VNA Help
Click here to see this page in full context

Setting System Impedance

The system impedance can be changed for measuring devices with an impedance other than 50 ohms, such as waveguide devices. The VNA mathematically transforms and displays the measurement data as though the VNA ports were the specified impedance value. Physically, the test ports are always about 50 ohms.

How to change the System Impedance

Using Hardkey/SoftTab/Softkey

  1. Press Scale > Constants > System Z0

System Z0 softtab help

Allows you to change the system impedance (default setting is 50 ohms).

Z0  Displays the current system impedance.

For 75 ohm devices:

  1. Change the system Z0 to 75 ohms.

  2. Connect minimum loss pads (75 ohm impedance) between the analyzer and the DUT to minimize the physical mismatch.

  3. Perform a calibration with 75 ohm calibration standards.

For waveguide devices

When selecting a Cal Kit with an impedance other than 50 ohms (Waveguide = 1 ohm), it is NO LONGER NECESSARY to change the System Impedance setting before performing a calibration. The impedance for the calibration is now derived from the Cal Kit 'Connector' impedance setting.