System Impedance (Z0)

The PLTS system impedance can be changed when measuring devices with an impedance other than 50 ohms, such as waveguide or 75 ohm devices. PLTS mathematically computes and displays the measurement data as though the test ports were the specified impedance value. Physically, the test ports are always about 50 ohms.

All ports are set to the same System Impedance value.
The system impedance value applies to data that is measured with both Network Analyzer systems or TDR.
When the system impedance value is changed, the data is visibly changed only in Time Domain plots. It has no impact on other data formats.
PLTS performs the impedance math regardless of the impedance settings in which the data is measured. For example, if a measurement is made using a PNA with a 75 ohm system impedance, but the PLTS system impedance is set to 50 ohms, then PLTS will display the data with the 50 ohm system impedance setting.
System Impedance is saved with Touchstone (*.sNp) files. Therefore, when *sNp files are imported with a system impedance value which is different from the current PLTS setting, the current setting is ignored and data is displayed using the system impedance setting with which the imported data was saved.
System Z0 value is displayed in both the PLTS status bar and Files tab of the DUT viewer.
System Z0 is saved with a *.DUT file.

How to change the System Impedance

Click Utilities, then System Z0

System Z0 dialog

This function corrects the measurement and displays the results as if the measurement had been made into the specified impedance value. However, the physical port termination is still approximately 50 ohms.

System Z0 - Enter an impedance value, then click Apply

Enable Arbitrary Mixed Mode Impedance Conversion - Check to use Differential or Common Mode Impedance values.

Differential impedance value for each balanced port. The default value for R: is the SUM of the impedance values for both ports that make the logical port.

Common Mode Impedance value for each balanced port. The default value for R: is calculated as follows.

(Z1 * Z2) / (Z1 + Z2)

Where ports 1 and 2 comprise the logical port:

Z1 = the Port Impedance values for port 1

Z2 = the Port Impedance values for port 2

Last Modified:

19-Oct-2011	Add Mixed Mode Impedance Z0
7-Apr-2008	New topic