What is Modulation? Modulation is the conversion of an digitalsignal to a analog signal. Modulation is also the process of varying one waveform in relation to another waveform.
Process of Modulation Modulation Demodulation Modem Analog Modulated Signal Binary Data PSTN Modem PSDN Modem Server Client
Types of Modulation There are several forms of modulation Amplitude modulation (ex telephone, radio) Frequency modulation (ex high-fidelity radio, analog television) Phase modulation (ex wireless networks) Quadrature amplitude modulation (QAM), which combines amplitude and phase modulation (ex digital cable, HDTV, ADSL and Cable Modems)
AM deals with the volume or amplification of the signal. Amplitude (low) Low Amplitude (0) Amplitude (high) High Amplitude (1) 1 0 Amplitude Modulation (1011) 1 1 Amplitude Modulation
FM has to deal with the size or length of the wave rather then the volume of the signal. Wavelength Low Frequency (0) Wavelength High Frequency (1) 0 1 Frequency Modulation (1011) 1 1 Frequency Modulation
Phase Modulation Two types of waves are used Easier for electronic equipment to deal with phase differences In Phase (0) 180 degrees out of phase (1) 0 1 Frequency Modulation (1011) 1 1
Quadrature Modulation QAM uses two carrier waves, Sine and Cosine. Sine wave is out of sync with the cosine wave Uses multiple possible amplitude levels
References N6MB.pptx “Modulation” http://wps.prenhall.com/bp_panko_bdnt_6/52/13436/3439647.cw/index.html Business Data Networks and Telecommunications, 6/e; Panko, Raymond R. “More on Modulation” Module B pages 496-499