The Marconiscope was a primitive form of radio telescope invented in 1911 by Laurence Scarman. The Fourth Doctor was surprised by this, as the radio telescope was not officially invented for another forty years.
The apparatus featured numerous tubes, cylinders, and wires, as well as a revolving graph to record any signals detected. This machine, though relatively simple, was capable of picking up a distress signal transmitted from Mars. The signal was intended to warn listeners of the Osiran Sutekh, who had been imprisoned on Earth by his own people.
When the Doctor first met Scarman, the scientist was happy to demonstrate his new invention. When it picked up the signal from Mars, the apparatus overloaded and couldn't be turned off. It then burned out, at which point the Doctor produced a similar device from his pocket, in order to check and decode the signal. It proved simple to decipher as "Beware Sutekh".
The Doctor and Scarman managed to repair and reconfigure the Marconiscope to transmit a signal which blocked Sutekh's psionic control of Scarman's brother, Marcus. However, the signal only worked for a few seconds, since one of Sutekh's service robots smashed it beyond repair. The robot was deactivated by the electrical current from the machinery. (TV: Pyramids of Mars)