MT Modulate AM VI

LabView Analog Modulation

MT Modulate AM VI

Performs amplitude modulation (AM) on an RF carrier wave, with optional suppression of the carrier wave, according to a baseband information signal specified by the message signal parameter. The complex envelope of the amplitude-modulated signal is returned in the AM modulated waveform indicator.

This VI performs signal processing on data and operates independently of hardware settings. This VI can be used in simulated as well as hardware-equipped applications.

Use the pull-down menu to select an instance of this VI.

Details

MT Modulate AM (DSB)

This polymorphic instance performs double sideband (DSB) amplitude modulation.

MT Modulate AM (DSB)

message signal specifies the message signal used to modulate the carrier wave.

	t0 specifies the trigger (start) time of the signal data.
	dt specifies the time interval between data points in the signal data.
	Y specifies the normalized message signal array.

modulation index specifies the 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 (1) may cause overmodulation and distortion. This parameter is ignored when suppress carrier? is set to TRUE. The default is 1.0.

peak message amplitude specifies the peak message amplitude of the message signal. This value is used to scale (normalize) the input message signal prior to modulation. This value must be positive. The default is 1.0.

suppress carrier? specifies whether to suppress the carrier of the modulated signal. When suppress carrier? is set to FALSE (the default), the output amplitude-modulated baseband signal consists of a DC component corresponding to the carrier tone.

error in (no error) accepts error information wired from previously called VIs. Use this information to decide if any functionality should be bypassed in the event of errors from other VIs. Right-click the front panel error in control and select Explain Error or Explain Warning from the shortcut menu for more information about the error displayed.

	status is either TRUE (X) for an error, or FALSE (checkmark) for no error or a warning. Right-click the front panel error in control and select Explain Error or Explain Warning from the shortcut menu for more information about the error displayed.
	code identifies the error or warning. Right-click the front panel error in control and select Explain Error or Explain Warning from the shortcut menu for more information about the error displayed.
	source describes the origin of the error or warning. Right-click the front panel error in control and select Explain Error or Explain Warning from the shortcut menu for more information about the error displayed.

AM modulated waveform returns the AM-DSB-modulated complex baseband time-domain data for demodulation.

	t0 returns the trigger (start) time of the Y array.
	dt returns the time between values in the Y array.
	Y returns 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.

error out passes error or warning information out of a VI to be used by other VIs. Right-click the front panel error out indicator and select Explain Error or Explain Warning from the shortcut menu for more information about the error displayed.

	status is either TRUE (X) for an error, or FALSE (checkmark) for no error or a warning. Right-click the front panel error in control and select Explain Error or Explain Warning from the shortcut menu for more information about the error displayed.
	code identifies the error or warning. Right-click the front panel error in control and select Explain Error or Explain Warning from the shortcut menu for more information about the error displayed.
	source describes the origin of the error or warning. Right-click the front panel error in control and select Explain Error or Explain Warning from the shortcut menu for more information about the error displayed.

MT Modulate AM (SSB)

This polymorphic instance performs single sideband (SSB) amplitude modulation.

Instance Details

MT Modulate AM (SSB)

message signal specifies the message signal used to modulate the carrier wave.

	t0 specifies the trigger (start) time of the signal data.
	dt specifies the time interval between data points in the signal data.
	Y specifies the normalized message signal array.

hilbert filter specifies the complex-valued Hilbert filter used for sideband cancellation during generation of the AM-SSB baseband complex signal. This filter is internally applied to the message signal to generate the baseband complex analytic signal.

Note Changes to the Hilbert filter take effect when reset? is set to TRUE.

taps specifies the length, in taps, of the Hilbert filter (N).

design specifies the underlying design of the Hilbert filter.

Windowed Hilbert Transformer (0)	Generates the length N Hilbert filter based on the impulse response.
Equiripple Hilbert transformer (1)	Generates an equiripple Hilbert filter.

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

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-SSB signal (corresponding to the pure carrier tone) provides a coherent reference for phase and frequency offset correction, so the pilot tone is not needed.

frequency specifies the 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).

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 AM-SSB demodulation. For example, if you specify a negative pilot tone frequency, specify an upper sideband in the sideband input.

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

sideband specifies whether the AM-SSB modulator retains the lower or upper sideband of the message spectrum to generate the AM-SSB baseband complex analytic signal.

lower sideband (0)	Retains the portion of the message spectrum lying in the negative frequency range [-(1/2dt),0] and eliminate the positive sideband spectrum.
upper sideband (1)	Retains the message spectrum spanning the positive frequency range [0,1/2dt]. This is the default value.

reset? specifies whether the VI continues AM-SSB modulation using internal states from previous iterations.

TRUE	When reset? is TRUE, the VI restarts AM-SSB modulation, redesigns the Hilbert filter, and clears internal filter states on each call. This is the default value.
FALSE	When reset? is FALSE, the Hilbert filter design is unchanged across multiple calls, and the internal filter state is set to ensure continuous filter operation.

	status is either TRUE (X) for an error, or FALSE (checkmark) for no error or a warning. Right-click the front panel error in control and select Explain Error or Explain Warning from the shortcut menu for more information about the error displayed.
	code identifies the error or warning. Right-click the front panel error in control and select Explain Error or Explain Warning from the shortcut menu for more information about the error displayed.
	source describes the origin of the error or warning. Right-click the front panel error in control and select Explain Error or Explain Warning from the shortcut menu for more information about the error displayed.

AM modulated waveform returns the AM-SSB-modulated complex baseband time-domain data for demodulation.

	t0 returns the trigger (start) time of the Y array.
	dt returns the time between values in the Y array.
	Y returns 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.

	status is either TRUE (X) for an error, or FALSE (checkmark) for no error or a warning. Right-click the front panel error in control and select Explain Error or Explain Warning from the shortcut menu for more information about the error displayed.
	code identifies the error or warning. Right-click the front panel error in control and select Explain Error or Explain Warning from the shortcut menu for more information about the error displayed.
	source describes the origin of the error or warning. Right-click the front panel error in control and select Explain Error or Explain Warning from the shortcut menu for more information about the error displayed.

MT Modulate AM (SSB) Details

MT Modulate AM (VSB)

This polymorphic instance performs vestigial sideband (VSB) amplitude modulation.

Instance Details

MT Modulate AM (VSB)

message signal specifies the message signal used to modulate the carrier wave.

	t0 specifies the trigger (start) time of the signal data.
	dt specifies the time interval between data points in the signal data.
	Y specifies the normalized message signal array.

VSB FIR filter design specifies 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.

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

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

	#taps specifies the number of taps used to generate the VSB filter. For error-free operation, specify a filter length of 85 taps or greater.
	lower PB specifies the normalized lower passband frequency, in hertz, of the VSB filter spectrum, relative to the carrier frequency.
	upper PB specifies the normalized upper passband frequency, in hertz, of the VSB filter spectrum, relative to the carrier frequency.
	lower SB specifies the normalized lower stopband frequency, in hertz, of the VSB filter spectrum, relative to the carrier frequency.
	upper SB specifies the normalized upper stopband frequency, in hertz, of the VSB filter spectrum, relative to the carrier frequency.

reset? specifies whether the VI continues AM-VSB modulation using internal states from previous iterations.

TRUE	When reset? is TRUE, the VI restarts AM-VSB modulation, redesigns the vestigial filter, and clears internal filter states on each call. This is the default value.
FALSE	When reset? is FALSE, the vestigial filter design is unchanged across multiple calls, and the internal filter state is set to ensure continuous filter operation.

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

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-VSB signal (corresponding to the pure carrier tone) provides a coherent reference for phase and frequency offset correction, so the pilot tone is not needed.

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 tone and message signals can cause a residual carrier phase and frequency offset error after AM-VSB demodulation. For example, if you specify a negative pilot tone frequency, specify upper sideband in the sideband input.

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

	status is either TRUE (X) for an error, or FALSE (checkmark) for no error or a warning. Right-click the front panel error in control and select Explain Error or Explain Warning from the shortcut menu for more information about the error displayed.
	code identifies the error or warning. Right-click the front panel error in control and select Explain Error or Explain Warning from the shortcut menu for more information about the error displayed.
	source describes the origin of the error or warning. Right-click the front panel error in control and select Explain Error or Explain Warning from the shortcut menu for more information about the error displayed.

AM modulated waveform returns the baseband AM vestigial sideband modulated signal data and its complex envelope.

	t0 returns the trigger (start) time of the Y array.
	dt returns the time between values in the Y array.
	Y returns 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.

	status is either TRUE (X) for an error, or FALSE (checkmark) for no error or a warning. Right-click the front panel error in control and select Explain Error or Explain Warning from the shortcut menu for more information about the error displayed.
	code identifies the error or warning. Right-click the front panel error in control and select Explain Error or Explain Warning from the shortcut menu for more information about the error displayed.
	source describes the origin of the error or warning. Right-click the front panel error in control and select Explain Error or Explain Warning from the shortcut menu for more information about the error displayed.

MT Modulate AM (VSB) Details

Details

Tip To adjust the carrier phase, use the initial phase parameter of the MT Upconvert Baseband VI.

Note To avoid distortion, amplitude normalize the message signal to ±1.0. This VI prescales the message signal by the scalar peak amplitude prior to modulation. The default value of 1.0 indicates that no prescaling occurs.

Double Sideband (DSB) Amplitude Modulation

The output amplitude-modulated signal is represented by the following equations:

where

m(t) represents the message signal data

S _DSB (t) and S _DSBSC (t) represent the AM modulated signal

k represents the modulation index

Single Sideband (SSB) Amplitude Modulation

AM-SSB modulation ensures bandwidth reduction by only retaining either the upper or lower sideband in the message spectrum after the modulation process. The following figure illustrates the series of algorithms applied to the incoming signal m(t). The VI applies the AM-DSB algorithms and then applies the Hilbert filter to remove the signal.

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

where

m(t)represents the message signal data

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

S _SSB (t) represents the single sideband AM modulated signal (unsuppressed carrier)

k represents the modulation index

A _pilot represents the amplitude of the pilot tone

ω _pilot represents the frequency of the pilot tone

h _i represents the real component of the Hilbert filter

h _q represents the imaginary component of the Hilbert filter

When suppress carrier? is set to TRUE,

where

m(t)represents the message signal data

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

S _SSBSC (t) represents the single sideband AM modulated signal (unsuppressed carrier)

k represents the modulation index

A _pilot represents the amplitude of the pilot tone

ω _pilot represents the frequency of the pilot tone

h _i represents the real component of the Hilbert filter

h _q represents the imaginary component of the Hilbert filter

In both suppressed and unsuppressed carrier cases, one of two possible Hilbert filter designs is specified using the design element in the Hilbert filter cluster. Select either a Windowed Hilbert transformer or an Equiripple Hilbert transformer.

The Windowed Hilbert transformer generates a length N Hilbert filter with an impulse response h(n) given by the following equation:

The Equiripple Hilbert transformer generates a length N Hilbert filter with an impulse response h(n) given by the following equation:

where g(n) represents an equiripple lowpass filter with a normalized cutoff frequency of 0.25 Hz.

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 VI applies the AM-DSB algorithms and then applies the Vestigial filter to remove the vestige.