From 12:00 PM - 4:00 PM CST on Thursday, October 18, ni.com will be undergoing system upgrades that may result in temporary service interruption.

We appreciate your patience as we improve our online experience.

Table Of Contents

MT Demodulate AM (MT Demodulate AM (DSB)) (G Dataflow)

Version:
    Last Modified: February 7, 2018

    Demodulates a double sideband (DSB) amplitude-modulated signal.

    connector_pane_image
    datatype_icon

    AM modulated waveform

    The modulated complex baseband time-domain data for demodulation.

    datatype_icon

    t0

    The trigger (start) time of the Y array.

    Default: 0.0

    datatype_icon

    dt

    Time interval between data points in the Y array.

    Default: 1.0

    datatype_icon

    Y

    The complex-valued time-domain data array. The real and imaginary parts of this complex data array correspond to the in-phase (I) and quadrature-phase (Q) data, respectively.

    datatype_icon

    modulation index

    The expected modulation index of the AM demodulated waveform parameter. This value is used to scale the AM demodulated waveform parameter.

    • Set this value to the estimated modulation index of the incoming AM modulated waveform signal to scale the AM demodulated waveform parameter by this value. The resulting scaled AM demodulated waveform can be used to quantify error between the actual and expected modulation index.
    • Set this value to 1.0 to return an AM demodulated waveform with no scaling. When you set suppressed carrier? to FALSE, the peak amplitude value of the unscaled AM demodulated waveform represents the true modulation index of the incoming AM modulated waveform.
    spd-note-note
    Note  

    The node ignores the modulation index parameter if you set the suppressed carrier? to TRUE.

    Default: 1.0

    datatype_icon

    error in

    Error conditions that occur before this node runs.

    The node responds to this input according to standard error behavior.

    Standard Error Behavior

    Many nodes provide an error in input and an error out output so that the node can respond to and communicate errors that occur while code is running. The value of error in specifies whether an error occurred before the node runs. Most nodes respond to values of error in in a standard, predictable way.

    error in does not contain an error error in contains an error
    If no error occurred before the node runs, the node begins execution normally.

    If no error occurs while the node runs, it returns no error. If an error does occur while the node runs, it returns that error information as error out.

    If an error occurred before the node runs, the node does not execute. Instead, it returns the error in value as error out.

    Default: No error

    datatype_icon

    suppressed carrier?

    A Boolean that determines whether the carrier has been suppressed in the incoming AM-DSB-modulated waveform.

    Demodulation proceeds according to one of the following methods, depending on whether suppressed carrier? is set to TRUE or FALSE.

    TRUE

    The incoming baseband AM-DSBSC modulated signal r ( t ) can be expressed as the following equations:

    r ( t ) = s D S B S C ( t ) e j φ ( t )

    where s D S B S C ( t ) is an AM-DSBSC modulated waveform, and φ ( t ) is any time-varying phase ambiguity.

    The node squares the signal r ( t ) when computing the phase estimate of φ ( t ) . This squaring operation removes the 180 degrees phase ambiguity relative to the sign of m ( t ) . The computed phase estimate is used to generate a complex tone that is added back to the input signal r ( t ) to generate the equivalent DSB signal with carrier and unity modulation index. Thereon, envelope detection is performed for computing the AM demodulated waveform output m ^ ( t ) .

    The recovered message signal m ^ ( t ) can be obtained from the following relationships:

    r ( t ) = S D S B S C ( t ) e j ϕ ( t )
    ϕ ^ ( t ) = 0.5 * arg ( r 2 ( t ) )
    r D S B ( t ) = r ( t ) + e j * ϕ ^ ( t ) = s D S B S C ( t ) e j ϕ ( t ) + e j * ϕ ^ t
    m ^ ( t ) = | r D S B ( t ) | | r D S B ( t ) | 1
    FALSE

    The incoming baseband AM-DSB modulated signal r ( t ) can be expressed by the following equations:

    r ( t ) = s D S B ( t ) e j φ ( t )

    where s D S B ( t ) is a DSB modulated waveform and φ ( t ) is any time-varying phase ambiguity. AM-DSB demodulation involves performing envelope detection. The AM demodulated waveform (t) is given by the following equation:

    m ^ ( t ) = 1 k * [ | r ( t ) | | r ( t ) | 1 ]

    where k represents the modulation index.

    Default: FALSE

    datatype_icon

    AM demodulated waveform

    The recovered message signal.

    spd-note-note
    Note  

    Wire the AM demodulated waveform parameter to any LabVIEW waveform measurement node for further analysis. If the information signal is a single tone (normalized) and modulation index is set to 1.0 with suppressed carrier? set to FALSE, the peak amplitude value of the AM-demodulated waveform represents the true modulation index of the incoming AM-modulated waveform.

    datatype_icon

    carrier amplitude

    The mean zero-to-peak amplitude, in volts, of the IF carrier wave.

    datatype_icon

    error out

    Error information.

    The node produces this output according to standard error behavior.

    Standard Error Behavior

    Many nodes provide an error in input and an error out output so that the node can respond to and communicate errors that occur while code is running. The value of error in specifies whether an error occurred before the node runs. Most nodes respond to values of error in in a standard, predictable way.

    error in does not contain an error error in contains an error
    If no error occurred before the node runs, the node begins execution normally.

    If no error occurs while the node runs, it returns no error. If an error does occur while the node runs, it returns that error information as error out.

    If an error occurred before the node runs, the node does not execute. Instead, it returns the error in value as error out.

    AM-DSB Demodulation

    Demodulation using this node depends on whether suppressed carrier? is set to TRUE or FALSE.

    Where This Node Can Run:

    Desktop OS: Windows

    FPGA: Not supported

    Web Server: Not supported in VIs that run in a web application


    Recently Viewed Topics