Modern buildings are being built with pre-installed wiring capable of digital transmission. At the same time, old buildings are being modernized in order to use benefits of digital transmission. However, some of them might be using telephone lines for internet access. Unfortunately, telephone lines can transmit only analog signals. If computer needs to access network through the telephone lines, the signal must be first converted to analog signal and converted back at the ISP’s access server. The device used for modulating digital signal to analog and demodulating it back is called modem.
Data modulation is a process of converting signal to be applicable for transmission over a communication path. The signal is combined of two waves – one is carrier wave – that has presets of frequency, amplitude, and phase. Carriers waves purpose is to convey information that is being transmitted in second wave – data wave. When two waves are blended (modulated) they are forming new analog signal that is ready for transmission. Predefined properties of the carrier wave allows data separation back in two waves at the receiver end.
There are two main types of data modulation:
Frequency modulation – data signal is applied to the carrier modifying its frequency;
Amplitude modulation – data signal is applied to the carrier modifying its amplitude;
Figure 1 shows carrier wave, data wave and the result of FM.
