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balanced modulator

Discussion in 'General Electronics Discussion' started by deepak kumar panda, Mar 21, 2012.

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  1. deepak kumar panda

    deepak kumar panda

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    Mar 21, 2012
    why is it called balanced?it is doing modulation,but is der ne specific reson to call it balanced?
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    This page explains it: http://www.tiaonline.org/resources/telecom-glossary (enter balanced modulator in the search field):
    balanced modulator:
    A modulator constructed so that the carrier is suppressed and any associated carrier noise is balanced out. Note 1: The balanced modulator output contains only the sidebands. Note 2: Balanced modulators are used in AM transmission systems. (188)
    Unbalanced modulator:
    A modulator in which the modulation factor is different for the alternate half-cycles of the carrier. (188) Synonym asymmetrical modulator.

    See also here http://dictionary.reference.com/browse/asymmetrical+modulation

    Harald
     
  3. deepak kumar panda

    deepak kumar panda

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    Mar 21, 2012
    That is correct that it only contaons USB n LSB n carrier is ruled out,but this can also be done by a analog mutiplier which is Gilbert cell right..For carrier suppressing we are only multiplying the modulating signal and carrier signal ,output is only two sidebands.but in what way it is balanced.I am not getting sir.
    And sir would u mind explaining me the concept behind this modulation factor(M)."M" only depends on the carrier amplitude (Ac) and signal ampl(Am) .ratio of Am/Ac.how it is varying?
     
  4. Shyamal796

    Shyamal796

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    Mar 19, 2012
    Get more information about modulatopn from "Harald Kapp"
     
  5. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Sorry,
    this is as much information as I am able to supply. I'm not an expert in modulation technology and it's been quite some years I haven't done anything in this field.
    But from what I understand the paradigm of aunbalanced or balanced modulator says nothing about how this type of modulation is achieved. A multiplier may as well be used as any other circuit that gives the same result. Balanced vs. unbalanced only refers to the spectrum of the modulated signal. If the spectrum is mirror symmetrical around the carrier frequency, this would be the result of a balanced modulation, whatever technology was employed to achieve this.
    If the spectrum of the modulated signal is asymmetrical around the carrier frequency, this would be the result of a unbalanced modulation, whatever technology was employed to achieve this.

    Harald
     
  6. john monks

    john monks

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    Mar 9, 2012
    A sideband balanced modulator is made so that a carrier signal and its inverted signal are combined into a diode array and no carrier is coming out when no modulating signal is fed into the modulator. Now when the modulating signal becomes positive relative to a no signal condition the output of the modulator passes through one of the carrier signals. And when the modulating signal becomes negative the other carrier phase is fed through. The amplitude of the carrier phase coming out of the modulator is proportional to the plus or minus amplitude of the modulating signal. The term "balanced" comes from the fact that no net signal is coming out of the modulator when no modulating signal is applied to the modulator. The resultant output signal generates an upper and lower frequencies with no carrier signal. In single band operation one of the bands is filtered off in the transmitter, usually with a crystal filter, while the other band gets passed to the power stage. This is done to reduce bandwidth of the transmitted signal. And the receiver usually is designed to receive either the upper or lower band only so as to reduce the incoming signal. Modulation factor usually applies to amplitude modulation which is different from sideband modulation. The formula for this is (Vmax - Vmin)/(2Vavg).
     
  7. deepak kumar panda

    deepak kumar panda

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    Mar 21, 2012


    But sir in full AM where carrier is present ,there also the side bands are present at equal distance 4m d carrier frequencey,but the diff is dat in DSB-SC the carrier is absent .so if we take the distance of USB and LSB 4m carrier frequency den in that case both will be balanced.
     
  8. deepak kumar panda

    deepak kumar panda

    8
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    Mar 21, 2012
    But John,
    U r telling this balanced concept taking the diode circuit for the balanced modulator circuit into consideration,but if we use the analog multiplier,u might have come across in some book that it can be used for balanced modulatoion.thats y in that case how it can be called balanced?please clear my doubts....
     
    Last edited by a moderator: Mar 23, 2012
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