Earlier in the month we posted about the NanoVNA, an open source VNA project by @edy555 and ttrftech that has recently become extremely affordable at US$50 for a fully assembled unit thanks to Chinese manufacturing.
Nucclearrambo provides a Python script which can be used with the NanoVNA's S1P output data to create a TDR graph. His tests with RG405 and LMR200 cable show that the length reported by the script comes remarkably close to the actual length.
A vector network analyzer (VNA) is an instrument that can be used to measure antenna or coax parameters such as SWR, impedance and loss. It can also be used to characterize and tune filters. It is a very useful tool to have if you are building and tuning home made antennas, filters or other RF circuits. For example if you are building a QFH or ADS-B antenna to use with an RTL-SDR, a VNA can help ensure that your antenna is properly tuned to the correct frequency. Compared to a standard SWR or network analyzer a VNA supplies you with phase information as well.
Until just recently, VNA's have cost roughly US$500 for a decent USB PC based unit like the miniVNA or PocketVNA, and have set people back thousands to tens of thousands of dollars for bench top units.
However, the cost of owning a VNA has now been reduced to only US$50 thanks to the NanoVNA. The open source NanoVNA project by @edy555 and ttrftech has been around since 2016, but only recently have Chinese sellers begun mass producing the unit and selling them on sites like Aliexpress, eBay and now Amazon. We note that it seems that there are some sellers selling them without shielding, so it might be worth double checking the listing to see if they mention that. All the listings we've seen seem to come with simple calibration kits as well.
The NanoVNA is a small credit card sized VNA. It has a built in LCD screen that can be used to display graphs directly, or it can also be connected to a PC and the graphs viewed via the NanoVNA Windows software. When purchasing you can opt to include a small battery for portable operation for a few dollars extra. The frequency range is from 50 kHz to 900 MHz, although you should note that above 300 MHz dynamic range performance is reduced.
Over on YouTube several hams and radio enthusiasts have recently uploaded videos demonstrating and reviewing the NanoVNA. The overall consensus is that the unit is accurate and works well. For additional support there is forum available at Groups.IO.
Below YouTube user IMSAI Guy reviews the NanoVNA. Check out IMSAI Guy's other videos too as he has several where he tests the NanoVNA on difference filters and antennas, and checks the accuracy.
#350 NanoVNA Vector Network analyzer 900MHz VNA for $50
Below is YouTube user joe smith's review. He also has two other NanoVNA videos on his channel where he shows how to use the NanoVNA to measure antenna impedance, and how to use the NanoVNA to create SPICE models for simulation.
The NanoVNA, a beginners guide to the Vector Network Analyzer
Finally YouTube user Oli gives another overview. Please note that the following video is in Polish, but YouTube captions can be set to English.
NanoVNA - omówienie, kalibracja, pomiar anteny i filtra [english subtitles]
We've also seen several recent text reviews:
NanoVNA - A short review. In this review nuclearrambo shows off the calibration kit, and shows a practical measurements of a directional coupler and 137 MHz QFH antenna.
The NanoVNA, a real VNA at less than 48 €!. A review written in French, but Google Translate can be used. In this review David Alloza compares the NanoVNA against an Agilent E5062A benchtop VNA, and results look comparable.
As a follow on to the previous post on fake SDRplay units, we also wanted to provide some guidance on fake RTL-SDR Blog V3 clones which are on the market. We are starting to receive an increase in support requests for fake RTL-SDR Blog V3 units. Please be aware that we cannot support these devices, and most of them are missing key features like the bias tee and the TCXO despite advertising these features on the listing and writing on the dongle body. Also as mentioned below a good majority of them appear to have a defect and poor performance.
Please check our store at www.rtl-sdr.com/store for our official stores on Amazon, eBay, Aliexpress and this site. We also have links on our store to our official local resellers.
We note that we tested a few of the "RTL.SDR" clones, and all had a defect causing very strange distorted spectrums where the signals where wider than they should be, and some units introduced a mysterious high pitched whine into every signal.
To be clear, different brands of RTL-SDR are perfectly fine - no one owns the RTL-SDR hardware concept and we are not any more "official" than any other brand (although we believe we were the first to start designing and producing significantly improved units and the first to design in a factory fitted TCXO, SMA connector, bias tee, thermal pad, and a redesigned PCB for lower noise and less spurs).
However, these clones shown in the image above can be considered a sort of scam as they attempt to trick buyers into believing that they are purchasing our RTL-SDR Blog V3 units with false advertising and by copying the enclosure design, when in fact the PCB inside is something inferior.
2021 Supply Chain Updates
As many of you may know the world is currently dealing with a major shortage of many electronics parts so we wanted to provide an update on the supply chain for the RTL-SDR Blog V3.
In particular, the world is very short on temperature compensated oscillators (TCXO's), a critical component used in our units to ensure frequency stability. The TCXO shortage is actually much worse than other components as AKM, the Japanese semiconductor factory that produces a critical component for making TCXOs burned down late last year. There are alternative suppliers, however their pricing is many multiples higher, and they are also inundated with orders increasing lead times.
We believe that we have enough TCXO stock in storage to last us several more months, however we may run into a shortage in the later months of this year. After we expend our current TCXO stock, we expect to have TCXO again around December, with more RTL-SDRs being ready by January 2022. We want people to be aware, as during these months of no stock more clones may appear on the market. Most clones do not use TCXOs, and hence have poor frequency stability.
Also on a related note our Amazon stock levels may be a little spotty throughout this year as there are currently often delays with shipping and the ports.
We also note that other products that we resell on our store such as the FlightAware Prostick Plus and NanoVNA V2+ are also experiencing supply issues, and may not have stock for a while. Production of some of our other products like the L-band Patch are also delayed due to shortages.
Due to the shortages component prices are also significantly increasing, and you may notice an increase in RTL-SDR pricing from us and competitors too. We hope that we will be able to reduce our pricing again once the global shortage is over, most likely around early next year.
Over the course of 2020 Tomaž Šolc from Avian's Blog has been slowly working on an RTL-SDR based vector network analyzer system. The system currently consists of an ERASync Micro signal generator, a custom time multiplexing board, an RF bridge, an RTL-SDR with E4000 tuner and some custom software.
A vector network analyzer allows the measurement of antenna or coax parameters such as SWR, impedance, phase and loss. It can also be used to characterize and tune filters. In his last post Tomaž copmares his RTL-SDR based system with a NanoVNA-H and shows similar results, confirming that the system is working.
Recently he's also swapped out the RTL-SDR for a HackRF which allows him to make measurements up to 6 GHz. Although he notes that the dynamic range quickly degrades after 3.5 GHz presumably due to connector and phase noise issues.
The entire post chain is a good read to see how he ended up designing the system, and we link to each post below for easier reading:
Thank you to Alexander, the original author of scikit-rf (aka skrf) for writing in and sharing his project which he believes may be of interest to some readers. Scikit-rf is an open source, BSD-licensed RF/Microwave engineering package implemented in Python. The package can be used for simulating various RF components such as transmission lines and waveguides, as well as creating models from data measured from real components which can then be used in a simulated system.
As an example, Alexander shows how you can plot Touchstone data on a Smith chart in 3 Python lines.
With skrf you can also do all your own calibrations offline, time gate when you feel like it, connect and manipulate microwave networks and plot all the results. And... you can read all the source code!, which is really important for proto-typing and research. Check out the Documentation or Examples for a more in-depth look at scikit-rf.
Here are a couple links to projects using scikit-rf
scikit-rf was created in 2009 by Alex Arsenovic while he was a graduate student at the University of Virginia’s millimeter wave research lab in 2009. scikit-rf is licensed under the BSD License and is currently being actively developed by a group of volunteers on Github.
Thank you to Majodi Ploegmakers who wrote in and wanted to share a product he's created that might be useful for some RF enthusiasts. The product is called the "RF Power Snitch", and is a tool used to quickly measure RF input power to determine if input power from a signal source is too strong and could damage measurement equipment such as an SDR or NanoVNA. The product is not yet for sale, but Majodi has an availability notification signup page.
The Netherlands: Today, NickStick Design, an electronics design company for Makers, announced their RF Power Snitch. After a successful launch of SwarmDrive through Crowd Supply last year, NickStick Design went on and designed another useful tool for makers in the RF (Radio Frequency) domain this time.
Of the company’s recent crowd funding campaign, Majodi said, “We were very pleased with the interest our last, somewhat niche, product received. It spurred us on to develop and realize our next idea”.
Today, the RF domain has become accessible to everyone through affordable tools that many could only dream of before. The only tool missing though, is a simple device for checking the, potential, destructive power of the signals one would want to analyze. Because, although tools like the TinySA, NanoVNA or SDR devices are extremely affordable today, for a maker it is still an investment worth protecting.
That’s why our goal was to develop a low-cost companion device that can help makers and experimenters (especially beginners) in the RF domain to gain insight in the power levels of a signal before hooking things up to their valuable test equipment. As an extra to this we also made it possible to attach an MCU for doing power readings and plotting.
I was never satisfied with the commercially available wide band antennas. They were all too large or did not have suitable VSWR over the frequency range generally required by SDRs. I read many research papers and ultimately made a omni-directional ultra wide band antenna, but it was too expensive for most people. Details regarding that antenna can be found at https://www.rtl-sdr.com/constructing-a-3d-printed-wideband-900-mhz-to-11-ghz-antenna/
However, a bi-directional antenna was good enough for most people, so I have made a flat one. The antenna I ended up with is 5 inches by 4 inches and about 3 mm thick with an SMA connector. It is quite definitely not a square patch antenna, which usually has a narrow bandwidth.
This antenna has a VSWR measured to be under 2.00 from around 750 MHz to over 3 GHz. It simulates to have a VSWR under 2.00 out to over 6 Ghz. This is enough for most of the available SDRs. It works very well with WiFi, Bluetooth, Zigbee and other systems within the bandwidth.
The log antenna, Figure 2, has a wide bandwidth, but it is specified as having ranges, because the VSWR rises over 2.00 several times over that range. The antenna measure sover 40 centimeters long, which is problem for me in a laboratory setting. It is too large to fit anywhere and wants to be permanently fixed to a pole or something like that.
The other antenna I have is a discone type device, Figure 3. It is huge. There is not practical for it to fit on a lab bench around various RF devices. It is measures around 28 centimeters at its base. It needs to be elevated above any ground planes, which complicates a laboratory environment with metal bench tops. I have it sitting on a shelf above the computer monitors on the opposite side of the room away from the lab bench. This does not work well when I am trying to deal with wireless devices connected to USB hubs on the bench with short range features.
Figure 4 shows the Flat Antenna next to the Log Antenna for a size comparison that illustrates just how much space saving there is with this new device. This is no small feat. This Flat Antenna is useful around all manner of RF devices on the bench without causing space issues, getting in the way of instruments and couples well with all of the wireless devices I am using. It is small enough with a convenient shape for moving it around and keeping it above a metal bench top. It only needs to be a few centimeters above any ground planes when perpendicular, not horizonal.
Due to its size and shape, near field problems have not been a problem, as with the other antennas. The antenna is quite directional, which is not much of a problem, since the RF bounces around all over the place. A Faraday shield is the only way to keep this device from picking out everything in the vicinity. The neighbors IoT devices create mountains of RF clutter. This antenna picks up all of it. If you only want restricted bandwidths, band pass and reject filters can be used. The load impedance is 50 Ohms across the band making an excellent match for all of the filters I have here.
Figure 5 shows the VSWR as measured by the NanoVNA Version 2. It only goes out to 3 Ghz. The device must be calibrated before use, or you will get extraneous results. I am told the VSWR never goes above 2.00 until after 6 GHz. This is a remarkable antenna. I never found anything comparable to it on the Internet.
It can be used for all wireless and SDR applications normally within the 750 MHz to 6 GHz bandwidth. This is not guess work or speculation. The network analyzer shows the response clearly.
The antenna is 5 inches long by 4 inches wide by roughly 3 mm thick, not counting the SMA connector.
What You Get
You get one (1) antenna, as shown in Figure 1, for each US$50. You cannot do this yourself for that price. Your time alone is worth more than that after you do the calculations, simulations and prototyping. You also would have to deal with fab shops to get this done correctly, which is not always convenient for many people.
In other words, this is a remarkable Ultra Wide Band Antenna at a remarkable price.
This has already been done. I have a Masters Degree in RF Engineering. I also have all of the simulation tools that are not available to most people, with the exception of some university students.
I have sources that I use all the time. I just put this one into the queue. We also have a minimum order, which is why we Crowd Fund this operation.
Once in the queue, it takes about two (2) weeks. After that, we are only concerned with delivery time. We intend to use ordinaty Postal Service mail, to keep the cost down, so time of delivery may vary depending upon the destination.
Risks and challenges
We already have laboratory results, so there is nothing to risk in performance. The only other thing that could be troublesome is the lead time by the vendor that manufactures the main component or any delays caused by the Postal Service.
UPDATE 16 Dec 2020:John has provided us with this document that addresses a few questions people had about the antenna.
Thank you to a few readers for suggesting a post about the "tinySA". The tinySA is a low cost standalone spectrum analyzer which was made recently available from Chinese manufacturer "Hugen" who was the manufacturer that popularized the original NanoVNA. It can be found on Aliexpress for about $49 shipped worldwide. R&L also have US based stock available. The official specs from tinysa.org/wiki read:
Spectrum Analyzer with two inputs, high quality MF/HF/VHF input for 0.1MHZ-350MHz, lesser quality UHF input for 240MHz-960MHz.
Switchable resolution bandpass filters for both ranges between 2.6kHz and 640kHz
Color display showing 290 scan points covering up to the full low or high frequency range.
Input Step attenuator from 0dB to 31dB for the MF/HF/VHF input.
When not used as Spectrum Analyzer it can be used as Signal Generator, MF/HF/VHF sinus output between 0.1MHZ-350MHz, UHF square wave output between 240MHz-960MHz.
A built-in calibration signal generator that is used for automatic self test and low input calibration.
Connected to a PC via USB it becomes a PC controlled Spectrum Analyzer
Rechargeable battery allowing a minimum of at least 2 hours portable use
A spectrum analyzer allows you to view a defined slice of the frequency spectrum on a graph. It does not allow for demodulation of signals. We note that SDRs like the RTL-SDR could be used as a spectrum analyzer too with software like QSpectrumAnalzyer and Spektrum, however the advantage of the tinySA is that it is a standalone package with it's own screen that can easily be used in the field. Unlike an SDR extra computing devices like a computer or smartphone are not required.
Over on YouTube IMSAI Guy has been uploading a few videos reviewing the tinySA. From his videos he found a few issues including a slow update rate, harmonics and high phase noise. However, later he finds that most of the harmonic issues disappear as long as the input signal level is kept below -30dBm. In some more recent videos he also finds a fault with the attenuator chip on one of his tinySA units and repairs it by replacing the chip.