Radio transmitters were shortwave communications devices.
Keillor used a radio transmitter to contact Gavrok and inform him of Delta's location. Gavrok used a high impulse beam locked onto the signal to detonate the transmitter so he would not have to pay the informer. (TV: Delta and the Bannermen)
Research stations used radio waves for tests and often transmitted them into space to search for signs of intelligent life. In the 1970s, the Nestenes tried to materialise on Earth through radio waves at one station, but they were stopped by the Third Doctor and the Master. (TV: Terror of the Autons)