transmitter

noun

a person who transmits
a thing that transmits; specif.,
1. the part of a telegraphic instrument by which messages are sent
2. the part of a telephone, behind or including the mouthpiece, that converts speech sound into electric impulses for transmission
3. the apparatus that generates radio waves, modulates their amplitude or frequency, and transmits them by means of an antenna

See transmitter in American Heritage Dictionary 4