I recently bought NanoVNA. It was a great choice!
This tiny device measures everything that an OM needs for his experiments and there is a ton of help on the NanoVNA forums and YouTube.
I got a lot of controversial feedbacks on the instrument, especially when used at frequency higher that UHF (theoretically the instrument reaches 3GHz..) so I decided to do a simple test with a 2 ports measurement.
Please note that the following tests don’t claim to be a complete characterization of NanoVNA. I simply write some results after some simple test.
I tested a Nooelec notch filter for FM broadcasst (88-108MHz) and compared the results with the Nooelec measurements. Nooelec made S parameters csv files available on the website, from DC to 200MHz and from DC to 1200MHz. I appreciated this files very much, because it’s unusual and I always find pdf plots.
I accurately calibrated the VNA with the calibration kit in bundle.
Important Note: As suggested by NanoVNASaver during the guided calibration procedure, it’s necessary to calibrate the instrument in “stand alone” mode and store the results in one internal memories (I used “Save 0”), for better results! If I skip this step, the S21 calibration becomes really bad at higher frequencies (about 3-4 dB instead of 0dB with the through connection)! I don’t understand very well why this happens, but at the end it’s mandatory to follow the suggestion of calibration assistant.
After the verification of the S21 calibration with the SMA through connector (flat line around 0dB), I started to measure the filter with NanoVNASaver.
With NanoVNASaver it’s possible to export the graph in S2P csv file. This file is in “touchstone” format and data are stored as Real and Imaginary part for every S parameter. I imported this file in excel and then calculated the S21 in dB with the well known formula 20*log[sqrt(Re^2+Im^2)] and I easily got a result comparable to the Nooelec files.
I set the NanoVNA for 1000 points sweep, while the Nooelec includes only 600 points, but Excel can plot different series on the same graph although the “X” axis are different.
The result from DC to 200MHz is here below:
Here below, the results from 0 to 1200MHz, plotted in the same way:
It’s not too bad, considering that the Nooelec measurement is not taken on my filter and one specimen can different from other due to component tolerances. Moreover, as previously explained , the frequency resolution is different between the plots and this could giustify the deeper “hole” in the plot.
In the second figure, a ripple is present in the NOOELEC plot at higher frequencies, so I don’t know if their VNA is properly calibrated.
I’m going to do some other tests up to 3GHz. For the moment, I hope these results could be helpful to those are going to buy ad NanoVNA or a NOOELEC Filter.
73’s de Alfredo IZ7BOJ