andriej:
Code works - the third interrupt gets data. But - again - strange thing happens...
It reads the code only when sensor is very,very near the Mega.
On Uno it read without problems from outside.I have no clue why it could happen now...
I can only guess the Mega is generating RF noise that interferes badly at 433Mhz. I'm not sure if you could test this by laying the Mega in a biscuit tin lined with something to prevent Mega shorting out and and lay the lid on top. Run the wires to the receiver outside of the tin. This wont stop all noise but may eliminate radiated RF. Beyond this you may need RF chokes but this is not my field and someone else may have better suggestions.