I've now posted this loads of times! - you can't send standard RS232 via these radio modules - because they are AC coupled!. So a continuous high level (as provided by RS232 between bytes) will only last for a short time, then will breakup and go low.
By using software UART's you can invert the data, so you get a continuous LOW instead of a continuous HIGH - RS232 will then work. But it's not a good solution, you should investigate Manchester coding, or some other kind of NRZ system.