For anyone using a radio scanner or communications receiver, this reference will unlock a world of listening possibilities. Robert Kelty and James E. Tunnell have compiled a source of services, frequencies, callsigns, and user IDs on the 25 MHz to 2110 MHz radio spectrum. This work makes it easy for radio professionals and hobbyists alike to tune in and listen to the confidential communications of the FBI, Secret Service, National Parks, Forest Service, Drug Enforcement Administration, and other agencies.