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:
Over on his channel Tech Minds has uploaded a new video where he tests the N1201SA / PS100 vector impedance analyzer. This is a US$160 antenna analyzer from China that allows you to measure the VSWR of your antennas. In the video Tech Minds explains a bit about VSWR, and goes on to show the unit in action on several of his antennas.
Compared to the NanoVNA V2 these units seems less useful with a smaller frequency range, and are also more expensive. The unit is also only 1-port, meaning that it can only do S11 measurements and cannot analyze devices like filters. But on the other hand it does come in a metal case with a battery and has a fairly easy to understand and use interface.
Easily Check Your Antennas Tuning - VNA N1201SA / PS100
We've received a few notices that the NanoVNA V2 design that we've been following since last year is now available for sale on eBay and Tindie (or Taobao if you live in China). The original official sales appear to have been from Tindie, where it is priced at $58.25 + shipping, although it is now out of stock. On eBay resellers are selling it for up to $150. If you're interested in purchasing the V2 we recommend entering your email into the Tindie form as they will notify you when it's back in stock. Initial reviews posted on the Tindie store indicate that the unit has excellent performance for the price so we expect that it will be popular enough to manufacture many more in the future.
The original NanoVNA brought expensive Vector Network Analyzer (VNA) capabilities to the masses with it's low $40 pricing. A VNA is an extremely useful tool for radio hobbyists as it allows you to tune antennas, filters and measure cable loss among other applications. However, the original design was limited to only a frequency of 900 MHz maximum. The new design pushes this up to 3 GHz official, and unofficially up to 4.4 GHz whilst also improving dynamic range and maintaining the low price point.
The description and specs of the NanoVNA V2 are shown below:
3GHz second generation NanoVNA vector network analyzer, designed in collaboration with OwOComm.
Note: Micro USB cable not included. Fully assembled, without enclosure. Ships within 5 business days.
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.
Over on YouTube Kevin Loughin has reviewed the miniVNA Pro Vector Network Analyzer (VNA). A VNA is a tool that can be used to measure antenna or coax parameters such as SWR, impedance, loss as well as characterize filters. It is a very useful tool to have if you are building antennas, filters or RF circuits. The RTL-SDR with a noise source can somewhat be used as a network analyzer, but a fully functional VNA will be a lot more accurate and easier to use. The miniVNA costs US$490 and is significantly cheaper compared to desktop based VNAs.
In the video Kevin explains what a VNA is and that the miniVNA Pro is, shows how to calibrate the unit, shows some measurements on his roof mounted dipole, measures a home made filter, and then demonstrates portable operation of the device on an Android phone. The miniVNA Pro has a built in battery so it can be used portably in the field together with an Android phone and bluetooth.
We ourselves have the miniVNA tiny which operates in frequency from 1 MHz all the way up to 3 GHz, whereas the miniVNA Pro operates from 0.1 MHz to 200 MHz. However the tiny does not have portable operation. The miniVNA tiny is excellent for building things like ADS-B and Inmarsat antennas.
Thanks to Cary Wang for submitting news about his new Kickstarter for a $200 open hardware VNA called the xaVNA. The xaVNA is PC USB based, has a guaranteed frequency range of 140 MHz to 2.5 GHz (typical 137 MHz - 3.5 GHz), and is supposed to be a lower cost alternative to other low end PC based VNAs such as the PocketVNA and miniVNA Tiny. In addition to the lower cost, the xaVNA is advertised as being superior to its competitors as it has less trace noise and no warm up time is required, as well as the hardware and software being open source.
A VNA (Vector Network Analyzer) is a tool that can allow you to easily measure things like the SWR curve of an antenna, the characteristics of a filter, or the loss of a coax cable for example. So it is a very useful tool to have around if you are building home brew antennas or filters for your SDRs. Compared to a standard antenna analyzer, a VNA gives you complex impedance/phase information as well, making it possible to design better circuits and antennas.
Currently the closest competitors on the market are other PC based VNA's like the PocketVNA ($430) and the miniVNA Tiny ($580). The main advantage of the competitors so far is that they go down to the HF frequencies, but a stretch goal of the Kickstarter is to create an xaVNA that goes down to 10 MHz.
At the moment they only have a functional prototype with the second iteration soon to be ready. The delivery date of a completed unit is expected to be around April 2018. But as with any crowdfunded project remember to only back the project if you are willing to lose your money as there is no guarantee that a product will actually be delivered on time, or even delivered at all.
Over on YouTube user Mile Kokotov has uploaded a very nice tutorial video that shows how the Airspy can be used as a low cost scalar network analzyer from between 0.1 – 1800 MHz. A network analyser allows you to characterize the performance of antennas, by determining the antenna SWR curve. A low point on an SWR graph indicates the frequency at which an antenna is resonant/tuned, so a network analyzer is very useful for tuning homemade or adjustable antennas.
In this video I am showing how Airspy SDR can be used for measuring Return Loss, Antenna SWR and Antenna Bandwidth of several commercial and homemade antennas.
The impedance of the Radio Station (transmitter or receiver) must be well matched to the antenna’s impedance if we want maximum available power to be delivered to antenna.
The return loss and SWR measurements show us the match of the system.
A poorly matched antenna will reflect costly RF energy which will not be available for transmission and will instead end up in the transmitter. This extra energy returned to the transmitter will not only distort the signal but it will also affect the efficiency of the transmitted power and the corresponding coverage area.
Return Loss and SWR both display the match of the system, but they show it in different ways. The return loss displays the ratio of reflected power to reference power in dB.
The return loss view is usually preferred over the SWR linear scale, because is easier to compare a small and large number on a logarithmic scale.
More than 20 dB system return loss is considered very efficient as only less than 1% of the power is returned and more than 99% of the power is transmitted. In that case the SWR is around 1.2
For radio amateur usage, Return loss more than 14 dB is acceptable. This is adequate to SWR of 1.5 which means that 4% of the power is returned and 96% of the power is transmitted.
0 dB Return loss represent an open or a short antenna terminal, while 45 or more dB Return loss would be close to a perfect match.
Many different methods can be used to measure standing wave ratio. Professionals usually use a vector network analyzer or frequency analyzer with sweep signal generator and directional coupler.
In this video I will show you very cheap and very good method for antenna characterizing which means measuring the Return loss versus frequency and usable antenna bandwidth like measuring with much, much more expensive, state of the art Network Analyzers and similar measuring equipment.
Airspy SDR as a Network Analyzer using for Antenna Characterization
EDIT: It has been pointed out that we incorrectly used the term vector network analyzer in the previous title, when we should have instead used scalar network analyzer. A scalar network analyzer can measure amplitude, but a vector network analyzer can measure amplitude and phase and is a more complex device. Apologies for any confusion.