A radio telescope was a device that used radio waves to observe the heavens. It was far more powerful than an optical telescope.
The radio telescope was officially invented in 1951. However, in 1911 Dr. Laurence Scarman invented a primitive form of this device, which he called a Marconiscope, which intercepted a signal from Mars.
The Fourth Doctor carried a pocket-sized radio telescope, which he used to detect and decode the signal when the Marconiscope was damaged. (TV:Pyramids of Mars)
A few years later, Dr. Louis French, a radio telescope director in Australia, developed and tested a radio wave accelerator in the hopes of making instantaneous contact with other planets. Instead, his device disrupted Earth's atmosphere, creating huge storms around the world, and devastated the planet Morrax. (COMIC: Is Anyone There?)