Frequency Modulation
(FM) Fundamentals
What Is Frequency Modulation?
 Frequency modulation is a technique or a process of encoding information on a
particular signal (analogue or digital) by varying the carrier wave frequency in
accordance with the frequency of the modulating signal. As we know, a modulating
signal is nothing but information or message that has to be transmitted after being
converted into an electronic signal.
 Much like amplitude modulation, frequency modulation also has a similar
approach, where a carrier signal is modulated by the input signal. However, in the
case of FM, the amplitude of the modulated signal is kept, or it remains constant.
Frequency Modulation
Equations
Frequency modulation equations mainly consist of a sinusoidal expression with the
integral of the baseband signal that can be either a sine or cosine function.
It can be represented mathematically as;
m(t) = Am cos (ωmt + Ɵ) ……………… 1
m(t) → modulating signal
Where,
Am → Amplitude of the modulating signal.
ωm → Angular frequency of the modulating signal.
Ɵ → It is the phase of the modulating signal.
Same as amplitude modulation, when we try to modulate an input signal
(information), we need a carrier wave, and we will experience
C(t) = Ac cos (ωct + Ɵ) ………….. 2
Angular modulation, which means ωc (or) Ɵ of the carrier wave, starts varying
linearly with respect to the modulating signal, like amplitude modulation.
Expression for Frequency Modulated
Wave
As we know, from amplitude modulation, we need two sine (or) cosine waves for
modulation.
m(t) = Am cos (ωmt) and
c(t) = Ac cos (ωct)
or
m(t) = Am cos (2π fmt)
c(t) = Ac cos (2πfct)
Then frequency modulated wave will be:
fm(t) = fc + k Am cos (2π fm t )
fm (t) = fc + k m(t)
Where,
fm(t) = is frequency modulated wave
fc → frequency of the carrier wave
m(t) → modulating signal
k → proportionality constant
What are the 3 basic components of a
frequency modulated FM system?
Frequency Demodulation
When there is modulation, usually, we need to successfully
demodulate it and, at the same time, recover the original
signal. In such cases, an FM demodulator, also known as
an FM discriminator or FM detector, is used. While there are
several types of FM demodulators, the main functionality of
these devices is to convert the frequency variations of the
input signal into amplitude variations of the output signal.
The demodulators are used along with an audio amplifier
or possibly a digital interface.