623]\fR
.ce
TABLE\ 5/G.623
.ce
\fBTake\(hyup factor values\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(48p) | cw(48p) | cw(72p) .
Number of pairs in cable {
Take\(hyup factor,
last layer
} {
Weighted take\(hyup factor,
entire cable
}
_
.T&
cw(48p) | cw(48p) | cw(72p) .
4 or 6 1.003
.T&
cw(48p) | cw(48p) | cw(72p) .
8 1.005
.T&
cw(48p) | cw(48p) | cw(72p) .
12 1.009 1.007
.T&
cw(48p) | cw(48p) | cw(72p) .
18 or 20 1.012 1.010
_
.TE
.nr PS 9
.RT
.ad r
\fBTable 5.623 [T5.623], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.sp 1
.sp 1P
.LP
2.4
\fICrosstalk\fR
.sp 9p
.RT
.PP
The crosstalk between pairs should be such as to allow of
compliance with provisions of \(sc\ 3.4 below
.
.RT
.sp 1P
.LP
2.5
\fIDielectric strength\fR
.sp 9p
.RT
.PP
The pair should withstand for one minute an a.c. voltage of 2000\ V r.m.s.
at 50\ Hz (or 3000\ V d.c.) applied between the centre conductor and the
outer conductor connected to the sheath. This dielectric strength test
should be made on each factory length.
.RT
.sp 1P
.LP
2.6
\fIInsulation resistance\fR
.sp 9p
.RT
.PP
The insulation resistance between the centre and outer conductors of the
coaxial pair, measured with a perfectly steady voltage of between 100
and 500\ V, should not be less than 5000\ M\(*Q\(hykm after electrification
for one
minute at a temperature not lower than 15 | (deC. The measurement of the
insulation resistance should be made after the dielectric strength test.
This measurement should be made on each factory length.
If investigations or definition studies show that measurements
with shorter pulse durations are required, the duration of 2 ns
will be adopted.
.LP
\ub\d\u)\d
It is enough to check that one of the three conditions A, B or C
is fulfilled.
.LP
\uc\d\u)\d
As long as there does not exist an echometer with impulses of
10 ns capable to explore half a repeater section, the measurement
will be done with 50 ns impulses.
.nr PS 9
.RT
.ad r
\fBTableau 6/G.623 [T6.623], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 1P
.LP
3.4
\fICrosstalk\fR
.sp 9p
.RT
.PP
The far\(hyend crosstalk ratio between two coaxial pairs of a cable at
any frequency in the band transmitted should be at least equal to the values
listed in Table\ 7/G.623.
.RT
.ce
\fBH.T. [T7.623]\fR
.ce
TABLE\ 7/G.623
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(48p) | cw(60p) | cw(60p) .
Lengths (km) Frequency band (MHz) {
Far\(hyend crosstalk radio
(dB)
}
_
.T&
cw(48p) | cw(60p) | cw(60p) .
9 | 0.06\(hy4.3 {
\ 85\fB | fR\(ua\fBa\fR\(ua\fB)\fR
}
.T&
cw(48p) | cw(60p) | cw(60p) .
4.5 0.3\(hy12.5 \ 94 | ua\d\u)\d
.T&
cw(48p) | cw(60p) | cw(60p) .
1.5 4\(hy62 130\fB | fR\(ua\fBa\fR\(ua\fB)\fR
.TE
.LP
\ua\d\u)\d
If the cable operates both in the 0.3\(hy12 MHz frequency band and the lower frequency band with longer repeater sections, the value of the far\(hyend crosstalk should be increased by a few decibels to frequencies higher than
300 kHz to allow for the differences in levels across some points of the cable. A limit of 100 dB suffices.
.nr PS 9
.RT
.ad r
\fBTable 7/G.623 [T7623] p.\fR
.sp 1P
.RT
.ad b
.RT
.PP
With cables operating at 60\ MHz, the near\(hyend crosstalk
attenuation at 60\ MHz between pairs transmitted in opposite directions
should be at least 140\ dB. No limit is fixed for other systems, previous
studies
having shown that the near\(hyend crosstalk ratio under service conditions was
greater than the far\(hyend crosstalk ratio. These values include the contribution
of accessories which are associated to elementary cable section, such as
flexible cords and coaxial connector.
.PP
\fINote\ 1\fR \ \(em\ The values given for cables operating at 60\ MHz
are derived from general considerations on crosstalk between sound\(hyprogramme
circuits given in Recommendation\ J.18\ [2]. These values are easy to obtain,
although in the
present state of the art it is difficult to test them with ordinary measuring
equipments.
.PP
\fINote\ 2\fR \ \(em\ The values given for cables operating at 12\ MHz or less
suffice for telephone transmission. For sound\(hyprogramme circuit transmission,
this value must be increased to 105\ dB, a value which is easily obtained
with all types of cable at frequencies above 300\ kHz.
.PP
\fINote\ 3\fR \ \(em\ These limits enable at far\(hyend crosstalk ratio
of 65\ dB to be obtained on the worst homogeneous 280\(hykm section, assuming
that for the
frequencies in question only far\(hyend crosstalk due to the cable is to be
considered
.FS
In practice, it is possible to forget the influence of line
equipments on intelligible crosstalk, but this is only true for low frequencies
of the band (less than 300\ kHz).
.FE
. When there is no phase inversion, it is assumed that the variation in
the minimum far\(hyend crosstalk ratio as a function of the distance approximately
follows a 20\ dB/decade law for distances below a limit distance\ \fIL\fR\d1\uand
a 10\ dB/decade law for distances
above\ \fIL\fR\d1\u. The value of \fIL\fR\d1\udepends on a number of
factors, mainly the system used, the type of cable and the considered
frequency. A value of 30\ km appears suitable in most cases, although values
of\ \fIL\fR\d1\uranging from a few kilometers to 30\ kilometres have been
observed in practice, ensuring the consistency of the limits in Table\
7/G.623 with a 65\ dB limit on a 280\ km section.
.RT
.sp 1P
.LP
3.5
\fIDielectric strength\fR
.sp 9p
.RT
.PP
The pair should withstand for one minute a d.c. voltage of 2000\ V applied
between the centre conductor and the outer conductor connected to the sheath.
This dielectric strength test should be made on each elementary cable section
on completion of laying.
.RT
.sp 1P
.LP
3.6
\fIInsulation resistance\fR
.sp 9p
.RT
.PP
The insulation resistance between the centre and outer conductors of the
coaxial pair, measured with a perfectly steady voltage of between 100
and 500\ V, should not be less than 5000\ M\(*Q\(hykm after electrification
for one
minute; the measurement of the insulation resistance should be made after
the dielectric strength test. This measurement should be made on every
section.
.bp
.RT
.ce 1000
ANNEX\ A
.ce 0
.ce 1000
(to Recommendation G.623)
.sp 9p
.RT
.ce 0
.ce 1000
\fBDescription of a\fR
\fBcopper\(hyaluminium coaxial pair\fR \fBhaving the same\fR
.sp 1P
.RT
.ce 0
.ce 1000
\fBelectrical characteristics as the 2.6/9.5\(hymm copper coaxial pair\fR
.ce 0
.PP
The constitution of this copper\(hyaluminium coaxial pair is as follows:
.sp 1P
.RT
.LP
\(em
The centre conductor is a solid copper wire 2.8\ mm in
diameter.
.LP
\(em
The insulation is such that the permittivity of the
combination of gas and low\(hyloss solid dielectric material is low enough to
meet the requirements of this Recommendation.
.LP
\(em
The outer conductor consists of an aluminium tape 0.7\(hymm
thick formed into a cylinder of internal diameter 10.2\ mm around the
insulation and welded longitudinally.
.PP
Such coaxial pairs can be jointed with each other or with
2.6/9.5\(hymm copper pairs easily and reliably. They meet with all the
electrical characteristics of this Recommendation. In particular, the values
of far\(hyend
crosstalk of \(sc\ 3.4 of the text are obtained between pairs transmitting
in the same direction.
.sp 2P
.LP
\fBReferences\fR
.sp 1P
.RT
.LP
[1]
Annex\ 2 to CCITT Question\ 17/XV, Green Book, Vol.\ III.3, ITU,
Geneva,\ 1973.
.LP
[2]
CCITT Recommendation \fICrosstalk in sound\(hyprogramme circuits set
up on\fR \fIcarrier systems\fR , Vol.\ III, Rec.\ J.18.
.LP
.rs
.sp 30P
.LP
\fBMONTAGE:\ \fR REC. G.631 A LA FIN DE CETTE PAGE
