NAME:R.MANJUSHREE
REG.NO:19056UEL07
ANGLE MODULATION
Angle Modulation is the process in which the frequency or
the phase of the carrier varies according to the message signal.
This is further divided into frequency and phase modulation.
Thus a modulation system can be classified as follows:
Frequency Modulation:
 Frequency Modulation is the process of varying the
frequency of the carrier signal linearly with the message
signal.
 The amplitude and the phase of the carrier signal remains
constant whereas the frequency of the carrier changes.
The frequency of the modulated wave remains constant as the carrier
wave frequency when the message signal is at zero. The frequency
increases when the message signal reaches its maximum amplitude
Mathematical Representation:
fi=fc+kfm(t)fi=fc+kfm(t)
Where,
Fc- is the carrier frequency
kt- is the frequency sensitivity
m(t)m(t) is the message signal
Equation of FM:
s(t)=Ac cos(2πfct+βsin(2πfmt))s(t)=Accos⁡(2πfct+βsin⁡(2πfmt))
Where,
ββ = modulation index =Δf fm=k fAm fm
Narrowband FM:
the features of Narrowband FM.

This frequency modulation has a small bandwidth when
compared to wideband FM.

The modulation index ββ is small, i.e., less than 1.

Its spectrum consists of the carrier, the upper sideband and the
lower sideband.

This is used in mobile communications such as police wireless,
ambulances, taxicabs, etc.
Wideband FM
the features of Wideband FM.

This frequency modulation has infinite bandwidth.

The modulation index ββ is large, i.e., higher than 1.

Its spectrum consists of a carrier and infinite number of
sidebands, which are located around it.

This is used in entertainment, broadcasting applications such as
FM radio, TV, etc.
Advantages
Disadvantages
Less interference and
noise.
Equipment cost is higher. Has a large
bandwidth.
Power Consumption is less
as compared to AM.
More complicated receiver and
transmitter
Adjacent FM channels are
separated by guard bands.
The antennas for FM systems should
be kept close for better
communication.
Phase Modulation (PM):
Phase modulation is another type of angle modulation in which the
phase of the carrier wave is changed according to the amplitude
(magnitude) of the message (modulating) signal.
In phase modulation, the amplitude of the carrier signal remains
unchanged while phase change occurs.
while phase modulating any signal, the phase, as well as the frequency of the
carrier signal, shows variation.
As when the signal moves from positive to negative amplitude then
negative phase reversal exists. While, when the message signal shows
movement from negative to positive amplitude then positive phase
reversal takes place.
The carrier phase deviation will be more if the input signal amplitude
increases and vice versa. When the input amplitude increases (+ve
slope) the carrier undergoes phase lead. When the input amplitude
decreases (-ve slope) the carrier undergoes phase lag.
the phase deviation is given as
θ(t) α x(t) rad
θ(t) = Kp x(t) rad
: Kp is the deviation sensitivity
Kp = rad / V
Also, the modulation index of a phase modulated wave is given as
mp = KpVm
Advantages of Phase Modulation

The process of phase modulation is quite east than
frequency modulation.

This technique is used to determine the speed of the mobile
target. Because for this the carrier is required to be constant
and this is obtained in case of phase modulation.

A phase modulated signal is more immune to noise effects.
Disadvantages of Phase Modulation

In order to raise the modulation index of a phase modulated
signal, frequency multipliers are needed.

The system cost is quite expensive.

Sometimes phase ambiguity exists when the modulation
index exceeds a certain value.
Applications of Phase Modulation
This technique is widely used in the transmission of radio waves. This
process is also employed in wireless signal transmission like satellite
and Wi-Fi transmission etc.