how do we justify that there is no carrier i.e,carrier is suppresed in DSBSC ?

by seeing an impulse at frequency Fc in the frequency spectrum of DSB SC ,we can say that whether there is carrier or not but how can we recognize
from the amplitude vs time graph in time domain that there is no carrier in DSB SC .
with out using any equations just from plot how can we recognize it?

There will be no phase reversal in the plot, if there is no carrier.

can you please tell me the same for SSB and VSB

VSB stands for vestigial sideband it is the standard used for analogue TV and it has a full carrier, one complete upper sideband and the lower side band that is flat to Fc -.5MHz, then falls with a -3Db point at Fc -1.25 MHz then to zero at Fc -1.5 MHz check these figures against your transmission system.
If you look at the time/amplitude plot of a SSB signal with one tone on it the wave form you see is a sinewave of the selected side band. E.G. Fc = 1MHz, Fmod = 1KHz, upper side band transmitted then the output will be a sine wave of frequency 1.001 MHz. If lower sideband, .999 MHz.
With double sideband suppressed carrier, you get a RF envelope which is modulated by two out of phase sinewaves, so it looks like a series of "eyes" filled with RF. The cross over of the envelope is very sharp and goes through zero. If there is any carrier it will not.
Frank

by seeing an impulse at frequency Fc in the frequency spectrum of SSB and VSB ,we can say that whether there is carrier or not but how can we recognize
from the amplitude vs time graph in time domain that there is no carrier in SSB and VSB .
with out using any equations just from plot how can we recognize it?

SSB and VSB are from DSB, so the idea is to avoid sending double the required data. Essentially, for a good receiver you should see no difference in time domain since your not transmitting the redundant data. VSB is there since low freq components in analog comm were needed so a vestige of the other band is transmitted. If there was a problem with VSB such a reflections of analog signal, in old television sets there used to be ghost images die to this but in the time domain once again it is similar to the DSB signal. If it weren't then reconstruction of the original signal would not be possible...i.e. not viable to use.

It is not so easy if you don't know what is the modulating signal.
If the signal has silences (like in telephony), then during the silences there is no signal in linear modulation methods (SSB, VSB, DSB) with supressed carrier. Otherwise, during the silences the carrier is present.
N.B.: in post #2 there is a mistake: there is no phase reversal in the signal if the carrier is present and has a level high enough.
Regards

Z

will there be any minor changes in the graph when comapare vsb and ssb with DSBSC or no change at all?

kalyanasv said:

SSB and VSB are from DSB, so the idea is to avoid sending double the required data. Essentially, for a good receiver you should see no difference in time domain since your not transmitting the redundant data. VSB is there since low freq components in analog comm were needed so a vestige of the other band is transmitted. If there was a problem with VSB such a reflections of analog signal, in old television sets there used to be ghost images die to this but in the time domain once again it is similar to the DSB signal. If it weren't then reconstruction of the original signal would not be possible...i.e. not viable to use.

Click to expand...

will there be any minor changes in the graph when comapare vsb and ssb with DSBSC or no change at all?

Time Domain:
In VSB there could be a slight non-linear distortion due to the quadrature component, but typically in old TV standards the VSB occupied 1/6th bandwidth approx, so it causes tolerable distortion.

SSB -SC you should not see any difference. The problem with SSB is it requires a sharp cut-off filter which is typically expensive.

With a good receiver you will not observe any difference.

Hi,

It seems to me that maybe there is a misunderstanding.
Immadi.jagadish, are you speaking about the modulated signal? (this is what I understood)
Kalyanasv, are you speaking about the signal after demodulation?
Regards

Z

i am asking about after modulation not after demodulation