FPV Repair Shop #3 – Damaged antenna cable

The antenna on my drone sticks out a little too much. After a few crashes the insulation on the coax cable as well as some of the shielding got damaged.
In this article I’ll fix the antenna cable and shorten it to make it less prone to hitting objects and the ground.

How bad is it?

Not that bad, but if I keep flying like this, the antenna would get even more damaged, risking it breaking completely, causing me to lose video mid-flight and probably crash hard.

How to repair an antenna

This specific antenna has a crimped RP-SMA connector, so it can’t be removed from the cable without damaging it. I also don’t have a crimping tool for this type of connectors, so reinstalling it would be impossible.

I decided to replace the connector with a soldered one and cut the cable after the point where it’s damaged.
Conveniently, shortening the cable is beneficial and would make it not stick out above the battery.

Cut and Strip Cable

The coax cable has a solid copper core, insulation layer and a shield mesh.

The core needs to go into the center pin of the connector so it needs to stick out from the shielding.
The shielding needs to be soldered to the connector body so it has to be exposed.

3 cuts need to be made:
– A cut all the way through. This cut will determine the overall length of the cable.
– A cut through the shielding and the insulation, leaving the core intact and sticking out about 5mm. It’s very important not to damage the core as it would make a weak spot that might break when flexing.
– A cut through the outer insulation. Again, careful not to cut the shielding. There needs to be a bit more shielding exposed than what is inserted to the connector so be able to solder it once it’s inserted.

Solder Connection

The connector comes with as two parts. The connector itself with the threaded nut and body of the connector and a center pin (either a pin or a tube, depending if it’s SMA or RP-SMA).

The core of the cable fits into the pin and soldered or crimped to it.

Then the cable with the pin on it fits into the connector itself. The shielding needs to be soldered to the outer ring of the connector. Flux and a decent soldering iron really helps here.
Careful not to solder the nut to the ring.

Heat Shrink

For insulation and protection, heat shrink is essential.
I used heat shrink that has hot glue on the inside, which melts and bonds to the cable once heated.

The End Result

Here is a comparison between a new RP-SMA lollipop antenna and the shortened one.

Recycling

The original removed connector is still usable, there’s nothing really wrong with it apart from having a really short cable connected to it.

I decided to turn it into an adapter instead of throwing it away.
I took another solderable connector and followed the same steps as before.
Here’s the result.

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