Modify Si4703 FM Tuner evaluation board to add an external antenna
Just came across another description of that same mod: http://www.electronic.lt/failai/news/2016/si4703_arduino/Si470x-Eval-v11_ant_mod.pdf

Electrically he did the same mod you describe. Not sure how he did it physically. You can:


cut the trace on the board
desolder C5, turn it by 180 degrees and solder the (formerly) right contact back to the right contact on the board (so the other is “dangling” freely)
desolder just the left contact of C5 and insulate it against the board


Then solder the antenna cable to the free (left) connection of C5, and solder the shielding to one of the ground connection on the board (e.g. the GND pin).



EDIT: Just found the manufacturer’s recommendations for adding various types of antennas: https://www.silabs.com/documents/public/application-notes/AN383.pdf

You might want to take a look at these. Unfortunately, antenna jacks are not covered, but I’d follow the procedures for a whip antenna.



If you want to improve reception, I highly recommend placing the whole board in a shielded and grounded enclosure. In my case (of a Si470x-based USB dongle, which I ended up wrapping in aluminium foil), that improved things by roughly the same level as going from a pigtail antenna to a proper cable.