Modulation & Demodulation(MoDem)

Modulation: the process of transforming digital information (1’s an 0’s) into analog (perceived as sound) signals. In the case of modems, capable of being transmitted over telephone lines. The aim of digital modulation is to transfer a digital bit stream over an analog communication channel, for example over the public switched telephone network (where a bandpass filter limits the frequency range to 300–3400 Hz) or over a limited radio frequency band.

Types of Modulation

1. Amplitude modulation(AM): With the changes in main signal amplitude, the carrier signal also change its amplitude.
2. Frequency Modulation(FM): With the changes in main signal amplitude, the carrier signal change its frequency.
3. Phase Modulation(PM): With the changes in main signal amplitude, the carrier signal change its phase.

Demodulation: the process of transforming analog signals, previously modulated, back into digital information. Demodulation is extracting the original information-bearing signal from a carrier wave. A demodulator is an electronic circuit (or computer program in a software-defined radio) that is used to recover the information content from the modulated carrier wave. There are many types of modulation so there are many types of demodulators. The signal output from a demodulator may represent sound (an analog audio signal), images (an analog video signal) or binary data (a digital signal).

MoDem

Modem is short for modulator-demodulator. A modem is a device or program that enables a computer to transmit data over, for example, telephone or cable lines. Computer information is stored digitally, whereas information transmitted over telephone lines is transmitted in the form of analog waves. A modem converts between these two forms.