Source Power Calibration is very slow.

Question

I perform a source power calibration with an NRP-Z21 at –30 dBm on port 1, and the source power calibration takes several minutes to complete one sweep.

Answer

When the VNA makes a source power calibration with an NRP power sensor at a very low output level, the NRP power sensor automatically switches averaging on.

The power level below which averaging starts as well as the averaging number depend on the NRP power sensor used.

For example, the NRP-Z21 power sensor starts averaging below –25 dBm and the averaging number can be 128

at –30 dBm.

To avoid this, you can perform the source power calibration at a higher output power (e.g. –20 dBm) and decrease the output power to –30 dBm after the source power calibration has been completed. The output power linearity of the VNA is so good that the accuracy for both output power values is nearly the same.