+ Post New Thread
Results 1 to 12 of 12
  1. #1
    Newbie level 1
    Points: 462, Level: 4

    Join Date
    May 2010
    Posts
    1
    Helped
    0 / 0
    Points
    462
    Level
    4

    The differences between DSB-SC and AM modulation

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

  2. #2
    Advanced Member level 4
    Points: 19,911, Level: 34
    Aya2002's Avatar
    Join Date
    Dec 2006
    Location
    Malaysia
    Posts
    1,143
    Helped
    393 / 393
    Points
    19,911
    Level
    34

    DSB-SC and AM

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



    •   Alt22nd May 2010, 22:38

      advertising

        
       

  3. #3
    Full Member level 4
    Points: 2,306, Level: 11

    Join Date
    Nov 2006
    Location
    Guwahati, India
    Posts
    206
    Helped
    1 / 1
    Points
    2,306
    Level
    11

    Re: DSB-SC and AM

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

    regards



  4. #4
    Advanced Member level 3
    Points: 9,408, Level: 23

    Join Date
    Oct 2008
    Location
    Sindh, Pakistan
    Posts
    910
    Helped
    178 / 178
    Points
    9,408
    Level
    23

    Re: DSB-SC and AM

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



  5. #5
    Advanced Member level 4
    Points: 7,913, Level: 21
    KerimF's Avatar
    Join Date
    May 2011
    Location
    Syria
    Posts
    1,463
    Helped
    376 / 376
    Points
    7,913
    Level
    21

    Re: The differences between DSB-SC and AM modulation

    Quote Originally Posted by klemens View Post
    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)
    ---------------------------------------------------
    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)
    -------------------------------------------------------------
    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)
    -----------------------------------------------------------------------------
    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)
    ------------------------------------------
    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

    You may like to comment on:

    Is it possible to build this demodulator?
    Last edited by KerimF; 22nd May 2011 at 03:38.



    •   Alt20th May 2011, 23:45

      advertising

        
       

  6. #6
    Full Member level 5
    Points: 3,040, Level: 12
    Ahmed Alaa's Avatar
    Join Date
    Jul 2009
    Location
    Egypt
    Posts
    317
    Helped
    65 / 65
    Points
    3,040
    Level
    12

    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. #7
    Advanced Member level 4
    Points: 7,913, Level: 21
    KerimF's Avatar
    Join Date
    May 2011
    Location
    Syria
    Posts
    1,463
    Helped
    376 / 376
    Points
    7,913
    Level
    21

    Re: The differences between DSB-SC and AM modulation

    Quote Originally Posted by Ahmed Alaa View Post
    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. #8
    Full Member level 5
    Points: 3,040, Level: 12
    Ahmed Alaa's Avatar
    Join Date
    Jul 2009
    Location
    Egypt
    Posts
    317
    Helped
    65 / 65
    Points
    3,040
    Level
    12

    Re: The differences between DSB-SC and AM modulation

    Quote Originally Posted by KerimF View Post
    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. #9
    Advanced Member level 4
    Points: 7,913, Level: 21
    KerimF's Avatar
    Join Date
    May 2011
    Location
    Syria
    Posts
    1,463
    Helped
    376 / 376
    Points
    7,913
    Level
    21

    Re: The differences between DSB-SC and AM modulation

    Quote Originally Posted by Ahmed Alaa View Post
    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



  10. #10
    Full Member level 5
    Points: 3,040, Level: 12
    Ahmed Alaa's Avatar
    Join Date
    Jul 2009
    Location
    Egypt
    Posts
    317
    Helped
    65 / 65
    Points
    3,040
    Level
    12

    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. #11
    Advanced Member level 4
    Points: 7,913, Level: 21
    KerimF's Avatar
    Join Date
    May 2011
    Location
    Syria
    Posts
    1,463
    Helped
    376 / 376
    Points
    7,913
    Level
    21

    Re: The differences between DSB-SC and AM modulation

    Quote Originally Posted by Ahmed Alaa View Post
    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. #12
    Full Member level 5
    Points: 3,040, Level: 12
    Ahmed Alaa's Avatar
    Join Date
    Jul 2009
    Location
    Egypt
    Posts
    317
    Helped
    65 / 65
    Points
    3,040
    Level
    12

    Re: The differences between DSB-SC and AM modulation

    OK :) Good luck.



+ Post New Thread
Please login