Serial communication stops when I connect the tx cable I'm using the apc220 rf modules. Now I'm having the following problem:

My receiving arduino uno only receives data when the tx pin on the arduino (rx pin on the rf module) is disconnected. As soon as I connect the tx pin my serial monitor receives only the value 0. 

Is my rf module broken, or can someone help me with this?
To have two serial ports on Arduino board like Uno use SoftwareSerial.h.

Example

#include &lt;SoftwareSerial.h&gt;

SoftwareSerial mySerial(2,3); // RX, TX

void setup()  
{
  // Open serial communications and wait for port to open:
  Serial.begin(9600);


  Serial.println("Hello!");

  // set the data rate for the SoftwareSerial port
  mySerial.begin(9600);
}

void loop() // run over and over
{
  if (mySerial.available())
    Serial.write(mySerial.read());
  if (Serial.available())
    mySerial.write(Serial.read());
}


Now after opening Serial monitor you should see Hello! and then you can test SoftwareSerial. 

DO NOT FORGET!!!

When you connect to pins 2,3 or etc, this is TTL voltage level. You can't connect direct to RS232.