I'm using the following two rf433 modules in combination with two Arduino Unos.
After testing them both at 5V (in combination with the RadioHead library), which worked, I decided to test the improvement in the range, while powering the transmitter with 12V (I'm using an external power supply). This answer suggested that a NPN transistor can be used to provide enough voltage for a logic HIGH (I tried connecting everything as depicted on that picture). I used a RFP30N06LE MOSFET and wired everything as depicted in the picture below:
After a minute or so, I noticed that two wires started to melt, so I quickly disconnected everything. One wire is the orange one, connecting the drain of the MOSFET with the DATA pin of the transmitter, the other one is the ground wire from the source of the MOSFET to the GND. I also noticed that the MOSFET got quite hot.
Can someone explain what I'm doing wrong? Thank you.
**EDIT:**As @Andy aka suggested, the data pin doesn't need level shifting. Upon removing the MOSFET and both resistors from the circuit the transmitter is now working at 12V. The grounds of the external power supply, the transmitter and the Uno have to be tied together.