I’ve recently bought the MT300A on amazon and it was the internal-antenna version. I’ve noticed that there are uFL connectors on the PCB (contrary to what the store page says…) and I found uFL to SMA connectors on ebay. Would I be able to just plug-in such a connector and add external antennae? Would I have to disconnect the internal antennae in any way?
No. it is not uFL connector. It is for radio calibration. The uFL connector actually as a little different in the middle.
If you want to modify it it, you have to use a solder. Otherwise, just buy the external antenna version.
Do i have to remove any resistor or just to connect the external antenna?
Yes. Notice the C44 capacitor in this image of the CON2 antenna connector. Above and to the left of it are two empty pads. You need to un-solder the C44 capacitor and completely move it to those two pads and re-solder. Repeat for CON1.
This will be a fun project. I’ll write back with results.