The goal of the transmitter is to convert the modulated signal into a signal that matches the transmission medium.

The goal of the transmitter is to convert the modulated signal into a signal that matches the transmission medium. Unless the fiber optic cable is the transmission medium,  the signal must be converted to light using the required optoelectronic circuits. If the transmission medium is not air, it will need to be converted to electromagnetic waves. Transducers are tools that convert mechanical energy into electrical energy in the form of vibration, pressure, and force changes. It functions as an input device that converts "information" into electrical energy. One such part is a piezoelectric system that can do this. This type of technology can also return electrical energy to mechanical power. When you do that, it looks like an output computer. The microphone becomes the input transducer and the speaker becomes the output transducer.  Modulation is the phase in which a carrier wave is modulated by a modulation system, whether it is frequency modulation or  amplitude modulation. This may include changing the  amplitude of the carrier depending on the data signal. You may also need to change the frequency depending on the information signal. Demodulation is the opposite of extracting useful information about a carrier. The source of the carrier wave is usually an oscillator circuit that produces a sine wave. Carrier waves have constant amplitude, frequency, and phase. The second wave that carries the information is usually superimposed on the carrier.