Single-channel Instrument, Complex Stimulus-Response Measurement

To perform a stimulus-response measurement with a single-channel instrument, you will need to measure the stimulus signal and save a trace of the signal's time data into a Data Register. Then you can measure the response signal from the 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. and compare the two signals.

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). This is generally found in the AMPTD menu ("User Power Max" for the N5182A MXG).

This procedure assumes you have configured an Keysight signal generator to provide the stimulus signal (perhaps by creating the signal in the Keysight Signal Studio software). If this describes your situation, you can skip to Initial Setup. If this is not exactly your situation, see the following paragraphs for variations on the procedure.

You can use something besides an Keysight signal generator as the stimulus; just be sure to provide a trigger signal from the stimulus source to the measurement hardware.

You can skip the Measure Stimulus section if you already have your stimulus signal recorded in a format that can be recalled by the VSA. Make sure the measurement hardware is being triggered when the beginning of the stimulus is sent into the DUT. In the case where you want to use an Keysight signal generator to send the stimulus signal, see the Use Keysight Signal Generator for Stimulus Signal topic.

Lastly, if your stimulus is inherently non-repeating, such as an AWGN Additive White Gaussian Noise - Statistically random radio noise characterized by a wide frequency range with regards to a signal in a communications channel. signal, you can still perform a stimulus-response measurement by recording a section of the stimulus signal and using an Keysight signal generator to play the segment in a loop into your DUT. To do this, skip step 5f and use Free Run triggering instead when recording the stimulus (Measure Stimulus section). Then set triggering to External after the Measure Stimulus section. You will also need to download the segment of the stimulus you recorded into your signal generator.

Initial Setup

  1. Connect the trigger output (for Keysight signal generators, use the EVENT 1 signal) of the source to the trigger input of the measurement instrument (make sure you use the primary trigger for your measurement hardware when there is more than one; for example, Trigger 1 IN).

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

  4. Connect the signal generator to your computer. See the Creating Hardware Configurations topic for more information.

  5. 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 2)

      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)

      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.

    6. Configure triggering

      Set triggering to External (click Input > Trigger and set Style to External).

Measure Stimulus

  1. Connect the signal generator RF Radio Frequency: A generic term for radio-based technologies, operating between the Low Frequency range (30k Hz) and the Extra High Frequency range (300 GHz). Output to the RF Input of your measurement instrument.

  2. Run the measurement by clicking the Restart button in the toolbar and verify that your stimulus signal appears as expected.

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

  4. Pause the measurement by clicking the Pause button.

  5. Save the stimulus signal

    1. Click the Trace menu and select Trace B (Main Time).

    2. Click File > Save > Save Trace

    3. Set Save as type: to SDF (Fast)

    4. Specify a location to save the Main Time trace.

    5. Click Save

    Instead of saving the stimulus trace, you can copy the stimulus directly into a register (File > Copy Trace > D1) and then skip step 16 below.

Measure Stimulus-Response

  1. Connect the RF Output of the signal generator to the input of the device you are testing (DUT).

  2. Connect the output of the DUT to the RF Input of the measurement instrument.

  3. Switch to acquiring data from hardware by clicking Input > Data From > Hardware.

  4. Run the measurement by clicking the Restart button in the toolbar and verify that your response signal appears as expected.

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

  6. Recall the stimulus data recording into data register D1

    Click File > Recall > Recall Trace and select the saved stimulus trace file. Click Open and then specify register D1 when prompted.

  7. 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 Register D1

      3. Set Response Data to Ch1 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.

  8. Run the measurement

    Click the Restart button in the toolbar.

See Also

Measurement Overview