An experiment with NanoVNA and series through impedance measurement… more concluded with:
The NanoVNA-H4 v4.3 NanoVNA-D v1.2.30 using 5 term calibration does not appear to give good accuracy on series through measurement of impedance.
Further investigation identifies several possible contributions, the main one being the s21 correction algorithm and implementation.
Dislord confirmed that the s21 correction algorithm did not include Enhanced Response correction, and has released v1.2.32 which includes the feature (which has to be enabled on the calibrate menu).
Note the E in the cal status column at left.
The nanoVNA-H4 v4.3 with Dislord v1.2.32 was calibrated using a SDR-kits test board and its associated OSL components. The test board is used without any additional attenuators, it is directly connected to the nanoVNA-H4 using 300mm RG400 fly leads.
Test inductor
The test inductor gives a small DUT that has similar characteristics to a HF common mode choke.
Above, the test inductor mounted in the s11 shunt measurement position, but the tests below are in the s21 series through connection.
Above is a plot of |Z| from 1 to to 30MHz without Enhanced Response correction.
Above is a plot of |Z| from 1 to to 30MHz with Enhanced Response correction, and the without case shown in cyan for comparison. In this case the non ERC trace is inflated about 10%.
Above, it is interesting to compare three methods of impedance measurement. The series-π method is often known as the K6JCA Y21 method.
200Ω
A s21 series through measurement of the 200Ω SM 1% resistor was also conducted and results were very close to the measured value of the resistor.
Conclusions
The NanoVNA-H4 v4.3 using 5 term calibration does not appear to give good accuracy on series through measurement of impedance unless Enhanced Response correction is enabled (Dislord NanoVNA-D v1.2.32 and later).