Pointless Circuits

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May 24, 2020 - Comments - RF electronics

NanoVNA 2 - First Impressions

This week, after some Corona-induced delays, I finally found my NanoVNA 2 in my post box. Now, for everyone that is not familiar with this family of devices, the NanoVNA-Series are tiny vector network analyzers for an affordable price. While I never owned the first version, I heard a lot of good about them, and when version 2 with an increased frequency range came on the market, I ordered one for myself on Tindie.

While commercially available VNAs obviously feature capabilities far in advance of small hobbyist devices, they also come with hefty price tags somewhere between a car and a single-family home and in form factors only usable for rather large bench-tops. The NanoVNA v2 offers a frequency range from 50kHz to 3Ghz with a calibrated dynamic range of 60dB in the worst case. This suffices for most home-use applications up to the 2.4Ghz ISM Band.

Device and Accessories, as delivered

After opening the - surprisingly toll-free - package, i was presented with the VNA itself, a simple calibration kit and some surprisingly high-quality SS405 SMA-Cabling with more than adequate performance in the achieveable frequency range.

Measuring the transmission

While being adequate, the recommended software to use, NanoVNA Qt runs reasonably well on both Windows and Linux (Windows also needs a driver for the Cypress USB Chip), it is still quite limited in function and a bit buggy (Frequent crashes when doing a full calibration). The reference software NanoVNA-Saver for the old NanoVNA has some unofficial patches, but is not very reliable and user-friendly with the NanoVNA 2. Nonetheless, I managed to calibrate mine after updating to the newest firmware and get some measurements on two devices I have lying around. One being a Mini-Circuits ZFBT-4R2FW+ Bias-Tee, where I just looked at the Isolation between the RF and the DC port. The other DUT was a custom board with an Mini-Circuits AMK-2-13+ Frequency doubler, for which I measured the base frequency isolation.

Hacky Reference Setup As a reference, I used a combination of an Rohde+Schwarz ESU26 EMC Test Receiver with an R+S SMBV100A as tracking generator. This can be combined to mimic a surprisingly good scalar network analyzer substitute for measuring the forward transmission gain of a DUT.

Comparing both results, the NanoVNA v2 shows a pretty good agreement with my reference system. This will definitely be a welcome addition to my hobby test bench. In the future, I plan to also characterize the cal-kit with one of our VNAs at work, to provide additional correction factors for the calibration algorithm and obviously provide those to everyone interested. Also, I will have a look at the vector components of my device and some vector-capable reference system and also some more DUTs - somewhere I should have a GNSS-Amplifier - as soon as I have some more available.

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