Table Of Contents

MT Modulate AM (VSB) (G Dataflow)

Last Modified: January 9, 2017

Performs vestigial sideband (VSB) amplitude modulation. This node performs signal processing on data and operates independently of hardware settings. Use this node in both simulated and hardware-equipped applications.

connector_pane_image
datatype_icon

message signal

Message signal used to modulate the carrier wave.

datatype_icon

modulation index

Desired modulation index of the AM modulated waveform parameter. A value of 0.7, for example, corresponds to a modulation index of 70%. A value greater than unity may cause overmodulation and distortion. The node ignores this parameter if you set the suppress carrier? parameter to TRUE.

Default: 1.0

datatype_icon

VSB FIR filter design

The vestigial filter design parameters corresponding to the desired VSB spectrum. The vestigial filter is generated when reset? is set to TRUE, and the filter is applied to the input message signal. Default values in this cluster correspond to NTSC analog picture carrier specifications.

spd-note-note
Note  

The normalized frequencies are specified with respect to a 1 S/s sample rate.

spd-note-tip
Tip  

Changes to the FIR filter design take effect when reset? is set to TRUE.

datatype_icon

#taps

Number of taps used to generate the VSB filter. For error-free operation, specify a filter length of 85 taps or greater.

datatype_icon

lower PB

The normalized lower passband frequency, in Hertz (Hz), of the VSB filter spectrum, relative to the carrier frequency.

datatype_icon

upper PB

The normalized upper passband frequency, in Hz, of the VSB filter spectrum, relative to the carrier frequency.

datatype_icon

lower SB

The normalized lower stopband frequency, in Hz, of the VSB filter spectrum, relative to the carrier frequency.

datatype_icon

upper SB

The normalized upper stopband frequency, in Hz, of the VSB filter spectrum, relative to the carrier frequency.

datatype_icon

peak message amplitude

Peak message amplitude of the message signal parameter. The node uses this value to scale or normalize the input message signal prior to modulation. This value must be positive.

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.

Default: no error

datatype_icon

suppress carrier?

A Boolean that determines whether to suppress the carrier of the modulated signal.

TRUE The DC component corresponding to the carrier tone in the amplitude-modulated baseband signal is suppressed.
FALSE The output amplitude-modulated baseband signal consists of a DC component corresponding to the carrier tone.

Default: FALSE

datatype_icon

reset?

A Boolean that determines whether the node continues AM-VSB modulation using internal states from previous iterations.

TRUE The node restarts AM-VSB modulation, redesigns the vestigial filter, and clears internal filter states on each call.
FALSE The node does not change the vestigial filter design across multiple calls, and sets the internal filter state to ensure continuous filter operation.

Default: TRUE

datatype_icon

pilot tone

Parameters for specifying pilot tone generation. The pilot tone is added to the Hilbert-filtered complex baseband signal to generate the modulated waveform. The pilot tone provides a coherent phase reference during demodulation for performing carrier phase and carrier frequency offset correction. Set the amplitude parameter to 0 to disable addition of the pilot tone.

spd-note-tip
Tip  

Adding a pilot tone is optional when suppress carrier? is set to FALSE. In this case, the presence of the DC component in the AM signal (corresponding to the pure carrier tone) provides a coherent reference for phase and frequency offset correction, therefore the pilot tone is not needed.

datatype_icon

frequency

Frequency of the complex exponential tone that is added to the complex baseband signal. Ensure that the absolute value of this tone frequency is less than the Nyquist frequency 1/(2 * dt).

spd-note-note
Note  

When specifying pilot tone parameters, ensure that the pilot tone is added to a portion of the spectrum where the message component of the signal is absent. Conflict between the pilot tone and message signals can cause a residual carrier phase and frequency offset error after demodulation. For example, if you specify a negative pilot tone frequency, specify an upper sideband in the sideband parameter.

datatype_icon

amplitude

Amplitude of the complex exponential tone that is added to the complex analytic baseband signal.

datatype_icon

AM modulated waveform

The baseband AM vestigial sideband modulated signal data and its complex envelope.

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 signal-only baseband modulated waveform. The real and imaginary parts of this complex data array correspond to the in-phase (I) and quadrature-phase (Q) data, respectively.

datatype_icon

error out

Error information. The node produces this output according to standard error behavior.

Adjusting the Carrier Phase

Use the initial phase parameter of MT Upconvert Baseband to adjust the carrier phase during the upconversion process. The initial phase parameter specifies the initial phase, in degrees, of the software local oscillator used in the upconversion process.

Avoiding Distortion

To avoid distortion, amplitude-normalize the message signal parameter to ±1.0 with respect to the absolute maximum amplitude of the message signal.

Prescaling Behavior

This node prescales the message signal parameter by the scalar peak amplitude prior to modulation. The default value of 1.0 for peak message amplitude indicates that no prescaling occurs.

Vestigial Sideband (VSB) Amplitude Modulation

VSB amplitude modulation involves retaining a portion of the unwanted sideband (called the vestige) in the message spectrum prior to transmission, rather than completely eliminating it as in single-sideband modulation. The following figure illustrates the series of algorithms applied to the incoming signal m(t). The node applies the AM-DSB algorithms and then applies the Vestigial filter to remove the vestige.

The output amplitude-modulated signal is represented by the following equations, depending on the setting of the suppress carrier? parameter:

When suppress carrier? is set to FALSE, the output amplitude-modulated signal is represented by the following formula:

s D S B ( t ) = 1 + k × m ( t ) max | m ( t ) |
s V S B ( t ) = s D S B ( t ) ( h i ( t ) + j × h q ( t ) ) + A p i l o t e j ω p i l o t t

where

m(t) represents the message signal data

SDSB(t) represents the double sideband AM modulated signal (unsuppressed carrier)

SVSB(t) represents the vestigial sideband AM modulated signal (unsuppressed carrier)

k represents the modulation index

Apilot represents the amplitude of the pilot tone

ωpilot represents the frequency of the pilot tone

hi represents the real component of the vestigial filter

hq represents the imaginary component of the vestigial filter

When suppress carrier? is set to TRUE, the output amplitude-modulated signal is represented by the following formula:

s D S B S C ( t ) = m ( t ) max | m ( t ) |
s V S B S C ( t ) = s D S B S C ( t ) × ( h i + j × h q ( t ) ) + A p i l o t e j ω p i l o t t

where

m(t) represents the message signal data

SDSBSC(t) represents the double sideband AM modulated signal (unsuppressed carrier)

SVSBSC(t) represents the vestigial sideband AM modulated signal (unsuppressed carrier)

k represents the modulation index

Apilot represents the amplitude of the pilot tone

ωpilot represents the frequency of the pilot tone

hi represents the real component of the Hilbert filter

hq represents the imaginary component of the Hilbert filter

Where This Node Can Run:

Desktop OS: Windows

FPGA: Not supported


Recently Viewed Topics