Abstract:
Radio frequency cables have a inner circular conductor and an outer circular conductor. The inner and outer circular conductors are usually formed from copper and are separated by a heavy insulation layer usually cellular polyethylene. The outer side of the outer conductor may further be coated with a heavy polymeric insulation layer. In preparing these radio frequency cables for coupling it is necessary to have a flush cut surface. These flush cuts have been effected in the past by sawing, which has proved to be troublesome as metallic particles are dispersed throughout the insulation. The outer conductor may be prepared for coupling by:
   1. Placing a tear collar over the outer conductor and   2. Tearing the outer conductor against the tear collar.
 
This tearing creates an integral and desirable flange in the tearing process.

Description:
FIELD OF THE INVENTION 
   This invention is concerned with radio frequency cables (herein after R.F. cables). More particularly this invention is concerned with the preparation of the outer conductor of an R.F. cable for coupling. In accordance with this invention the outer conductor component of an R.F. cable is torn at a predetermined point. In the tearing an integral flange is formed. Upon tearing and after the trimming of the insulation and inner conductor, the R.F. cable is ready for coupling. 
   BACKGROUND OF THE INVENTION 
   Cellular telephones have become very popular in recent years. With the advent of this popularity a tremendous need has developed for towers to relay the phone calls which result from these cellular telephones. In operation a cellular phone transmits radio waves which are received by a nearby cellular telephone tower, (herein after cell tower). The function of the cell towers is to pick up the radio frequency signals which are transmitted by the cell phone and convert these radio frequency signals into electrical signals which can be transmitted over land lines to a central switching station. The antennas for the radio signals transmitted by the cell phones are usually located high up on cell towers. In operation the cell tower receives a radio frequency signal high up on the tower and transfers this signal down the tower to a converter which is located at ground level. The radio frequency signal is sent down the tower in an R.F. cable. This invention is concerned with making connections between two sections of an R. F. cable. In the process of making a connection between two sections of an R.F. cable, it is necessary to make flush cuts on both segments of the R.F. cables which are being joined. This invention relates to a process and apparatus whereby the flush cuts can be made. As will be explained in detail herein below, R.F. cables are complex structures. Joined R. F. cables will not function correctly if they are not perfectly cut or if contaminants are present in the insulation layer of the R.F. cable. In accordance with this invention virtually perfect flush cuts can be made on R.F. cable without introducing contaminants into the insulation component of the cable. After opposing flush cuts are made on opposing sections of an R.F. cable these opposing sections can be readily joined with an appropriate connector. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of an R.F. cable. 
       FIG. 2  is a perspective view showing the placement of an O Ring on an R.F. cable. 
       FIG. 3  is a perspective view showing a prior art method for cutting an R.F. cable. 
       FIG. 4  is a perspective view showing a finished prior art cut on an R.F. cable. 
       FIG. 5  is a perspective view showing the chamfering of the inner conductor of an R.F. cable. 
       FIG. 6  is a perspective view showing the placement of a tear collar on a section of an R.F. cable. 
       FIG. 7  is a perspective view showing the tear collar seated on a section of an R.F. cable. 
       FIG. 8  is a cut away side view along line  7 — 7  showing the seating of a tear collar on an O ring. 
       FIG. 9  is a perspective view showing the formation of a tearing tab on the outer conductor of an R.F. cable. 
       FIG. 10  is a perspective view showing the tearing of the outer conductor of an R.F. cable. 
       FIG. 11  is a perspective view showing the outer conductor of an R.F. cable torn. 
       FIG. 12  is an expanded section view along line  11 — 11  of  FIG. 12  of an R.F. cable after the outer conductor has been torn. 
       FIG. 13  is a perspective view showing the placement of a cutter in an R.F. cable after the outer conductor has been torn away. 
       FIG. 14  is a perspective view showing the cutting of the insulation and the inner conductor segments of an R.F. cable. 
   

   OBJECTS OF THE INVENTION 
   The primary object of the invention is a process whereby the outer conductor of an R.F. cable can be torn to facilitate the formulation of a flush cut. 
   Another object of the invention is a tear collar which allows the precise tearing of the outer conductor of an R.F. cable. 
   Still another object of this invention is a process for flush cutting an R.F. cable without introducing contaminants into the insulation layer of the R.F. cable. 
   Still another object of this invention is a process for making flush cuts on R. F. cables without tearing the insulation layer. 
   BRIEF SUMMARY OF THE INVENTION 
   This invention is concerned with a process for making flush cuts on R.F. cables. More particularly this invention is concerned with a process for tearing the outer conductor of an R.F. cable at a predetermined point. 
   The process of this invention is effected by placing a tear collar over the outer conductor of an R.F. cable. A segment of the outer conductor is then twisted in such a manner that a precise tear is made against the tear collar. After the outer conductor is torn the inner conductor and the insulating layer are removed by other means. The process of this invention eliminates the introduction of contaminants into the insulation layer of the R.F. cable. 
   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   As is briefly discussed above this invention is concerned with a process for making flush cuts on R.F. cable segments in order that opposing sections of cable might be joined together with a suitable connector. 
   In order to understand this invention the component parts of an R.F. cable and their function must be understood. In this regard referring to  FIG. 1  it can be seen that R. F. cable  2  is an axial structure. This structure is used to conduct radio frequency signals along the length of a cable. Signals in the frequency range of from about 800 MGz to about 2.2 GHz are usually conducted in an R.F. cable. Referring to  FIG. 1 , it can be seen that R.F. cable  2  incorporates a heavy insulating layer  4  on its outer side. Insulating layer  4  is usually formed from a polymeric material. Insulating layer  4  does not play a significant part in the subject invention as it is usually removed for the portion of the R.F. cable on which a flush cut is to be made. R.F. cable  2  further incorporates an outer conductor  8  an insulating layer  10  and an inner conductor  12 . Radio energy is transmitted along the axial length of R.F. cable  2  by radio wave length energy being reflected off of outer surface  14  of inner conductor  12  to inner surface  16  of outer conductor  8  through insulation layer  10 . 
   Insulation layer  10  functions to separate inner conductor  12  from outer connector  8 . Insulation layer  10  is formed from a polymeric, dielectric material such as polyethylene. In order to minimize weight in most instances insulation layer  10  is formed from a cellular polymeric material such as cellular polyethylene. Cut or ruptured cells in insulation layer  10  present a problems, in R.F. cables. These cut or ruptured cells are troublesome as they tend to trap impurities which may result in the cutting of R.F. cable  2 , i.e. metal particles which may result from the cutting of inner and outer conductors  8  and  12 . 
   Inner and outer conductors  12  and  8  are formed from a conductive material preferably a metal and preferably copper. Copper is preferred due to its outstanding conductive properties. 
   In installing R.F. cable  2  it is often necessary to bend certain cable sections. As can be seen from  FIG. 1 , inner and outer conductors  12  and  8  are tubular in structure. If a tube is bent it tends to kink and deform. In order to prevent the kinking and deformation of R.F. cable  2  in bending, inner and outer conductors  12  and  8  are corrugated. It is well known to one skilled in the art that a corrugated tubular structure can be bent, to a limited degree, without kinking or deformation. In the R.F. cable structure illustrated in  FIG. 1 , outer conductor  8  incorporates a plurality of non spiral corrugations  18 . Inner conductor  12  incorporates a continuous spiral corrugation  20  as is shown in  FIG. 8 . Corrugations  18  of outer conductor  8  present special problems in the cutting of this segment of R.F. cable  2 . 
   In the prior act in order to make a flush cut outer conductor  8 , inner conductor  12  and insulation layer  10  were cut with a saw, usually a hack saw. This cutting is illustrated in  FIG. 3  wherein it can be seen that saw blade  22  is cutting through the components of R.F. cable  2 . A guide  24  has been positioned around outer conductor  8  at a predetermined position. Saw blade  22  is biased against vertical surface  26  of guide  24  for purposes of guiding saw blade  22  to make an approximate vertical cut. Saw blade  22  in cutting outer conductor  8  forms rough edges  28  and  30  on outer conductor  8  and inner conductor  12 . These rough edges are illustrated in  FIG. 4 . In order to smooth rough edges  28  and  30 , these edges are chamfered with a knife blade  32  as is shown in  FIG. 5 . This chamfering after creates further problems as the chips which are formed work their way into the interfaces between insulation layer  10  and inner and outer conductors  12  and  8 . 
   In the cutting as is illustrated in  FIG. 3 , metallic particles  36  are created. These metallic particles are metallic saw dust. The reciprocal action of saw blade  22  draws these particles into the saw cut  38 . The continued reciprocal action of saw blade  22  causes metallic particles  36  to be embedded into insulation layer  10 . Because insulation layer  10  is cellular, this embedding process is very effective. 
   Having metallic particles  36  embedded into insulation layer  10  is undesirable, as these metallic particles interfere which the transmission of radio waves through R. F. cable  2 . 
   As a result of this interference, it is necessary to remove all metal particles from the cut face of insulation layer  10  and from the interface between insulation layer  10  and inner and outer conductors  12  and  8 . This removal of these metal particles becomes difficult if not impossible due to the fact that these particles are embedded into cellular insulation layer  10 . This difficulty is further magnified by the fact that the cutting and connecting of R.F. label  2  is often done under adverse cramped conditions. i.e. high up on a cell tower or in a small box at the bottom of a cell tower. 
   Another problem with the cutting of R.F. cable  2  as is shown in  FIG. 3  is that the teeth of saw blade  22  tend to snag insulation layer  10  with this snagging insulation layer  10  is torn as saw blade  22  is drawn back and forth. This tearing action creates voids in insulation layer  10 . These voids become air pockets which further interfere with the transmission of radio frequency energy through R.F. cable  2 . 
   The above set forth problems are eliminated by the process and apparatus of this invention wherein a clean cut can be made on an R.F. cable without the formation of voids in the insulation layer or the contamination of the insulation lager with metallic particles. 
   The process of this invention relates to the use of a tear collar to control the point at which the outer conductor is torn. Referring to  FIG. 6  it can be seen that tear collar  40  has a circular cross section and is generally tubular. Tear collar  40  has a main body section  42 , a bore  44 , an angular tool rest  46 , a stop  48  and a tearing edge  50 . 
   In usage a rest is provided whereby tear collar  40  can be seated on cable  2 . In the preferred embodiment of this invention tear collar  40  is seated on the O ring which is later used to seal a connector to cable  2 . 
   In usage an O ring  52  is seated in a valley of a pre-selected corrugation on outer conductor  8 . Tear collar  40  is then placed over outer conductor  8 , such that outer conductor  8  penetrates bore  44  of tear collar  40 . Tear collar  40  is then firmly seated on O ring  52 , such that O ring  52  is biased against stop  48 . When tear collar  40  is seated against O ring  52 , tear collar  40  is located at a predetermined point on outer conductor  8 . 
   O ring  52  is formed from an elastic polymeric material to aid in the sealing of the connector which is used to join the R.F. cable sections. 
   The applicant does not understand the full ramifications of how the elastic nature of O ring  52  affects the tearing of outer conductor  8 . It has been observed that the ability of tear collar  40  to flex against O ring  52  has beneficial effects on the tearing process. 
   In the preferred embodiment of this invention tear collar  40  is biased against an elastic stop i.e. an elastic O ring. The elastic stop can have a durometer of from about 50 to about 75, with a more preferred range being from about 55 to about 65, with a most preferred durometer for the elastic stop being 60. 
   The length of tear collar  40  is such that when stop  48  is biased against O ring  52 , tearing edge  50  is positioned at a predetermined point on outer conductor  8 . 
   As is illustrated in  FIG. 8  it is preferred that tearing edge  50  be located approximate the apex of one of the corrugation of outer connector  8 . In the most preferred embodiment tearing edge  50  is located just forward of the apex of a corrugation in the direction of arrow  54 . This location facilitates the formation of a desirable flange on outer conductor  8 , when tearing is effected. 
     FIGS. 9 and 10  illustrate the actual tearing process, as can be seen in  FIG. 9  a tool  56  is used to grab a segment of outer conductor  8 . In the illustrated process tool  56  is a needle nose pliers. The pliers is opened slightly and one jaw of the pliers is inserted into insulation layer  10 . Tool  56  is then closed and rotated causing the formation of tabs  58  and  60  on outer connector  8 . Tool  56  is then used to grip one of tabs  58  or  60 , the gripping of tab  60  being illustrated. Once this gripping is effected tool  56  is biased against tool rest  46  and rotated in the direction of arrow  62 . Prior to rotation the axis of tool  45  is angularly disposed to the axis of tearing collar  40  at a compound angle. One segment of this compound angle is controlled by the angle of tool rest  46  in relation to the axis of tearing collar  40 . The angle of tool rest  46  in relation to the axis of tearing collar  40  can be from about 15 to about 45 degrees with a more preferred range being from about 25 to about 35 degree with a most preferred angle being 30 degrees. 
   The rotation of tool  56  is continued until the tearing of outer conductor  8  is effected over 360°. Tearing is effected by the biasing of outer conductor  8  against tearing edge  50 . 
     FIGS. 11 and 12  illustrate the composite structure with tearing collar  40  attached after the tearing of outer conductor  8  is completed. As can be seen the tearing of outer conductor  8  against tearing edge  50  is effected with great precision. When the tearing is completed a section of insulation  10  protrudes from the structure with inner conductor  12  therein. These segments are then subsequently cut flush with outer conductor  8 . 
   In the tearing of outer conductor  8  a flange  64  is formed, this flange is very useful in connecting a connector to outer conductor  8 . The size of flange  64  must be minimal in order less it prevent the removal of tearing collar  40  off of the trimmed R.F. cable. 
   The size of flange  64  is affected by the clearance of outer conductor  8  in bore  44 . The clearance of outer conductor  8  in bore  44  can be from about 0.002 to about 0.030 inches, with a more preferred range being from about 0.005 to about 0.020 inches with a most preferred range being 0.008 to 0.015 inches with a clearance being 0.010 inches. 
   After outer conductor  8  is torn from cable  2  in accordance with the process and apparatus described above a post  66  of insulation layer  10  with inner conductor  12  therein remains protruding from cable  2 . This post can be trimmed by any convenient means such as trimming insulation layer  10  with a knife and then cutting inner conductor  12  with a specialized tubing cutter. 
     FIGS. 13 and 14  show a method for trimming post  66  with hand operated trimmer  68 . To trim post  66  mandrel  70  of trimmer  68  is inserted into inner conductor  12 . Trimmer  68  is then rotated in the direction of arrow  72  while pressure is applied in the direction of arrow  74 . This procedure causes blades  76  of cutter  68  to bite into post  66  thereby trimming both insulation layer  10  and inner conductor  12 . 
   This trimming of post  66  can be effected with tear collar in place. With tear collar  40  in place the composite structure can be gripped, during the trimming of post  66 , without danger of deforming outer conductor  8 . 
   Once the trimming of post  66  is completed tear collar  40  is removed and the coupling of opposing sections of flush cut R.F. cable sections is completed using a suitable connector. Various embodiments of connectors can be used, these connectors are not part of this invention. 
   As to these connectors it should be noted that this invention is highly advantageous as the O ring  52  which is used to seal the connector is used as a stop for tear collar  40 , thereby allowing precise placement for the tearing of outer conductor  8  at tearing edge  50 . 
   While O ring  52  is shown as a stop for tear collar  40  it is understood by one skilled in the art that other stops can be utilized. These alternate stops can be part of a connector system or they can be attached solely as a stop for tear collar  40 . 
   The above description and drawings are illustrative only since modifications can be made without departing from the present invention, the scope of which is to be limited only by the following claims.