The differences between DSB-SC and AM modulation

1. The differences between DSB-SC and AM modulation

comment on the advantages and disadvantages of DSB-SC modulation compared with AM

2. DSB-SC and AM

what do you mean my friend, the DSB-SC is one type of the AM modulation types !!!!!!!!!!!!

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3. Re: DSB-SC and AM

in DSB-SC since carrier is suppressed,hence power consumption is reduced and nominal.

regards

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4. Re: DSB-SC and AM

Originally Posted by klemens
comment on the advantages and disadvantages of DSB-SC modulation compared with AM
Is it a homework question?

5. Re: The differences between DSB-SC and AM modulation

Originally Posted by klemens
comment on the advantages and disadvantages of DSB-SC modulation compared with AM
AM modulation is characterized by its amplitude modulation index m which can be calculated as:

m = Vm / Vc
where
Vm is the peak voltage of the modulating signal.
Vc is the peak voltage of the carrier.

or

m = (Vmax - Vmin) / (Vmax + Vmin)
where
Vmax is the maximum voltage of the AM signal.
Vmin is the minimum voltage of the AM signal.
Note:
Vmin is positive for m < 1 and zero for m = 1
Vmin is negative for m > 1
Vmin = -Vmax for m = infinity

So let us explore 4 cases based on m:

Case 1: 0 < m < 25% (known as AM or DSB)
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Modulation is relatively easy.
Demodulation is very easy using diode detector.
But...
Power efficiency is relatively low.

Case 2: 25% < m < 100% (also known as AM or DSB)
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Modulation is not difficult.
Demodulation is easy by using an active detector.
But...
Power efficiency is not high.

Case 3: 100% < m < infinity (known DSB-RC, RC= Reduced Carrier)
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Modulation is also not difficult.
Power efficiency tends to be high (it increases with m).
But...
Demodulation needs to be of the synchronous type (PLL is used to generate the local carrier).

Case 4: m = infinity (known DSB-SC)
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Modulation is also not difficult (same as case 2 and 3).
Power efficiency is highest.
But...
Demodulation needs a digital costly system to restore the carrier (both frequency and phase).

As expected from above, DSC-SC system is usually not recommended for the general use since its demodulation is not as practical as in DSB and DSB-RC systems.
But...
A simple DSB-SC demodulator does exist (much like of case 3) and it has to wait for the scientific community, usually in charge of the science progress (academic and applied), to hear of it first!

Kerim

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6. Re: The differences between DSB-SC and AM modulation

DSB-SC is a subset of AM techniques, I think you mean to compare DSB-SC with DSB-LC; the DSB-SC has less power consumption with no redundant carrier added to the signal, the circuits used to generate both will certainly differ.

7. Re: The differences between DSB-SC and AM modulation

Originally Posted by Ahmed Alaa
DSB-SC is a subset of AM techniques, I think you mean to compare DSB-SC with DSB-LC; the DSB-SC has less power consumption with no redundant carrier added to the signal, the circuits used to generate both will certainly differ.
For instance, did you hear of a simple AM demodulator that can be used for any modulation index; from zero (carrier only) to infinity (carrier suppressed)?

The one I designed (as an MS thesis), built and implemented in some of my private links (in the 80's) is based on a conventional PLL with a minor modification (no coils, no selective filters or amplitude tracker). I am surprised how after decades no one in the world had the chance to also find its concept as I did!!! Even FCC group has no idea for example that a simple and low cost DSB-SC detector does exist and can be built even by a radio amateur and be as reliable as the ones based on the complex Costas Loop technique implemented in relatively costly digital ICs.

Kerim

8. Re: The differences between DSB-SC and AM modulation

Originally Posted by KerimF
For instance, did you hear of a simple AM demodulator that can be used for any modulation index; from zero (carrier only) to infinity (carrier suppressed)?

The one I designed (as an MS thesis), built and implemented in some of my private links (in the 80's) is based on a conventional PLL with a minor modification (no coils, no selective filters or amplitude tracker). I am surprised how after decades no one in the world had the chance to also find its concept as I did!!! Even FCC group has no idea for example that a simple and low cost DSB-SC detector does exist and can be built even by a radio amateur and be as reliable as the ones based on the complex Costas Loop technique implemented in relatively costly digital ICs.

Kerim
Hi Kerim,

Could you tell us more about your demod ? I did one demod for DSB-SC recently that divides by the carrier and requires no filtering, but as you say, PLL is the source of complexity in DSBSC.

Thanks and Good bless Syria :)

9. Re: The differences between DSB-SC and AM modulation

Originally Posted by Ahmed Alaa
Hi Kerim,

Could you tell us more about your demod ? I did one demod for DSB-SC recently that divides by the carrier and requires no filtering, but as you say, PLL is the source of complexity in DSBSC.

Thanks and Good bless Syria :)
Hi Alaa,

If the suppressed carrier is for example 455 KHz (as for AM band IF), do you mean a demodulator using a PLL IC as CD4046 could be seen as complex?

For instance, are you a student? or an old-fashion engineer as I

Kerim

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10. Re: The differences between DSB-SC and AM modulation

I am a fresh graduate :) I'm not an Analog comm. expert but as far as I know, the PLL and filters are the source of complexity in DSBSC, I was asking about the new thing in your demod.?

11. Re: The differences between DSB-SC and AM modulation

Originally Posted by Ahmed Alaa
I am a fresh graduate :) I'm not an Analog comm. expert but as far as I know, the PLL and filters are the source of complexity in DSBSC, I was asking about the new thing in your demod.?
To be honest, I was looking for a graduate student in communications who would like introducing this new concept as a thesis project to surprise his professors and lecturers Later his university will be the first one to add this novel idea (though I found it since 1979) in the world's literature. Obviously an interested person living abroad will likely patent it as well, after then I will be out of the game for good But at least, I will be glad that I was able to give something good for a young student (no matter where he lives) who may even work further on it and design its simple digital version as well.
I hope you understand the point

Kerim

12. Re: The differences between DSB-SC and AM modulation

OK :) Good luck.

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