Find the hidden signal in one of the Rat Man's Dens
This is another achievement/trophy that you can get in Chapter 2, test chamber 6. When you press the button to release the cube, a bunch of trash will fall out including a radio. You want to grab the radio and then enter the opening to the right of the angled platforms. Once you grab the radio, toss a portal on the higher angled platform and one up high on the wall to the left of the angled platform, across from the opening. Head back to the beginning with the radio and then launch off the kicker and fly through, entering the office. Take the radio to the far end of the room and the transmission will begin.
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