Multi-channel Instrument, Complex Stimulus-Response Measurement

With an instrument that has two or more channels, you can connect both the stimulus and response signals to the instrument and make continuous stimulus-response measurements. This is probably the best setup for measurement accuracy because you can use Fixed Equalization to correct for the Ch1 to Ch2 frequency response due to your hardware setup (connectors, couplers, etc.). This scenario is also the simplest to set up.

Observe maximum input power limits. See the technical specifications for your measurement hardware to determine the maximum input limits.

Some Keysight signal generators provide user power limiting (e.g. to set a max input power level to your DUT Device under Test: An acronym used to describe some type of electrical apparatus connected to test instrumentation. The apparatus can range from a single component to a complex subsystem such as a mobile phone, base station or MSC.). This is generally found in the AMPTD menu ("User Power Max" for the N5182A MXG).

Since you are using a single instrument, both measurement channels capture data at the same time so the instrument does not need to be triggered. In addition, you can use any stimulus signal source you wish since the stimulus signal will be measured along with the response for each measurement acquisition.

Initial Setup

  1. Connect the measurement instrument to your computer. See the Creating Hardware Configurations topic for more information.

  2. If you are using an Keysight signal generator as the stimulus, connect the 10 MHz Megahertz: A unit of frequency equal to one million hertz or cycles per second. OUT of the measurement instrument to the REF IN of the signal generator.

  3. Connect the stimulus signal to your DUT and to Channel 1 of the measurement instrument (using a coupler, for example).

  4. Connect the output (response) of the DUT to Channel 2 of the measurement instrument. Note that for some oscilloscopes, the VSA Channel 2 is mapped to the oscilloscope's channel 3 by default (because of shared ADCs). In this case, connect the output of the DUT to oscilloscope Channel 3.

  5. (optional) Set up Fixed Equalization to correct for known differences between Channel 1 and 2.

  6. Configure the VSA

    1. Preset the VSA (File > Preset > Preset Setup). This will reset the VSA back to a basic Vector measurement.

    2. Select the Analyzer Configuration that contains your measurement hardware (from step 1)

      Click Utilities > Hardware > Analyzer and choose from the list.

    3. Set the center frequency

      Click MeasSetup > Frequency to open the MeasSetup dialog and then set the Center parameter.

    4. Set the Span (also in the MeasSetup dialog). Make sure the edges of your stimulus signal are outside the measurement span.

      Span must be the same for both stimulus and response signals.

    5. Set Main Time Length

      Click the Time tab in the MeasSetup dialog. See Choosing the Time Length for a discussion on choosing an appropriate time length.

      To increase the range of the Main Time Length parameter, select the MeasSetup > ResBW > Frequency Points > Auto check box.

Measure Stimulus-Response

  1. Run the measurement by clicking the Restart button in the toolbar and verify that your stimulus and response signals appears as expected.

  2. Set the range for each channel (Input > Analog > Range) or click the Auto-range button in the toolbar to ensure the best dynamic range for an accurate measurement.

  3. Add Graph traces

    1. Add a new trace to the VSA (Click Trace >  )

    2. Select the type of Graph trace you want (Click Trace > Data > Graph).

      Initially, you might want to view AM Amplitude Modulation - CW modulation using amplitude variation in proportion to the amplitude of the modulating signal. Usually taken as DSB-LC for commercial broadcast transmissions and DSB-SC for multiplexed systems./AM, AM/PM, and Gain Compression. Then, when you are trying to track down the cause of a high-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. event, you might want to view the Delta EVM Time, Stimulus Time, and Response Time traces.

    3. Configure Graph Settings (click Trace > Graph Settings)

      You can skip steps i-iii. They are shown for your reference (the Auto selection should choose the correct data in this scenario).

      1. Clear the Auto check box

      2. Set Stimulus Data to Ch1 Main Time

      3. Set Response Data to Ch2 Main Time

      4. Customize any of the other settings as desired.

    4. Autoscale the trace

      When you don't see any data, the trace may be outside the limits of the trace grid. Try right-clicking in the center of the trace grid and choosing Auto Scale.

    5. Repeat a-d to add more Graph traces if desired.

      Instead of configuring each Graph trace in step c, you can configure one trace and skip step c for the other Graph traces. Once you are finished adding the Graph traces, select the configured trace and click Copy To > All Traces.

  4. Run the measurement

    Click the Restart button in the toolbar.

See Also

Measurement Overview