Amateur Radio

How-To

How To Install a Male SMA connector on RG-58

The Problem

I've got a small mag-mount antenna which I have always used with an HT and it works fine except for one problem. The antenna has a crimp-on PL-259 connector (shown right) which has gotten damaged and the radio has an SMA connector. I've decided to kill both birds with one stone and replace the crimp-on PL-259 with an SMA connector (shown below).

SMA Connector

The connector I am using consists of three parts. The crimp ring, connector and center pin. Without all three parts I can't hope to assemble the connector.

Tools and Materials Needed

To install the SMA connector I have, it requires a few tools and materials.
  • SMA Connector
  • RG-58 Coax
  • Utility Knife
  • Soldering Iron
  • Rosin Core Solder
  • Crimper with die suitable for RG-58

Optionally I am using:
  • 1/4 Inch Heat Shrink Tubing
  • 3rd Hand Tool
  • Tape measure
  • Scissors or Fine Cutters (Not Shown)

* Heat Shrink and Crimp Collar *

Before you start stripping the cable you must first place the Heat Shrink Tubing (Optional) and the Crimp Ring onto the coax. Do this now so you don't have to disassemble the connector later when you realize you forgot to do it before you started.

Strip Coax

You will need to strip a little more than 1/2 Inch of the outer jacket of the coax off. Use your utility knife to very gently cut through the outer jacket of the coax taking care to not cut the shield wires.

Spread Shield and Strip Center Conductor

Carefully spread the shield braid so the wires go straight out like a cone. Leave the braid intact at this point, but carefully strip the plastic insulator that is around the center conductor. Expose aproximately 1/4 Inch of the Center Conductor.

Trim Braid and Solder Pin

First use your utility knife or scissors to trim the outer shield braid so that it is roughly as long as the center conductor insulator. You also need to insert the center conductor into the center pin and solder it in place. On my connector there is a little window (arrow) that will show you the solder has flowed into the pin correctly.

Insert Pin into Connector

Fold the braid back to make sure it does not go into the connector as you insert the center pin and insulator into the connector.

Verify Pin

Verify the pin is sticking well out of the connector to ensure it is properly inserted. Make sure there are not any stray wires from the shield stuck in the connector.

Test Fit

Next I like to screw the connector down onto an actual SMA Female connector to make sure the center pin is set to the correct length. Normally I have the pin pushed too far though, and this allows it to move to the proper length. I also verify the length between the outer jacket and the back of the connector. The picture to the left shows there is too much distance between the connector and the outer jacket so I will have to shorten the center conductor. The Female SMA connector I am using is a PL-259 to SMA Female adapter.

Verify Pin

As you can see the pin does not stick out as far as it did before the test fit. There should be a little lip inside the connector on the pin that is now flush with the plastic insulator inside the connector.

Fold braid over connector

Fold the braid over the connector and fit the crimp ring. As you can tell, the outer jacket is not close enough to the connector which can make the crimp weak. Slide the connector off, unsolder the center pin and trim the center conductor.

Trim center conductor

This is how much I trimmed from the center conductor after I unsoldered the center pin. Resolder the center pin and re-insert into the connector.

Check Fit

Snug up the connector and verify it fits correctly. Now you can see the connector is properly fitted to the cable and I'm ready to crimp the outer shield.

Check Shield

As you can see, the shield wires are too long. They should just reach the back of the connector so when the connector is crimped they don't stick out the side. This needs to be trimmed.

Check Shield

Now the shield wires are properly trimmed.

Ready to Crimp

Slide the crimp ring all the way to the connector so it sits flush. No wires should be sticking out, and there should be as much outer jacket inside the connector as will easilly fit.

Position Crimper

Position the crimp ring and connector in the jaws so that the jaws will only crimp the ring. You want the ring and the jaws as close to the connector as you can get them without actually damaging the connector.

Crimp

Grip the crimper and squeeze all the way until the jaws touch. Most crimpers will have a ratchet system so they will not release until you have fully closed the jaws. As you can see the jaws are not as long as the Crimp ring.

Connector Crimped

This shows how much of the jaws were in contact with the connector. You can stop here or you can continue to get a neater looking connector.

Fully Crimped

I like to crimp the rest of the crimp ring down so it as as much contact with the cable and the connector as possible. This gives you a stronger connection that is more resistant to being pulled out.

Position Heat Shrink Tubing

Now slide the heat shrink tubing up to the back of the connector so that it will cover the crimp and the back of the connector. This will help to weather seal the connector as well as provide some strain relief.

Shrink Tubing

Apply heat using either a lighter or a heat gun to shrink the tubing fully. This will form fit the back of the connector to seal it up.

Finished!