Method of making coaxial cable

A method of making a flexible coaxial cable is provided. The method comprises advancing a cable core comprising a conductor and an expanded foam dielectric surrounding the conductor along a predetermined path of travel, directing an elongate strip of copper onto the advancing cable core and bending the copper strip into a generally cylindrical form so as to loosely encircle the core. Opposing longitudinal edges of the thus formed copper strip are then moved into abutting relation and a longitudinal weld is formed joining the abutting edges to thereby form an electrically and mechanically continuous tubular copper sheath loosely surrounding the cable core. The cable core and the surrounding sheath are simultaneously advanced while the tubular sheath is deformed into an oval configuration loosely surrounding the core. The longitudinal weld of the advancing sheath is then directed against a scarfing blade and weld flash from the sheath is scarfed from the sheath. The advancing copper sheath is sunk onto the advancing cable core to form the coaxial cable. A polymer composition may be extruded around the copper sheath to form a protective jacket surrounding the coaxial cable and may be bonded thereto. The present invention also includes a flexible coaxial cable having excellent electrical and bending properties.

FIELD OF THE INVENTION 
The present invention relates to a coaxial cable, and more particularly to 
an improved low-loss coaxial cable having enhanced bending and handling 
characteristics and improved attenuation properties for a given nominal 
size. 
BACKGROUND OF THE INVENTION 
The coaxial cables commonly used today for transmission of RF signals, such 
as cable television signals and cellular telephone broadcast signals, for 
example, include a core containing an inner conductor, a metallic sheath 
surrounding the core and serving as an outer conductor, and in some 
instances a protective jacket which surrounds the metallic sheath. A 
dielectric surrounds the inner conductor and electrically insulates it 
from the surrounding metallic sheath. In many known coaxial cable 
constructions, an expanded foam dielectric surrounds the inner conductor 
and fills the space between the inner conductor and the surrounding 
metallic sheath. 
One of the design criteria which must be considered in producing any 
coaxial cable is that the cable must have sufficient compressive strength 
to permit bending and to withstand the general abuse encountered during 
normal handling and installation. For example, installation of the coaxial 
cable may require passing the cable around one or more rollers as the 
cable is strung on utility poles. Any buckling, flattening or collapsing 
of the tubular metallic sheath which might occur during such installation 
has serious adverse consequences on the electrical characteristics of the 
cable, and may even render the cable unusable. Such buckling, flattening 
or collapsing also destroys the mechanical integrity of the cable and 
introduces the possibility of leakage or contamination. 
Traditionally, the preferred material for the metallic sheaths used in 
coaxial cables has been aluminum. Aluminum has been selected because of 
its low cost and good mechanical and electrical properties. Nevertheless, 
despite its benefits, aluminum does have some disadvantages. In 
particular, aluminum is susceptible to corrosion at the connector 
interface which can cause intermodulation distortion of the RF signals. 
Furthermore, although highly conductive, other metals exhibit greater 
conductivity than aluminum. 
One alternative to aluminum as the outer conductor or sheath is copper. 
Copper possesses better electrical properties than aluminum. However, 
copper is more expensive and has a higher compressive yield strength than 
aluminum, which contributes to poor bending properties. For these reasons, 
copper has not been used traditionally as the sheath material for coaxial 
cables. The use of a thinner copper layer can reduce the cost, but thin 
copper sheaths are even more susceptible to buckling and are very 
difficult to process. 
SUMMARY OF THE INVENTION 
In view of the foregoing, it is an object of the present invention to 
provide a method of forming a coaxial cable having excellent electrical 
properties. 
It is a further object of the present invention to provide a method of 
forming a coaxial cable having a copper outer conductor which is 
mechanically and electrically continuous. 
It is a still further object of the present invention to provide a method 
of forming a coaxial cable which possesses excellent bending properties 
and is not subject to buckling. 
These and other objects are achieved in accordance with the present 
invention by a method wherein a cable core comprising a conductor and an 
expanded foam dielectric surrounding the conductor is advanced along a 
predetermined path of travel and an elongate strip of copper is directed 
onto the advancing cable core and bent into a generally cylindrical form 
so as to loosely encircle the core. Opposing longitudinal edges of the 
thus formed copper strip are then moved into abutting relation and a 
longitudinal weld is formed joining the abutting edges to thereby form an 
electrically and mechanically continuous tubular copper sheath loosely 
surrounding the cable core. The cable core and the surrounding sheath are 
simultaneously advanced while the tubular sheath is deformed into an oval 
configuration loosely surrounding the core, the oval configuration having 
a major axis generally aligned with the longitudinal weld of said sheath. 
The longitudinal weld of the advancing sheath is then directed against a 
scarfing blade and weld flash from the sheath is scarfed from the sheath. 
The advancing copper sheath is sunk onto the advancing cable core to form 
the coaxial cable. A polymer composition may be extruded around the copper 
sheath to form a protective jacket surrounding the coaxial cable and may 
be bonded thereto. 
The present invention also provides a coaxial cable comprising a core 
including at least one inner conductor and a foam polymer dielectric 
surrounding the inner conductor, an electrically and mechanically 
continuous smooth-walled longitudinally welded tubular copper sheath 
closely surrounding said core and adhesively bonded thereto, and a 
protective outer jacket surrounding said sheath, wherein the ratio of the 
thickness of said tubular copper sheath to the diameter of said tubular 
copper sheath is less than about 1.6 percent. The coaxial cable may 
further include a layer of adhesive between the sheath and the protective 
outer jacket serving to bond the protective outer layer to the sheath. The 
tubular copper sheath is thin, preferably, having a thickness of less than 
0.013 inch. 
These and other features of the present invention will become more readily 
apparent to those skilled in the art upon consideration of the following 
detailed description which describes both the preferred and alternative 
embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 illustrates a coaxial cable produced in accordance with the present 
invention. The coaxial cable comprises a core 10 which includes an inner 
conductor 11 of a suitable electrically conductive material, and a 
surrounding continuous cylindrical wall of expanded foam plastic 
dielectric material 12. Preferably, the foam dielectric 12 is adhesively 
bonded to the inner conductor 11 by a thin layer of adhesive 13 such that 
the bond between the inner conductor 11 and dielectric 12 is stronger than 
the dielectric material. The inner conductor 11 is preferably solid 
copper, copper tubing or a copper-clad aluminum. The inner conductor 11 
preferably has a smooth surface and is not corrugated. In the embodiment 
illustrated, only a single inner conductor 11 is shown, as this is the 
most common arrangement for coaxial cables of the type used for 
transmitting RF signals such as cable television signals, or radio signals 
such as cellular telephone broadcast signals. However, it would be 
understood that the present invention is applicable also to coaxial cables 
having more than one inner conductor insulated from one another and 
forming a part of the core 10. 
The dielectric 12 is a low loss dielectric formed of a suitable plastic 
such as polyethylene, polypropylene, and polystyrene. Preferably, in order 
to reduce the mass of the dielectric per unit length and hence reduce the 
dielectric constant, the dielectric material should be of an expanded 
cellular foam composition, and in particular, a closed cell foam 
composition is preferred because of its resistance to moisture 
transmission. Preferably, the cells of the dielectric 12 are uniform in 
size and less than 200 microns in diameter. One suitable foam dielectric 
is an expanded high density polyethylene polymer such as described in 
commonly owned U.S. Pat. No. 4,104,481, issued Aug. 1, 1978. Additionally, 
expanded blends of high and low density polyethylene are preferred for use 
as the foam dielectric. The foam dielectric has a density of less than 
about 0.28 g/cc, preferably, less than about 0.22 g/cc. 
Although the dielectric 12 of the invention generally consists of a uniform 
layer of foam material, the dielectric 12 may have a gradient or graduated 
density such that the density of the dielectric increases radially from 
the inner conductor 11 to the outside surface of the dielectric, either in 
a continuous or a step-wise fashion. For example, a foam-solid laminate 
dielectric can be used wherein the dielectric 12 comprises a low density 
foam dielectric layer surrounded by a solid dielectric layer. These 
constructions can be used to enhance the compressive strength and bending 
properties of the cable and permit reduced densities as low as 0.10 g/cc 
along the inner conductor 11. The lower density of the foam dielectric 12 
along the inner conductor 11 enhances the velocity of RF signal 
propagation and reduces signal attenuation. 
Closely surrounding the core is a continuous tubular smooth-walled copper 
sheath 14. The sheath 14 is characterized by being both mechanically and 
electrically continuous. This allows the sheath 14 to effectively serve to 
mechanically and electrically seal the cable against outside influences as 
well as to seal the cable against leakage of RF radiation. Alternatively, 
the sheath can be perforated to allow controlled leakage of RF energy for 
certain specialized radiating cable applications. The tubular copper 
sheath 14 of the invention preferably employs a thin walled copper sheath 
as the outer conductor. The tubular copper sheath 14 has a wall thickness 
selected so as to maintain a T/D ratio (ratio of wall thickness to outer 
diameter) of less than 2.5 percent and preferably less than 1.6 percent or 
even 1.0 percent or lower. Preferably, the thickness of the copper sheath 
14 is less than 0.013 inch to provide the desired bending and electrical 
properties of the invention. In addition, the tubular copper sheath 14 is 
smooth-walled and not corrugated. The smooth-walled construction optimizes 
the geometry of the cable to reduce contact resistance and variability of 
the cable when connectorized and to eliminate signal leakage at the 
connector. 
In the preferred embodiment illustrated, the tubular copper sheath 14 is 
made from a copper strip S formed into a tubular configuration with the 
opposing side edges of the copper strip butted together, and with the 
butted edges continuously joined by a continuous longitudinal weld, 
indicated at 15. While production of the sheath 14 by longitudinal welding 
has been illustrated as preferred, persons skilled in the art will 
recognize that other methods for producing a mechanically and electrically 
continuous thin walled tubular copper sheath could also be employed. 
The inner surface of the tubular sheath 14 is continuously bonded 
throughout its length and throughout its circumferential extent to the 
outer surface of the foam dielectric 12 by a thin layer of adhesive 16. A 
preferred class of adhesive for this purpose is a random copolymer of 
ethylene and acrylic acid (EAA). The adhesive layer 16 should be made as 
thin as possible so as to avoid adversely affecting the electrical 
characteristics of the cable. Desirably, the adhesive layer 16 should have 
a thickness of about 1 mil or less. 
The outer surface of the sheath 14 is surrounded by a protective jacket 18. 
Suitable compositions for the outer protective jacket 18 include 
thermoplastic coating materials such as polyethylene, polyvinyl chloride, 
polyurethane and rubbers. Although the jacket 18 illustrated in FIG. 1 
consists of only one layer of material, laminated multiple jacket layers 
may also be employed to improve toughness, strippability, burn resistance, 
the reduction of smoke generation, ultraviolet and weatherability 
resistance, protection against rodent gnaw through, strength resistance, 
chemical resistance and/or cut-through resistance. In the embodiment 
illustrated, the protective jacket 18 is bonded to the outer surface of 
the sheath 14 by an adhesive layer 19 to thereby increase the bending 
properties of the coaxial cable. Preferably, the adhesive layer 19 is a 
thin layer of adhesive, such as the EAA copolymer described above. 
Although an adhesive layer 19 is illustrated in FIG. 1, the protective 
jacket 18 can also be directly bonded to the outer surface of the sheath 
14 to provide the bending properties of the invention. 
FIG. 2 illustrates a suitable arrangement of apparatus for producing the 
cable shown in FIG. 1. As illustrated, the inner conductor 11, typically a 
solid copper wire, a hollow copper tube or a copper-clad aluminum wire, is 
directed from a suitable supply source, such as a reel 31. In order to 
provide a coaxial cable having a continuous inner conductor 11, the 
terminal edge of the inner conductor from one reel is mated with the 
initial edge of the inner conductor from the subsequent reel and welded 
together. It is important in forming a continuous cable to weld the copper 
tubes or wires from different reels without adversely affecting the 
surface characteristics and therefore the electrical properties of the 
inner conductor 11, especially when using hollow copper tubes. 
The inner conductor 11 is subsequently straightened to remove kinks. In the 
illustrated embodiments this is accomplished by advancing the conductor 11 
through a series of straightening rolls 32 and through a drawing die 33. 
Once the inner conductor 11 has been straightened, a gas burner 34 is used 
to heat the surface of the inner conductor to remove excess water and 
organics from the surface of the inner conductor. If the inner conductor 
11 and the foam dielectric 12 are to be adhesively bonded, heating the 
surface of the inner conductor 11 also serves to facilitate adhesion of 
the adhesive layer 13 on the surface of the inner conductor 11. 
Preferably, an adhesive layer 13 is applied to the inner conductor 11 
which allows the foam dielectric 12 to adhere to the inner conductor but 
which still provides a strippable core 10. The adhesive layer 13 used to 
bond the inner conductor 11 to the foam dielectric 12 is typically 
extruded onto the surface of the inner conductor using an extruder 35 and 
crosshead die or similar device. 
The coated inner conductor 11 is advanced through an extruder apparatus 36 
which applies a foamable polymer composition used to form the foam 
dielectric 12. In the extruder apparatus 36 the components to be used for 
the foam dielectric 12 are combined to form a polymer melt. Preferably, 
high density polyethylene and low density polyethylene are combined with 
nucleating agents in an extruder apparatus to form the polymer melt. These 
compounds once melted together are subsequently injected with nitrogen gas 
or a similar blowing agent to form the foamable polymer composition. In 
addition to or in place of the blowing agent, decomposing or reactive 
chemical agents can be added to form the foamable polymer composition. The 
foamable polymer composition then passes through screens to remove 
impurities in the melt. In extruder apparatus 36, the polymer melt is 
continuously pressurized to prevent the formation of gas bubbles in the 
polymer melt. The extruder apparatus 36 continuously extrudes the polymer 
melt concentrically around the advancing inner conductor 11. Upon leaving 
the extruder 36, the reduction in pressure causes the foamable polymer 
composition to foam and expand to form a continuous cylindrical wall of 
the foam dielectric 12 surrounding the inner conductor 11. 
In addition to the foamable polymer composition, an ethylene acrylic acid 
(EAA) adhesive composition is preferably coextruded with the foamable 
polymer composition to form adhesive layer 16. Extruder apparatus 36 
continuously extrudes the adhesive composition concentrically around the 
polymer melt. Although coextrusion of the adhesive composition with the 
polymer melt is preferred, other suitable methods such as spraying, 
immersion, or extrusion in a separate apparatus may also be used to apply 
the adhesive composition to the core 10. 
In order to produce low foam dielectric densities along the inner conductor 
11 of the cable, the method described above can be altered to provide a 
gradient or graduated density dielectric. For example, for a multilayer 
dielectric having a low density inner foam layer and a high density foam 
or solid outer layer, the polymer compositions forming the layers of the 
dielectric can be coextruded together and can further be coextruded with 
the adhesive composition forming adhesive layer 16. Alternatively, the 
dielectric layers can be extruded separately using successive extruder 
apparatus. Other suitable methods can also be used. For example, the 
temperature of the inner conductor 11 may be elevated to increase the size 
and therefore reduce the density of the cells along the inner conductor to 
form a dielectric having a radially increasing density. 
After leaving the extruder apparatus 36, the adhesive coated core 10 may be 
directed through an adhesive drying station 37 such as a heated tunnel or 
chamber. Upon leaving the drying station 37, the core is directed through 
a cooling station 38 such as a water trough. Water is then generally 
removed from the core 10 by an air wipe 39 or similar device. At this 
point, the adhesive coated core 10 may be collected on suitable 
containers, such as reels 40 prior to being further advanced through the 
remainder of the manufacturing process illustrated in FIG. 3. 
Alternatively, the adhesive coated core 10 can be continuously advanced 
through the remainder of the manufacturing process without being collected 
on reels 40. 
As illustrated in FIG. 3, the adhesive coated core 10 can be drawn from 
reels 40 and further processed to form the coaxial cable. Typically, the 
adhesive coated core 10 is straightened by advancing the adhesive coated 
core through a series of straightening rolls 41. A narrow elongate strip S 
from a suitable supply source such as reel 42 is then directed around the 
advancing core and bent into a generally cylindrical form by guide rolls 
43 so as to loosely encircle the core. Opposing longitudinal edges of the 
thus formed copper strip S are then moved into abutting relation and the 
strip is advanced through a welding apparatus 44 which forms a 
longitudinal weld 15 by joining the abutting edges of the copper strip S. 
As illustrated in FIG. 4, the longitudinally welded strip forms an 
electrically and mechanically continuous copper sheath 14 loosely 
surrounding the core 10. As a result of the longitudinal welding of the 
copper sheath 14, weld flash 45 is present adjacent the longitudinal weld 
15. 
As the core 10 and surrounding sheath 14 simultaneously advance, the sheath 
14 is formed by a pair of shaping rolls 46 into an oval configuration 
(FIG. 5) loosely surrounding the core and having a major axis A generally 
aligned with the longitudinal weld 15 of the sheath. As illustrated in 
FIG. 6, the longitudinal weld 15 of the advancing sheath 14 is then 
directed against a scarfing blade 48 which scarfs weld flash 45 from the 
sheath 14. The oval configuration of the thin sheath 14 increases the 
compressive strength of the thin copper sheath when directed against the 
scarfing blade 48 and prevents buckling, flattening or collapsing of the 
sheath. Once the weld flash 45 is scarfed from the sheath 14, the 
simultaneously advancing core 10 and surrounding sheath 14 are then 
advanced through a shaping die 49, which reforms the sheath 14 from an 
oval configuration into a generally circular configuration loosely 
surrounding the core. The simultaneously advancing core 10 and surrounding 
sheath 14 are then advanced through at least one sinking die 50 which 
sinks the copper sheath onto the cable core as shown in FIG. 7, and 
thereby causes compression of the foam dielectric 12. A lubricant is 
preferably applied to the surface of the sheath 14 as it advances through 
the sinking die 40. 
Once the sheath 14 has been formed on the core 10, any lubricant on the 
outer surface of the sheath is removed to increase the ability of the 
sheath to bond to the protective jacket 18. An adhesive layer 19 and the 
polymeric jacket 18 are then formed onto the outer surface of the sheath 
14. In the present invention, the outer protective jacket 18 is provided 
by advancing the core 10 and surrounding sheath 14 through an extruder 
apparatus 52 where a polymer composition is extruded concentrically in 
surrounding relation to the adhesive layer 19 to form the protective 
jacket 18. Preferably, a molten adhesive composition such as an EAA 
copolymer is coextruded concentrically in surrounding relation to the 
sheath 14 with the polymer composition which is in concentrically 
surrounding relation to the molten adhesive composition to form the 
adhesive layer 19 and protective jacket 18. Where multiple polymer layers 
are used to form the jacket 18, the polymer compositions forming the 
multiple layers may be coextruded together in surrounding relation and 
with the adhesive composition forming adhesive layer 19 to form the 
protective jacket. Additionally, a longitudinal tracer stripe of a polymer 
composition contrasting in color to the protective jacket 18 may be 
coextruded with the polymer composition forming the jacket for labeling 
purposes. 
The heat of the polymer composition forming the protective jacket 18 serves 
to activate the adhesive layer 16 to form an adhesive bond between the 
inner surface of sheath 14 and the outer surface of the dielectric 12. 
Once the protective jacket 18 has been applied, the coaxial cable is 
subsequently quenched to cool and harden the materials in the coaxial 
cable. The use of adhesive layers between the inner conductor 11, 
dielectric 12, sheath 14, and protective jacket 18 also provide the added 
benefit of preventing the migration of water through the cable and 
generally provide the cable with increased bending properties. Once the 
coaxial cable has been quenched and dried, the thus produced cable may 
then be collected on suitable containers, such as reels 54, suitable for 
storage and shipment. 
The coaxial cables of the present invention are beneficially designed to 
limit buckling of the copper sheath during bending of the cable. During 
bending of the cable, one side of the cable is stretched and subject to 
tensile stress and the opposite side of the cable is compressed and 
subject to compressive stress. If the core is sufficiently stiff in radial 
compression and the local compressive yield load of the sheath is 
sufficiently low, the tensioned side of the sheath will elongate by 
yielding in the longitudinal direction to accommodate the bending of the 
cable. Accordingly, the compression side of the sheath preferably shortens 
to allow bending of the cable. If the compression side of the sheath does 
not shorten, the compressive stress caused by bending the cable can result 
in buckling of the sheath. 
The ability of the sheath to bend without buckling depends on the ability 
of the sheath to elongate or shorten by plastic material flow. Typically, 
this is not a problem on the tensioned side of the cable. On the 
compression side of the tube, however, the sheath will compress only if 
the local compressive yield load of the sheath is less than the local 
critical buckling load. Otherwise, the cable will be more likely to buckle 
thereby negatively effecting the mechanical and electrical properties of 
the cable. For annealed aluminum sheath materials, the local compressive 
yield load is sufficiently low in cable designs to avoid buckling failures 
on the compression side of the cable. However, for materials having 
significantly higher compressive yield strengths, such as copper, the 
possibility of buckling increases significantly because the higher 
compressive yield loads can exceed the critical buckling loads of the 
sheath. This is particularly true as the thickness of the outer conductor 
decreases because the corresponding critical buckling load tends to 
decrease at a faster rate than the compressive yield load. Therefore, 
there is a greater tendency for thin copper sheaths to buckle than thicker 
aluminum sheaths. 
For the cables of the present invention, it has been discovered that the 
critical buckling load can be significantly increased by adhesively 
bonding the sheath to the core and to the protective jacket. In 
particular, adhesive bonds between the sheath and the jacket having the 
bond peel strengths discussed herein, provide high critical buckling loads 
and thus reduced buckling. This allows thin copper sheaths to be used in 
the present invention therefore increasing the flexibility of the cable. 
Furthermore, the critical buckling load can be significantly increased by 
increasing the stiffness of the core. Although the stiffness can be 
increased by increasing the density of the dielectric, higher densities 
result in increased attenuation along the inner conductor. An alternative 
method, as described herein, is providing a low density foam dielectric 
along the inner conductor for low attenuation and a high density foam or 
solid dielectric along the copper sheath to increase the stiffness of the 
core along the sheath thereby supporting the sheath in bending. 
The coaxial cables of the present invention have enhanced bending 
characteristics over conventional coaxial cables. As described above, one 
feature which enhances the bending characteristics of the cable is the use 
of a very thin copper sheath 14. Another feature which enhances the 
bending characteristics of the coaxial cable of the invention is that the 
sheath 14 is adhesively bonded to the foam dielectric 12 and the 
protective jacket 18. In this relationship, the foam dielectric 12 and the 
jacket 18 support the sheath 14 in bending to prevent damage to the 
coaxial cable. Furthermore, increased core stiffness in relation to sheath 
stiffness is beneficial to the bending characteristics of the coaxial 
cable. Specifically, the coaxial cables of the invention have a core to 
sheath stiffness ratio of at least 5, and preferably of at least 10. In 
addition, the minimum bend radius in the coaxial cables of the invention 
is significantly less than 10 cable diameters, more on the order of about 
7 cable diameters or lower. The reduction of the tubular sheath wall 
thickness is such that the ratio of the wall thickness to its outer 
diameter (T/D ratio) is no greater than about 2.5 percent and preferably 
no greater than about 1.6 percent. The reduced wall thickness of the 
sheath contributes to the bending properties of the coaxial cable and 
advantageously reduces the attenuation of RF signals in the coaxial cable. 
The combination of these features and the properties of the sheath 14 
described above results in a tubular copper sheath with significant 
bending characteristics. 
As stated briefly above, the bending characteristics of the coaxial cable 
are further improved by providing an adhesive layer 19 between the tubular 
copper sheath 14 and the outer protective jacket 18. The bending 
properties of the coaxial cable (as measured by the number of reverse 
bends the cable can sustain on a thirteen inch diameter mandrel without 
buckling) increase generally as the bond peel strength of the adhesive 
layer increases. Nevertheless, as illustrated in FIG. 8, it has been 
discovered that when the strength of the bond reaches a certain level, 
e.g. 36 lb/in, the protective jacket becomes too difficult to remove to 
provide electrical connections between the coaxial cable and other 
conductive elements. Furthermore, the increased use of adhesive results in 
an increase in the cost of manufacturing the cable and a decrease in 
electrical properties. On the other hand, when the strength of the 
adhesive bond is below a certain level, the adhesive bond is not 
sufficient to provide the desired bending characteristics of the coaxial 
cable. Although the lower level for the bond peel strength of the adhesive 
bond illustrated in FIG. 8 is 10 lb/in, it has been discovered (as 
demonstrated in FIG. 9) that by controlling the smoothness of the sheath, 
e.g., by controlling the lubrication of the sheath in the sinking die, 
that the lower level can be as low as 5 lb/in. 
The bond peel strength described herein is determined using an 1800 jacket 
peel back test. For the 180.degree. jacket peel back test, an eighteen 
inch sample is cut from each reel of cable to be tested. A twelve inch 
piece of the sample is placed in a jacket slicing device and the slitter 
blade in the slicing device is set to cut through the jacket. The cable is 
pulled through the slicing device until a twelve inch slit is cut in the 
sample or until the end of the sample is reached. For smaller cables, four 
slits equally spaced apart are cut into the cable. For larger cables, six 
slits equally spaced apart are cut into the cable. A knife is used to 
loosen the jacket from the cable at the slit end. The jacket is then 
pulled back about four inches from the end of the cable. A loop is formed 
from the peeled back jacket and stapled. A MG100L force gauge is turned on 
and set to a Peak T setting. The force gauge is hooked onto the loop and 
slowly pulls on the loop until the force stops changing. The force on the 
gauge is recorded and the procedure repeated for each section of the cable 
(quadrant for smaller cables). The minimum and maximum width for each 
section is also measured using calipers and recorded to determine the 
average width. The force/unit width (e.g., lb/in) is determined by the 
equation: 
EQU force/unit width=force/average width 
which is measured for each quadrant and recorded. The bond peel strength is 
the average of the four (six) measurements. 
The present invention provides a coaxial cable with excellent bending 
properties and having an outer protective jacket which can be easily 
removed from the cable to provide an electrical connection between the 
coaxial cable and other conductive elements. In order to provide a cable 
which possesses both of these properties, it has been determined that the 
bond peel strength of the adhesive layer between the tubular copper sheath 
and the outer protective layer as measured by a 180.degree. jacket peel 
back test should be no more than about 36 lb/in. Preferably, the bond peel 
strength should be between about 5 and 36 lb/in. In one embodiment of the 
invention, the bond peel strength is between about 10 and 36 lb/in. This 
range of bond peel strengths has been discovered to be an especially 
important range for copper sheaths. Because copper has a higher 
compressive yield strength and modulus than aluminum, the bond strength of 
the adhesive layer 19 generally must be stronger for a copper sheath than 
for an aluminum sheath. Therefore, defining a range of suitable bond 
strengths for copper sheaths is important in the manufacture of the 
coaxial cables of the invention. 
The coaxial cables of the invention have found particular utility in 50 ohm 
applications. As is known to those skilled in the art, 50 ohm applications 
are the standard for the precision signal industry and provide cables with 
good signal propagation, power delivery and breakdown voltage. As a 
result, the coaxial cables of the invention are useful in applications 
when one or more of these benefits are desired. 
It is understood that upon reading the above description of the present 
invention, one skilled in the art could make changes and variations 
therefrom. These changes and variations are included in the spirit and 
scope of the following appended claims.