In analog communication DSBSC (Double side band suppressed carrier) is way of modulating signal.

In this the carrier is simply multiplied with the message signal.

At the demodulator the carrier is multiplied back which gives the message signal back. In the below picture

The first signal is my message signal
The second is the modulated signal
The Third is the demodulated signal i.e I can get the msg by simply tracking the peak voltages \

My Question is well now the demodulation process seems to be complete but the part that I am missing is a LPF at demodulator  .Why is it required? Anyway I have my signal back  .Why should I pass it through LPF? All the books have the LPF.

Please explain why is LPF required at demodulator ?

Matlab code

t=0:1e-4:30;
f=5;
y=sind(2*pi*f*t);
subplot(3,1,1)
plot(t,y)
hold on
yline(0)
xline(0.2)
ylim([-2 2])
hold off
subplot(3,1,2)
y1=sind(2*pi*100*t);

y3=y1.*y;

plot(t,y3)
hold on

yline(0)
hold off
subplot(3,1,3)

y4=y3.*sind(2*pi*100*t);

plot(t,y4)
hold on
ylim([-2 2])
plot(t,y);
hold off

In analog communication, DSBSC (double side band suppressed carrier) is way of modulating signal.

In this the carrier is simply multiplied with the message signal.

At the demodulator, the carrier is multiplied back which gives the message signal back.

• The first signal is my message signal
• The second is the modulated signal
• The third is the demodulated signal i.e I can get the msg by simply tracking the peak voltages

Now the demodulation process seems to be complete but the part that I am missing is a low pass filtee at demodulator. Why is it required? I have my signal back. Why should I pass it through a low pass filter? All the books have the filter.

Please explain why the low pass filter is required after the demodulator.

Matlab code

t=0:1e-4:30;
f=5;
y=sind(2*pi*f*t);
subplot(3,1,1)
plot(t,y)
hold on
yline(0)
xline(0.2)
ylim([-2 2])
hold off
subplot(3,1,2)
y1=sind(2*pi*100*t);

y3=y1.*y;

plot(t,y3)
hold on

yline(0)
hold off
subplot(3,1,3)

y4=y3.*sind(2*pi*100*t);

plot(t,y4)
hold on
ylim([-2 2])
plot(t,y);
hold off

In analog communication DSBSC (Double side band suppressed carrier) is way of modulating signal  .
In this the carrier is simply multiplied with the message signal  .\

At the demodulator the carrier is multiplied back which gives the message signal back. In the below picture  

The first signal is my message signal
The second is the modulated signal
The Third is the demodulated signal i.e I can get the msg by simply tracking the peak voltages \

My Question is well now the demodulation process seems to be complete but the part that I am missing is a LPF at demodulator .Why is it required? Anyways I have my signal back .Why should I pass it through LPF? All the books have the LPF.

Please explain why is LPF required at demodulator ? Thank you

Matlab code %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

t=0:1e-4:30;
f=5;
y=sind(2*pi*f*t);
subplot(3,1,1)
plot(t,y)
hold on
yline(0)
xline(0.2)
ylim([-2 2])
hold off
subplot(3,1,2)
y1=sind(2*pi*100*t);

y3=y1.*y;

plot(t,y3)
hold on

yline(0)
hold off
subplot(3,1,3)

y4=y3.*sind(2*pi*100*t);

plot(t,y4)
hold on
ylim([-2 2])
plot(t,y);
hold off

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

In analog communication DSBSC (Double side band suppressed carrier) is way of modulating signal.

In this the carrier is simply multiplied with the message signal.

At the demodulator the carrier is multiplied back which gives the message signal back. In the below picture 

The first signal is my message signal
The second is the modulated signal
The Third is the demodulated signal i.e I can get the msg by simply tracking the peak voltages \

My Question is well now the demodulation process seems to be complete but the part that I am missing is a LPF at demodulator .Why is it required? Anyway I have my signal back .Why should I pass it through LPF? All the books have the LPF.

Please explain why is LPF required at demodulator ?

Matlab code

t=0:1e-4:30;
f=5;
y=sind(2*pi*f*t);
subplot(3,1,1)
plot(t,y)
hold on
yline(0)
xline(0.2)
ylim([-2 2])
hold off
subplot(3,1,2)
y1=sind(2*pi*100*t);

y3=y1.*y;

plot(t,y3)
hold on

yline(0)
hold off
subplot(3,1,3)

y4=y3.*sind(2*pi*100*t);

plot(t,y4)
hold on
ylim([-2 2])
plot(t,y);
hold off

In analog communication DSBSC (Double side band suppressed carrier) is way of modulating signal .
In this the carrier is simply multiplied with the message signal .\

At the demodulator the carrier is multiplied back which gives the message signal back. In the below picture

The first signal is my message signal
The second is the modulated signal
The Third is the demodulated signal i.e I can get the msg by simply tracking the peak voltages \

My Question is well now the demodulation process seems to be complete but the part that I am missing is a LPF at demodulator .Why is it required? Anyways I have my signal back .Why should I pass it through LPF? All the books have the LPF.

Please explain why is LPF required at demodulator ? Thank you

In analog communication DSBSC (Double side band suppressed carrier) is way of modulating signal .
In this the carrier is simply multiplied with the message signal .\

At the demodulator the carrier is multiplied back which gives the message signal back. In the below picture

The first signal is my message signal
The second is the modulated signal
The Third is the demodulated signal i.e I can get the msg by simply tracking the peak voltages \

My Question is well now the demodulation process seems to be complete but the part that I am missing is a LPF at demodulator .Why is it required? Anyways I have my signal back .Why should I pass it through LPF? All the books have the LPF.

Please explain why is LPF required at demodulator ? Thank you

Matlab code %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

t=0:1e-4:30;
f=5;
y=sind(2*pi*f*t);
subplot(3,1,1)
plot(t,y)
hold on
yline(0)
xline(0.2)
ylim([-2 2])
hold off
subplot(3,1,2)
y1=sind(2*pi*100*t);

y3=y1.*y;

plot(t,y3)
hold on

yline(0)
hold off
subplot(3,1,3)

y4=y3.*sind(2*pi*100*t);

plot(t,y4)
hold on
ylim([-2 2])
plot(t,y);
hold off

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%