Analog and Digital Communication Laboratory Manual
Experiment No-2
Aim:
To generate Double Sideband Suppressed Carrier (DSB-SC) modulated and
demodulated signal.
To generate Single Sideband Suppressed Carrier (SSB-SC) signal using Phase shift
method and the demodulated signal.
To generate the frequency spectrum of Double Sideband Suppressed Carrier
(DSB-SC) and Single Sideband Suppressed Carrier (SSB-SC) modulated signal.
Software used: MATLAB R2023b
Theory:
Double Sideband Suppressed Carrier (DSB-SC)
Double Sideband Suppressed Carrier is an amplitude modulation technique where both
sidebands (upper and lower) are transmitted, but the carrier is suppressed This saves power
compared to conventional AM but still uses the same bandwidth.
Message signal:
m(t) = Am cos(2π fm t)
Carrier signal:
c(t) = Ac cos(2π fc t)
DSB-SC modulated signal:
DSB-SC(t) = m(t) c(t)
Substituting: DSB-SC(t) = Am Ac cos(2π fm t) cos(2π fc t)
Using the identity cos A cos B = ½[cos(A+B) + cos(A−B)]:
DSB-SC(t) = (Am Ac / 2) [cos 2π(fc + fm_)t + cos 2π(fc − fm)t]
Analog and Digital Communication Laboratory Manual
Single Sideband Suppressed Carrier (SSB-SC):
Single Sideband Suppressed Carrier (SSB-SC) is a type of amplitude modulation in which only one
sideband (either upper or lower) is transmitted, and the carrier is suppressed. This improves power
efficiency and reduces bandwidth to half of conventional AM.
Message signal:
m(t) = Am cos(2π fm t)
DSB-SC signal:
DSB-SC(t) = m(t) cos(2π fc t)
= (Am / 2) [cos 2π(fc + f_m)t + cos 2π(fc − fm)t]
This contains both upper and lower sidebands.
SSB-SC signal:
Using the Hilbert transform m̂ (t):
SSB(t) = m(t) cos (2π fc t) ± m̂ (t) sin(2π f_c t)
Algorithm:
DSB-SC Modulation:
1. Generate a modulating signal m(t) with amplitude and Frequency of 1Vm and Frequency of
100Hz. With sampling frequency of 10KHz.
m(t) = Am cos(2π fm t)
2. Generate a Carrier signal C(t) with amplitude and Frequency of 1Vc and Frequency of 1000Hz
with sampling frequency of 10KHz.
c(t) = Ac cos(2π fc t)
3. Generate the Double Sideband Suppressed Carrier (DSB-SC) signal using the expression
DSB-SC(t) = m(t) c(t)
DSB-SC(t) = Am Ac cos(2π fm t) cos(2π fc t)
SSB-SC Modulation:
1. Generate a modulating signal m(t) with amplitude and Frequency of 1Vm and Frequency of
100Hz. With sampling frequency of 10KHz.
m(t) = Am cos(2π fm t)
2. Generate a modulating signal m(t) with 90-degree phase shift.
Analog and Digital Communication Laboratory Manual
3. Generate a Carrier signal C(t) with amplitude and Frequency of 1Vc and Frequency of 1000Hz
with sampling frequency of 10KHz.
c(t) = Ac cos(2π fc t)
4. Generate a Carrier signal C(t) with 90-degree phase shift.
5. Multiply m(t) with C(t) to get the DSBSC signal
6. Multiply m(t) (phase shifted signal) with C(t) (phase shifted signal) to get the DSBSC signal
(phase shifted signal)
7. ADD and SUBTRACT the two DSBSC signal to get the LSB SSBSC and USB signal.
Algorithm:
Demodulation: DSB-SC and SSB-SC
1. Perform product demodulation by multiplying the DSB-SC modulated signal with the carrier
signal.
2. Design a low-pass filter using MATLAB’s butter () function with an appropriate cutoff
frequency.
3. Apply the low-pass filter using the filter () function to the product signal to remove high-
frequency components.
4. Scale the output of the filter by a factor of 2 (to recover the original amplitude level).
5. Plot the original message signal and the recovered signal for comparison
6. Repeat the same process for demodulation of SSB-SC.
Algorithm: Frequency Spectrum of DSB-SC and SSB-SC
1. Determine the number of samples (N) and create a time vector for the simulation.
2. Apply the FFT (Fast Fourier Transform) to the AM signal using MATLAB’s fft() function.
3. Create the frequency vector using the sampling frequency and signal length.
4. Plot the magnitude spectrum of the DSB-SC and SSB-SC to visualize the carrier and
sidebands.
Plot the magnitude spectrum of the AM signal to visualize the carrier and sidebands.
Simulation Code:
Analog and Digital Communication Laboratory Manual
Expected Graph:
DSB-SC
SSB-SC
Analog and Digital Communication Laboratory Manual
Analog and Digital Communication Laboratory Manual
Inference:
