Making Crimp coax connectors for RG-213 & LMR-400
 

As of August 2009, much of the material on this page has been updated and repackaged into a PowerPoint presentation.

To download the package click here

February 09, 2010 -- LMR-400 (EZ400) crimp connector page added

 

Everything in radio is a learning process. The design and building of antennas is no exception. When the outside work is done and it's time to test the newest creation, one final step always remains -- the PL-259 coax connector. Having done my share of these, I always wondered about the mechanical integrity of the finished product. The application of heat in the process of completing the connector can have some devastating effects on even the best connectors.
 

This is a cross-section of a mil-spec silver barrel, gold tip and Teflon core 'solder-on' PL-259 connector. Look closely and you can the braid appears to have migrated somewhat with the application of heat. There also appears to be significant deforming of the braid. Would you really want 2 KW running through this connector?

So what's the answer to producing the absolute best PL-259 coax connector? For all commercial work, the standard is crimp-on connectors. The mechanical quality of these connectors is excellent and they are easy to produce.  The required tools are not that expensive, the connectors are similar in cost and the end product is perfect each and every time. Many well known DXer's and contest operators have all transitioned to these mil-spec silver/silver and Teflon crimp-on connectors for one-hundred per cent of their needs. Spend a few minutes and take a look at the process.
 

The terminology associated with coaxial cable



Note: the 'outer conductor' will be referred to as the "braid" in this document and
 the 'inner conductor' will be referred to as the "centre conductor"


The construction process

This series of images details the construction process from start to finish.
For best results, the steps must be executed in the order shown.
 


These are the basic tools. Key to the process in the
 top right is the crimping tool and in the bottom right
 is the Cablematic stripping tool. All items are available
 from a variety of mail order suppliers online.




This is the Cablematic DXE-UT8000
stripping tool for RG-8 and RG-213. It can be ordered
online from DX Engineering in Tools section

  
A simple, but important modification to this tool is required.
The tool has a *blind plug in the centre that needs to be drilled
 out before it can be used properly. Remove both cutting
 blades. Secure the tool in a vise. Use a new 3/16" drill bit
 and drill out the plug. The bore will be clear and
the tool will operate flawlessly. Replace the cutting blades.

*With the plug in place, the stripped length of the centre
 conductor is too short. The centre conductor bottoms
 out on the plug and becomes deformed as the tool turns.
 


RG58 cut length


RG-213 cut length
Note: these cut lengths are shown for information
 purposes only. The Cablematic tool cuts to the proper length.
 

Use good quality coax cable

 
Use good quality crimp connectors that are
SST (silver body, silver barrel with a Teflon centre)
 
 


Step #1
Slip a short piece (1½") of 3/4" shrink tubing
 and the crimp barrel onto the coax
 

Step #2
Using the "First Cut" end of the Cablematic tool, smoothly rotate the tool while applying even pressure towards the cable. All layers down to the centre conductor will be cut in this single step. About 10 turns of the tool should give you the correct length of exposed centre conductor. As you release cutting pressure on the tool, the cutting action will stop. 
Use non-slip gloves for a good grip on the tool and the cable.
 


Step #3
Here is the trimmed RG-213
 

Step #4
Using the opposite end of the Cablematic tool, trim
 off the jacket of the cable. The tool will stop automatically
 when the correct length has been trimmed off.
 


Step #5
The jacket has been fully trimmed off
 

Step #6
Using very sharp nippers, carefully trim
 back about 1/4" of the braid
 


Step #7
Carefully slip the connector onto the prepared coax
 and ensure the connector is fully seated. The braid
 should just meet the edge of the connector.
 
    
Step #8
Hold the assembly on a slight angle to solder the
 centre conductor. While you can crimp the centre conductor,
 a better mechanical connection is made if it's soldered.
It helps to have a vise or support for the soldering iron.
 


Step #8
Close-up view of the process
 
Step #9
After the solder has cooled, slip the barrel up to
the connector. Ensure the barrel is fully seated
against the end of the connector body.


Step #9A
Using the crimp tool, apply even pressure until the
 ratchet stops. Ensure the crimp tool sits very close
to the body of the connector
 

Step #9B
The finished crimp!
The next steps are beautification


Step #10
The excess centre conductor must be cut
 

Step #10A
Use line pliers to cut the centre conductor
 


Step # 10B
Apply even pressure in one cut
 
Step #10C
The finished cut should be just ahead of the connector tip.
Do not cut the connector.
 


Step #11
Slip the piece of 3/4" shrink tubing into place
 

Step #11A
Use a good quality heat gun to shrink the tubing.
Be careful not to apply too much heat.
See note below about the heat gun
 


Step #11B
With the right touch, the shrink
 tubing will run perfectly
 

Step #11C
Nearly done


Step #11D
Shrink is fully seated
 
Step #12
File off the rough end of the centre conductor


Step #12A
Use a small fine file for this process
 

Step #12B
Apply short even strokes while holding the connector
 


Step #12 C
The finished job with a little of the centre
 conductor showing beyond the connector
 
The finished connector!
This is a perfect connector in every way

Some connector construction and tool tips:

  • If you want to make very short (say less than 6") interconnect cables, start with a long piece of coax. Make the first connector on the long piece of cable, then cut to the desired length and make the second connector. This approach will prevent pulling the centre conductor or braid through the jacket of a short piece of coax.


     

  • Buy a good quality crimping tool. The unit shown above is the RF Industries RFA-4005. The crimp tool is sold with 2 dies that cover most popular cables. The kit contains: (1) RFA-4005-20, Crimp Tool Handle; (1) RFA-4005-01, Crimp Die Set for RG-58/U, RG-59/U,RG-142/U,RG-8/X, LMR-195, LMR-200, LMR-240 & Proflex Coaxial Cables; (1) RFA-4005-02, Crimp Die Set for RG-8/U, RG-213/U, LMR-400 & Belden 9. Note: The RF Industries RFA-4005 tool set can be purchased from a variety of suppliers or direct from RF Industries at http://www.rfindustries.com/
     

  • Make sure you have the correct die-set in the crimp tool for the type of coax cable you are using.
     

  • During Step #6 (as shown above) dry fit the connector a couple of times to ensure you have trimmed the correct amount of braid. It's easier to trim the braid at this stage as opposed to once you have the connector in place and the centre conductor soldered.
     

  • Once you have completed Step #6 and placed the connector on the cable, hold the (seated) connector firmly in place while soldering the centre conductor. It's important to have the connector firmly seated before you solder the centre conductor.


     

  • The Klein cable cutters shown above are the ideal tool for cutting coax. The tool cuts the coax without squashing the cable in the process. It also make a very clean end cut. Use caution working with this tool and make sure you know where your fingers are all the time.
     

  • The Cablematic DXE-UT8000 stripping tool can be ordered online from DX Engineering in Tools section. Consider ordering several sets of replacement blades when placing your order... there a very inexpensive.


     

  • The small side cutters shown above are the perfect tool for trimming braid from coax. Try to keep one of these cutters for only trimming braid, that will ensure the cutter is always sharp. Keep another one of these for flush cutting plastic tie wraps... it makes a very clean job.
     

  • The 3/4" shrink tubing used in the Step #11 of the assembly process is not really required -- it's purely cosmetic, but it makes a very professional looking finished product. Shrink tubing can be used as a means of color coding cables for different applications.
     

  • In Step #9B, resist the temptation to re-crimp (or crimp down) the raised portion of the barrel on the left. The raised portion is above the  jacket of the coax whereas the crimped portion is against or crimped directly to the braid. Do not crimp this small raised portion.
     

  • After Step #6 -- and before you begin Step #7, make sure you have no tiny fragments of braid laying on the dielectric or touching the centre conductor.
     

  • Crimp connectors are usually packaged individually in small plastic bags. If you are buying crimp connector inventory for several different types of coax, label the plastic bags to ensure you can tell the connectors from one another. Some of the connectors look very similar.
     

  • Always use the best crimp connector you can purchase. There is no such thing as good quality cheap connectors. The RF Industries brand of connectors are very reliable, their quality control is excellent and the technical support provided is superb. The connector demonstrated here (for RG-213 cable) is RFI part number RFU-507ST. The ST stands for silver Teflon.
     

  • Keep the entire connector assembly process as clean as possible.
     

  • The heat gun used is a Makita HG1100 with variable temperature output from 250 - 1100 F which is more than enough heat to handle any type of shrink tubing. For the shrink tube applications shown on this page, the gun is operated at about 500 F which gives a very even flow of heat for running the shrink. This is an industrial grade heat gun that will give many years of very reliable service unlike many hobbyist grade units.
     

  • If you're looking for information about connectors for LMR400 series cable, here are a few good links:
    - http://www.timesmicrowave.com/content/pdf/L400PN.PDF
     

A few final comments...

  • This process takes practice to perfect.

  • Working with the Cablematic stripping tool can be frustrating at first, but steady even pressure towards the centre line of the cable will yield nice results after a few test runs. For the best cutting action, the tool must be started square to the end of the cable and a little more pressure is required for the first couple of rotations. It takes practice -- do not be discouraged with your first attempts. Cut off the mess and start again.

  • IMHO, a crimp connector is far superior to any solder-on connector.

  • Yes I use these connectors for outdoor work... but like any connector they are very well sealed. Living here in the Pacific Northwest dictates that all outdoor antenna connections be waterproof.  A properly enclosed outdoor connector at my station starts with a piece of 1" shrink tubing over the entire connector. Next is the first layer of plastic tape (over the shrink tubing).. and it extends at least 1" beyond the ends of the shrink tubing. Next is a second layer of self vulcanizing 3M rubber tape -- applied in the opposite direction to the first layer of tape. Finally I add third layer of plastic tape in the opposite direction to the second layer of self vulcanizing 3M rubber tape.  To achieve the best results, gently stretch the tape during application to ensure all layers are very wrapped tightly. In so doing, the tape will mold to the shape of the connector.

    Some examples of weatherized outdoor connectors:




    I have not had or experienced any water or moisture contamination problems using this process. I do leave a small tab of tape folded over at the end of each layer -- that makes it easy to find the start point if I ever want to open up the connection.
     

  • If you have any questions after reading through this page or trying your hand at making crimp-on connectors, please click my email link below and I will try to help you.

All photographs in this series were taken with a Nikon COOLPIX 5700 digital camera (on a tripod).
My thanks to Jilly for her assistance during the production of this page.
   
   

Last modified February 09, 2010 by Paul B. Peters, VE7BZ
Copyright © 2000 -2006 Paul B. Peters, VE7BZ. All rights reserved.