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The present invention relates to a telecommunication cable comprising at
least two telecommunication sub-assemblies, each sub-assembly comprising at
least one group of at least two signal conductors, said at least one group being
surrounded by a conductive shield, and the conductive shields of adjacent sub-assemblies
being in electrical contact with each other.
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Such a telecommunication cable is already known in the art, e.g. from the
International Patent Application PCT/US98/08027 (WO 98/48430). In such a cable,
the individual telecommunication sub-assemblies need to be separated from each
other by shielding means in order to avoid cross-talk and electro-magnetic
interferences. Therefore, in the cable of this document, four unshielded twisted
pairs or telecommunication sub-assemblies are nested in channels formed by fins
of a cross-shaped core, the core material being conductive and forming a
longitudinal shield, and the core itself is surrounded by a conductive shield. The
construction of the cross-shaped shielding core is complex and the corresponding
production cost is high.
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An object of the present invention is to provide a telecommunication cable
of the above known type but which is easier to manufacture, relatively cheaper in
production and in material, and more resistant to cable bending.
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According to the invention, this object is achieved due to the fact that said
at least one group is surrounded by an insulating medium and that each of said
conductive shields is made of a layer of conductive material deposited on said
insulating medium.
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In the present invention, because the transmission sub-assemblies are
individually shielded by providing a deposited metal layer on an insulation medium
surrounding the signal conductors, the cross-shaped shielding core of the cable is
no longer necessary. This reduces dramatically the production cost and the
complexity of the cable assembly.
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In this way, the disadvantages of the above existing solution are solved.
Additionally, the conductive material deposition technology allows applying an
acceptable metal thickness at a speed of several hundred meters per minute. The
deposition can be done either in a separate production step or on-line on the
insulation line before the "take-up". The total insulation process time may so be
reduced.
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Moreover, owing to the individual shielding of each telecommunication
sub-assembly, all these sub-assemblies are protected from mutual cross-talk or
any other outside influence.
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In a preferred embodiment of the present invention, the cross-section of
the telecommunication sub-assemblies has the shape of a portion of a pie. A cable
assembly with a circular section can so easily be obtained.
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According to the invention, the signal conductors of each group may be
twisted inside the insulating medium. They can also be longitudinally spaced and
located in parallel with respect to one another.
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In another advantageous embodiment, the conductors are embedded
within the insulating medium.
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When the conductors are located parallel in parallel with respect to one
another and embedded within the insulating medium, they are thus regularly
spaced, and the twisting of the conductors may no longer be necessary. This also
simplifies the production process while maintaining efficient characteristics against
cross-talk and electro-magnetic interferences owing to the signal conductors being
embedded into the insulating medium. This will also give a better guarantee for
overall uniformity of the transmission cable and therefore on the transmission
properties.
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Further characterizing embodiments of the present telecommunication
cable are mentioned in the appended claims.
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It is to be noticed that the term 'comprising', used in the claims, should
not be interpreted as being limitative to the means listed thereafter. Thus, the
scope of the expression 'a device comprising means A and B' should not be limited
to devices consisting only of components A and B. It means that with respect to
the present invention, the only relevant components of the device are A and B.
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The above and other objects and features of the invention will become
more apparent and the invention itself will be best understood by referring to the
following description of an embodiment taken in conjunction with the
accompanying drawings wherein:
- Fig. 1 shows two signal conductors embedded within an insulating
medium surrounded by a conductive shield in order to form a telecommunication
sub-assembly for use in a cable according to the invention;
- Fig. 2 shows four telecommunication sub-assemblies as of Fig. 1 and
arranged so as to form a cable assembly;
- Fig. 3 shows an improved version of the cable assembly of Fig. 2.
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All the figures show cross-sectional views of a telecommunication cable
according to the present invention. Such a telecommunication cable and a cable
sub-assembly for use therein will be described below.
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The telecommunication sub-assembly 10 shown at Fig. 1 comprises two
signal conductors 11 and 12 embedded in parallel in an insulating medium 13 in
order to form a balanced transmission pair. The single body insulating material 13
embedding the conductors is preferably polyethylene and the distance between
the conductors 11 and 12 is maintained constant along the whole transmission
path. The external surface of the so obtained form is covered with a conductive
material deposited layer 14 uniformly applied through e.g. plasma deposition. The
conductive material is preferably copper [Cu] or aluminum [Al]. The applied
thickness should be of several micrometers depending upon the required shielding
performance and on the used material.
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This layer 14 will act as an electro-magnetic shield around the pair of
conductors 11 and 12. As a result, the so obtained shielded telecommunication
sub-assembly 10 shows efficient characteristics against cross-talk and electro-magnetic
interferences, even at relatively high frequencies, although there is no
need to twist the signal conductors inside the embedding insulating medium 13.
The choice of material used for the conductive layer 14, its thickness and
uniformity influence the shielding efficiency. For example, the applied layer 14
should minimally be sufficient to meet the IS011801 Cat.7 cross-talk specification.
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By use of a metal plasma-deposit conductive layer 14, a relatively costly
production step is avoided. However, other known deposition techniques may be
used without going out of the scope of the present invention, as e.g. a sputteringdeposition
or ion-deposition techniques.
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The current plasma deposition technology allows applying the requested
thickness at a speed of several hundred meters per minute. The deposition can be
done in a separate production step or on-line on the insulation line before the
"take-up". By making the sub-assembly in one production step on the insulation
line, the total insulation process time will be reduced, and the pairing of the
individual wires is not necessary. This will also give a better guarantee for overall
uniformity and therefore transmission properties.
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The cross-section of the telecommunication sub-assembly 10 substantially
has the shape of a portion of a pie.
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Several, e.g. four, individually embedded shielded pairs 11, 12, 13, all
similar to the transmission cable 10, are arranged in order to form a cable 20 as
shown at Fig. 2. In this cable 20, the telecommunication sub-assemblies 10 to 13
fit together with their metal plasma-deposit conductive shields, as 14, into
electrical contact with each other. The resulting cable assembly 20 has a circular
cross-section.
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In a preferred embodiment, the cable assembly 20 is provided with a
central channel adapted to receive one or more drain wires 31 as shown at Fig. 3.
The drain wire 31 is into electrical contact with the conductive shields of all the
telecommunication sub-assemblies 10 to 13.
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The cable 20 further has an external metallic shield 32 surrounding the
telecommunication sub-assemblies 10, 11, 12 and 13, as shown at Fig. 3. The
external metallic shield 32 is constituted by a metallic tape or braided wires
applied around the cable core and into electrical contact with the conductive
shields, as 14, of all the sub-assemblies.
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It is to be noted that the flexibility of the cable 20 will be improved if the
transmission cables 10, 11, 12 and 13 are helicoidally arranged.
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This also facilitates the application of a wrapped metallic tape around the
cable.
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An extruded outer jacket 33 protecting and maintaining together the
sub-assemblies 10 to 13, with or without the external metallic shield 32, finally
covers the cable 20.
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It is to be noted that in the above description reference is made to
telecommunication sub-assemblies with a pair of signal conductors. This is
however not a limitation of the invention which can easily be extended to cables
with groups of more than two signal conductors in each sub-assembly.
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The indicated amount and shape of individually shielded
telecommunication sub-assemblies forming the cable is also not a limitation of the
invention.
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Depending on the shape of the cross-section of each sub-assembly, more
or less than four sub-assemblies may be used to form the cable according to the
invention.
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Moreover, all the sub-assemblies forming the cable need not to have a
same section, or a section having the shape of a portion of a pie.
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Besides, even if the cable and sub-assemblies of the invention have been
described as containing parallel conductors embedded in an insulating medium,
the invention also applies to such cables and sub-assemblies in which the
conductors are twisted in the form of pairs or quads, and the twisted or parallel
conductors need not necessarily be embedded in the insulating medium, as such a
medium may only surround them.
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While the principles of the invention have been described above in
connection with a specific embodiment, it is to be clearly understood that this
description is made only by way of example and not as a limitation on the scope of
the invention, as defined in the appended claims.