Time Domain Measurements

NI RF vector network analyzers that support time-domain measurements use an inverse FFT to transform data from the frequency domain to the time domain. Viewing data in the time domain allows you to discover information about device performance at specific locations. Time-domain measurements are primarily useful when analyzing broadband low loss devices such as transmission lines, connectors, test fixtures and similar components. Narrowband devices, such as filters, isolators, or matching networks, are less suited for time-domain measurements.

NI-VNA allows you to configure your time-domain measurement by selecting the type of time-domain measurement, choosing a window type, or selecting a gating shape.

The following figure shows the frequency data and the time domain data for a given measurement. In this figure, Trace 1 shows a time-domain lowpass step plot of the S11 data from Trace 2. The lowpass step time-domain data reveals information about the data that is difficult to interpret when viewing only the frequency-domain data.

Activating the Time-Domain Option on Your NI RF Vector Network Analyzer

Frequency measurements are supported on all NI RF vector network analyzers. Time-domain measurements, however, are a product option that is available for purchase from National Instruments. If you purchased the time domain option when you ordered your device, the device should ship from the factory with this option already activated. If you purchase the Time Domain option after you receive your module, use one of the following options to activate the Time Domain option on your device:

• Complete the following steps to use the NI-VNA SFP to activate the Time Domain option.
  1. Launch the NI-VNA SFP.
  2. Select System»Diagnostics from the Softkey Menu.
  3. Enter NIVNA as the password in the Diagnostics Access dialog box, and click OK.
  4. Select Enable Time Domain from the Softkey Menu.
  5. Enter the license key in the Enable Time Domain Option dialog box, and click OK.
• Complete the following steps to use Measurement & Automation Explorer (MAX) to activate the Time Domain option.
1. Launch MAX.
2. Select the VNA module from your chassis tree item.
3. Verify that the Time Domain Status displays Not Activated.
4. Right-click the VNA module, and select Activate Feature from the shortcut menu.
5. In the Activate Feature dialog box, use the Pick a feature to activate control to select Time Domain.
6. Enter the license key, and click OK.
• In LabVIEW, call the niVNA Activate Feature VI and set the feature parameter to Time Domain. Enter the key as the value of the activation key parameter.
• In C or LabWindows/CVI, call the niVNA_ActivateFeature function and set the feature parameter to NIVNA_VAL_TIME_DOMAIN. Enter the key as the value of the activationKey parameter.

Related Topics:

• Activating Time Domain in MAX
• Configuring Your Time-Domain Measurement
• Understanding How Resolution and Aliasing Impact Time-Domain Measurements