Abstract:
An RF connector of a coaxial cable having an inner conductor, an outer conductor surrounding the inner conductor, a dielectric cylinder located between the inner and outer conductors, an outer radial barb projecting radially inwardly from the outer conductor into the cylinder, and an axial barb projecting axially from the outer conductor into the cylinder. The outer radial barb and axial barb work in cooperation to decrease the effect of contraction in the dielectric cylinder during colder temperatures, thereby providing a seal which prevents water and moisture from entering the connector.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a watertight RF connector of a coaxial cable, and more particularly to a watertight RF connector having an axial barb seal. 
     2. Description of the Related Art 
     A coaxial cable, which is used to transmit radio frequency (RF) signals, is a cylindrical transmission line made up of an inner conductor and a tube-shaped outer conductor separated by a dielectric spacer. Coaxial cables are connected or terminated using an RF connector. The RF connector has an inner conductor and tube-shaped outer conductor, which connect to the respective conductors of the cable. 
     It is sometimes required to place coaxial cables and RF connectors outdoors. The RF connectors must therefore be adequately weatherproofed so as to prevent water and moisture due to rain and humidity from entering the connector bodies and adversely affecting the components, within the connectors and cables. 
     Most conventional RF connectors rely on a mating interface connector to prevent moisture ingress. An improved connector will use O-rings to seal the interface between the dielectric spacer and outer conductor of the connector. This will prevent moisture ingress along the axis of connector. Although the moisture seal provided by the O-ring is effective, the O-ring is an additional component resulting in a more complex and costly assembly. 
     Attempts have therefore been made to eliminate the O-ring from the construction of the connector by providing ring-shaped radial barbs that project from the conductors and press fit into the spacer. However, radial barbs alone are not sufficient to provide a reliable moisture seal over a wide enough temperature range. That is, most dielectric materials (e.g., Teflon) suitable for manufacturing spacers of RF connectors have a larger coefficient of expansion than the conductive material (e.g., brass) used to form the outer conductor portion of the connector. At colder temperatures the spacer therefore shrinks away from the outer conductor, thereby compromising the intended seal between the outer conductor and the spacer. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to effectively seal an RF connector from water and moisture without the use of an O-ring. 
     This object is fulfilled by providing a connector with a combination of an outer radial barb projecting radially inwardly and an axial barb projecting axially from the outer conductor into the dielectric cylinder. When the dielectric cylinder attempts to shrink away from the outer conductor during colder temperatures, the outer radial and axial barbs work in cooperation to oppose the force of thermal contraction of the cylinder to thereby ensure that the moisture seal of the connector is maintained. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above objects and advantages of the present invention will become more apparent by describing in detail a preferred embodiment thereof with reference to the attached drawings in which: 
     FIG. 1 illustrates a longitudinal cross sectional view of an RF cable and connector having a barb seal according to the present invention; and 
     FIG. 2 illustrates an exploded view of the barb seal of the connector of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates an RF cable and connector having a barb seal according to the present invention, and FIG. 2 illustrates an exploded view of the barb seal shown in FIG. 
     The cable, shown in the left-hand side of FIG. 1, has a hollow inner conductor  13  concentrically spaced from center line A—A, an outer conductor  4  disposed about the inner conductor  13  and concentrically spaced from center line A—A. The space between the cable inner conductor  13  and the cable outer conductor  4  is filled by a dielectric spacer  14 . 
     The connector, shown in the right-hand side of FIG. 1, has an inner conductor  10  concentrically spaced from center line A—A, and a connector body or an outer conductor  5  disposed about the inner conductor  10  and concentrically spaced from center line A—A. A dielectric cylinder  7  having an axial opening therethrough is disposed over the connector inner conductor  10  for the purpose of maintaining the connector inner conductor  10  in the proper location with respect to the connector outer conductor  5 . The dielectric cylinder  7  may be press-fit onto the connector inner conductor  10 . An inner radial barb  9  and shoulders  11  and  12  of the connector inner conductor  10  and the connector outer conductor  5 , respectively, prevent the inner conductor  10  from moving axially with respect to the dielectric cylinder  7  disposed thereover. Preferably, both connector conductors  10  and  5  are made of brass, and the dielectric cylinder  7  is preferably made of Teflon. 
     Attachment of the connector to the cable is accomplished by attaching the outer conductor  5  of the connector with a backnut  1  and collet  15 , which is secured to the jacket of the cable. An O-ring seal  3  is positioned between the backnut  1  and the outer conductor  5  to seal out moisture, dirt and other contaminants. Similarly, an O-ring seal  2  is positioned between the backnut  1  and the outer conductor  4  of the cable. 
     The barb sealing arrangement of the present invention for sealing the outer conductor  5  of the connector with the dielectric cylinder  7  will now be described with reference to FIG. 2. A ring-shaped outer radial barb  6  projects radially inwardly from the connector outer conductor  5  and penetrates the dielectric cylinder  7 . Also, a ring-shaped axial barb  8  projects axially from the stepped surface of the shoulder  12  of the outer conductor  5  to penetrate the dielectric cylinder  7 . Each of these barbs is shaped like a right triangle, with the base of the triangle lying along the conductor and a point of the triangle projecting into the dielectric cylinder  7 , as shown in FIG.  2 . The sides of the triangle forming the projection of the outer radial barb  6  are the inclined surface  6   a  and the vertical surface  6   b.  According to the preferred embodiment, the vertical surface  6   b  of the outer radial barb is parallel to the step surface of the shoulder  12 , as shown in FIG.  2 . Similarly, the sides of the triangle forming the projection of the axial barb  8  are the outwardly facing inclined surface  8   a  and the surface  8   b.  This right triangle shape allows for easy penetration of the barbs into the dielectric cylinder  7 . 
     However, the invention is not limited in this respect. For example, the outer radial barb  6  could be designed so that the surface  6   b  forms an acute angle with the surface of the outer conductor, so that the barb penetrates the dielectric cylinder more easily. 
     During colder temperatures the dielectric cylinder  7  tends to shrink radially away from the outer conductor  5 . The dielectric cylinder  7  as it shrinks presses against the axial barb  8 . The inclined surface  8   a  of the axial barb  8  pushes the dielectric cylinder  7  back against the vertical surface  6   b  of the outer radial barb  6 . Thus, when the dielectric cylinder  7  shrinks, it is urged against the inclined surface  8   a  of the axial barb  8  and the vertical surface  6   b  of the outer radial barb  6 , both of which circumscribe the connector. Therefore, these two surfaces act to seal the connector to the dielectric cylinder  7 . Accordingly, even though the shrunk dielectric cylinder  7  may not contact the inner surface of the outer conductor, sealing is still achieved by the inclined surface  8   a  of the axial barb  8  and the vertical surface  6   b  of the radial barb  6 . 
     To achieve this effect, the outer radial barb  6  should be placed in close proximity to the axial barb  8 . If the distance between the outer radial barb  6  and the axial barb  8  is too great, the dielectric cylinder  7  will shrink away from both barbs. In addition to sealing the dielectric cylinder  7 , the outer radial barb  6  also prevents the cylinder  7  from moving in the axial direction, similar to the inner radial barb  9 , discussed above. 
     The shape and orientation of the axial barb  8  and outer radial barb  6  are important in providing a good seal as temperature varies. In a preferred embodiment the outer radial barb  6  and axial barb  8  are each shaped like a right triangle as described above. However, the shape and orientation of the radial barb  6  and axial barb  8  are not limited, but can instead be adjusted to compensate for the axial shrinkage of the dielectric cylinder  7 . 
     The sizes of the barbs in the figures are enlarged for the sake of clarity. Preferably, the height of the barbs should be greater than the amount of radial shrinkage of the dielectric cylinder  7 . For example, in a typical environment, a Teflon cylinder  7  may shrink 0.003 inches in the radial direction. In this case, the barb height should be greater than 0.003 inches, and preferably in the range of 0.008 to 0.012 inches. 
     Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as other embodiments of the present invention, will become apparent to persons skilled in the art upon reference to the description of the invention. It is therefore contemplated that the appended claims will cover any such modifications or embodiments as fall within the true scope of the invention.