Solder a SMA connector to a SX1276 LoRa Module

Thread Starter

Jwrede

Joined Mar 11, 2021
15
I have a SX1276 board that looks like this:
1618957160804.png
and I'd like to solder a standard SMA connector like this to it:
1618957273155.png
How exacly do I need to connect it and what are some potential mistakes I could run into, I've heard that there are problems if I e.g. connect too long wires to the connector it could reduce the transmission range.
 

Yaakov

Joined Jan 27, 2019
3,317
I should add that stripping the coax takes a little skill but it's not that hard.

Here's how I do it:

1) Gently bend the coax at the point where you want to remove the outer insulation. Make this somewhat longer than you need so you will have something to work with for the next step.

2) With an Xacto or similar razor knife very carefully saw into the outer jacket while flexing the cable. The goal is to cut through the plastic without knocking the braid underneath. The flexing will cause it to separate before oyu actually cut through. Rotate the coax and make the cut all the way around.

3) Get a fingernail in the cut groove and careful pull off the outer insulation while applying enough pressure with the fingernail to prevent the insulation from tightening on the cable like a finger trap.

4) Carefully push back the braid so it expands at the place where it meets the remaining insulation. It will be like a basket weave. With a very small screwdriver (preferably philips to avoid snagging) poke a hole in the weave and expand it.

5) Make the hole large enough that you can pass the screwdriver behind the center conductor and back then out of the hole again so you can pull it out of the braid. Do this carefully so you end up with a conductor and an empty braid.

6) Pull the braid down to reform it into a conductor and collapse the hole.

7) Cut it to length, strip the center conductor, and tin both it and the braid.

Because you are solder to .1 inch spacing, it will have to be very small but don't make it too small to work with. I might be inclined to put a header on the board and a connector on the coax. If you can do that, you should, otherwise solder them in place.
 

click_here

Joined Sep 22, 2020
260
Because the antenna and ground are so close together, I'd also just solder a 50ohm cable directly to the board with the SMA on the other end, rather than trying to doctor an SMA socket on the side.

Just pull some shielding back, and then twist it.

Make sure that the length that you pull back is as short as possible.
 

Thread Starter

Jwrede

Joined Mar 11, 2021
15
The best way for you to do this is to get a small piece of 50Ω miniature coaxial cable and solder it to the ANT and GND terminals. You do want to keep it short, but a few inches will be OK.

Better than the PCB mount connector would be a pigtail like this:

https://www.amazon.com/Pigtail-Antenna-Connector-Coaxial-Adapter/dp/B01J7S00PA

You can cut off the connector you don't need.
Thanks alot for the detailed answers! Actually I have some IPEX to SMA cables, that should work as well! So if I understand you correctly I should just wire it like this:
1618960142765.png
but with the middle pad to ant and the two outer pads are in my case ground right?
 
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