Another step by step may be not necessary since it's just about soldering 2 wires, so I go with a photo album.
This alternative mainly shows a few differences:
- My transmitter's got hidden screw below black plastic cover. May be this model with 3 buttons always got this hidden screws?
- Instead of removing the capacitor (C2) near the antenna, I preferred to bypass it by soldering a small wire between antenna and closest connection (L1).
- You need to unsolder batteries connectors before being able to access the circuit board, then solder them again (many times for me) to test the new antenna (or maybe you can test with power-in connector?).
- I glued the antenna wire to the board because onboard "antenna" is fragile and a bend is enough to break it.
Some pictures are blurred because I don't have a decent macro camera, I switched to USB microscope but x20 is too detailed in this case.
Hope this helps other hacks! ;)