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?

[Kaja]

Hi,

if you want to change out the pcb antenna with an external antenna, you still need to have C3, L1 and C4 on the board because this is the matching components for the radio. Changing the impedance of the radio to 50 Ohm. 

C25, R1 and C26 is matching components for the antenna, if you change out the on board antenna with the external antenna, and you connect the SMA connector to the 50 Ohm transmission line, you should be okay without matching components as long as the SMA connector and the antenna has a 50 Ohm impedance.

Best regards,

Kaja 

[Aleksej]

Hi Kaja,

Many thanks for the fast response and clarifying, which components are for which matching.

[Kaja]

Your welcome! 

And we are always happy to do HW reviews of your customs designs. 

Best regards,
Kaja