Everybody knows, the range of bluetooth modules varies. Original HM-10 modules for example, have quite a nice range. However, there are a LOT of clones floating around. Transmission ranges of many clones are extremely bad. So, how can you make them better?

Replace the onboard PCB antenna with a wire antenna!

The length of the wire should be 3.125cm, which is a lambda/4.
After you finish add a drop of hot glue to the solderspot, SMD pads are very sensitve and fragile, without fixating the joint, the antenna could lever the pad of the PCB and break it. So add hot glue or some other lacquer.

Solder the antenna to the capacitor