1) The document discusses analog communication systems including amplitude modulation. It defines key concepts like modulation, channels, transmitters and receivers. 2) Amplitude modulation varies the amplitude of a carrier wave using a modulating signal. This generates sidebands at frequencies above and below the carrier frequency. 3) The modulation index is the ratio of the modulating signal amplitude to the carrier amplitude. It indicates the percentage of modulation.

1. UNIT I
ANALOG COMMUNICATION

2. UNIT I
ANALOG COMMUNICATION
Introduction to Communication Systems
Modulation - Types - Need for Modulation.
Theory of Amplitude Modulation
Evolution and Description of SSB Techniques
Theory of Frequency and Phase Modulation
Comparison of Analog Communication Systems
(AM – FM – PM).

3. INTRODUCTION TO COMMUNICATION
SYSTEMS
COMMUNICATION:
Process of establishing connection between two points
for exchanging information.
Elements of communication system:
 Transmitter
 Channel
 Receiver

4. BLOCK DIAGRAM

5. Transmitter:
The transmitter consists of a transducer, modulator,
amplifier, and transmitting antenna in radio transmission.

6. A transducer converts sound signals into electric signals.
Modulator performs mixing of the electric audio signal
with the high-frequency radio wave.
The amplifier boosts the power of the modulated signal.
The signal is radiated in the space with the aid of an
antenna.

7. Communication channel:
The duty of the communication channel is to carry the
modulated signal from transmitter to receiver.
The communication channel is also called a transmission
link or medium.
Type of communication Channels or links
Radio communication (The
basic elements of radio
communication system are a
transmitter and a receiver)
Free space
Telephony and Telegraphy
communication
Transmission line
Optical communication Optical fibre

8. Receiver:
The receiver consists of Pickup antenna,
Demodulator, Amplifier and Transducer.

9. Pickup antenna: To pick the signal
Demodulator: To separate the audio signal from the
modulated signal
Amplifier: To boost up the weak audio signal
Transducer: converts back audio signal in the form of
electrical pulses into sound waves.

10. Modulation:
Digital and analogue signals are of low frequency and
hence cannot be transmitted to long distances. These
signals require some carrier. These carriers are known as
carrier waves or high-frequency signals. The placement of
a low frequency (LF) signal over the high frequency (HF)
signal is known as modulation.
Demodulation:
The modulated signal receives by receiver, it
separated the message signal from the modulated carrier
signal.

11. Amplitude Modulation (AM)
Amplitude modulation (AM) is the process in which
the amplitude of the modulated wave is varied in
accordance with the amplitude of modulating wave. In
AM, the frequency of the carrier wave is unchanged.

13.  Let us represent the modulating signal by em and it is
given as,
em = Em sin wm t
 Let us represent the modulating signal by ec and it is
given as,
ec = Ec sin wc t
Where,
Em = Amplitude of modulating signal
Ec = Amplitude of carrier signal
Wm = frequency of modulating signal
Wc = frequency of carrier signal

14. By using mathematical expression for above equation,
it is given by,
EAM = Ec + em
EAM = Ec + Em sin wm t
 using instantaneous value of the amplitude
modulated wave can be given as,
eAM = EAM sin θ
eAM = EAM sin wc t
eAM = (Ec + Em sin wm t)sin wc t

15. Modulation Index:
It is defined as the ratio of maximum amplitude of
modulating signal to maximum amplitude of carrier signal
is called modulation index.
m = Em / Ec
When the modulation index is expressed in
percentage is called percentage modulation.
m = (Em / Ec ) * 100

16. Frequency spectrum & Bandwidth:
The modulated carrier has new signals at different
frequencies called sidebands.
Upper sideband frequencies fUSB = fc + fm
Lower sideband frequencies fUSB = fc - fm

17.  Consider the expression for AM wave equation is
given by,
eAM = (Ec + Em sin wm t)sin wc t
 We know that,
m = Em / Ec
Em = m Ec
eAM = (Ec + mEc sin wm t)sin wc t
eAM = Ec sin wc t + mEc sin wm t .sin wc t

18.  We know that,
Sin (A) . Sin (B) = 1 / 2 Cos (A-B) – 1 / 2 Cos (A+B)
 Applying to the eAM equation,
eAM = Ec sin wc t + mEc/2 {Cos(Wc–Wm)t } -
mEc/2 {Cos(Wc+Wm )t }
Bandwidth: It is defined as the difference between
upper frequency and lower frequency.
B/W = fUSB – fLSB = (fc + fm ) – (fc + fm)
B/W = 2 fm