GoingForGold:
I have a lot to think about, thanks. I don't want to let the Arduino produce the pulse, because it also has to deal with several interrupts. With every interrupt there will be some calculations, and I'm afraid this will mess up the pulse, making it useless for the receiver. And since the moment of transmission is relevant, I do not want to have it sent multiple times.Or is this no problem after all? Of course, I wont use any delay()s.
You can generate the signal in hardware, it uses no CPU.
If you have enough time left over to toggle a 555 timer then you have enough time to turn the signal on/off.