Date Added: Jan 2013
The selection of the particular modulation method used is determined by the application intended as well as by the channel characteristics such as bandwidth as susceptibility of the channel to fading. When radio communication in intended it must take account of antenna characteristics. When data transmission using a telephone channel is intended it take account of the fact that the channel may not transmit dc and low frequencies because of transformers which may be included in the transmission path. In each of these situations, a modulator at the transmitter and, at the receiver, a demodulator to recover the baseband signal. Such a modulator demodulator combination is called a MODEM. The Modulation techniques are of two types one is Analog and another one is Digital modulations.