During launch there are rescue teams standing by at two different sites in Europe and/or Africa. These sites are called TAL sites. At these Transoceanic Abort Landing (TAL) sites medical teams are preparing for the worst. About a week prior to launch you can pick up communication from these teams as they travel from the US to the TAL sites. The week before launch they do a lot of radio checks on UHF SatCom satellites. All the TAL traffic is FM modulated.
You can read more about these TAL sites here.
PATRICK AIR FORCE BASE, Florida -- The crew of "King 2", HC-130 rescue aircraft from the New York Air National Guard's 106th Rescue Wing, gather for a group photograph on Monday, May 11, as they wait for the launch of the Space Shuttle Atlantis. This mission marked the 100th time that Airmen from the Long Island wing provided rescue support to Space Shuttle launches. Joining the HC-130 crews from Gabreski Field Air National Guard Base at Westhampton Beach, New York, were pararescuemen from the California Air National Guard's 131st Rescue Squadron, based at Moffett Federal Airfield, located near Mountain View, California. If the shuttle crew had been forced to leave the spacecraft near the Kennedy Space Center these men would have been responsible for pulling the astronauts from the water.
Below are the recordings I have made since I started out in 2007.