Tuesday, March 10, 2020

How to install a PL-259 coax connector on LMR-400 coax.


     Every ham radio operator has little tricks to help him do things such as installing a PL-259 coax connector on a piece of coax cable.  I would like to share my method.
     First, I strip off about 1" of insulation from the end of the coax cable with a utility knife (aka box cutter).  Then I take a cable stripper and position it right in the middle of the exposed coax braid.  Put your finger in the loop and make 4 or 5 turns around the coax.  You should end up with about 3/8" of coax braid on the coax.  

     Now, get a small file and file off the nickel plating from around the 4 holes in the barrel of the connector.  I have found that solder does not like to stick to nickel very well.  

     Before you begin this next step, make absolutely sure there are no small wires sticking up near the center conductor of the coax.  If even one of those little whiskers gets in the wrong place, it can cause a short in the coax if it makes contact with the center conductor.   
      I have a very handy little tool that a good ham friend of mine made which consists of a PVC Tee and an SO-239 coax connector  glued into the middle hole.  Thread the coax connector on to the T with the connector's bezel.  Now carefully stick the end of the coax into the back of the connector.  Grab the T firmly with one hand and the coax in the other and twist the T toward you about 11 times until you feel resistance.  

     Now take the Tee off the connector and check to see that you can see the braid through the 4 holes in the barrel and check the center pin to see that the center conductor is poking through. 

     Now we are going to dab some soldering paste on the 4 holes in the connector barrel.  You can use any little stick such as a Q-Tip with the cotton cut off the tip to dab it on.  This step insures that the solder will flow down into the holes, creating a good seal.  This step is important because if those holes are not sealed, RF can leak out and cause interference to other components of your ham station.

     Next, we solder the center conductor to the center pin of the connector with my Weller 200 watt soldering gun.  I strongly suggest putting the coax in a vise but don't tighten it down too tight.  You don't want to damage the cable in any way.   The vise will keep the coax from turning while you solder.  

     Now, we solder the 4 holes in the barrel.  Position the coax connector so that the center pin is pointing to your left.  Now, position one of the 4 holes so that it is looking directly at you.  Make sure your soldering iron is up to operating temperature, then apply solder to the tip while holding the iron on the area just above the hole.  Now slowly drag the iron down over the hole and pull it away.  If the iron does not completely cover the hole, do it again.  If you are successful, repeat for the other 3 holes.  Let the coax connector cool off before removing it from the vise. 

     Next, we check continuity with a multimeter set to the OHMS setting so that when you hook the two leads together, the meter emits a beep.  Connect the black lead to the center pin and the red lead to the barrel of the connector.  If  NO beep sounds, then there are no shorts in the connection.  If there IS a beep, you will not be able to use that piece of coax.  You will have to cut the connector off and install a new one.   The last thing you need to do is scrape the brown rosin off the center pin of the coax connector with a knife then shine it up with some Scotch-brite.



   


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