Range (Input Analog Tab)

Setting the IF input level as high as possible without saturating the input range of the ADC enables you to make full use of your ADC sensitivity. Some RF engineers will set the input range for best possible EVM, observing a local minimum as a function of input range. This minimum is due to a typical trade-off between noise and distortion. If you crank up the input range to high, distortion might degrade EVM. If you back away too far from the overload condition, then the signal-to-noise ratio dominates the EVM measurement. It’s a balance and matter of preference.

Here's one good approach. Slowly turn the input range down until you get a red overrange LED and the overload indicators turn on. Now, trace back one step on the input range to just before the overload indication. Doing this enables the best dynamic range for your measurement.

We use the expression "Range" to specify the range of the selected Logical Channel, which has a direct impact on the signal level to the ADC. The range can be changed in one of two ways: from the Input Analog dialog box ( Input > Analog > Range) or from Range listed above the trace on the display. In either case, when the field is highlighted there are two ways to change the range setting:

Use the mouse wheel or the arrow keys (↑ or ↓) on the keyboard to scroll through the valid ranges.
Type the desired range setting, select the units (volts or dBm) and click OK or press Enter. The VSA sets the range to the closest valid value.
To determine what ranges are available, click the Range hotspot on the display and use the keyboard up and down arrow keys or the mouse wheel to scroll through the available ranges.

This parameter can be selected for All channels or individually for each available channel. The available channels are displayed in Logical Channel located at the top of the dialog box. If the selections for individual channels are different, the arrow button () after the Range text box will be orange. Click the arrow button to view the Range selection for each available channel.

Optimum range: For information on how to choose the optimum range, see Selecting the Optimum Range Value.

I+jQ or Dual I+jQ channel mode: Use the Couple Paired Channels parameter to couple the I and jQ channel ranges.

For information on range with measurement hardware, see the Measurement Platforms section of the online help for a link to your specific hardware.