Recently I needed to join some lengths of RG316 antenna cable following an office move. This cable is used for a mobile phone repeater/booster on the input side and where it was wired into the building, the N-type plug had been fitted afterwards and was too large to pull out through the hole in the wall and the cable had to be cut.
After looking online and not really finding much useful information for this very thin cable I thought I’d detail what I did to make it work.
I started by cutting off the plug end, but leaving about 18 inches of cable just in case it went wrong then I had some extra cable to work with. Once you’re ready to reattach it in it’s new location, I stripped about 1.5 inches of the outer insulation from both ends to be joined, being careful not to damage the braid/shield conductor.
Next, you’ll want to push the shielding back to expose the inner core, it may be tight and not move easily but with a bit of a wiggle I was able to do this.
Take some suitable size heat shrink tubing that is large enough to fit over the outer cable and slide that on before we go any further. Then, cut off about a quarter of an inch of the inner core on one side and strip a small amount of insulation from both inner cores. Take a piece of very thin heat shrink tubing and cut it to a suitable length to put over the inner core to cover your join and then solder the core, slide the tubing over the join and heat it up to shrink it on.
We’re almost done now. Push the braiding back over the inside join, if you have cut the lengths right there should be an overlap of about a quarter of an inch on the braiding and both sides of it should ‘mesh’ together in the middle. Now carefully, you want to solder the outside of these braids together, I’d suggest doing it in small spots and don’t hold the soldering iron on it for very long otherwise you’ll end up melting the heat shrink tubing in the inner core. If you’ve got good quality cable and solder it should work easily and the solder will flow nicely around the braid to create a very good joint.
Finally, slide the larger heat shrink tubing we put on earlier over the whole join and heat it up to shrink it which will protect the join and help strengthen it.
It’s important that you join the cable in this way so that the braid surrounds the join. Many people would just twist up the braid and join both the braid and inner core using a screw terminal block but this is very bad for the signal and makes is susceptible to a lot of external interference. When we are working with cellular or otherwise very weak signals this would make it very problematic. After what I have done here, we have a 30 meter length of cable from the antenna to the booster box and we are receiving a full 5 bars of signal on the input side which is very good considering the length of the cable run and goes to show that using good quality cable along with quality fittings can really make or break a job.
I wish I had taken some photos along the way when I was working on this but hopefully you can work out what I am trying to explain here. As always, if you have any questions please feel free to let me know in the comments.