2.1 Introduction Analog communication system The most common carrier is the sinusoidal wave. (Analog) Carrier wave
2.1 Introduction Modulation A process by which some characteristic of a carrier is varied in accordance with a modulating wave (baseband signal). Sinusoidal Continuous-Wave (CW) modulation Amplitude modulation Angle modulation
Sinusoidal carrier 2.1 Introduction Baseband signal Amplitude Modulation Frequency Modulation
2.2 Double-Sideband with Carrier or simply Amplitude Modulation Carrier c(t ) Ac cos(2f c ) Baseband m(t ) Modulated Signal s(t ) Ac [1 ka m(t )] cos(2f ct ), where ka is amplitude sensitivity or modulation index Two required conditions on amplitude sensitivity 1 + ka m(t) 0, which is ensured by |ka m(t)| ≦ 1. The case of |ka m(t)| > 1 is called overmodulation. The value of |ka m(t)| is sometimes represented by “percentage” (because it is limited by 1), and is named (|ka m(t)|100)% modulation. fc >> W, where W is the message bandwidth. Violation of this condition will cause nonvisualized envelope.