I may start this as a new thread titled Measurement of Components... again.
In any case, I put together the nice n' easy alligator BNC connector interface which is easy to deal out.
The part under investigation is a 1 uH inductor whose SRF is above 150 MHz. Nice. I can measure it down at 3 MHz or so with no worry about SRF complications.
I do a shunt mode measurement, one port only and a SOL calibration directly at the VNA CH0 port.
The frequency range is 1-30 MHz, 101 data points. I then add on the BNC alligator clip interface to the VNA.
My first observation is that this test set system with the alligator clips open and laying on the table has a shunt C of 10 pF at 3 MHz. I then short the clips together and find that the series inductance of this test system is 300 nH.
Next I connect my 1 uH inductor and note the CW movement of the chart with a readout of 1.37 uH at 3 MHz. I have at this point an inductor under measure with a shunt C of 10 pF and a series L of 300 nH.
I can remove the shunt C first by noting that the measured reactance must be of the form of the product over sum of the DUT and the shunt C of the fixture. Hence, the actual reactance measured, Xa must be:
Xa=(Xc*Xm)/(Xc+Xm) where Xa is the actual reactance of the DUT, Xc is the shunt C of the fixture and Xm is the measured reactance. You will note, if the Xc value is significantly LARGE then Xa=Xm and the only fixture component that I would have to remove is the stray series inductance.
The measured value of above experiment returns an Xa equivalent to 1.37 uH. Now I must remove the stray 300 nH and I arrive at a corrected value of 1.07 uH. This value correlates with an independent vector Z meter measurement within 50 nH measured at the same operating frequency.
Key here, you must calibrate with know standards to remove the aberrations-imperfections of the VNA instrument hardware, this is level one. Then level two must address the inherent parasitic values of the test set. This is essential. Then apply the appropriate arithmetic to find the unknown DUT itself.
Alan
