Radio waves were part of the electromagnetic spectrum which could only be detected with radios.
Pulsars emitted powerful beams of energy in the form of radio waves. (PROSE: Ghost Devices [+]Simon Bucher-Jones, Virgin New Adventures (Virgin Books, 1997).)
The Daleks could convert radio waves into light waves so that they could see anything that was happening around them, even millions of miles away. (COMIC: City of the Daleks [+]The Dalek Book (Dalek annuals, Souvenir Press, 1964).) One Dalek Emperor could read thoughts through radio waves. (COMIC: The Brain Tappers [+]Brad Ashton and Terry Nation, The Dalek Outer Space Book (Dalek annuals, Panther Books, 1966).)
In October 1963, Susan Foreman suffered from headaches caused by a hypersonic signal being transmitted over radio waves. (AUDIO: Hunters of Earth [+]Nigel Robinson, Destiny of the Doctor (Big Finish Productions, 2013).)
Professor Neob Frankel provided Kurt Wurlitzer with a rubber spacecraft which was designed to absorb radio waves. (COMIC: Operation Wurlitzer [+]TVC comic stories (1969).)
Star whales transmitted their song as radio waves. (AUDIO: The Song of Megaptera [+]Error: Code 2 - no data stored in variables, cache or SMW.)