thank you for the reply..(good explanation)
follow-up Question
1.What does split ground mean? anyway im using ASK module, which i think its noisy, and i dont have any choice on adding some components, as it is a module.(except adding some capacitor on ground and supply)
http://spiriton.manufacturer.globalsources.com/si/6008800301304/pdtl/RF-module/1003362502/ASK-Regenerative-Receiver-Module-RF-Module.htm

According to the datasheet(not that complete), it uses same voltage as of the processor on the receiver side.

2. About the UART(2051), i read all the output(transmitter are off) and it outputed 00H that is:
....
mov a,sbuf
....
mov sbuf,a
and if i filter out the 00H that my code is:
mov a,sbuf
cjne a,#00,senddata
reti

the output changes to a random data. what im thinking is that(with-out filtering 00H), because i send my data and therefore have some delay on jnb TI,$, the mcu has time for some error checking on UART...not sure

and also, how do i communicate on a 2 buadrate? example would be, ill receive on a 4800 baudrate and send on 9800? does the timer on baudrate needs to have some delay? or do i need to stop my timer,interrupt before changing from Th1 value to another?

I found out some solution: that would be, my processor would work only on interrupt time. I did this because, my UART is always triggered(serial interrupt) and my processor could not do anything at that time, this approach work for me. And now, because im on interrupt mode only, my code are limited(tried and tested), can you suggest another approach?(still have problem)

if a suggestion on stopping the interrupt, i guest it will not work.