Answer: It’s MICROPHONE
Explanation: from PF book
A transmission system at a radio station consists of these devices:
1. Anoscillator,whichconvertsadirectcurrentintoahigh- frequency alternating current
2. Atransmittingantenna,whichsendsoutradiowaveshavingthe same frequency as the current supplied by the oscillator
3. Amicrophone,whichpicksupthesoundwavesandconverts them into a suitable electric current with the same pattern as the sound waves
4. A modulator, which enables the waves produced by the antenna to “carry” the pattern of the sound waves picked up by the microphone