Making a Custom IQ Measurement

This topic describes how to configure the VSA to make a Custom IQ measurement.

Overview

You must manually configure the VSA Custom IQ demodulator to measure your signal. To do so, configure the measurement setup parameters, e.g. constellation, symbol rate, result length, etc.

Signal Setup

Before selecting the Custom IQ demodulation mode, make sure that the input signal is correctly captured by the analyzer. Specify the VSA basic signal measurement setup parameters so that the input signal is fully captured including; the center frequency, span, input range, etc.. You can use the Spectrum and Time traces to verify that the signal of interest is properly captured.

Demo Signals

To use a demo signal, click File > Recall > Recall Demo > navigate to the "%PROGRAMFILES%\Keysight\89600 Software <ReleaseVersion>\89600 VSA Software\Help\Signals\CustomIQ" folder and select a Demo File.

Configuring the Demodulator

Step 1 - Specify the signal parameters

To begin, select the Custom IQ demodulator, click MeasSetup > Measurement Type > General Purpose > Custom IQ. Then open the Custom IQ Demod Properties dialog, click MeasSetup > Custom IQ Demod Properties.. .

Step 2 – Configure the Measurement Parameters

The setup options for the Custom IQ demodulator are similar to other demodulation formats; however, the Custom IQ demodulator provides the ability to create an IQ constellation, set parameters, and save as a Quick Setup, or choose an existing Quick Setup and customize it to match your signal.

Format Tab

• Quick Setups/Save As Quick Setups
  • select an existing Quick Setup or save a custom constellation/setup as a Quick Setup.
• Constellation Editor
  • create and define all of the states in your signal's constellation, or modify an existing constellation to use in your setup.
• Symbol Rate
  • sets the symbol rate to match the symbol rate of the system.
• Result Length
  • selects the number of symbols to be displayed by the VSA.
• Search Length
  • determines the amount of time over which a search is performed.
• Pulse Search Enable
  • enables or disables pulse search.
• Pattern Search Enable
  • enables or disables the search for a user-entered bit pattern and offset.

Filter Tab:

• Measurement Filter
  • specifies the filter to apply to the time data before demodulation.
• Reference Filter
  • specifies the filter to apply to the reference signal that the demodulator creates based on the demodulated input signal.
• Alpha/BT Bandwidth Time Product
  • selects the Alpha/BT characteristics of the selected filter.
• Equalization Enable
  • applies the VSA's equalization filter to the measurement.

Advanced Tab:

• Points Per Symbol
  • determines the number of points displayed between symbols for digitally demodulated data.
• Clock Adjust
  • determines when the VSA's custom IQ demodulator samples the I/Q trajectory.
• Coarse Frequency Estimation Enable
  • enables or disables frequency estimation and compensation prior to the synchronization phase.
• IQ Normalization Enable
  • enables or disables IQ trace normalization.
• EVM Error vector magnitude (EVM): A quality metric in digital communication systems. See the EVM metric in the Error Summary Table topic in each demodulator for more information on how EVM is calculated for that modulation format. Normalization Reference
  • sets the normalization value for certain error summary metrics.
• Synch Persistence Target
  • allows the user to tune the algorithm for higher frequency lock range or higher constellation lock consistency.

See Also

Selecting the Custom IQ Demodulator

Troubleshooting Custom IQ Measurements