Ring Modulation

Ring modulation (RM) (e.g. beat note): modulator is applied directly to the amplitude of the carrier:

$$x(t) = \cos(2\pi f_\Delta t)\cos(2\pi f_ct).$$

Results in the sum of sinusoids:

$$x(t) = \frac{1}{2}\cos(2\pi(f_c-f_\Delta)t) + \frac{1}{2}\cos(2\pi(f_c+f_\Delta)t),$$

Figure 5: Spectrum of ring modulation.

Neither carrier nor modulator are in the spectrum.

Sometimes called double-sideband (DSB) modulation because of 2 produced sidebands.