Unable to send LOW bits to RF Transmitter

I am using 433MHz RF Transmitter and Receiver in My Project.
I want to send ASCII Characters A,B,C and D from Arduino and Receiver will be connected to My PC. I have made GUI in MATLAB that will read that ASCII character and will show massage on GUI according to the character.
I just tested my Pair of RF using serial monitor by sending 0 and 1 bits to Transmitter. but the problem is that Receiver shows HIGH value when ever Transmitter DATA pin is connected to Arduino Pin. Receiver only gives digital LOW when DATA pin of Transmitter is OPEN. I tried connect DATA pin of Transmitter to ground but still Receiver gives HIGH Value.

And I also want ask about how I can send ASCII Characters using RF.

Forget about Matlab for the moment. These radios don't work the way you think they do.

I suggest to try the VirtualWire library, with two Arduinos.

Thank You for Your Reply I saw the Library and I will try working on it,