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(11) | EP 0 768 736 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Moisture migration proof unpressurized radio frequency transmission system and method |
| (57) A water migration proof radio frequency transmission system and method is disclosed.
The system comprises an unpressurized foam dielectric coaxial cable having a center
conductor surrounded by a foam dielectric which is surrounded by an outer conductor.
The system also comprises a connector for connecting the center and outer conductors
of the cable to the center and outer conductors of an antenna. The connector includes
sealing means for preventing moisture migration into the cable from the center conductor
of the antenna. In one embodiment the connector has an insulative center conductor
contact bead with an O-ring positioned on its outer periphery and with a bore in the
bead press fit to an inner conductor contact which in turn connects to the coaxial
cable center conductor. In another embodiment the bead includes a second O-ring within
the bore for moisture sealing engagement with the inner conductor. The method uses
such a connector within a dielectric foam coaxial cable to form a moisture proof radio
frequency transmission system. |
BACKGROUND OF THE INVENTION
Field of the Invention
[0001] The present invention generally relates to coaxial cable connectors for connecting coaxial radio frequency (RF) cables to other cables, antennas and transceivers. More particularly, the present invention relates to a moisture migration proof unpressurized radio frequency transmission system which includes the use of a coaxial RF cable connector structure that has internal and external seals.
Description of the Prior Art
[0002] Foam dielectric coaxial cable is typically used for cell-site antenna feed line cables and antenna interconnects for RF transmission. Such cable is often installed in vertical runs of up to 250 feet. Field reports from cell-site operators, as well as other two-way repeater operators, have indicated that transmission performance of cell-site antennas can be adversely affected by moisture migration within antenna feed line cables. Moisture migration is particularly troubling for cellular base station radio sites because such sites are often located in remote areas, subjected to harsh environments, exposed to radical temperature swings and barometric pressure changes day-in and day-out, as well as, in some areas, exposed to frequent precipitation.
[0003] One of the primary driving forces for moving moisture into a cable's interior is pressure changes within the cable caused by changes in temperature. During the daytime in certain environments, a cable can be heated as much as 50 degrees Celsius or more from its night time low temperature. When heated, the pressure inside the cable increases causing air within the cable to escape through connector interfaces. Then, usually during the night, when the cable cools, the air pressure inside the cable is reduced causing a partial vacuum at the cable connector joints. If moisture is present near a cable connector joint, the partial vacuum at the joint can draw moisture into the cable connector.
[0004] Once moisture enters a cable, it can migrate anywhere within the cable. For example, the moisture may migrate between the center conductor and the foam dielectric The moisture may also migrate through the center conductor. The moisture may even migrate between the outer conductor and the foam dielectric.
[0005] Depending upon where such moisture ultimately collects, the moisture can cause minimal to serious signal degradation. Moisture collecting between the outer conductor and the foam dielectric surface can cause significant signal attenuation. Moisture collecting on the cross-section of the dielectric foam adjacent to the connector can cause a mismatch which results in VSWR degradation.
[0006] While it has been well recognized that moisture can migrate into the cable through exterior cable joints, and that measures have been taken to prevent this migration as shown by the use of O-rings at external connector joints as shown in U.S. Patent No. 5,137,470, it has not been recognized, until now, that moisture may also migrate into unpressurized cables through internal joints, such as along a center conductor contact assembly connected to an antenna, even though the exterior of the connector is moisture proof. Such internal migration also causes the same signal degradation problems when the moisture collects on the foam dielectric surface or the cross-section of the dielectric adjacent to the connector.
[0007] Connectors designed with air-tight seals between the cable and the outer conductor assembly, and between the outer conductor assembly and the center conductor assemblies, have been fabricated and used to enable a hollow center conductor of a coaxial cable to be pressurized or to enable pressurization of the region between the cable's center and outer conductors. The pressurized cable is further used to pressurize hollow antenna elements to provide them with structural rigidity. It has been discovered by the applicant that these connectors for pressurized cables are useful in unpressurized applications to prevent internal moisture migration into foam dielectric cable, such as along a center conductor contact assembly connected to an antenna.
SUMMARY OF THE INVENTION
[0008] It is a primary object of the present invention to provide a moisture migration proof radio frequency transmission system and a connector for use in such a system.
[0009] Other objects and advantages of the invention will be apparent from the following detailed description and the accompanying drawings.
[0010] In accordance with the present invention, the foregoing primary objective is realized by using a cable connector with a center conductor contact having press fit thereon an electrically insulative, cylindrically shaped center conductor contact bead having an O-ring seal receiving recess on its outer surface and an O-ring seal positioned in the recess. The bead includes a central bore which is dimensioned so as to require press fitting over the center conductor contact's bead receiving shaft. It has been discovered that the snug, press fit bead provides an adequate moisture barrier or seal between the center conductor contact's bead receiving shaft and the insulative bead even when the coaxial cable is subjected to widely variable ambient conditions. The O-ring seal on the bead provides a moisture barrier between the bead and an opening in an outer coupling body in an assembled connector. The use of a connector with the aforementioned moisture barriers in an unpressurized foam dielectric cable provides superior internal moisture migration resistance.
[0011] An O-ring may also be positioned within the central bore of the bead in lieu of press fitting the bead over the center conductor contacts' bead receiving shaft.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The drawings, not drawn to scale, include:
FIG. 1 which is a perspective view of an exterior of a coaxial cable connector;
FIG. 2 which is a longitudinal cross-sectional, semi-exploded view of a coaxial cable connector employing the insulative internal moisture barrier center conductor coupler bead;
FIG. 3 which is a longitudinal cross-sectional view of the same coaxial cable connector of FIG. 2 also including an external heat shrinkable boot as an additional external moisture migration barrier; and
FIG. 4 is a longitudinal cross-sectional view of an alternative embodiment of the center conductor contact bead having an O-ring positioned within the central bore of the bead in lieu of press fitting the bead over the center conductor contacts' bead receiving shaft.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
[0013] Referring generally to the drawings, there is shown a coaxial cable connector 10. Referring more specifically to FIG. 2, the connector 10 generally comprises several component parts which are shown in a semi-exploded view. The component parts include a nose assembly 20, an outer conductor contact body 40, an center conductor contact assembly 60, and an outer conductor contact securing assembly 80. As will be more fully explained below, to prevent moisture migration into the cable, the method of the present invention uses, a cable connector which is provided with seals or moisture barriers at all critical interfaces between its component parts. Most importantly, the method of the present invention uses a center conductor contact assembly that is fitted with a press fit insulative bead which provides internal moisture barriers to dramatically improve resistance to internal moisture migration. A detailed description of a connector embodiment employing the insulative bead is presented below. Connectors having the below described structure including a press fit bead have been used in pressurized cable applications wherein the cable is pressurized so as to pressurize antenna elements for structural rigidity purposes.
[0014] Referring to FIG. 2, the nose assembly 20 of the connector 10 is generally cylindrically shaped and includes a body coupling end 22 and an antenna coupling end 24. The nose includes a varying diameter bore 26 extending from the body coupling end 22 to the antenna coupling end 24. An O-ring seal receiving recess 28 is provided at the body coupling end 22. A portion 30 of the interior diameter of the nose assembly 20, adjacent to the O-ring seal receiving recess 28, is threaded. The nose assembly 20 also includes an exterior threaded portion 32, between the body coupling end 22 and the antenna coupling end 24.
[0015] Connector body 40 is generally cylindrically shaped with a varying outside diameter along its length. The connector body 40 includes a threaded outer conductor coupling end 42, a threaded nose assembly coupling end 44 with an O-ring seal receiving surface 45, and a varying diameter cylindrical bore 46 extending from the outer conductor coupling end 42 to the nose assembly coupling end 44. An insulative bead receiving portion 48 of the bore 46 is dimensioned to snugly receive an center conductor insulator bead 62. The connector body 40 also includes an O-ring seal receiving recess 50 in which an O-ring seal 52 resides.
[0016] The center conductor contact assembly 60, also generally cylindrically shaped, includes a metal center conductor contact body 64 having a threaded shank 66 dimensioned to fit within the center conductor of an RF cable, a bead receiving shaft 68 and a diametric bore 69. The threaded shank 66 of the metal center conductor contact body 64 provides electrical connection to the center conductor of the RF cable. A pin 70, for connection to another coaxial connector or an antenna, such as a type NF contact, is attached to the bead receiving shaft 68 and may be held in place by solder or any other suitable securing means such as threading, for example. The contact assembly 60 also includes the previously mentioned cylindrically shaped bead 62 having a lengthwise bore 61 therein and an O-ring receiving recess 72 on its outer surface in which an O-ring seal 74 may reside. In the preferred embodiment, the bead 62 is fabricated from virgin white poly-tetra-fluoro-ethylene, commonly known under the trademark TEFLON. Other insulative materials may be used for the bead 62 provided such materials have adequate electrical insulating properties. The diameter of the lengthwise bore of the TEFLON bead 62 is dimensioned to lit as snugly as possible to the bead receiving shaft 68. Also, in the preferred embodiment, the bead 62 is dimensioned such that it must be press fit onto the bead receiving shaft 68. A moisture barrier between the bead 62 and the bead receiving shaft 68 is created by the tight press fit between the bead and shaft.
[0017] FIG. 4 illustrates an alternative embodiment of the cylindrically shaped bead 62' where a second O-ring receiving recess 71 is positioned within the lengthwise bore 61 for receipt of an O-ring 73. In this embodiment the diameter of the central bore is dimensioned to slide over receiving shaft 68, with O-ring 73 providing the moisture barrier therebetween.
[0018] The outer conductor contact securing assembly 80 comprises a collet 82 which is generally angularly shaped and includes a cable jacket end 83. The collet 82 is used to grasp the outer conductor and make electrical contact therewith. The inside diameter of the collet 82 is shaped to match the ribbed outer conductor 102 of a cable 100 having a foam dielectric 103. Typically, the collet 82 comprises two collet halves which are positioned bound the outer conductor 102 of the cable 100 and held together by a retaining spring or clip 83 substantially surrounding the collet halves. An example of two collet halves held together by a retaining spring is shown in U. S. Patent 5,454,735, assigned to the assignee of the present invention, and the description therein is incorporated by reference.
[0019] In addition to the collet 82, the assembly 80 includes a back nut 84 which has a body coupling end 86, a collet abutting end 88, and a threaded portion 90 between the body coupling end 86 and the collet contacting end 88. The assembly 80 also includes an O-ring seal receiving surface 87 adjacent to the body coupling end 86 to which O-ring 52 may be positioned against. The assembly 80 also includes an O-ring seal 90 positioned between the outer conductor 102 of the cable and the back nut 88.
[0020] FIG. 2 illustrates the connector 10 in the fully assembled, externally and internally moisture migration proof site suitable for use in severely varying ambient conditions. According to the method, the connector 10 is assembled and attached to the cable 100 in a conventional manner so as to form an unpressurized radio frequency transmission system 105. Ordinarily, a sufficient length of the outer protective jacket 103 of the cable 100 is stripped off, exposing a length of outer conductor 102. The cable 100 is inserted through the back nut 84, and through the O-ring seal 90 which has an inside diameter approximately the same size as the outside diameter of the outer conductor 102. The collet 82 is attached to the exposed outer conductor 102 so that one end is adjacent to the O-ring seal 90 and the other end is adjacent to the end of the cable 100.
[0021] The center conductor threaded shank 66 is threaded to the center conductor 101. A rod (not shown) may be inserted into the diametric bore 69 to facilitate threading of the threaded shank 66 of the center conductor into the center conductor 101 of the cable 100 since the metal conductor 64 is generally cylindrically shaped. The O-ring groove 72 in the bead 62 is fitted with the O-ring seal 74.
[0022] Once the shank 66 of the center conductor assembly 60 is secured to the center conductor 101, O-ring seal 52 is placed in O-ring seal receiving groove 50 and the body 40 is securely threaded to the back nut's threaded portion 88. When the back nut 84 and the body 40 are secured, the O-ring seal 52 is snugly positioned between back net 84 and the O-ring seal receiving groove 50 and forms a tight, moisture proof seal. Also, when the back nut 84 and the body 40 are securely coupled, the insulative bead 62 resides in the bead receiving portion 48 of bore 46. A moisture barrier between the bead 62 and the bead receiving portion 48 of bore 46 is formed by O-ring 74 positioned between recess 72 and bead receiving portion 48. A moisture barrier between the bead 62 and the center conductor's bead receive shaft 68 is provided by the press fitting of the bead 62 on the shaft 68, or for the alternative bead embodiment 62' shown in FIG. 4, by O-ring 73. It has been found that the two aforementioned moisture barriers provide greatly improved internal moisture migration resistance in an unpressurized coaxial cable.
[0023] Finally, after an O-ring seal 47 is positioned on O-ring receiving surface 45 of the body, the nose assembly 20 is securely coupled to the body 40. After the nose assembly 20 and body 40 are securely coupled via their respective opposing threaded portions, O-ring seal 47, positioned between the nose assembly 20 and the body 40, provides a moisture seal for the joint therebetween.
[0024] FIG. 1 illustrates the appearance of the assembled connector 10 which may be used in the method of the present invention. It should be appreciated by those skilled in the art that the joints between the body 40 and back nut 84, as well as between the back nut 84 and the cable jacket 103, are still exposed to the environment and the joints, if small enough, could provide some capillary action to draw moisture therein. A heat shrinkable sleeve 120 of sufficient length, may be fitted over the connector so as to cover the above mentioned joints between the body 40 and the back nut 84, and between the back nut 84 and the cable jacket 103. Once sleeve 120 is fitted over the connector 10, heat may be applied to the sleeve 120 to shrink the diameter of the sleeve 120 so as to provide a continuous, tight fitting exterior moisture barrier over the above mentioned joints.
[0025] As can be seen from the foregoing detailed description and drawings, the present invention provides a moisture migration proof radio frequency transmission system formed by foam dielectric coaxial cable in combination with the above-described connector. The present invention also describes a method for forming a moisture proof radio frequency transmission system and although such a system and method has been described with respect to one or more particular embodiments, it will be understood that other embodiments of the present invention, such as the type of coaxial cable used and the like, may be employed without departing from the spirit and scope of the present invention. Hence, the present invention is deemed limited only by the appended claims and the reasonable interpretation thereof.
an unpressurized foam dielectric coaxial cable further comprising:
a center conductor,
a foam dielectric surrounding the center conductor, and
an outer conductor surrounding the foam dielectric; and
a connector for connecting the unpressurized foam dielectric cable to an antenna, the connector further comprising:
means for connecting the outer conductor of the dielectric foam cable to an outer conductor of the antenna, and
means for connecting the center conductor of the dielectric foam cable to a center conductor of the antenna, the means further including sealing means for preventing water migration from the antenna's center conductor to the cable.
a connector body having an opening formed therethrough,
an insulative center conductor contact bead positioned within the opening of connector body, the bead including a bore, and an O-ring receiving groove on the surface of the bead adjacent the connector body,
an O-ring positioned between the O-ring receiving groove of the bead and the connector body forming a moisture migration barrier between the bead and the body,
an inner conductor contact having means for electrical connection to the center conductor of the unpressurized foam dielectric coaxial cable, and having a shaft press fit in the bore of the bead so as to form a moisture migration barrier therewith, and
means for electrically connecting the inner conductor contact to the center conductor of the antenna.
a connector body having an opening formed therethrough,
an insulative center conductor contact bead positioned within the opening of connector body, the bead including a bore, an O-ring receiving groove on the surface of the bead adjacent the connector body, and an O-ring receiving groove in the bore of the bead,
an O-ring positioned between the O-ring receiving groove of the bead and the connector body forming a moisture migration barrier between the bead and the body,
an O-ring positioned within the O-ring receiving groove in the bore to form a moisture migration barrier between the bead and the center conductor of the coaxial cable,
an inner conductor contact having means for electrical connection to the center conductor of the unpressurized foam dielectric coaxial cable, and having a shaft for sliding engagement with the bore of the bead and for engagement with the O-ring positioned within the O-ring receiving groove in the bore so as to form a moisture migration barrier therewith, and
means for electrically connecting the inner conductor contact to the center conductor of the antenna.
an unpressurized foam dielectric coaxial cable further comprising:
a center conductor,
a foam dielectric surrounding the center conductor, and
an outer conductor surrounding the foam dielectric; and
a connector assembly for connecting the outer and inner conductors of the unpressurized foam dielectric coaxial cable to an antenna, the connector assembly having internal moisture migration resistance, the connector assembly comprising:
a connector body having an opening therein for receiving an insulative center conductor contact bead,
means for electrically connecting the body to the outer conductor of the coaxial cable,
means for electrically connecting the connector body to the outer conductor of an antenna,
an insulative inner conductor contact bead positioned within the opening of the connector body, the bead including a bore, and further including an O-ring receiving groove on its surface adjacent to the connector body,
an O-ring positioned between the O-ring receiving groove of the bead and the connector body forming a moisture migration barrier between the bead and the body,
an inner conductor contact having means for electrical connection to the center conductor
of the unpressurized foam dielectric cable, and having a shaft press fit in the bore
of the bead so as to form a moisture migration barrier;
and
means for electrically connecting the inner conductor contact to the center conductor of the antenna.
an unpressurized foam dielectric coaxial cable having:
a center conductor,
a foam dielectric surrounding the center conductor, and
an outer conductor surrounding the foam dielectric; and
an antenna for communication therewith;
wherein the connector assembly is used for connecting the outer and inner conductors
of the unpressurized foam dielectric coaxial cable to the antenna, the connector assembly
having internal moisture migration resistance, the connector assembly comprising:
a connector body having an opening therein for receiving an insulative center conductor contact bead;
means for electrically connecting the connector body to the outer conductor of the coaxial cable;
means for electrically connecting the connector body to the outer conductor of an antenna;
an insulative inner conductor contact bead positioned within the opening of the connector body, the bead including a bore and further including an O-ring receiving groove on its surface adjacent to the connector body;
an O-ring positioned between the O-ring receiving groove of the bead and the connector body forming a moisture migration barrier between the bead and the body;
an inner conductor contact having means for electrical connection to the center conductor of the unpressurized foam dielectric cable, and having a shaft press fit in the bore of the bead so as to form a moisture migration barrier; and
means for electrically connecting the inner conductor contact to the center conductor of the antenna.
providing an unpressurized foam dielectric coaxial cable further comprising:
a center conductor,
a foam dielectric surrounding the center conductor, and
an outer conductor surrounding the foam dielectric;
providing a connector for connecting the unpressurized foam dielectric coaxial cable to an antenna, the connector further comprising:
means for connecting the outer conductor of the dielectric foam coaxial cable to an outer conductor of the antenna, and
means for connecting the center conductor of the dielectric foam coaxial cable to a center conductor of the antenna, the means further including sealing means for preventing water migration from the antenna's center conductor to the coaxial cable.