Nano VNA

In 2019 the Nano VNA (vector network analyser) was launched. VNA's are not new, but they have previously been classed as being way too expensive the ordinary man. Something that once cost £50K is now £50. 100th of the price. Do they work, YES. They work just as well as all those high priced offerings. The difference is really down to it's frequency range.  We're not talking microwaves here, but a typical Nano VNA will work superbly up to about 450Mhz, and reasonably up to 900Mhz.  Firmware updates can take this to 1500Mhz but dynamic range is poor and measuring reactance is next to useless. It will however perform quite well as a basic SWR meter. Firmware mods can be done using DFU-UTIL software to upload firmware. For more resources, including PC software, user help and firmware images click here and here.  All the notes and resources here refer to the originally supplied versions. Newer versions have modified screens, firmware and enclosures. I was so impressed with the performance of the Nano VNA that I purchased a second one as a spare, just in case I have an accident or something and they become unavailable.

As originally supplied, the Nano VNA is not properly cased, the product is supplied as a "sandwich board" and requires some user modification to beef it up a bit. Here I'll describe how I did mine. Firstly I found a suitable aluminium box to use as a case. I then cut out a rectangle for the display to be viewed.  I wired a suitable external power switch so that it was panel mounted instead of on the side of the original PCB.  NOTE - do not simply insert a switch between the battery. This is because there's a part of the switching circuit that requires a power supply to always be present in order to switch the power supply directly to the main Nano VNA unit. (Same as any othe consumer "soft" switched device).

There's a multifunction selector on the original PCB,  but to replicate this externally would be messy. The solution is to use a stylus on the touch screen. ALL functions are available with this method. I  reused the original front sandwich plate to form it's own front panel. No need to add labels on the new enclosure, since the original front panel takes care of that. I recommend using VHT spray paint for the new enclosure. VHT paint, Very High Temperature paint is used on automotive engines as a convenient spray paint. It dries to a crackle finish, much like old electronic equipment used to have. An undercoat (primer) is recommended despite claims to the contrary. For charging the battery pack, or connecting to a PC I used a magnetically coupled USB cable.  This protects the PCB mounted USB-C connector from wear and tear, or damage if you accidentally  pull the cable. They self align, even a blind man can use them. They come as DC supply or DC and data  lines. Just pull it off to detach. Ensure that you use the correct 4 wire cable for data and power. BELOW - Nano VNA as originally supplied.

New enclosure using SMA to SO239 connectors and detachable magnetic USB cable.

General view of finished product.

Just about everything I have here uses PL259 so it made sense to use bulkhead mounted convertors. They are perfectly OK to use. We're not looking to make repeatable measurements at 10Ghz here and are thus perfectly acceptable. I then have available some PL259 to SMA adapters (as shown) when required. It's also very easy to  make your own PL259 calibration kit good enough upto 150Mhz. Above this you might want to invest in a simple SMA based calibration kit. If you use it as a signal generator, it's within 1Hz at HF.  Output power is about 100mv RMS, that's about -7dbm, from Port 0,  and that's also the typical maximum input power to Port 1. Battery life is about 2 hours using the supplied 400maH pack.  A stable non flashing LED means that the battery is charged. 

You MUST properly calibrate the VNA when you use it otherwise it is useless.  Don't rely on the factory calibration at all. The calibration procedure is below and will be used upon each boot up.



Nano VNA Saver on a Raspberry Pi.

I recently produced an RPI image that gave the Raspberry Pi a working Nano VNA Saver software.  My method of getting the required dependencies etc installed took quite long route to achieve the same, However I recently came across what appears to be a simpler way of doing things, although I have NOT tried this route since my version already works. However it is presented here for anyone who might like to try it themselves. It is recommended that a  recent edition of the Raspberry PI operating system is used. 

The instructions are -

Install scipy ( sudo apt-get install python3-scipy) and pyQT (sudo apt-get install qt5-default qt5-default qtcreator).

And then run the program with the command " Python3 nanovna-saver.py" which you download from the official repo.

Quick start for Linux Mint users. Should be OK with Debian or Ubuntu.

Use Nano VNA Saver files here.

Or here. (NOTE, my QSL.NET site is pushing the storage limits now so my Google site is tending to host some newer files).

Measuring components with a Nano VNA.

Actually this applies to the use of any VNA. You can use a VNA as an LCR bridge, but you need to be aware that any VNA can give confusing results especially when a high test frequency is used.  Best to use something low like 100KHz. Components are constructed in many ways and can include (for example) capacitance and inductance, such as that caused by paper foil construction of large capacitors, or resistors that are actually a spiral of laser cut carbon (at VHF or UHF this small amount of inductance becomes increasingly significant. In some cases, capacitors would look more like an inductor ! Also inductances have inter-winding capacity too which may confuse the VNA or even a simple LCR bridge. It's wise to familiarise yourself with any measurement tool and component construction before getting yourself confused.

Quick intro to S-Parameters.

S11 (e.g. port 0 as it's normally called on a VNA) is where you hook up an antenna etc to measure it's impedance.

S21 is used in conjunction with the S11 port to measure things like coax loss or filters. You connect the part under test between the two ports and select in the menu to measure S21. You can read off db attenuation vs frequency with this method. Don't panic over the name s-params, you'll see immediately what it represents in a second!

Never connect ANYTHING that sends a signal more than -10dbm (0.1mw) into any port. You will break it. If you are attempting stuff like measuring the gain of a small amplifier then you MUST use suitable attenuation in series.

Use a DC block on the inputs too. Do NOT apply more than 5v to the input ports. (In reality that just means a high quality capacitor that in an ideal world with have no measurable inductance at the frequency of measurement, and has a high enough value to pass the measured frequency with zero loss).

Also, if you use the magnetic USB method for connecting the device to a PC then here's a small tip. Sometimes the software like Nano VNA Saver cannot connect to the device. For us Linux users we simply type lsusb in the terminal to see if it's there (STM microcontroller). Now then those magnetic controllers can get dirty and tarnished over time. You might be able to charge the device, but not see the data connection. The cure, simply rotate slowly the connector on the cable upon the mating half in the VNA to scrape off the dirt. Re-run lsusb and hopefully you can now see it.  The other possibility is that you have incorrect user dialout settngs. Please read my Linux page for help.

Electrostatic prevention. Things like Nano VNA's and Spectrum analysers are VERY sensitive to electrostatic discharge. Your antenna could easily be charged with 10,000 volts of static (seriously) and you'd never know. So before connecting it, touch the outer and the inner to a nearby ground to discharge it just in case. Also if you wear what I call "safety boots", you could be charged up too. Discharge yourself in the same manner just in case you end up sending lots of volts up the input.