Consider two sinusoids, or cosinusoids, cos (mt) and cos (wt). A double sideband suppressed carrier signal, or DSBSC, is defined as their product, namely:
Generally, and in the context of this experiment, it is understood that:
Equation (3) can be expanded to give:
Equation 3 shows that the product is represented by two new signals, one with a frequency that is the sum frequency (w+m) and the other with a frequency that the difference (w-m)- see Figure 1. Remembering the inequality of equation (2) the two new components are located close to the frequency ω rad/s, one just below, and the other just above it. These are referred to as the lower and upper sidebands respectively.
These two components were derived from a carrier term with a frequency of w rad/s, and a message with a frequency of m rad/s. Due to the absence of the carrier component in the product signal, this product signal is described as a Double Sideband Suppressed Carrier (DSBSC) signal.The term carrier comes from the context of double sideband amplitude modulation (commonly abbreviated to just AM). AM is introduced in a later experiment (although, historically, AM preceded DSBSC). The time domain appearance of a DSBSC (equation. 1) is generally as shown in Figure 2.