problem with rf transmitter and receiver

hi
i am using RF transmitter SM TX 01 and receiver SM RX 04
i have connected TXD of 8051 to transmitter module and RXD of 8051 to receiver
and my program is
On transmitter side
-->sending 0x0f to SBUF
on receiver side
-->i just transfer the values from SBUF to LEDS
but i doesn't works...can anyone help me to check out this module
thanks in advance