The Arduino Mega is receiving a message every 1/2 second. Note that the message has a checksum attached. This enables the module to check that the message has been received correctly. I use a 5v step-down voltage regulator, a 220uF capacitor and 1N4001 diode. The diode drops the voltage from 5v to around 4.5v, so it does not overheat the HC-12. The range of the device (using the wire antenna) is around 100m.to check transmission quality here.