The problem of using a direct transmition of RS-232 into that kind
of radio is their filters. When
large qty of 111 and 000 are transmited
togoether the filters distort the signal
and you don't receive what you sent.
I reccomend you to encode in manchester
before tranmitting this eliminate this
problems. Look at radiometrix appnotes
I look a manchester app i think i have
if you want it let me know

Sergio