What's the probable reason for noise?

i am trying to interface microcontroller with pc serially via rf transmitter-reciever. but i an getting lot of noise. infact most time i am getting only noise. i am using two rf transmitter-reciever pairs of 433 and 313 mhz to make full duplex. i using standard max232 circuit but with capacitors of 1.1 uf instead of 1 uf. can anybody tell whats the probable reason for noise
MOD: Note that your subject was too short. I have corrected it as your querry has already got 7 replies. Next time do write the heding in detail to avoid your querry going to the trash.

Where is the noise? At the receiver output or MAX232 output?

Keith

at the reciever i suppose. because it recieves junk data even if i remove transimmter from otther end

Added after 10 minutes:

noises are considerably reduced and sometimes completly eliminated if i directly connect max232 module with mcu through wires instead of through rf modules.

It's normal operation with a simple receiver that don't implement a link protocol. Simple transmitter/receiver pairs are not
necessarily suited to transmit raw UART data without additional encoding (typically Manchester encoding is used). That's
because the AC coupled AM or FM receiver only works with duty cycles around 50%. Also start synchronisation is an issue.

Having still noise with a direct link suggests, that's something really bad with your design.

You don't say what the transmitter and receiver are, but if the receiver has an RSSI output you will be able to tell if it is receiving the carrier.

Keith

i tested output of reciever by manually controlling data pin at transmitter, it works fine. also on reducing baud rate noise also reduces.

this is correct due to change in baud rate case to tweak the filter also, hence reduce in the noise level.

what should i do now? i am using it at 100 bps. should i decrease it further?