A transmitter can be a separate piece of electronic equipment, or an electrical circuit within another electronic device. A transmitter and a receiver combined in one unit is called a transceiver. The purpose of most transmitters is radio communication of information over a distance.
In the world of process control, a Transmitter is a device that converts the signal produced by a sensor into a standard instrumentation signal representing a process variable being measured and controlled.
A transmitter is a different kind of antenna that does the opposite job to a receiver: it turns electrical signals into radio waves so they can travel sometimes thousands of kilometers around the Earth or even into space and back.