NanoVNA as a RLC meter

Building anything RF-related, like filters or amplifiers for ham radio, you quickly find you need a way to measure capacitors and inductors, especially homemade ones like air-wound coils. You can use online calculators to get the number of windings, but there are just too many variables that affect the result.

You will also find the value varies with the operating frequency, this is normal and fine if the change is not too fast. I never really thought of this and kind of ignored things like parasitic capacitance, but you can’t get away with that at RF.

High quality components vary less, but none are perfect. When choosing components for a build, it’s good to check their response at the operating frequency, even if they have something written on them. I had some cheap capacitors that simply stopped being capacitive above a few MHz.

I recently bought a NanoVNA and spent some time figuring this out. Guides on YouTube were more misleading than helpful but it’s surprisingly easy in the end

Note: I use the program NanoVNASaver for this, as I find the device’s display too fiddly to use.

To keep it short, here’s a list of things to do to get accurate readings:



Here’s an example measurement of a 23uH inductor (seen above in the screw adapter) that I wanted to use on the 40m band. It looks fine up to about 15 MHz, the rolloff is probably caused by the material in the ferrite ring, parasitic capacitance between windings, etc.

NanoVNASaver interface showing inductor measurement