FIELD OF THE INVENTION
[0001] The present invention relates generally to connectors for coaxial cables, and, more
particularly, to an improved connector having mechanical features allowing for efficient
installation. The invention also relates to methods of attaching such connectors and
cables, and to the resulting assemblies.
BACKGROUND OF THE INVENTION
[0002] Coaxial cable is characterized by having an inner conductor, an outer conductor,
and an insulator between the inner and outer conductors. The inner conductor may be
hollow or may be solid. At the end of coaxial cable, a connector is attached to allow
for mechanical and electrical coupling of the coaxial cable.
[0003] Connectors for coaxial cables having hollow inner conductors have been used throughout
the semi-flexible coaxial cable industry for a number of years. For example, Rauwolf
U.S. Patent No. 5,167,533 describes a connector for coaxial cables having hollow inner
conductors. Vaccaro et al. U.S. Patent No. 5,154,636 describes a connector for coaxial
cables having helically corrugated outer conductors. Doles U.S. Patent No. 5,137,470
describes a connector for coaxial cables having hollow and helically corrugated inner
conductors. Juds et al. U.S. Patent No. 4,046,451 describes a connector for coaxial
cables having annularly corrugated outer conductors and plain cylindrical inner conductors.
Van Dyke U.S. Patent No. 3,291,895 describes a connector for cables having helically
corrugated outer conductors and hollow, helically corrugated inner conductors. A connector
for a coaxial cable having a helically corrugated outer conductor and a hollow, plain
cylindrical inner conductor is described in Johnson et al. U.S. Patent No. 3,199,061.
[0004] The Johnson et al. patent describes a self-tapping connector for the inner conductor
of the coaxial cable. Such connectors are time-consuming to install and expensive
to manufacture. Also, when the inner connector is made of brass, overtightening causes
the threads to strip off the connector rather than the end portion of the inner conductor
of the cable, and thus the connector must be replaced.
SUMMARY OF THE INVENTION
[0005] It is a primary object of the invention is to provide an improved coaxial cable connector
which can be installed easily and quickly.
[0006] Another object is to provide an improved connector including an inner connector with
a self-tapping region that allows for easy connection to a coaxial cable having a
hollow inner connector. A related object is for such an improved connector to be self-locating
as it is applied to the end of a coaxial cable, and which can be easily installed
by hand. A further related object of this invention is to provide an improved connector
in which overtightening results in stripping of the threads formed in the hollow inner
conductor in the cable rather than the connector.
[0007] Yet a further object of the invention is to provide an improved connector assembly
which allows the outer connector to make good electrical contact and maintain that
contact with the outer conductor of a coaxial cable with a minimal amount of effort
by the installer.
[0008] Another object of this invention is to provide an improved method of attaching a
connector assembly to a coaxial cable having a hollow inner conductor, so that good
electrical contact is maintained between the inner connector and inner conductor of
the cable over a long operating life.
[0009] It is still another object of this invention to provide an improved method of attaching
the outer conductor of the cable to the outer connector of the connector assembly
with a minimal amount of effort while making good electrical contact therebetween.
[0010] It is another object of the invention to provide an improved connector which can
be efficiently and economically manufactured at a relatively low cost.
[0011] Other objects and advantages of the invention will be apparent from the following
detailed description and the accompanying drawings.
[0012] In accordance with the present invention, the foregoing objectives are realized by
providing a connector assembly having an outer connector for engaging the outer conductor
of the cable, an inner connector having a threaded portion adapted to fit into a hollow
inner conductor in threaded engagement with the interior surface of the inner conductor.
The threaded portion includes a plurality of interleaved concentric threads. A dielectric
spacer is disposed between the inner and outer connectors. In a preferred embodiment,
the multiple interleaved threads are self-tapping threads so that the inner connector
can be simply threaded into the hollow inner conductor without any advance tapping
of the inner conductor.
[0013] Furthermore, the outer connector of the connector assembly may include two members
that can be threadably attached via a plurality of interleaved concentric threads
formed on each of the two members. The plurality of threads provides for easy attachment
of the two members while maintaining good electrical contact between each member of
the outer connector and outer conductor of the cable.
[0014] The inner connector is preferably made of a relatively hard conductive alloy, such
as a copper-zinc alloy (e.g., UNS-C67400) or a beryllium-copper alloy (e.g., UNS-C17300).
The use of such materials facilitates the self-tapping operation, and also protects
the connector in the event of overtightening because the threads will strip on the
conductor before they strip on the connector. Thus, the connector can be re-installed,
after cutting off a short length of the end of the conductor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015]
FIG. 1 is a side elevation, partially in section, of a connector embodying the present
invention, and a coaxial cable for receiving the connector;
FIG. 2 is an enlarged side elevation of the end portion of a metal rod that has been
machined to form the connector of FIG. 1, prior to the forming of the threads on the
connector;
FIG. 3 is an enlarged side elevation of the metal rod shown in FIG. 2, after the forming
of the threads;
FIG. 4 is an end elevation of the connector shown in FIG. 3;
FIG. 5 is an isometric view, partially cut away, of the connector assembly embodying
the present invention;
FIG. 6 is a view of the unrolled interleaved threads from one member of the connector
assembly; and
FIG. 7 is a view of the unrolled interleaved threads from the other member of the
connector assembly.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0016] While the invention is susceptible to various modifications and alternative forms,
a specific embodiment thereof has been shown by way of example in the drawings and
will be described in detail. It should be understood, however, that it is not intended
to limit the invention to the particular form described, but, on the contrary, the
intention is to cover all modifications, equivalents, and alternatives falling within
the spirit and scope of the invention as defined by the appended claims.
[0017] Turning now to the drawings, there is shown a connector assembly for a coaxial cable
10 having an annularly corrugated outer conductor 11 concentrically spaced from a
hollow inner conductor 12 by a foam dielectric 13. As is well known to those familiar
with this art, an "annularly" corrugated conductor is distinguished from a "helically"
corrugated conductor in that the annular corrugations form a series of spaced parallel
crests which are discontinuous along the length of the cable, and, similarly, a series
of spaced parallel valleys which are also discontinuous along the length of the cable.
That is, each crest and valley extends around the circumference of the conductor only
once, until it meets itself, and does not continue in the longitudinal direction.
Consequently, any transverse cross-section taken through the conductor perpendicular
to its axis is radially symmetrical, which is not true of helically corrugated conductors.
[0018] To prepare the cable 10 for attachment of the connector assembly, the end of the
cable is cut along a plane extending through the apex of one of the crests of the
corrugated outer conductor and perpendicular to the axis of the cable. This exposes
the clean and somewhat flared interleaved surface of the outer conductor 11. The foam
dielectric 13 normally does not fill the crests of the corrugated outer conductor
11, so a small area of the inner surface of the outer conductor is exposed adjacent
the cut end of this conductor at the apex of the crest through which the cut is made.
However, if the foam dielectric does fill the entire crest, then a portion of the
dielectric should be removed to permit contact with the inner surface of the outer
conductor 11 adjacent the cut end thereof. Any burrs or rough edges on the cut ends
of the metal conductors are preferably removed to avoid interference with the connector.
The outer surface of the outer conductor 11 is normally covered with a plastic jacket
14 which is trimmed away from the end of the outer conductor 11 along a sufficient
length to accommodate the connector assembly.
[0019] Electrical contact with the inner conductor 12 of the cable 10 is effected by an
inner connector element 20 having an anchoring member 21. When the inner conductor
12 of the cable 12 is hollow as it is shown in FIG. 1, the anchoring member 21 includes
a threaded portion. In a preferred embodiment, the threaded portion is self-tapping
as it is threaded into the hollow inner conductor 12. An enlarged collar 22 engages
the end of the inner conductor 12 and an elongated pin 23 connects the inner conductor
12 to a conventional complementary female member (not shown). An insulator 24 assists
in centering the pin 23 within the main body member 30 of the connector assembly while
electrically isolating these two elements from each other. It will be noted that the
interior of the body member 30 includes a recess 31 for receiving the insulator 24,
which is also conventional in the art of coaxial cable connectors. The inner connector
20 is described in further detail with reference to FIGS. 2-4.
[0020] A coupling nut 40 secured to the body member 30 around the pin 23 is a conventional
fitting, and is secured to the body member 30 by a spring retaining ring 41 which
holds the nut 40 captive on the body member 30 while permitting free rotation of the
nut 40 on the body member 30. As will be apparent from the ensuing description, this
coupling nut 40 serves as a part of the electrical connection to the outer conductor
11 of the cable 10, and is insulated from the inner conductor 12 by the insulator
24 carried by the inner connector pin 23.
[0021] The body member 30 includes a conically beveled clamping surface 32 which engages
the inner surface of the outer conductor 11. This clamping surface 32 is formed as
an integral part of the interior surface of the body member 30, and is continuous
around the entire circumference of the cable to ensure good electrical contact with
the inner surface of the outer conductor 11. Cooperating with the beveled clamping
surface 32 is a second clamping surface 50 formed on one end of an annular clamping
member 51 for engaging the outer surface of the outer conductor 11. More specifically,
this second clamping surface 50 is formed on one side of an inner bead 52 which projects
from the inside surface of the clamping member 51 into the last valley of the corrugated
outer conductor 11 adjacent the end of the cable so as to lock the clamping member
51 to the cable 10 in the axial direction. The body member 30 and the clamping member
51 comprise an outer connector which is coupled to the outer conductor 11.
[0022] For the purpose of drawing the beveled clamping surface 32 and the second clamping
surface 50 firmly against opposite sides of the flared end portion of the outer conductor
11, the two members 30 and 51 include respective telescoping sleeve portions 33 and
53 with cooperating threaded surfaces 37 and 57. Thus, when the two members 30 and
51 are rotated relative to each other in a first direction so as to engage threaded
surface 37 with threaded surface 57, they are advanced toward each other in the axial
direction so as to draw the clamping surfaces 32 and 50 into electrically conductive
engagement with the outer conductor 11. When the annular flared end portion of the
outer conductor 11 is clamped between the beveled surface 32 and the second clamping
surface 50, it is also flattened to conform to the planar configuration of the clamping
surfaces 32 and 50. To detach the connector assembly from the outer conductor 11,
the two members 30 and 51 are simply rotated relative to each other in the opposite
direction to retract the two members 30 and 51 away from each other until the threaded
surfaces 37 and 57 are disengaged to permit inner bead 52 to pass over the crest of
the corrugated outer conductor 11 as the clamping member 51 is advanced longitudinally
over the end of the cable 10.
[0023] The threaded surfaces 37 and 57 each may include a single thread. In a preferred
embodiment, however, the threaded surface 37 of the main body member 30 and the threaded
surface 57 of the clamping member 51 each include a plurality of interleaved concentric
threads. Due to the plurality of threads, the clamping member 51 and the main body
member 30 are quickly advanced toward each in the axial direction when clamping the
annular end of the outer conductor 11 therebetween. Typically, the axial length of
the threaded surface 37 of the main body member 30 is greater than the axial length
of the threaded surface 57 of the clamping member 51. The threaded surfaces 37 and
57 are described in more detail with reference to FIGS. 6 and 7 which illustrate the
threaded surfaces 37 and 57 in unrolled, planar views.
[0024] For the purpose of avoiding rotation of the clamping member 51 around the cable 10
while the body member 30 is threaded thereover, a raised bead 55 projects from the
outer surface of the member 51. As can be seen in FIG. 1, the raised bead 55 minimizes
the area of frictional engagement between the two members 30 and 51, and spaces the
unthreaded portions of the opposed surfaces of these two members 30 and 51 away from
each other. After the two members 30 and 51 are threaded together, the engagement
of the inner surface of the body member 30 with the raised bead 55 maintains the locking
action of the inner bead 52 by preventing any outward deflection of the resilient
segments as long as the two member 30 and 51 remain connected.
[0025] To provide a moisture barrier between the inner surface of the clamping member 51
and the outer surface of the cable conductor 11, an O-ring 70 is positioned in a valley
on the exposed portion of the outer conductor 11 before the clamping member 51 is
applied thereto. Then when the clamping member 51 is installed on the cable 10, it
slightly compresses the rubber O-ring 70 so that the O-ring 70 bears firmly against
both the outer surface of the conductor 11 and the inner surface of the clamping member
51. The adjacent end portion of the clamping member 51 forms a slightly enlarged recess
71 so that it can fit over the end of the plastic jacket 14 on the coaxial cable.
A moisture barrier similar to that provided by the resilient O-ring 70 is provided
by a second O-ring 72 positioned between the opposed surfaces of the sleeve portions
33 and 53 of the body member 30 and clamping member 51, respectively.
[0026] Returning now to the inner connector 20 which makes electrical contact with the inner
conductor 12, the threaded anchoring member 21 is self-tapping so that the connector
20 can be installed by simply turning it into the hollow inner conductor 12 until
the shoulder 25 (FIGS. 2-4) formed by the collar 22 engages the cut end of the inner
conductor 12. A diametrical hole 26 is formed in the body portion of the connector
20 for receiving a tommy bar wrench for turning the inner connector 20 into the inner
conductor 12.
[0027] The threaded portion 80 of the anchoring member 21 includes four interleaved concentric
threads 81, 82, 83 and 84 which are equally spaced from each other along the length
of the connector. Each of the four threads 81-84 has the same lead, but, as can be
seen in FIG. 4, the ends of the four threads are spaced 90 degrees from each other.
Thus, the ends of the four threads 81-84 are symmetrically spaced from each other
around the axis of the connector assembly.
[0028] As can be seen most clearly from FIG. 2, which is a side elevation of the inner connector
20 before it has been threaded, the anchoring member 21 includes a tapered distal
end 90, a recessed region 91, a raised region 92, and a second recessed region 93.
When the connector 20 is threaded, the threading tool is maintained at a constant
distance from the axis of the connector, so that the distance between the axis of
the connector and the troughs of the threads 81-84 remains constant throughout the
entire threaded portion 21. The taper of the threading tool and the thread dimensions
are selected so that the cross-sectional profile of the threads in the raised region
92 has an inverted V shape, i.e., the crest of each thread forms an inverted V so
that there is essentially no flat surface along the thread crest (in a preferred embodiment
the crest of the thread forms a flat surface that is only 0.003 inch wide). It is
this region 92 and a tapered region 91a located between recessed region 91 and region
92 of the threads that are self-tapping, and the sharp V profile of the crests of
the threads in this region assist in cutting into the inner wall of the hollow inner
conductor 12. The crests of the threads in the region 92 lie in a cylindrical plane
that has the same diameter as the region 92 in the unthreaded part shown in FIG. 2.
This diameter is slightly larger than the inside diameter of the hollow conductor
12 so that the threads penetrate into the metal of the inside wall of the conductor.
The depth of penetration of these threads into the inside wall of the inner conductor
12 is preferably at least 0.005 inch.
[0029] When the inner connector 20 is inserted into the hollow inner conductor 12, the tapered
end 90 and the recessed region 91 enter the conductor before the region 92. The tapered
end 90 facilitates the initial entry of the connector 20 into the hollow conductor
12. The region 91 has a diameter that is the same as, or only slightly smaller than,
the inside diameter of the hollow conductor 12 so that the crests of the threads in
this region 91 slide on the inside wall of the hollow conductor 12. Because the diameter
of this region 91 is smaller than the diameter of region 92, and all the threads are
formed by the same threading tool, the crests of the threads in the region 91 have
relatively flat surfaces, as can be seen in FIG. 3.
[0030] Because the region 91 of the connector 20 fits snugly within the hollow conductor
12, the inner connector 20 is centered in coaxial alignment with the conductor 12
before the self-tapping threads in the tapered region 91a and region 92 begin to cut
into the metal of the inside wall of the conductor. This ensures that the plane of
the shoulder 25 is perpendicular to the axis of the conductor 12. The flat surfaces
on the thread crests in the region 91 also help to center the connector coaxially
within the conductor 12.
[0031] In the tapered region 91a, the flat surface on the crests of the threads in region
91 transition to the sharp, pointed thread crests in the region 92.
[0032] To enable the shoulder 25 to fit snugly against the cut end of the inner conductor
12, the region 93 has the same reduced diameter as the region 91. A short tapered
region 94 between the end of the most proximal threaded region 93 and the shoulder
25 flares the cut end of the inner conductor 12 slightly outwardly to ensure parallelism
between the centerlines of the conductor 12 and the connector 20. In addition, the
tapered region 94 ensures firm engagement between the end of the conductor 12 and
the connector shoulder 25.
[0033] As the inner connector 20 is threaded into the hollow inner conductor 12, all four
threads 81-84 cut into the inside wall of the conductor. The lead of the four threads
81-84 can be made considerably longer than the lead of a single-threaded connector.
As a result, each complete revolution of the multiple-thread connector 20 relative
to the conductor 12 advances the connector 20 farther into the conductor. Indeed,
in most applications, a single revolution of the connector is sufficient to firmly
attach the inner connector 20 to the conductor 12, thereby shortening the installation
time with corresponding reductions in installation costs. In a preferred embodiment,
the lead of the threaded portion 31 is about 0.160 inch, and the axial length of the
region 92, including the two adjacent tapers, is about 0.0655 inch.
[0034] As in most connector assemblies, the shapes and dimensions of the various parts are
selected to provide impedance matching between adjoining parts, so that the complete
connector and cable assembly has a low VSWR.
[0035] FIG. 5 illustrates the connector assembly with the body member 30 and the clamping
member 51 disassembled. A portion of the main body member 30 has been broken away
to reveal its threaded surface 37. The telescopic sleeve portion 33 of the body member
30 slides over the sleeve portion 53 of the clamping member 51. The threaded surface
57 of the clamping member 51 matches the threaded surface 37 on the telescopic sleeve
portion 33 of the body member 30.
[0036] A plurality of slits 60 extend through a substantial length of the sleeve portion
53 of the clamping member 51 to a point near the threaded surface 57. The slits 60
thus form a plurality of resilient segments which act like spring fingers when a radial
force is applied thereto. Consequently, when the sleeve portion 53 of the clamping
member 51 is slipped over the cable 10 with the inner bead 52 engaging the cut edge
of the outer conductor 11 as illustrated in FIG. 1, continued application of pressure
to the member 51 causes the resilient segments to be deflected radially outwardly
until the inner bead 52 clears the crest at the end of the corrugated outer conductor
11. The bead 52 then slides over the crest of the outer conductor 11 and snaps into
the last corrugation valley, as illustrated in FIG. 1, thereby locking the clamping
member 51 to the cable 10 in the axial direction.
[0037] The raised bead 55 is formed on the sleeve portion 53 of the clamping member 51 near
the end of the slits 60. The inner bead 52 extends inwardly from the end of the sleeve
portion 53 of the clamping member 51 in a direction generally away from the raised
bead 55. The second clamping surface 50 which engages the beveled clamping surface
32 (not shown) of the body member 30 is adjacent the inner bead 52.
[0038] FIGS. 6 and 7 illustrate the threaded surface 37 along the inside of the body member
30 and the threaded surface 57 of the clamping member 51 in unrolled, planar views.
Four separate threads 37a-37d form the internally threaded surface 37 of the main
body 30 (FIG. 7) and four corresponding threads 57a-57d form the externally threaded
surface 57 (FIG. 8) of the clamping member 51. Because the ends of the threads are
typically uniformly spaced around each member, the ends of the four threads for each
threaded surface 37 and 57 are substantially 90° apart.
[0039] In general, fewer than two full revolutions are needed for complete engagement of
the outer conductor 11 by the beveled clamping surface 32 and the second clamping
surface 50. Typically, between 0.75 revolution (270 degrees) and 1.5 revolutions (540
degrees) are required for complete engagement of the outer conductor 11 by the beveled
clamping surface 32 and the second clamping surface 50. In a preferred embodiment
with four threads, approximately one revolution of the clamping member 51 effects
complete engagement of the clamping surfaces 32 and 52.
[0040] Due to the utilization of multiple threads (e.g. four threads), the clamping member
51 is attached to the body member 30 with a minimal amount of effort. Therefore, the
time required to assemble the outer connector to the cable 10 is reduced which decreases
the overall installation cost. This reduced effort required for installation is also
beneficial when the installer is performing this task in a spatially-confined area
or in inclement environmental conditions wherein multiple revolutions of the clamping
member 51 relative to the main body member 30 may be difficult.
[0041] Furthermore, because there is less engagement between each of the plurality of threads
and its corresponding thread since roughly one revolution is needed to fully advance
the clamping member 51 relative to the main body member 30, the frictional wear on
each of the threads is reduced. This is advantageous when the connector assembly is
recycled for multiple uses. On the other hand, if a signal thread were used, the multiple
revolutions needed to advance the clamping member 51 relative to the main body member
30 would result in additional wear on the single thread.
[0042] The threads 57a-57d of the clamping member 51 and the threads 37a-37d of the main
body member 30 have a pitch in the range from approximately 0.0625 inch to approximately
0.05 inch. The preferred pitch is about 0.055 inch. In the preferred embodiment where
four threads are used, the lead, which is the pitch multiplied by the number of threads,
is approximately 0.222 inch. If it is desired to maintain the lead constant at about
0.222 inch, but change the number of threads, then the pitch could change accordingly.
[0043] Although the number of interleaved concentric threads shown is four, the number of
threads can vary to accomplish the same result. Also, the threads do not need to include
ends which are uniformly spaced as long as the corresponding threads of the mating
piece have the same spatial relationship at their ends.
1. A connector assembly for a coaxial cable having an outer conductor and an inner conductor,
said connector assembly comprising:
an outer connector for engaging said outer conductor of said coaxial cable;
an inner connector for engaging said inner conductor of said coaxial cable to form
an electrical contact with said inner conductor; and
a threaded portion having a plurality of concentric threads on at least one of said
inner and outer connectors, said plurality of threads for bringing said at least one
of said inner and outer connectors into engagement with the corresponding one of said
inner and outer conductors.
2. The connector assembly of claim 1 wherein said threaded portion is located on said
inner connector.
3. The connector assembly of claim 2 wherein said plurality of threads are self-tapping.
4. The connector assembly of claim 2 wherein said threaded portion has a distal section
and a proximal section, the distal section having a smaller diameter than the proximal
section.
5. The connector assembly of claim 4 wherein the interior surface of said hollow inner
conductor has an outside diameter, said distal section having a diameter equal to
or slightly smaller than the inside diameter of said hollow inner conductor, said
proximal section having a diameter slightly greater than the inside diameter of said
hollow inner conductor.
6. The connector assembly of claim 2 wherein said threaded portion includes a proximal
end and said inner connector includes an outwardly extending flange adjacent the proximal
end of the threaded portion for engaging the inner conductor and thereby limiting
movement of the inner connector into the inner conductor.
7. The connector assembly of claim 2 wherein said outer connector includes at least two
components that are brought into engagement by mating threads.
8. The connector assembly of claim 2 wherein said hollow inner conductor is made of a
first material and said threaded portion of said inner connector is made of a second
material, said second material having a greater hardness than said first material.
9. The connector assembly of claim 1, wherein said threaded portion is located on said
outer connector.
10. The connector assembly of claim 9, wherein said outer connector includes a main body
member and a clamping member, said main body member and said clamping member each
include said threaded portions providing mating of said main body member to said clamping
member.
11. The connector assembly of claim 10, wherein said plurality of threads includes at
least four threads.
12. The connector assembly of claim 10, wherein said outer conductor is in complete engagement
with said outer connector in response to rotation of said clamping member relative
to said main body member by an amount less than two revolutions.
13. The connector assembly of claim 10, wherein said threaded portion of said main body
member is internal on said main body member, and said threaded portion of said clamping
member is external on said clamping member.
14. A connector assembly of claim 10, wherein said inner connector is brought into engagement
with said inner conductor through the use of threads.