U.S. patent number 3,622,683 [Application Number 04/778,073] was granted by the patent office on 1971-11-23 for telephone cable with improved crosstalk properties.
This patent grant is currently assigned to Superior Continental Corporation. Invention is credited to Walter L. Roberts, Frederic N. Wilkenloh.
United States Patent |
3,622,683 |
Roberts , et al. |
November 23, 1971 |
**Please see images for:
( Certificate of Correction ) ** |
TELEPHONE CABLE WITH IMPROVED CROSSTALK PROPERTIES
Abstract
Disclosed herein is an economical telephone cable structure and
method of making same, such cable structure possessing improved
crosstalk properties. A plurality of insulated electrical
conductors (pairs), of an otherwise conventional telephone cable
design are divided into at least two portions by plastic-coated
metal foil strip or tape. Measurements between pairs, divided by
this plastic-coated metal foil, of unwanted energy transferred from
one conductor to another by means of mutual inductive, capacity, or
conductive coupling (crosstalk), shows greatly improved properties
over undivided cable pairs or divided cable pairs of prior art. By
dividing electrical conductor telephone pairs within a telephone
cable structure with plastic-coated metal foil, the crosstalk
properties are so vastly improved that a greater spacing between
repeaters can be designed into a telephone cable system, as
compared to a cable system employing prior art divided or undivided
cable pairs.
Inventors: |
Roberts; Walter L. (Hickory,
NC), Wilkenloh; Frederic N. (Conover, NC) |
Assignee: |
Superior Continental
Corporation (Hickory, NC)
|
Family
ID: |
25112226 |
Appl.
No.: |
04/778,073 |
Filed: |
November 22, 1968 |
Current U.S.
Class: |
174/36; 174/25R;
174/25C; 174/27; 174/105R; 174/110PM; 174/115; 174/103; 174/107;
174/113R |
Current CPC
Class: |
H01B
11/085 (20130101); H01B 11/04 (20130101) |
Current International
Class: |
H01B
11/02 (20060101); H01B 11/00 (20060101); H01B
11/04 (20060101); H01B 11/08 (20060101); H01b
011/08 () |
Field of
Search: |
;174/102-109,113,115,116,119,36,27,25,26 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
105,876 |
|
Nov 1937 |
|
AU |
|
1,120,216 |
|
Jul 1956 |
|
FR |
|
775,841 |
|
Jan 1935 |
|
FR |
|
657,411 |
|
Mar 1938 |
|
DT |
|
314,564 |
|
Jul 1929 |
|
GB |
|
434,855 |
|
Sep 1935 |
|
GB |
|
449,582 |
|
Jun 1936 |
|
GB |
|
995,582 |
|
Jun 1965 |
|
GB |
|
367,814 |
|
Feb 1932 |
|
GB |
|
Other References
Communications News, Apr., 1969 .
M. C. Biskeborn & D. P. Dobbin, Jelly Blend Waterproofs Cable,
Bell Laboratories Record, March 1969, p. 71, 72, 73, 74, 75. Copy
in 174-23.
|
Primary Examiner: Myers; Lewis H.
Assistant Examiner: Grimley; A. T.
Claims
We claim:
1. A cable comprising:
a. a cable core having first and second groups of insulated
electrical conductors;
b. a metal foil shield covered on both surfaces with a plastic,
said metal foil shield peripherally surrounding said first group of
electrical conductors but not said second group of electrical
conductors;
c. a plastic tape peripherally surrounding said second group of
electrical conductors, but not said first group of electrical
conductors, and
d. a plastic sheath circumferentially surrounding said first and
second groups of electrical conductors.
2. The cable defined in claim 1, wherein the plastic covering both
surfaces of said metal foil shield also covers the longitudinally
extending edges of said metal foil shield.
3. A cable as defined in claim 1, wherein a further shield is made
of metal and circumferentially surrounds said metal foil shield and
said plastic tape.
4. A cable as defined in claim 1, wherein that space not otherwise
occupied by insulated electrical conductors inside of said metal
foil shield is filled essentially with polyethylene grease-like
material, having an average molecular weight below about 10,000 and
a density at 25.degree. C. of about 0.85 grams per milliliter.
5. A cable as defined in claim 1, wherein that space
circumferentially surrounded by said plastic tape and not otherwise
occupied by said second group of insulated electrical conductors is
essentially filled by a polyethylene grease-like material, having a
molecular weight below about 10,000 and a density of 25.degree. C.
of about 0.85 grams per milliliter.
6. A cable as defined in claim 1, wherein an additional plastic
tape circumferentially surrounds both said first and second groups
of insulated electrical conductors.
7. A cable as defined in claim 6 wherein a further grease-like is
made of metal and circumferentially surrounds said additional
plastic tape. grease-like
8. A cable as defined in claim 6, wherein a polyethylene greaselike
material essentially fills that space circumferentially surrounded
by said additional plastic tape and not otherwise occupied and
circumferentially surrounded by said metal foil shield and the
first mentioned one of said plastic tapes, said polyethylene
greaselike material having a molecular weight below about 10,000
and a density at 25.degree. C. of about 0.85 grams per
milliliter.
9. A cable as defined in claim 6, wherein that space
circumferentially surrounded by said additional plastic tape and
not otherwise occupied by said first shield, the first-mentioned
one of said plastic tapes, and said first and second groups of
electrical conductors is essentially filled by a polyethylene
grease-like material, having a molecular weight below about 10,000
and a density at 25.degree. C. of about 0.85 grams per
milliliter.
10. A cable comprising:
a. a core made up of a plurality of insulated electrical
conductors;
b. a shield circumscribing said core, said shield being made of a
metal foil that is coated on both sides by plastic;
c. a second plurality of insulated electrical conductors defining
an annular core distributed around the outermost surface of said
shield;
d. an integral plastic tube peripherally surrounding the composite
of said first and second plurality of electrical conductors and
said shield, and
e. a plastic tape circumferentially surrounding said second
plurality of electrical conductors.
11. A cable comprising a tubular covering being formed with an
inner peripheral surface that delimits a core-receiving cavity, a
tubular metallic shield forming a part of said covering, a core
made up of a plurality of electrically insulated conductors
received in said core-receiving cavity and nested within said
tubular metallic shield, and integral metallic crosstalk shield
disposed within said core-receiving cavity and extending
longitudinally in said core, said crosstalk shield extending
between circumferentially spaced-apart regions located on said
inner peripheral surface of said tubular covering to separate said
conductors into a plurality of longitudinally extending groups,
each group being delimited by said crosstalk shield and a portion
of said inner peripheral surface, the transverse cross section of
said crosstalk shield having first and second terminal portions and
an intermediate portion extending between and integrally joined to
said terminal portions, said first and second terminal portions
circumferentially extending around portions of the outer periphery
of said core and having respective spaced-apart free ends that lie
on opposite sides of that plane in which said intermediate portion
lies, and said terminal portions being in close proximity with said
inner peripheral surface and said metallic tubular shield.
12. The cable defined in claim 11 wherein said terminal portions
seat against said inner peripheral surfaces.
13. The cable defined in claim 11 wherein said crosstalk shield has
a serpentine-shaped configuration in transverse cross section.
14. The cable defined in claim 11 wherein said crosstalk shield has
an S-shaped configuration in transverse cross section.
15. The cable defined in claim 11 wherein said crosstalk shield is
made of metal foil.
16. The cable defined in claim 11 wherein said crosstalk shield is
a metal foil coated only on one side with a plastic.
17. The cable defined in claim 11 wherein said crosstalk shield is
made of metal foil, and wherein both sides and the longitudinal
edges of said crosstalk shield are completely covered with a
plastic.
18. The cable defined in claim 11 wherein said crosstalk shield is
the only crosstalk barrier between said groups, and wherein
crosstalk shield is formed in transverse cross section only with
said first and second terminal portions and said intermediate
portion.
19. The cable defined in claim 11 wherein said crosstalk shield is
made of non-magnetic electrically conductive material.
20. The cable defined in claim 19 wherein said crosstalk shield is
made of metal foil.
21. The cable defined in claim 19 wherein said metal foil is coated
on at least one side with plastic.
22. The cable defined in claim 19 wherein said metal foil is coated
on both sides with a plastic.
23. The cable defined in claim 11 wherein the space in said cavity,
not otherwise occupied by said conductors and said crosstalk
shield, is essentially filled with a greaselike material.
24. The cable defined in claim 23 wherein said crosstalk shield is
made of metal foil.
25. The cable defined in claim 11 wherein the space in said cavity,
not otherwise occupied by said conductors and said crosstalk
shield, is essentially filled with a polyethylene greaselike
material having an average molecular weight below about 10,000 and
a density at 25.degree. C. of about 0.8 grams per milliliter.
26. The cable defined in claim 11 wherein the width of said
crosstalk shield is less than the outer peripheral circumference of
said core.
27. The cable defined in claim 26 wherein the space in said cavity,
not otherwise occupied by said conductors and said crosstalk
shield, is filled with a greaselike material.
28. The cable defined in claim 26 wherein said crosstalk shield has
an S-shaped configuration in transverse cross section.
29. The cable defined in claim 26 wherein said tubular covering
further includes a plastic tape nested inside of said tubular
shield and defining said inner peripheral surface.
30. The cable defined in claim 29 wherein said terminal portions
are spaced from said tubular shield only by said plastic tape.
31. The cable defined in claim 30 wherein said terminal portions
seat against said inner peripheral surface.
32. The cable defined in claim 29 wherein said crosstalk shield is
made of metal foil.
33. The cable defined in claim 32 wherein said foil is
non-magnetic.
34. The cable defined in claim 33 wherein said foil is covered on
at least one side with a plastic.
35. The cable defined in claim 33 wherein said foil is covered on
both sides with a plastic.
36. The cable defined in claim 29 wherein said tubular covering
further includes a tubular plastic sheath, said tubular shield
being nested within said tubular plastic sheath.
37. A cable comprising:
a. a cable core having first and second groups of insulated
electrical conductors;
b. a metal foil shield peripherally surrounding said first group of
electrical conductors but not said second group of electrical
conductors;
c. a plastic tape peripherally surrounding said second group of
electrical conductors, but not said first group of electrical
conductors, and
d. a plastic sheath circumferentially surrounding said first and
second groups of electrical conductors.
Description
DETAILED DISCLOSURE
This invention relates to multiconductor cables and has particular
reference to arrangements for shielding certain of the conductors
of such a cable from other conductors of the cable. In order to
transmit currents of the same frequency in both directions within
the same cable, more particularly when the currents to be
transmitted are of carrier frequencies, it is desirable that the
conductors used for transmitting in one direction be shielded
(electrically) from those transmitting in the opposite direction.
Accordingly, it is the purpose of this disclosure, to show how to
arrange the conductors of a cable into two concentric groups, with
a shield between the two groups of conductors. In such an
arrangement of a cable, those conductors on one side of the shield
may all be used for transmitting carrier frequencies in one
direction, while the returned channels for transmission in the
opposite direction will be applied to the conductors on the other
side of the shield. The shield has the effect of reducing so called
"near end" crosstalk since the weak attenuated currents coming in
at a repeater point are in a compartment of the cable electrically
shielded from a large amplified current entering the conductors in
the other compartment of the cable. The instant invention also
envisions and incorporates the concept of two distinct bundles of
conductors inside a cable structure, one such bundle being
electrically shielded from the other bundles and neither one of the
aforesaid bundles necessarily being concentric around the
other.
In one embodiment, a cable with a shield is formed by arranging a
group of conductors into a cylindrical bundle, spirally wrapping or
twisting tapes of aluminum foil, either per se or coated with a
plastic such as polyethylene terapthalate (Mylar), upon the
cylindrical bundle of insulated wires, and then mounting another
group of insulated wires, preferably equal in number, outside of
the shielding tape in the form of a concentric cylindrical bundle,
upon which another sheath of plastic, or other material, is applied
in the usual manner.
The prior art has recognized the same problem to which the instant
invention only crosstalk and it is interesting to note that
Nyquist, U.S. Pat. No. 1,979,402, (179/78), teaches that the
shielding material should be thin tape of soft iron, alternating
with layers of copper. Nyquist goes on to teach that while various
materials may be used, iron (in particular soft iron) is preferred
for one group of the alternating layers. This, according to
Nyquist, is so because the product of the permeability by the
conductivity of the iron is large, thereby making its attenuating
effect large. Furthermore, Nyquist teaches that the ratio of
permeability of the iron to its conductivity is quite different
from that of the copper or other conductive material, which may be
used for the other alternating layers. Such a combination,
according to Nyquist, causes electromagnetic wave reflection losses
brought about by interfering waves penetrating through the shield.
For a sake of completeness and reference, the entire specification
of the aforementioned United States patent of Nyquist is
incorporated specifically herein by reference.
In passing, it might be well to note that the prior art teaching,
concerned with the transmission of carrier energy along
telecommunication cable, addresses its shield design solution to
the use of alternating layers of different metals, e.g., copper and
soft iron. At least one of these two metals is magnetic (soft
iron). In contradistinction, the instant invention addressed its
solution to the same problem by using alternating layers of a metal
and a nonmetal, neither one of which is magnetic. As stated above,
the instant invention uses as its shield, an aluminum foil either
per se or coated with a plastic, such as polyethylene terapthalate.
Furthermore, the prior art teaches that the materials to be used
must have electromagnetic properties such that the product of
permeability and conductivity should be as large as possible and
that the ratio of permeability to conductivity should be as much
different as possible from one material to the other. This is not
the case in the instant invention where there is used as a shield,
an aluminum foil either per se or coated with a plastic.
For the purposes of this disclosure, a foil is defined the same as
found on page 18 of the METALS HANDBOOK, Eighth Edition, published
by the American Society for Metals, to wit: A foil is a metal in
sheet form possessing a thickness of less than 0.006 inches.
The invention will now be more fully understood from the following
descriptions, when read in connection with the accompanying
drawing,
FIG. 1 of which is a cutaway pictorial view of one embodiment of
the instant invention, showing two groups of conductors separated
by a longitudinally disposed circumscribing foil shield;
FIG. 2 is a pictorial cutaway view of another embodiment of the
instant invention, similar to that shown in FIG. 1, wherein the
shield between the two groups of electrical conductors is not
longitudinally but helically disposed;
FIG. 3 is an additional pictorial cutaway view of one of the
embodiments of the instant invention, showing two groups of
electrical conductors separated by a shield made from a plurality
of tapes helically disposed, the lateral edges of which overlap
adjacently lying tapes;
FIG. 4 is a portion of that cable shown in FIG. 2 in a cutaway
view, emphasizing the helical seam formed by the overlapping
terminal edges of a helically wound tape shield;
FIG. 5 is a cross-sectional view of a metal foil coated on both
sides with a plastic, used to shield one group of electrical
conductors from another;
FIG. 6 is a cross-sectional view of an uncoated metal foil
shield;
FIG. 7 is a cross-sectional view of an embodiment of a foil tape
shield showing a metal foil coated only on one side by a
plastic;
FIG. 8 is a cross-sectional view of a piece of metal foil shield
having a plastic coating that completely surrounds said foil;
FIG. 9 is a cross-sectional view of that cable structure as shown
in FIG. 1, employing as a shield a metal foil coated on both sides
with a plastic;
FIG. 10 is a cross-sectional view of that cable structure as shown
in FIG. 3, employing a shield composed of a plurality of tapes made
from a metal foil coated on both sides with a plastic, the lateral
edges of which overlap adjacently disposed tapes;
FIG. 11 is a cross-sectional view of the cable structure as shown
in FIG. 1 wherein the metal foil shield is completely surrounded by
a plastic coating;
FIG. 12 is a cross-sectional view of that cable structure as shown
in FIG. 3, wherein a shield composite is shown, made up of a
plurality of metal foil tapes each of which is completely
surrounded on both sides by a plastic;
FIG. 13 is a cross-sectional view of a cable structure showing four
groups of insulated conductors, only two of which are
longitudinally circumscribed by a shield made of metal foil coated
on both sides with a plastic and the remaining groups being
longitudinally circumscribed by a plastic tape;
FIG. 14 is a cross-sectional view of a cable structure the same as
that shown in FIG. 13 except that the plastic coating on the metal
foil shield or screen completely surrounds the foil screen;
FIG. 15 is a cross-sectional view of a cable structure the same as
that shown in FIG. 14 except that the shield is composed of a
plurality of foil tapes, coated on both sides by a plastic, the
lateral edges of which overlap adjacently disposed tapes;
FIG. 16 is a cross-sectional view of a cable structure the same as
that shown in FIG. 15 except that the plastic coating of the metal
foil completely surrounds the foil;
FIG. 17 is a cross-sectional view of a cable structure showing a
screen or shield dividing groups of insulated electrical conductors
that does not longitudinally circumscribe any group of
conductors;
FIG. 18 through 21 inclusive are cross-sectional views of various
metal shields used in that cable structure of FIG. 17; FIG. 18
being a metal foil coated on both major surfaces with a plastic;
FIG. 19 being a metal foil coated only on one side with a plastic;
FIG. 20 being an uncoated metal foil; and FIG. 21 being a metal
foil completely surrounded by a plastic coating;
FIG. 22 shows in schematic form, a wire twisting apparatus used to
apply the plastic-coated metal foil shield in between first and
second groups of electrical conductors;
FIG. 23 is an enlarged diagrammatic view of a rotating die member
used to apply the plastic-coated metal foil shield between first
and second groups of electrical conductors; and,
FIG. 24 is an exemplary plot of crosstalk values derived from the
improved cable structure of the instant invention.
One embodiment of the cable to be considered herein is made up of
the usual cylindrical plastic or lead sheath with the conductors
arranged in the usual fashion, except that they are separated into
two equal or substantially equal but separate concentric groups by
means of an essentially cylindrical concentric shield. When a
signal is transmitted over any circuit in this cable, it is
permissable to consider an electromagnetic field as spreading out
from this circuit in the form of a wave motion. This wave reaches
other conductors and may induce currents and electromotive forces
in other circuits unless they are perfectly balanced. The first of
these circuits may be called the disturbing and the other the
disturbed circuit. If the disturbing and disturbed circuits are on
opposite sides of a shield, it is obvious that the disturbance is
reduced due to the attenuation the wave energy undergoes when
passing through a shield and such reflections as may occur. This
object is achieved in the instant invention by using a piece of
metal (copper, aluminum, silver, steel, and etc.) foil, either per
se, coated on both sides, coated only on one side, or completely
surrounded by a plastic such as polyethylene, polypropylene, or
polyethylene terapthalate (Mylar). It is, however, one of the many
preferred embodiments of the instant invention to use aluminum foil
coated on both sides with a plastic. The reason for this preference
is that the instant invention uses the plastic coating of the metal
(aluminum) foil as a dielectric to keep unwanted currents [emitting
from pinholes in the insulation of individual electrical
conductors], from reaching the metallic shield (aluminum foil). It
is quite obvious that when a metal foil, coated only on one side,
is employed, that the bundle of electrical conductors in nearest
proximity therewith is not protected by a dielectric from the
electrical conductors, other than that dielectric used as the
insulation on the electrical conductors themselves. Thus, there is
in this instance a preference for the aluminum foil shield, coated
on both sides with the polyethylene terapthalate (Mylar)
dielectric.
It is also an embodiment of the instant invention to employ as a
shield, a metal foil which is completely surrounded on all sides by
a plastic coating, e.g., an aluminum foil, completely surrounded by
polyethylene terapthalate (Mylar), polyethylene, polypropolyene,
polystyrene or PVC. An aluminum foil, which is coated only on its
two major surfaces with a plastic, still has exposed naked aluminum
surfaces at the edges thereof. When considering a cable of many
miles in length, this amount of exposed conductive metal becomes
significant. Therefore, the instant invention takes this into
account in one of two ways: the first way is to employ a metal foil
which is completely surrounded by plastic. As an example, such a
foil would be envisioned as being aluminum with the plastic
covering being polyethylene terapthalate (Mylar). Another way to
mitigate undesirable electrical properties created by having an
exposed surface (edge) of metal to the electrical conductors is to
fill that portion of the space created by the plastic-coated metal
foil shield not otherwise occupied by the electrical conductors
therein with a polyethylene greaselike material. This greaselike
material acts as both a dielectric protection, as well as an
inhibitor of any subsequent incoming moisture. This particular
feature will be more fully discussed later.
Turning now to FIG. 1, the overall general configuration of the
cable structure is exhibited by element (1). Shown at (14) is a
first group of insulated conductors, the outer peripheral surface
thereof being longitudinally circumscribed by a plastic-coated foil
shield shown at (15), this foil shield being either uncoated,
coated on one or both of its major surfaces as well as completely
surrounded by a plastic. Indicated by element (16), is a second
group of insulated electrical conductors disposed in an annular
fashion on the outermost surface of the plastic-coated metal foil
shield (15). Disposed in a longitudinally and circumscribed fashion
around the composite formed by the first and second group of
insulated electrical conductors (14) and (16) and the interposed
metal foil shield (15) is a polyethylene terapthalate (Mylar) tape
shown at (17). Longitudinally circumscribing the tape (17) is a
corrugated metal armor tape shown at (18). This metal armor, having
a thickness greater than a foil, (18), is a tapelike strip that has
been longitudinally folded or wrapped around the plastic tape (17).
This particular piece of armor is in a sense an electrical, as well
as a mechanical, shield and it can have a plastic, such as
polyethylene, firmly adhered to either one or more surfaces
thereof. Disposed on the outer most surface of metal shield (18) is
a molded plastic sheath (19). This outer most plastic sheath is the
customary extruded polyethylene that can be and usually is filled
with carbon black.
Shown in FIG. 2 is essentially the same cable structure as that set
forth in FIG. 1. The overall structure (2) differs from that cable
structure (1) only in the respect that the plastic-coated metal
foil shield (15) has lateral edges that overlap in a helically
rather than a longitudinal fashion. The metal shield (15) of FIG.
1, is longitudinally disposed, the lateral edges of the shield
overlapping one another. (See [15 a])
A further cable structure is shown at (3) in FIG. 3, wherein the
difference between structure (3) and (2) being that the shield of
element (2) is formed from a plurality of tapes [(15 b), (15 c),
and (15 d)] rather than a single tape. The lateral edges of the
helically disposed tapes overlap adjacently lying tapes. A
representative cross-sectional view of this particular cable
structure is shown in FIG. 9.
Element (4) of FIG. 4, is a portion of the helically wound tape, as
shown in FIG. 2. Here in this drawing, the low number of turns or
helical dispositions per linear length is emphasized. As will be
remembered, the tape (15) of FIG. 2 was a single tape, and it was
helically disposed around the first group of insulated electrical
conductors (14). The lateral edges of this tape (15) overlap,
forming the seam (14 e).
Elements (5), (6), (7), and (8) of FIGS. 5, 6, 7, and 8,
respectively, show a cross-sectional view of the particular metal
foil tapes, both plastic coated and otherwise, used by the instant
invention. Element (5) shows a metal foil (6), coated on both sides
with a plastic, whereas element (6) shows an uncoated metal foil
shield. Element (7), of FIG. 7, shows a metal foil (6), coated only
on one side, with a plastic coating [5 (a)]. Either one of the
embodiments (5), (6), (7), and (8), shown in respective figures,
are viable as a shield from both a structural and electrical
standpoint. Foil (6) has a thickness between 1 and 5 mils and is
generally twice the thickness of plastic coating [5 (a)]. All of
elements (5), (6), (7), and (8) of FIGS. 5, 6, 7, 8, as well as 18,
19, 20 and 21, can be corrugated to increase its mechanical
strength. For the purposes of this disclosure, when reference is
made to a shield, other than element (18), an electrical shield is
meant. Even though the word "shield" has an accepted double
meaning, i.e. electrical as well as mechanical (armor) protection,
the metal foil shield of the instant invention connote primarily an
electrical shield.
Element (9) of FIG. 9, shows a cross-sectional view of that cable
structure as depicted in FIG. 1. Like numbers of FIG. 1 also
represent like elements in FIG. 9. Here it will be noted that the
plastic-coated metal foil shield (15) is coated on its two major
surfaces with a plastic; however, it can be seen by element (20),
that thin strips of uninsulated metal are exposed to the first and
second group of electrical conductors (14) and (16) respectively.
It is quite obvious that pinholes in the electrical insulation of
the insulated electrical conductors (14) or (16), or the shield
(15), would allow unwanted electrical energy to reach exposed
portions (edges) of the aluminum foil shield, through the edges
(20) or pinholes in its plastic coating. From an electrical
standpoint, it is desirable to avoid this. It is also electrically
desirable to keep moisture away from the electrical conductors.
Thus, the instant invention envisions an embodiment in which a
polyethylene greaselike material (a flooding compound) is disposed
in that cavity created or defined by the foil shield (15) not
otherwise occupied by insulated electrical conductors (14).
Furthermore, it is also envisioned that the same polyethylene
greaselike material can be disposed in that cavity created by the
plastic-coated metal foil shield (15) and plastic tape (17) not
otherwise occupied by the insulated electrical conductors (16).
Such a polyethylene greaselike material is described as an
amorphous polyethylene, having an average molecular weight below
about 10,000 and a density of below about 0.91, namely [0.851 grams
per milliliter at 25 .degree. C.]. This grease is marketed by Dow
Chemical Company of Midland, Michigan, under the designation of
QX-4213.3, and has been tested by the same equipment used to test
well-known polyethylenes as defined by ASTM D-1238.65T. Essentially
the same method as employed by this ASTM designation was used to
test this polyethylene greaselike material, except for slight
modifications. One such modification was that the extrusion barrel
was heated to 100 .degree. C., instead of 125 .degree. C., as
called for in the aforementioned ASTM Specification. This
temperature modification was necessary because of the viscosity of
the polyethylene grease material, i.e., it is characteristic of
this grease to become highly fluid when exposed to any high degree
of heat. The melt index (flow rate) measured using this modified
ASTM method was 10 to 20. A 2,160 gram load (piston and weight) was
used in this modified ASTM test, as well as an orifice of 0.020
inches. Other data supplied by the Dow Chemical Company on other
properties of the polyethylene grease are as follows: ##SPC1##
By placing the above described polyethylene greaselike material in
the two areas indicated, two functions are served. The first
function is that of interposing a dielectric between the electrical
conductors and the exposed metal edge portion (20); the second
function is to exclude water, in any form, i.e., vapor or liquid,
from ingressing into that area where the electrical conductors are
situated. In essence, the polyethylene greaselike material is a
hydrophobic material, as shown by its extraordinary low (less than
0.01 percent) water absorption at 24 hours at 100 percent relative
humidity. Thus, by using the polyethylene grease as discussed,
water tight cable can be provided. That is to say, the cable using
the polyethylene grease as disclosed, can be directly buried in the
ground without the benefit of pressurization, and remain in service
for an indefinite length of time without the ingressing of water
into the area where the electrical conductors are situated.
Element (10) of FIG. 10 shows the overall cross-sectional view of a
further embodiment of the instant invention. The basic difference
between the cable (10) of FIG. 10 and cable (9) of FIG. 9, is that
the plastic-coated foil shield (15) is not a single unitary tape as
shown in element (9) of FIG. 9. In this particular embodiment, the
shield (15) is made up of a plurality of tapes, the lateral edges
of which overlap adjacently disposed like tapes. Elements (15),
(15'), and (15") show this particular feature with the individual
plastic-coated metal foil shields having lateral edges in an
overlapping relationship with each other. As was the case in
element (9) of FIG. 9, this particular plastic-coated metal foil
shield is used to separate a first group of insulated electrical
conductors (14) from a second group of insulated electrical
conductors (16). The balance of the cable structure is essentially
the same as that shown by element (9) of FIG. 9. Here again, that
innermost cavity defined by the overlapping plurality of
plastic-coated metal foil shields (15), (15'), and (15"), not
otherwise occupied by insulated electrical conductors (14), can be
essentially filled with the same polyethylene grease described in
association with the description of element (9) of FIG. 9. Also
that cavity defined between outer plastic tape (17) and the
plastic-coated metal foil shield (15), (15'), and (15"), not
otherwise occupied by insulated electrical conductors (16), can be
also filled with the polyethylene greaselike material described
above. In element (10) of FIG. 10, as was the case with element (9)
of FIG. 9, the exposed metal edges (20) present a problem.
Electrical energy escaping through pinholes in the insulation of
the electrical conductors into that uninsulated portion of shield
(14) and (16) where there is exposed metal foil is electrically
undesirable. As was the case with element (9) of FIG. 9, the
polyethylene greaselike material can be used here to serve two
functions: the first to provide a dielectric interposed between the
exposed metal edge (20) and the insulated electrical conductors
(16) or (14); and the second to insure the exclusion of water,
either in the liquid or vapor state, from that portion of the cable
structure where the electrical conductors are disposed.
Element (11) of FIG. 11, shows a cross-sectional view of a further
embodiment of the instant invention. The cross-sectional structure
of element (11) is essentially the same as element (9) of FIG. 9,
except for one specific deviation. It will be noted that in element
(9) of FIG. 9, there were exposed metal foil edges (20). Shield
(15) of FIG. 11, does not have any metal edges exposed. It will be
noted that in FIG. 11, a plastic-coated metal foil shield (15),
having a cross-sectional similar to that as shown by shield (8) of
FIG. 8, is employed. Thus, by using this particular embodiment, no
metal of the plastic foil shield is exposed at any time to any
electrical conductor. This is not to say, however, that the
polyethylene grease used in the structure of cable (9) or (10) can
not also be used here. Either that innermost cavity, not otherwise
occupied by insulating conductors (14), defined by plastic-coated
metal foil shield (15), or that cavity defined between the
plastic-coated metal foil shield (15) and plastic tape (17), not
otherwise occupied by electrical conductor (16), or both, can be
essentially filled with polyethylene greaselike material as
previously discussed. Thus it can be seen that in the case of a
cable structure like that of element (11), of FIG. 11, the
polyethylene greaselike material serves basically as a
water-repellant substance. However, in the case where there are
pinholes in both the insulation of the electrical conductors (14)
and (16) as well as the plastic-coated metal foil shield (15), the
polyethylene greaselike material serves as a dielectric and keeps
unwanted electrical energy from being transferred into the shield
(15).
Element (12) of FIG. 12 shows a cross-sectional view of a cable
structure essentially the same as element (10) of FIG. 10. The only
difference between element (12) and that of element (10) of FIG. 10
is that in element (12) a plurality of plastic-coated metal foil
shields is used, the plastic-coating of which completely surrounds
the metal foil. Generally speaking, a plastic foil completely
surrounded by an integral coating of plastic material would be
available to a manufacturer in essentially a limited number of tape
widths. Therefore, with only a single width availability, such as
shown in element (12), a cable structure configuration can be
designed for any size cable core circumference using just one given
width of shield tape. Thus, notwithstanding the fact that a
plastic-coated metal foil tape comes in only one width and that
width is less than the outer peripheral dimension of a core made up
of insulated electrical conductors (14), a plurality of tapes can
be used to circumscribe the core, the lateral edges of the
individual tapes overlapping adjacently disposed tapes. As was the
case with similar cable structures shown in FIGS. 9, 10 and 11, a
polyethylene greaselike material can be disposed in the innermost
cavity created by overlapping plastic-coated metal foil shield
(15), (15'), (15"), not otherwise occupied by electrical conductors
(14). Also, in combination with this filled core concept,
polyethylene grease can be disposed in that space created by the
plastic-coated metal foil shields (15), (15'), (15"), and plastic
tape (17), not otherwise occupied by electrical conductors (16).
Here again, as was the case in element (10) of FIG. 10, the
polyethylene greaselike material has the primary function to
exclude water from that space where the electrical conductors are
disposed. However, it has a secondary function to provide a
dielectric between the source of electrical energy, i.e., the
electrical conductors (14) and (16), and any pinholes or other
electrical access to the metal foil of the shields (15), (15'), and
(15").
Shown in FIG. 13, by element (22) is a further embodiment of the
instant invention which shows the insulated electrical conductors
divided into quad configuration. It is to be understood that like
numbers represent like cable components as was shown in previously
discussed figures. This exemplary quad is made up of four groups of
insulated electrical conductors (14) and (16). The two groups of
insulated conductors shown at (14) are longitudinally circumscribed
by shield or screen (15), which in this particular embodiment is
made up of a single tape, the lateral edges of which overlap one
another. These particular tapes not only have a width that is equal
to or greater than the outer peripheral dimension of the cores made
up by the insulated electrical conductors (14), but also are made
up of a metal foil coated on both sides with a plastic, such as
that shown in element (5) of FIG. 5. Making up the balance of the
quad configuration are two additional groups of insulated
electrical conductors (16). These particular insulated electrical
conductors are longitudinally circumscribed by a plastic tape (17
a) which in this particular embodiment can be made up of the
conventional polyethylene terapthalate (Mylar). Transmission of an
electrical signal in a given direction is carried on the insulated
conductors (14). Conversely, transmission of electrical signals in
opposite or returning direction, is carried over insulated
electrical conductors (16).
Polyethylene greaselike material, the same as previously discussed,
can be used in this particular embodiment. Here, one has many
options as to what particular cavity or combination of cavities
that can be filled with the polyethylene grease. Any one or any
combination of all of the following cavities can be filled with the
polyethylene greaselike material: that cavity defined by the
plastic-coated metal foil shield (15), not otherwise occupied by
insulated electrical conductors (14); that cavity defined by
plastic tape (17 a), not otherwise occupied by insulated electrical
conductors (16); or that cavity defined by plastic tape (17), not
otherwise occupied by insulated electrical conductors (16), plastic
tape (17 a), insulated electrical conductors (14), and
plastic-coated metal foil shield (15).
Shown in FIG. 14, by element (23) is another embodiment of the
instant invention, which shows insulated electrical conductors
divided into a quad configuration. Here again, like numbers
represent like cable components as was shown in previously
discussed figures. This exemplary quad is made up of four groups of
insulated electrical conductors (14) and (16). The two groups of
insulated electrical conductors shown at (14) are longitudinally
circumscribed by a shield or screen (15), which in this particular
embodiment is made up of a single tape as was the case in FIG. 13.
This tape has a width that is at least equal to but preferably
greater than the outer peripheral dimension of the cores made up by
the insulated electrical conductors (14), and are made up of a
metal foil completely coated on all sides with a plastic, such as
that shown by element (8) of FIG. 8. Making up the balance of the
quad configuration are two additional groups of insulated
electrical conductors (16). These particular insulated electrical
conductors are longitudinally circumscribed by a plastic tape (17
a), which in this particular embodiment can be made up of the
conventional polyethylene terapthalate (Mylar). Transmission of an
electrical signal in a given direction is carried on the insulated
electrical conductors (14). Conversely, transmission of electrical
signals in an opposite or returning direction, is carried over
insulated electrical conductors (16).
Polyethylene greaselike material, the same as previously discussed,
can be used in this particular embodiment. Here one has many
options as to what particular cavity or combination of cavities
that can be filled with the polyethylene grease. Any one or any
combination of all the following cavities can be filled with the
polyethylene greaselike material: that cavity defined by the
plastic-coated metal foil shield (15), not otherwise occupied by
insulated electrical conductors (14); that cavity defined by
plastic tape (17 a), not otherwise occupied by insulated electrical
conductors (16); or that cavity defined by a plastic tape (17), not
otherwise occupied by insulated electrical conductors (16), plastic
tape (17 a), insulated electrical conductors (14), and
plastic-coated metal foil shield (15).
Shown in FIG. 15, by element (20) is another embodiment of the
instant invention, which shows insulated electrical conductors
divided into a quad configuration. Like numbers represent like
cable components as was shown in previously discussed figures. This
exemplary quad is made up of four groups of insulated electrical
conductors (14) and (16). The two groups of insulated electrical
conductors shown at (14) are longitudinally circumscribed by a
shield or screen (15), which in this particular embodiment is made
up of a plurality of tapes. These particular tapes have a width
that is less than the outer peripheral dimension of the cores made
up by the insulated electrical conductors (14), and are a metal
foil and coated on both sides with a plastic, such as that shown in
element (5), FIG. 5. Making up the balance of the quad
configuration, are two additional groups of insulated electrical
conductors (16). These particular insulated electrical conductors
are longitudinally circumscribed by a plastic tape (17 a), which in
this particular embodiment can be made up of the conventional
polyethylene terapthalate (Mylar). Transmission of an electrical
signal in a given direction is carried on the insulated electrical
conductors (14). Conversely, transmission of electrical signals in
an opposite or returning direction, is carried over insulated
electrical conductors (16).
Polyethylene greaselike material, the same as previously discussed,
can be used in this particular embodiment. Here, one has many
options as to what particular cavity or combination of cavities
that can be filled with the polyethylene grease, any one or any
combination of all of the following cavities can be filled with the
polyethylene greaselike material: that cavity defined by the
plastic-coated metal foil shield (15), not otherwise occupied by
insulated electrical conductors (14); that cavity defined by
plastic tape (17 a), not otherwise occupied by insulated electrical
conductors (16); or that cavity defined by plastic tape (17), not
otherwise occupied by insulated electrical conductors (16), plastic
tape (17 a), insulated electrical conductors (14), and
plastic-coated metal foil shield (15).
Shown in FIG. 16, by element (21) is another embodiment of the
instant invention, which shows insulated electrical conductors
divided into a quad configuration. Like numbers represent like
cable components as was shown in previously discussed figures. This
exemplary quad is made up of four groups of insulated electrical
conductors (14) and (16). The two groups of insulated electrical
conductors shown at (14) are longitudinally circumscribed by a
shield or screen (15), which in this particular embodiment is made
up of a plurality of tapes. These particular tapes have a width
that is less than the outer peripheral dimension of the cores made
up by the insulated electrical conductors (14), and are made up of
a metal foil completely surrounded on all sides with a plastic such
as that shown by element (8) of FIG. 8. Making up the balance of
the quad configuration, are two additional groups of insulated
electrical conductors (16). These particular insulated electrical
conductors are longitudinally circumscribed by a plastic tape (17
a), which in this particular embodiment can be made up of the
conventional polyethylene terapthalate (Mylar). Transmission of an
electrical signal in a given direction is carried on the insulated
electrical conductors (14). Conversely, transmission of electrical
signals in an opposite or returning direction, is carried over
insulated electrical conductors (16).
Polyethylene greaselike material, the same as previously discussed,
can be used in this particular embodiment. Here, one has many
options as to what particular cavity or combination of cavities
that can be filled with the polyethylene grease. Any one or any
combination of all of the following cavities can be filled with the
aforementioned material: that cavity defined by the plastic-coated
metal foil shield (15), not otherwise occupied by insulated
electrical conductors (14); that cavity defined by plastic tape (17
a), not otherwise occupied by insulated electrical conductors (16);
or that cavity defined by a plastic tape (17), not otherwise
occupied by insulated electrical conductors (16), plastic tape (17
a), insulated electrical conductors (14), and plastic-coated metal
foil shield (15).
Much of the previous discussion has been centered around the use of
a plastic-coated metal foil shield, wherein the plastic coating is
one that either completely surrounds the metal foil, or is disposed
on the two major surfaces thereof. These particular embodiments
were also discussed in combination with using polyethylene
greaselike material, the latter to serve primarily as a
moisture-prohibiting material, along with an additional function of
serving as a dielectric interposed between the electrical
insulators and any exposed portion of the metal foil in the shield.
This is not to say, however, that a metal foil either per se or
coated only on one side with a plastic, cannot be used as a viable
shield for the same purposes as achieved by the foil coated on both
sides or completely surrounded by a plastic.
Cable structures having similar cross sections as that shown in
FIGS. 9 through 16 inclusive can be made using as the shield a foil
coated only on one side with plastic. Such an arrangement obviously
exposes an uncoated metal foil to the second group of electrical
conductors. When a metal foil is thus exposed, it is imperative
that the cavity defined either in whole or in part by the uncoated
foil, not otherwise occupied by insulated electrical conductors, be
essentially filled with the previously discussed polyethylene
greaselike material. It is in this particular combination that the
polyethylene greaselike material serves the dual function of (a) a
water inhibitor and (b) as a dielectric material. This is not to
say, however, that that cavity defined either in whole or in part
by the plastic-coated surface of the metal foil shield, not
otherwise occupied by insulated electrical conductors, can not be
filled with the grease. Quite to the contrary, it is often very
desirable to so fill this cavity with this material, not
withstanding the fact that the grease in this particular
combination serves primarily as a water inhibiting means, rather
than the dual function of water inhibitor and dielectric.
It is also within the scope of the instant invention to use a metal
foil per se as a shield, i.e., uncoated at all on any side by a
firmly adhering coating of plastic material. Thus, the cable
structures set forth in those embodiments of FIGS. 9 through 16
inclusive can employ in place of the plastic-coated metal foil, a
tape of metal foil alone. However, on both sides of this metal foil
there must be disposed in that cavity defined either in whole or in
part by either one of the surfaces of the metal foil, not otherwise
occupied by insulated electrical conductors, polyethylene
greaselike material. An embodiment such as this obviously makes
maximum usage of the polyethylene greaselike material as a
dielectric. As was the case in previous embodiments, this
dielectric keeps unwanted electrical energy, emitting from the
insulated electrical conductors, from finding its way to the
exposed aluminum foil shield. Furthermore, this polyethylene
material has the added function of excluding water, either in the
vapor or liquid state, from the electrical conductors. In a
comparison between plastic-coated foils and a foil per se as a
cable shield or screen, the strength or durability added to a metal
foil by a firmly adhering plastic coating enables the coated metal
foil to withstand more mechanical handling than a metal foil per
se. However, the choice as to whether one will use a metal foil per
se or a metal foil coated with a plastic in the variously disclosed
embodiments is a mere matter of manufacturing choice, so long as
the polyethylene greaselike material was used in the appropriate
place for its dielectric contribution.
In summary, it can be readily seen that the cable structures shown
in FIGS. 9 through 16 inclusive can be modified to incorporate
metal foil shields that are coated either on one side only, or are
uncoated. Where there is an exposed surface of metal foil to
electrical conductors, it is preferred that that cavity defined
either in whole or in part by the metal foil per se, otherwise
occupied by the electrical conductors, be essentially filled by the
previously described polyethylene grease. Thus, shields (15), (15')
and (15") can be replaced by a metal foil, either per se or coated.
This substitution obviously is predicated on the limitation that
where there is a major surface of the metal foil exposed to the
electrical conductors, the polyethylene greaselike material will be
used as described above.
Turning attention to FIGS. 13- 16, collectively, it is also
envisioned by the instant invention, a cable structure wherein
electrical conductors (16) are longitudinally surrounded not by
plastic tape (17 a), but by the same or similar plastic-coated
metal foil tape screen as shown by element (15). One can replace
plastic tape (17 a) with any of the metal foil screen or shield
tapes having a cross section like that shown in any of the FIGS. 5-
8 inclusive. Of course, where an exposed metal surface is involved,
use of polyethylene grease is preferred for the same reasons as
previously discussed.
Element (24) of FIG. 17, shows a cross-sectional view of a further
embodiment of the instant invention. Here, as is the case with
previously disclosed cable structures, there is an outer cable
sheath (19) longitudinally circumscribing a metal armor shield (18)
having overlapping edges, which in turn longitudinally
circumscribes and has nested therein, a plastic tape (17) the
longitudinal edges of which also overlap. Nested inside of the
plastic tape (17) is a plurality of insulated electrical conductors
(14) and (16). This plurality of insulated electrical conductors is
divided into essentially two groups by shield (15). It is to be
noted that this particular shield (15) deviates from similar or
like shields (15) in FIGS. 9 through 16, in that this particular
shield does not circumscribe any one group of insulated electrical
conductors (14) and (16). Specifically, this particular shield is
an "S" (serpentine) shaped shield or screen and can be made of
either metal foil per se, a metal foil coated on one side with a
plastic, a metal foil coated on both sides with a plastic, or a
metal foil completely surrounded by a plastic as shown by elements
(5), (7), (6), and (8) of FIGS. 18, 19, 20, and 21 respectively.
Both groups of electrical conductors (14) and (16) can be encased
(filled) with the previously discussed greaselike material. That is
to say that that cavity created or defined by plastic tape (17) not
otherwise occupied by electrical conductors (16) and shield (15)
can be essentially filled with the polyethylene greaselike material
discussed earlier. Obviously, many variations and permutations can
be used employing the combination of polyethylene greaselike
material and particular coated or uncoated metal foil shield. It is
suffice to say that where a major surface of a shield is an exposed
foil, the insulated electrical conductors facing such metal foil
should be encased in the polyethylene greaselike material. However,
this is not to imply that where a metal foil shield has a plastic
coating on a major surface that the polyethylene greaselike
material is not to be deposited adjacent to that surface. Depending
on the economics of a cable manufacturer, the polyethylene
greaselike material can be used on either side of that metal foil
shield (15) or both sides for that matter, when either a metal foil
per se, a metal foil coated on one side, a metal foil coated on
both sides, or a metal foil completely surrounded by a plastic is
used. Cable structure (24), shown in FIG. 17, possesses the obvious
advantage over those structures shown in FIGS. 9 through 16, in
that less shield material is used in this manufacture, without the
loss of any of the desired electrical properties [mitigation of the
near-end crosstalk problem]. FIGS. 18, 19, 20, and 21 indicate the
various cross sections of the foil shields that can be used in the
primary embodiment of FIG. 17, they being the same as that shown in
FIGS. 5, 6, 7, and 8.
FIG. 22 illustrates diagrammatically a method and apparatus (34)
for the production of a portion of the cable in the instant
invention as illustrated in part by element (4) in FIG. 4. As shown
in FIG. 22, a supply of the insulated electrical conductors (14)
and (16) is provided for by spools (25). As shown, spools (25)
rotate in a manner that feed electrical conductors (16) and (14)
through a composite die (34) made up of dieplate (30) and (30 a) in
a spaced apart predetermined manner. Obviously the axis of rotation
of spools (25) run into and out of the paper. All of the spools
(25) have a further rotation as shown by the large arrow just to
the left of the spools. This axis of rotation is one that runs
parallel to element (4) and element (17) and it is this rotation
that provides the twisting of the insulated electrical conductors
in the finished product (4). Surrounded by electrical conductors
(16) is foil shield or screen (15). Inside of and longitudinally
circumscribed by shield (15) are the electrical conductors
(14).
First die member (30) is connected to second die member (30 a) by
cross members (29). Both die members (30) and (30 a), along with
cross members (29) rotate about an axis parallel to element (4) and
in the direction shown by the arrow. Thus, the product (4) has a
first group of electrical conductors (14) surrounded by a shield or
screen (15) disposed in a helical fashion and nested inside of
electrical conductors (16), which in turn are helically disposed on
the outside surface of the shield (15).
Plastic tape (17) is run through dies (30) and (30 a) as shown, to
form an outside covering over the composite core (4). The
"finished" product, which is composite core (4) surrounded by
plastic tape (17), can then be sent through a known apparatus to
wrap armor (18) around tape (17) and thence this thus made
composite is traversed through an extruder head where plastic
sheath (19) is formed. The spools (25) are arranged to feed the
conductors, plastic tape, and shield tape through spaced apart
holes in a guideplate (30). As illustrated in FIG. 22, guideplate
(30) has a center hole or aperture and a plurality of apertures
spaced apart generally concentrically around a center hole. The
center hole receives the first group of electrical conductors (14)
and spaced-apart holes next adjacent to the center holes receives
the shield tape (15). Just out by the hole receiving tape (15) is
an additional plurality of holes spaced apart from the center hole
receiving electrical conductors (16) and the outermost hole in
plate (30) receives plastic tape (17). Thus, each conductor, foil
shield, and outer plastic tape is located in generally its
predetermined position relative to the other conductors in the
cable. Obviously, if a flooding compound [polyethylene grease] is
desired to be placed in a particular cavity, then provisions for
filling such a cavity can be made using this particular apparatus
by depositing the grease at the desired location during the
twisting operation as shown.
Shown in FIG. 23 by element (34) is a die means adapted to be used
in a somewhat similar manner as element (34) of FIG. 22. This
particular die means is made up of dieplates (30) and (30 a),
spaced apart by two crossbar means (29). Dieplate (30) has a
plurality of holes (31), (32) and (35). Holes (31) are slots which
are used to fasten the dieplate (30) to a rotating cage (not
shown). Holes (32) are analogous to like holes in dieplate (30) of
element (34) of FIG. 22, through which insulated electrical
conductors (14) and (16) are traversed. A center slot (35) in die
means (30) and (30 a) is used to pass foil screen or shield tape
(15) through both of these plates. Thus, die (30 a) has essentially
two kinds of holes, slot (35) through which shield means (15)
passes and holes (33) through which twisted electrical conductors
(14) and (16) pass. Insert or guide means (36), made up of
wear-resistant fired ceramic material, are inserted inside of holes
(13) so as to permit smooth passage of the electrical conductors
(14) and (16) therethrough.
The apparatus (34) shown in FIG. 23 is used primarily to
manufacture that cable structure as shown by element (24) in FIG.
17. It is to be understood, however, that electrical conductors
(14) and (16), along with shield (15) exit from their respective
guiding holes in die member (30 a) in a quasi-twisted manner. As
the composite made from elements (14), (15), and (16) is traversed
to the right, further twisting takes place due to the rotation of
die plate (30) and (30 a). No twisting or quasi-composite forming
is shown in FIG. 23. Such twisting was deleted for the sake of
simplicity and clarity. Nonetheless, it is to be understood that
due to the rotation of die member (30 a) and die (30) there is some
twisting and therefore composite forming taking place as elements
(14), (15), and (16) exit from die plate (30 a). It is to be
further understood that downstream from die plate (30 a) there is
subsequently placed on the twisted composite formed from elements
(14), (15), and (16), a plastic tape (17) as shown in FIG. 17. It
is also to be understood that the composite formed of elements
(14), (15), (16), and (17) is then traversed through a taping
machine where metal tape (18) is applied thereto as shown in FIG.
17. This composite is then traversed through an extruder head so as
to extrude on the outer peripheral surface of metal armor tape (18)
the plastic sheath (19). Obviously, anyone of the tapes shown by
elements (5), (7), (6), and (8) of FIGS. 18, 19, 20, and 21
respectively, can be used in the apparatus shown by element (34) of
FIG. 23.
It has been previously mentioned that polyethylene greaselike
material can be used in the cable structure as shown by element
(24) of FIG. 17. When manufacturing grease filled cable on die
means (34) of FIG. 23, the polyethylene grease can be placed in any
desired position, either on the downstream side of die plate (30 a)
or on the upstream side of such die plate. Generally speaking, it
is desirable to allow polyethylene greaselike material to traverse,
together with insulated electrical conductors, through ceramic
bushing or insert means (36). Such a method of grease application
results in an even distribution of the grease throughout the bundle
of insulated electrical conductors.
Near end crosstalk loss data in decibels (db.) for various
frequencies was measured, both for prior art cables, i.e., cables
not employing a shield or screening tape, and a shielded cable
structure as envisioned by the instant invention. Such exemplary
data is graphically delineated by plotting near end crosstalk loss
in decibels (db.) at the frequency (kHz.) at which this loss was
measured on the ordinate and abscissa of FIG. 24 respectively. The
curve represented by the solid line of FIG. 24 portrays exemplary
data taken from cable structures utilizing a screen or shield tape.
On the other hand, the dotted line curve, is that plot derived from
exemplary data taken from a conventional cable construction. The
data actually plotted are average values (x) minus one standard
deviation (.alpha.). Inasmuch as data gathered at any one
particular frequency had a maximum and minimum near end crosstalk
loss reading in decibels (db.), these values were averaged and then
a standard deviation was subtracted therefrom so as to achieve a
value that would be more likely to be representative of a design
value for inservice use.
Comparing the data represented by the two curves shown in FIG. 24,
it can be seen that at the higher frequencies, the decrease in
crosstalk loss is exhibited and generally averages about 6 db.
decrease per octave. It will be noted that the values for the
dotted line curve decrease as the frequency increases over a
substantial range (2 or 3 octaves). On the other hand, it will be
noted in comparison that the effective (electrical) thickness of
the metal foil screen or shield increases with an increasing
frequency. Such a phenomenon might possibly be related to the
attenuation or magnetic wave loss of an incident wave passing
through an electrical shield at high frequencies where preceding
electromagnetic waves are reflected. Such reflection could cause
attenuation loss, which would be additive to the expected loss due
to the shield per se.
Electrical shielding efficiency of the cable structure disclosed by
the instant invention is improved at about the same rate that
crosstalk coupling would degrade normal crosstalk performance in
otherwise unshielded cables. Such improvements will allow a
substantial increase in amplifier (repeater) spacing in systems
which employ similar frequencies for both directions of
transmissions, e.g. pulse code modulator systems. For example, such
pulse code modulated systems operate generally at a frequency of
some 172 kHz. At such a frequency, comparing the dotted line with
the solid line, there is approximately 15 db. improvement, using
the cable structure of the instant invention. Such an improvement
would allow a very substantial economic savings in repeater cost in
pulse code modulator carrier systems and would in fact achieve
about the same crosstalk performance characteristics as would be
obtained using separate cables, one such cable transmitting in one
direction and the other cable transmitting in an opposite
direction. This improved performance is achieved at much less
cost.
In summary, the instant disclosure has shown the advantages of
dividing a cable core into at least two groups by a metal foil. The
two groups thus formed are used for transmission, one group
transmitting in one direction and the other group transmitting in
an opposite direction. By screening or shielding one transmitting
group of insulated electrical conductors, improved nearend
crosstalk properties are realized. Because a metal foil screen or
shield is used, provisions should be made for preventing unwanted
electrical energy, escaping from imperfections in the insulations
around electrical conductors, from reaching the metal shield. The
instant disclosure has exhibited many embodiments, permutations,
and combinations, whereby the metal foil shield or screen is
protected by a dielectric material from this unwanted electrical
energy. Dielectric protection can take the form of a firmly
adhesive plastic coating or it can be a polyethylene greaselike
material disposed throughout that cavity either in whole or in part
defined by the metal foil screen. Metal foils made of aluminum,
copper, steel, platinum or gold can be used; however, aluminum is
preferred. By using the concept of a firmly adhering plastic
coating on a metal foil, the mechanical properties, i.e.,
resistance to flexing, bending or mechanical manipulations, can be
improved. Nonetheless, a completely uncoated metal foil can be
employed, in conjunction with a deposition of polyethylene
greaselike material to serve the same purpose as an otherwise
coated foil. The use of the polyethylene greaselike material allows
a cable to be classified as a direct buried cable, and such a cable
structure can be buried in the ground and exposed to the weather
elements inherent therein with complete assurance that water,
either in the vapor or the liquid state, will be kept from
penetrating into the electrical conductors of the cable. Such a
cable need not be pressurized (internally) in order to keep out the
unwanted water.
From the foregoing, it is believed that the invention may be
readily understood by those skilled in the art without further
description, it being born in mind that numerous changes may be
made in the details disclosed without departing from that invention
set fourth in the following claims.
* * * * *