Transmitter
In communications and information processing, a transmitter (sometimes abbreviated XMTR) is an object (source) which sends information to an observer (receiver).
A transmitter is an electronic device which with the aid of an antenna propagates an electromagnetic signal such as radio, television, or other telecommunications.
A transmitter usually has a power supply, an oscillator, a modulator, and amplifiers for audio (AF), intermediate frequency (IF) and radio frequency (RF). Sometimes a device, for example, a cell phone contains both a transmitter and a radio receiver or transceiver. The modulator is the device which piggybacks (or modulates) the signal information onto the carrier frequency, which is then broadcast.
Broadcasting
In broadcasting, the part which contains the oscillator, modulator, and sometimes audio processor, is called the exciter. Confusingly, the high-power amplifier which the exciter then feeds into is often called the "transmitter" by broadcast engineers. The final output is given as transmitter power output (TPO), although this is not what most stations are rated by.
Effective radiated power (ERP) is used when calculating station coverage, even for most non-broadcast stations. It is the TPO, minus any attenuation or radiated loss in the line to the antenna, multiplied by the gain (magnification) which the antenna provides toward the horizon. This is important, because the electric utility bill for the transmitter would be enormous otherwise, as would the cost of a transmitter. For most large stations, the transmitter power is no more than 20% of the ERP.
de:Sendeanlage fr:Émetteur radio