INTrODUcTION Modulation is the process by which some characteristics of a carrier is varied in accordance with a modulation wave . Modulation is the process of putting information onto a high frequency carrier for transmission (frequency translation). such a modification is achieved by mean of a process called modulation .
In the modulation process, the baseband signle is called “modulating signal” and anther higher frequency signal is called as the “carrier”. The carrier signal will carry the modulating signal to the destination.
DIffereNT Of MODULATION MeThOD Analog modulation - The modulating signal and carrier both are analogue signal. TYPES : Amplitude modulation (AM), Frequency modulation (FM), Phase modulation (PM)
Digital modulation - The modulating signal is a digital signal , but the carrier is an analogue signal. TYPES : Amplitude Shift Keying (ASK), Frequency Shift keying (FSK), Phase Shift Keying (PSK)
AMpLITUDe MODULATIONAmplitude Modulation is a process of changing the amplitude of a high frequency carrier signal in proportion with the instantaneous value of modulating signal (information). Amplitude Modulation is the simplest and earliest form of transmitters.
OverMODULATION When the modulation index is greater than 1, overmodulation is present
MODULATION INDex fOr MULTIpLe MODULATINg freqUeNcIesTwo or more sine waves of different, uncorrelated frequencies modulating a single carrier is calculated by the equation: 2 2 m= + • m m +• • 1 2
fULL-cArrIer AM: freqUeNcy DOMAIN Time domain information can be obtained using an oscilloscope f usb = f c + f m f lsb = f c − f m Frequency domain information can be calculated using mE c Fourier methods, but E lsb =E usb = trigonometric methods are 2 simpler and valid Sidebands are calculated using the formulas at the right
BANDwIDTh• Signal bandwidth is an important characteristic of any modulation scheme• In general, a narrow bandwidth is desirable• Bandwidth is calculated by: B = 2 Fm fc-fm fC fc+fm 2fm
AppLIcATIONs AMpLITUDe MODULATION AM applications include broadcasting in medium- and high-frequency applications, CB radio , and aircraft communications