Complete the chamber up to the point where the Chamberlock door opens.
Fire a portal through the door at the wall or floor in the secondary room.
Next throw a cube through the orange portal.
If you are unable to get the perfect momentum and angle to throw a cube through the portal use this method:
Grab a cube and jump up at the platform with the orange portal and without letting the cube go get it on the platform.
Attempt to move the cube through the orange portal.
If done correctly GLaDOS will say "You’re not a good person. You know that, right?", the Chamberlock will be opened and both buttons will freeze, making them unpressable.
Once entering the Chamberlock the game will resume.
Radio location
The radio in this level is located behind the door. Place a Cube on one of the buttons and stand on the other. Then shoot a portal under the radio to move it into the main chamber. To gain progress on the Transmission Recieved achiement, you need to bring the radio to the pit at the back of the chamber.
