Double Side band Suppressed carrier (DSB-SC) Modulation and Demodulation.

Communication Engineering

1. UNIVERSITY OF ASIA PACIFIC
Department Of
Electrical & Electronics Engineering
Course Code : EEE 310
Course Title : Communication Engineering
Fundamentals Sessional
Experiment No. : 02
Experiment Name : Double Side band Suppressed carrier
(DSB-SC) Modulation and Demodulation.
Submitted By : Group 2
16108013
16108024
16108025
16108035
Submitted To :
Sazzad Rahman
Assistant Professor ,EEE,UAP.
Date Of Performance : 09.12.2018
Date Of Submission : 22.12.2018

2. EXP NO: 02

Experiment Name : Double Sideband Supper Carrier(DSB-SC)
Modulation and Determination.

OBJECTIVES:

 To observe DSB-SC and SSB modulator.
 To examine the synchronous detection method for DSB-SC
signal .

EQUIPMENTS:

 MC 1496 DSB-SC and SSB modulator .
 MC 1496 DSB-SC and SSB demodulator .
 Oscilloscope.
 Function generator .
 Wires and Leads.

Theory:
Double Sideband suppressed carrier (DSB-SC) doed not mean no
carrier required. In this modulation carrier is a must . In DSB-SC
both carrier and modulated carrier signal are transmitted . But
in DSB-SC carrier signal suppressed before transmission only
modulated carrier is transmitted . So , power efficiency is
increased as transmission power decreases . But it requires twice
the bandwidth DSB-WC.

Message Signal :m(t)
Carrier Signal :c(t)=Ac cos(wct)=Ac cos (2fct)
DSB-SC modulated signal :m(t) cos (wct)
Amplitude Spectrum :

3. To generate DSB-SC signal a balanced modulator can be used. In a
balanced modulator, if we give message and carrier as input, we
can get the DSB SC modulated output. The waveform of DSB-SC
signal has a distinctive property. Whenever the message signal
crosses the zero line the phase of DSB-SB modulated signal will be
shifted by 180 degree;


DSB-SC signal cannot be detected using diode detection method
DSB-SC signal can he demodulated using synchronous detection/
coherent detection/ product detection method. In product
detection method, same carrier (frequency and phase must be
same) used in modulation is mandatory. If anyone (either
frequency or phase) losses synchronism demodulated output will
not be the original message signal. Using a balanced multiplier and
low pass filter synchronous detection is done .

4. After low pass filter block only low frequency can passed. So high
frequency is blocked and low frequency message signal will be the
output of the block.

Answer Of Report Question
1.

5. Circuit Connection

6. Data And Observation









Figure – carrier Signal









Figure – After Modulation

7. Figure- After Demodulation

8. Discussion
 That was our second experiment of the course on study on
Double sideband suppressed carrier (DSB-SC) modulation
and demodulation.

 In this experiment we generated Message signal m(t),carrier
signal c(t)=Ac cos(2fct) and DSB-SC modulated signal
DSB-SSC=m(t)cos (wct).

 Also we knew about single band suppressed carrier .

 We made circuit connection. We had to connect the
message signal in audio input and carrier signal in carrier
input port in ACS5 DSB-SC and SSB modulator. We produce
voltage from function generator.

 We observing the some waveform and set for block 1peak
amplitude 300 mv and frequency 1khz also we set for block
2 peak amplitude 300mv and frequency 100khz.

 We had adjust gain by variable resistor VR2 AND VR4.

 From this experiment we had to understand SSB-SC are more
efficient from DSB-SC because SSB -SC are more energy
efficient and bandwidth efficient.
 After observed waveform we had finished our experiment.