Hi,
You cannot put an analogue voltage directly onto the pin of this module. The module is for digital data transmission, for example connecting two computer serial ports together.
Ideally you need a microprocessor with a analogue to digital converter to turn your voltage into serial data at the transmitter. At the reciver you can directly connect to a PC serial port or use another micro and a digital to analogue converter to get your signal back to a voltage.
It may be possible to convert you voltage to a variable frequency or Pulse Width Modulation (PWM) data stream an transmit that but it depends on the TX and RX you are using. I've not looked at the data sheets for the ones you have, but simpler ones work beast for this.
HTH Robert.