Originally Posted by Joystiq

Valve has released a new patch for Portal on Steam, and the patch notes say only that it has "changed radio transmission frequency to comply with federal and state spectrum management regulations." A curious note, especially since Portal, as a computer game, doesn't actually transmit anything over the radio. That got the forum train a'moving on the Steam boards, and they eventually discovered that radios have been added to each level of the game which, when carried to the correct spots in each level, will tune in a series of coded messages. Connecting to all (or any, according to some reports) of the 26 messages in the game will supposedly unlock a new hidden achievement called "Transmission Received." At least, we think so -- as of this writing, no one seems to have unlocked it yet.

Originally Posted by Rock Paper Shotgun

Terrifyingly industrious members of the Steam forum have ascertained that some of the sound files contain hidden images, visible when run through a Slow Scan Television (SSTV) application.

Originally Posted by Rock Paper Shotgun

The latest is that they’ve been able to dial into an Aperture Science bulletin board and download a load of ASCII art. It’s quite clearly Portal / Weighted Companion Cube-related stuff, but it wasn’t giving much away. But then someone tried rotating some of it…