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I want to disconnect the PCB Bluetooth antenna and add a U.FL SMD for an external antenna.

Can someone please advise me what to cut/add/solder?

enter image description here

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  • \$\begingroup\$ I see no provisions for connecting an external antenna so any cut/add will be a "hack" and that means you will affect the characteristic impedance of the connection between antenna and transceiver IC. Despite such a mismatch it can probably still work but as the solution isn't optimized (not properly impedance matched) you will suffer from losses and reflections. In the end you might gain nothing and will probably suffer from worse performance than what you have now. \$\endgroup\$ Aug 20, 2020 at 14:01
  • \$\begingroup\$ If you want to use an SMD antenna properly (and get maximum performance) then you should change the PCB design and use the SMD antenna in the way that the manufacturer recommends. \$\endgroup\$ Aug 20, 2020 at 14:03

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As pointed out by Bimplerekkie, this is a hack, and might not be as efficient as the built-in antenna. But we can learn a lot from hacking, so why not try?

You can see a microstrip trace -- it's the wide PCB trace -- and it's probably about 50 ohms and would match the U.fl cable impedance well enough. There's a matching network halfway between the Bluetooth chip and the F-shaped antenna. Unsolder all the components from that cluster (I've marked in red). Next, scrape off the soldermask from the green patches, aiming for a footprint that will match the ground pads of the U.fl connector. Use flux, and tin the exposed ground pads, as well as end of the microstrip trace (blue square) where the matching network was removed. Put the U.fl connector on top, add flux again, and use a heat gun to reflow the solder. Pray. Try it!

U.fl hack

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