Any analog modulated signal (AM, FM
or PM) can be described by the following expression:

The Current in the network excited by u(t):

Any modulated
signal can be broken into orthogonal components.

One can show
that general expression is equal to the
REAL part of the phasor expression,
where phasor of carrier frequency f_{c} has a complex
envelope.

If the
network is excited by modulated signal,
all currents and voltages in the network will be also modulated.

In a general
way->>
we can express them again
by the complex phasor form.