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On Fri, Feb 12, 2021 at 06:33 PM, Ed Krome wrote:

Concerning how to measure capacitance and inductance on the RF Demo board (or
any capacitor or inductor), reference
/g/nanovna-users/wiki/16592. I can get the curves shown in
this demo just fine.. but how to read the actual values off of those curves
eludes me. On the item 8 inductor example, if I vary the frequency, I can make
that component read about any value I want. I must be missing something. Help,
please.

Ed,

There have been a number of good posts by others describing the characteristics of inductors and capacitors versus frequency. Parasitic capacitance is a big factor and needs consideration.

This post will hopefully be a direct answer to your question of how to read the inductance value on the NanoVNA.

The first step is to make sure that you have calibrated correctly using the open, short and load that are on the test board. This is cumbersome because those little u.fl connectors are not easy to work with. Once you are sure that your calibration is OK you can measure the component. The Smith chart has a readout that will give you the resistance and inductance or capacitance for the marker frequency. As you move the marker you will see the resistance increase on the inductor due to the "skin effect" . The inductor value shown at the marker is calculated by dividing the reactance by 2*pi*frequency. You have to be careful interpreting the results because parasitic capacitance will affect the reactance measured and the estimate of L by this method will get worse as the frequency increases.

I made some tests today on a small air-core inductor that measured 243 nH on a DE-5000 inductance meter at 100 kHz. I then connected it to a calibrated test jig and made some measurements. I attached a series of annotated screenshots showing the estimate of L by the NanoVNA at various frequencies up to 150 MHz. .

I then used the NanoVNA app by OneOfEleven to plot L, R and X versus frequency. You will note that at 50 kHz. the estimate of L is poor compared to my DE-5000 inductance meter. This is because the value of X is very small at this frequency and not in a reasonable measurement range for the NanoVNA. As the frequency increases to about 1 MHz. the accuracy of the estimate improves because the reactance is now a little over 1 ohm. Note the slight rise in calculated L with frequency due to the parasitic capacitance of the inductor.

Roger