In practice, the analog multiplication operation is difficult and expensive. For this reason, in amplitude modulators, it is necessary to find some alternative to multiplication of m(t) with cos(wt). Fortunately, for this purpose, we can replace multiplication with switching operation. A similar observation applies to demodulators. In the scheme depicted in the period of the rectangular periodic pulse x(t) is T= 2p/w(c) . The bandpass filter is centered.