The NanoVNA is a new low cost community developed VNA with assembled units coming out of China for <$50.
I have been evaluating one for common tasks around a ham station and noticed a persistent glitch around 7.5MHz in scenarios where |s21| is high.
The nanoVNA-H has firmware NanoVNA-Q-0.4.3-20f33ba.dfu installed. The nanoVNA appears to be a nanoVNA-H v3.3 but it is hard to be sure, it is from China, the land of copyists and fraud. Indeed the nanovna-Q author asserts that genuine nanoVNA-H have a green overlay whereas mine is blue. Uncertainty is part of the territory!
Above is an example where a ferrite cored inductor similar to an antenna common mode choke is measured, and the underlying curves should be smooth with some random measurement noise. The glitch around 7.5MHz is persistent and much larger than the random noise, so I have investigated further. Continue reading nanoVNA-H – a ferrite cored test inductor – drilling down on a glitch