Version:

Last Modified: February 7, 2018

Calculates the maximum possible peak amplitude, after pulse-shape filtering and resampling, of a waveform for the QAM modulation scheme.

Parameter values defining the QAM system. Wire this parameter to the corresponding **system parameters** cluster of MT Modulate QAM, MT Demodulate QAM, or MT Detect QAM.

Number of samples per symbol in the modulated output complex waveform. For error-free operation, the **samples per symbol** value must be an even number.

**Default: **16

An ordered array that maps each symbol to its desired coordinates in the complex plane. The number of QAM states in the array is 2^{ N }, where *N* is the number of bits per symbol. The vector length for the symbols farthest from the origin is 1.

An ordered array of filter coefficients corresponding to the desired filter response for the pulse-shaping filter used in modulation. The number of coefficients depends on the pulse-shaping filter characteristics specified in the pulse-shaping filter. Refer to MT Generate Filter Coefficients for more information about pulse-shaping filter coefficients.

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.

**Default: **No error

Inverse of the maximum amplitude of the I/Q waveform based on the specified system parameters.

For the frequency modulation schemes (FSK, MSK, and CPM), there is no known analytical method to calculate the maximum amplitude that accounts for effects such as resampling, filtering, and so on. Empirically, a **waveform scaling factor** of 0.8 should be sufficient for most of your applications. This value results in a maximum dynamic range loss of about 2 dB on third-party (non-NI) RF signal generator devices.

If you receive errors related to this value, your signal might be aliased. For more information about aliasing, refer to MT Modulate CPM or MT Modulate FSK.

Error information.

The node produces this output according to standard error behavior.

Standard Error Behavior

**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.

This node computes the worst case scaling factor using an interpolation factor of 128 for the pulse-shaping filter coefficients. If the modulated signal has a large amount of excess bandwidth (for example due to a high value of the **pulse shaping filter coefficients** parameter), any subsequent FIR filtering may cause significant ringing and subsequently the worst case scaling factor this node computes may no longer remain valid. For example, if the modulated signal undergoes resampling using MT Resample (Complex Cluster) with a resampling factor that has a large number of significant digits after the decimal point, the FIR filter in the fractional resampler may cause significant ringing to cause the maximum amplitude of the waveform to exceed the computed maximum amplitude by more than 3 dB.

**Where This Node Can Run: **

Desktop OS: Windows

FPGA: Not supported

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