GoingForGold:
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.
That troubles me. Since you have not actually explained to us what else you are proposing to do, we cannot definitively pontificate on this, but interrupts involving "some calculations" sounds like a fundamental design misunderstanding in the overall use of interrupts.