Radio transmitter
From Tardis Wiki, the free Doctor Who reference
Radio transmitters were shortwave communications devices.
The Doctor altered a normal Radio so that it could be a transmitter instead of a receiver. (DW: The Sea Devils)
Ivo used a radio transmitter to contact the rebels despite the Three Who Rule's ban on advanced technology. He hid it in a podium. (DW: State of Decay)
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. (DW: Delta and the Bannermen)
