If the carrier amplitude is influenced in a multiplier with a message signal without DC offset, an amplitude modulation with suppressed carrier is generated. This is known as the DSB-SC modulation.
DSB-SC modulation scheme:
Consider the scheme shown in Fig.1
Fig.1: DSB-SC modulation
- In fig. 1 m(t ) is a baseband message signal with M(f ) = 0 for f > W, c (t ) is a high frequency carrier, usually with fc >>W .
- DSB-SC modulator is basically a multiplier.
- Let gm denotes the amplitude sensitivity (or gain constant) of the modulator, with the units per volt (we assume that m(t ) and Ac are in volts).
- Then the modulator output s (t ) is,
- For convenience, let gm = 1. Then,
- As DSB-SC modulation involves just the multiplication of the message signal and the carrier, this scheme is also known as product modulation and can be shown as in Fig. 2
Fig. 2: Product Modulation scheme
- The time domain behavior of the DSB-SC signal (with Ac = 1) is shown in Fig. 3(b), for the m (t ) shown in Fig. 3(a).
Fig.3: (a) The message signal