nRF52840 Dongle matching network for ext. Antenna

[Aleksej]

Hi,

I'm about to develop a custom board with nRF52840 IC. For a first test I need an external antenna. I modified a dongle for a first proof of concept. I removed the antenna trace and soldered SMA connector on it. On the bottom side i connected the connector to the ground plane.

If I understand it correctly, I have to remove C4 and C26 for an eternal antenna design. On the development board, the C3 is 0.8pF and on the dongle it's 1pF. I think that would be ok for the first test.

Can somebody confirm, that the C4 and C26 have to be removed from the dongle, if I want to test it with external SMA connector?

[Quas7]

Just wanted to share an U.FL mod that worked for me very well to attach directional antennas. I used transparent UV soldermask after scratching off the solder pads for the connector. A bit hard to see in the pictures.

[BearRiver]

Greetings Quas7,

I was wondering how effective this application was and if it help up to your needs?. 

[Quas7]

It worked as expected with and I was able to locate smart tags with cheap aliexpress narrow beam high gain antennas by triangulation.

[BearRiver]

Great work. Happy to hear it worked. I am working on an application that requires the nRF to be outside and will go in a weather box. I was wondering if i could replicate this and use an Omni antenna. Would you mind sharing some details about what needs to be exposed on the board and anything else that worked for you during this project? Just for the antenna install..

[Quas7]

if I would do it again I would just solder a  pig tail SMA with thin cable and not use an UF.L port directly on the pcb.

Cable core to the thick "snaky trace" and disconnet the existing thin trace to the PCB antenna. Shield can go to the pad right next to it over the big "C" letter and act as a strain relief maybe.

I used a glassfiber scraper pen to remove the solder mask layer. But anything can be used to sand this down.