Question

In the equation x(t) = Re\([x_l (t) e^{j2πF_c t}]\), What is the lowpass signal xl (t) is usually called the ___ of the real signal x(t).

(a) Mediature envelope

(b) Complex envelope

(c) Equivalent envelope

(d) All of the mentioned

This question was addressed to me in semester exam.

The doubt is from The Representation of Bandpass Signals topic in section Sampling and Reconstruction of Signals of Digital Signal Processing

Answer 1

The correct choice is (b) Complex envelope

To explain I would say: In the equation x(t) = Re[xl(t)e^(j2πFct)], Re denotes the real part of the complex valued quantity in the brackets following. The lowpass signal xl (t) is usually called the Complex envelope of the real signal x(t), and is basically the equivalent low pass signal.