Name : Rohit Das
Roll :28602820008
Sem: 7th Year : 4th
❑ What is modulation ?
• Modulation is the process by which information is encoded from a message
source in order to optimize it for transmission.
❑What is Frequency modulation ?
• Frequency Modulation (FM) is the encoding of information in a carrier wave by
changing the instantaneous frequency of the wave. FM technology is widely used
in the fields of computing, telecommunications, and signal processing.
❑ How Frequency Modulation works
• In FM, a radio wave known as the "carrier" or "carrier wave" is modulated in frequency by the
signal that is to be transmitted. The amplitude and phase remain the same.
When the audio signal is modulated onto the radio frequency carrier, the new radio
frequency signal moves up and down in frequency. The amount by which the signal moves up and
down is important. It is known as the deviation and is normally quoted as the number of kilohertz
deviation. As an example the signal may have a deviation of plus and minus 3 kHz, i.e. ±3 kHz. In this
case the carrier is made to move up and down by 3 kHz.
Broadcast stations in the VHF portion of the frequency spectrum between 88.5 and 108
MHz use large values of deviation, typically ±75 kHz. This is known as wide-band FM (WBFM). These
signals are capable of supporting high quality transmissions, but occupy a large amount of
bandwidth. Usually 200 kHz is allowed for each wide-band FM transmission. For communications
purposes less bandwidth is used. Narrow band FM (NBFM) often uses deviation figures of around
±3 kHz.
❑ Graphical representation of Frequency Modulation
➢ If we observe the graph, we will notice that
the frequency of a carrier increases when
the amplitude of the input signal is
increased. Here, the carrier frequency is
maximum when the input signal is at its
highest. Meanwhile, the frequency of a
carrier decreases if the amplitude of the
modulating signal goes down. What it
means is that the carrier frequency is
minimum when the input signal is at its
lowest.
❑ Frequency Modulation Equations
• FM signal can be represented mathematically as;
m(t) = Am cos (ωmt + Ɵ)
m(t) → modulating signal
Where,
Am → Amplitude of the modulating signal.
ωm → Angular frequency of the modulating signal.
Ɵ → is the phase of the modulating signal.
Such as amplitude modulation, when we try to modulate an input signal (information), we need a
carrier wave, we will experience
C(t) = Ac cos (ωct + Ɵ)
❑Applications of frequency modulation
• FM radio and music: Frequency modulation is widely used in radio broadcasting. It
is a wideband FM, and its frequency is much larger than that of AM. Due to its low
radio frequency interference, it is preferred to use FM to broadcast music on the
radio.
• Television sound: The video information in a television broadcast is transmitted
using AM, while FM is used for sound transmission due to low interference.
• Satellite TV: Some satellites use FM to broadcast video signals on the receiver’s
station.
❑ Advantages of frequency modulation :
• No limit for the depth of modulation
• Less prone to noise
• Give high fidelity reception has more number of useful side-band are present for
modulations
• High efficient as all of the transmitted power is too much useful
• Noise reduction
❑Disadvantages of frequency modulation :
• FM transmitter and receiver are more complex as well as costly
• Increases bandwidth
• Use too much spectrum space
• Sideband extend to infinity either side
• Require more complicated demodulator
❑ Conclusions
Frequency Modulation (FM) is an important modulation scheme both because of
its widespread commercial use, and because of its simplicity. As we have seen in
this document, frequency modulation can be simplified to angle modulation with a
simple integrator. As a result, we can generate frequency modulated signals with
the National Instruments vector signal generator, because they require nothing
more than an I/Q modulator.
