Review of the Airspy Mini

The Airspy Mini is a recently released $99 USD software defined radio with a tuning range of 24 MHz to 1800 MHz, 12-bit ADC and up to 6 MHz of bandwidth. The Mini is the younger brother of the $199 USD Airspy R2, but despite the $100 USD price difference, both units are very similar, which makes the Mini a very attractive option. The idea is that the Mini is the cheaper version for those who do not need the more advanced features of the R2.

In a previous review we compared the Airspy R2 with the SDRplay RSP and the HackRF. In those tests we found that the Airspy had the best overall RX performance out of the three as it experienced the least amount of overload and had the most dynamic range. The SDRplay RSP was the main competitor in performance to the Airspy R2, and was found to be more sensitive due to its built in LNA. But the RSP experienced overloading and imaging problems much easier. With an external LNA powered by its bias tee, the Airspy gained a similar sensitivity and still had very good dynamic range. The main downside to the Airspy R2 was its higher cost compared to the $149 USD SDRplay RSP, and needing to fork even more for the $50 USD SpyVerter if you want to listen to HF signals.

In this review we'll compare the difference between the R2 and Mini, and also see if the cheaper Airspy Mini ($99 USD), or Airspy Mini + SpyVerter combo ($149 USD) can compete in this lower price range. 

Difference Between the Mini and R2

  Airspy Mini Airspy R2
Price $99 USD $199 USD
Tuning Range 24 - 1800 MHz 24 - 1800 MHz
ADC Bits 12 12
Maximum Bandwidth (Alias Free Usable) 6 MHz (5 MHz) 10 MHz (9 MHz)
Extras Bias Tee Bias Tee, External clock input, Multiple expansion headers
Dimensions (Including USB and SMA ports) 7.7 x 2.6 x 1 cm 6.4 x 2.5 x 3.9 cm
Weight 21 g 65 g

Right now the "early bird" price of the Mini is $99 USD. We are unsure if this price will go up in the future.

The external design between the two units is different. The Mini comes in a USB dongle form factor which is very similar to a standard RTL-SDR, whilst the R2 comes in a larger box with a female Micro USB input. In our tests this metal enclosure appears to provide good shielding from strong signals. One thing that was missing on the unit was a nut and washer on the SMA connector. Adding a nut helps the PCB ground make good contact with the aluminum enclosure. The Airspy team have said that future units will come with this nut provided.

Airspy R2 (top), Airspy Mini (Middle), RTL-SDR (bottom) for size comparison.
Airspy R2 (top), Airspy Mini (Middle), RTL-SDR (bottom) for size comparison.

Apart from the price and enclosure, the most noticeable feature difference between the two is the smaller bandwidth of the Airspy Mini. Unlike the Airspy R2, the Airspy Mini does not use a Si5351 clock generator chip. The lack of this chip limits the Mini's maximum bandwidth to 6 MHz and eliminates any ability to use an external clock. The main applications that you miss out on from the lack of an external clock input include: coherent clock, passive radar and direction finding experiments.

From the circuit photos below we can see that the Mini consists of mostly the same parts used in the Airspy R2. Missing is the Si5351 clock controller, expansion headers and the external clock input. 

The Airspy Mini Circuit Board.
The Airspy Mini Circuit Board
Airspy R2 PCB.
The Airspy R2 Circuit Board

Continue reading →

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Using the Airspy on an Odroid C2

The Odroid C2 is a $40 single board computer with a 2 GHz ARM-A53 quad core CPU and 2GB of RAM. Compared to a Raspberry Pi 3 it is more powerful and costs about the same. The Airspy R2/Mini is a $199/$99 USD software defined radio that can tune from 24 – 1800 MHz, uses a 12-bit ADC and has a bandwidth of up to 10 MHz. The Airspy wesbite generally recommends that a relatively powerful 3rd generation Intel Core i3 2.4 GHz processor is required for the Airspy.

However, recently the Odroid C2 has proved itself powerful enough to run the Airspy in full 10 MHz mode in GQRX, though without demodulation. On his website Michael DG0OPK shows some screenshots that show the Airspy+Spyverter upconverter combo running on an Odroid C2 and demodulating with the WSJT-X software, running GQRX and running as a spectrum analyzer.

Over on YouTube user radio innovation has also uploaded a video showing the Airspy running GQRX on an Odroid C2.

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Building a DIY Powered USB Hub for using an RTL-SDR on a Raspberry Pi

One problem that sometimes arises when using embedded single board computers like the Raspberry Pi is that they often cannot provide enough current to power devices through the USB port.

Over on YouTube user KD9 BVO wanted to use his RTL-SDR with a Raspberry Pi, but found that the Raspberry Pi shut down whenever he plugged it in, due to it using too much current. To get around this problem he decided to build a DIY powered USB hub. This solution allows the RTL-SDR to be powered via the hub itself, rather than through the Raspberry Pi USB port.

In the video he takes an existing unpowered hub and shows how to modify it to provide power directly to the RTL-SDR via an external power supply.

[Bits #4] How to DIY a Powered USB Hub

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SDRplay receiving a WPX CW CQ Contest

Over on YouTube user Mile Kokotov has uploaded a video showing him receiving a WPX CQ CW (morse code) contest on his SDRplay RSP. The SDRplay RSP is a $149 USD software defined radio with a tuning range of 0.1 – 2000 MHz, 8 MHz maximum bandwidth and 12-bit ADC.

In the video Mile shows that the SDRplay is capable of receiving many strong closely spaced CW signals at the same time as weaker ones without overloading. He uses the HDSDR software and a large 43.1m long delta loop antenna strung up in his backyard.

SDRplay receiving WPX CW Contest 2016

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More L-Band Videos from 9A4QV: Testing 2x LNA4ALL + Filter + Patch, Receiving the Outernet Signal, L-band Filter

Adam 9A4QV has once again uploaded three new videos to YouTube, all related to L-band satellite reception. The first video shows how much L-band reception can be improved by using two LNA4ALL low noise amplifiers together with a filter placed in between them. Using two LNA’s instead of one improves the reception by about 2-6 dB. He also shows that L-band Inmarsat satellite signals at 1.5 GHz can even be received by his 1090 MHz folded monopole ADS-B antenna placed indoors.

The second video shows a reception report of the new Outernet signal. The Outernet signal is a new satellite data service being provided that broadcasts up to date news as well as various files and information such as educational videos and books for people in third world countries without internet. They have said that they are working on free decoding software for their service which should be released soon. The Outernet signal is a bit weaker than typical AERO signals, but can still be received quite easily with an RTL-SDR, patch antenna and 2 x LNA4ALL. The Outernet downconverter mentioned in a previous post should of course also work well.

His third video shows some tests on his L-band filter, showing return and insertion loss.

2x LNA4ALL and L band filter test

L band filter test

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Slovenian University Student & Security Researcher Almost Jailed for Researching TETRA with an RTL-SDR

Dejan Ornig, a 26 year old student at the University of Maribor’s Faculty of Criminal Justice and Security was recently almost jailed for finding a security flaw in Police TETRA communications in his home country of Slovenia. Back in 2013 his University Computer Science class of 25 was assigned a task to research security vulnerabilities in TETRA. TETRA is a RF digital communications protocol often used by authorities due to its ability to be secured via encryption. During his research he used an RTL-SDR and the open source Osmocom TETRA decoder, and discovered a flaw in the Slovenian Police’s TETRA configuration which meant that encrypted communications were often being broadcast in the clear. Translated, Ornig said:

For $20 I bought a DVB-T receiver (RTL-SDR), on the Internet, I have found also freely available and open-source software OsmoCOM. Free access solution for decoding the signal Tetra eighth-tetra is already prepared in advance programming framework based on the platform GNU.

He goes on to say (translated):

I was even more surprised when I found that most users do not have authentication turned on the radio terminal, even though the Ministry of the Interior in the documents and tenders repeatedly wrote to all the radio terminals to access networks using authentication.

Shortly after discovering the flaw, Dejan privately contacted the authorities with his findings. But after two years of repeatedly contacting them and waiting for a fix, Dejan decided to take his story to a local news agency in February 2015. At this point the Slovenian Police became interested in Dejan, and instead of fixing the problem, decided to conduct a search on his house, seizing his computer and RTL-SDR. After the search the Police made life harder for Ornig by trying to lump on other problems. During the search they found a “counterfeit police badge” in his house and apparently accused him of impersonating a police officer, and after a search of his PC they also decided to charge him after finding out that he covertly recorded his ex-employer calling him an “idiot”.

Ornig has now been given a 15 month suspended jail sentence for attempting to “hack” the TETRA network. Fortunately the suspended part means that in order to not go to jail Ornig simply must not repeat his crime again within 3 years. While SDR’s and radios are not illegal in most countries this is a reminder to professional and amateur security researchers to check that what you are doing is legal in your country. Even if it is for the overall good, Police often do not have the technical competence to understand security researchers and may react illogically to findings. The good news about Ornig’s story is that apart from the suspended jail sentence the authorities appear to have now worked with him to fix the problems.

TETRA Decoding
TETRA Decoding

Story Sources:
[http://www.ibtimes.co.uk/researcher-jailed-finding-security-flaws-police-communications-1561600]
[http://siol.net/novice/slovenija/kako-za-20-evrov-prisluskovati-slovenskim-varnostnim-organom-video-44923]
[https://podcrto.si/odziv-na-trditve-policije-glede-varnosti-komunikacijskega-sistema-tetra]

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L-Band Reception with an LNA4ALL, Patch Antenna and RTL-SDR

Over on YouTube Adam 9A4QV has uploaded a video showing how good L-band reception can be with only a cheap home made patch antenna, RTL-SDR dongle and LNA4ALL. The video is in response to a question on our previous post, which discussed the prototype Outernet downconverter. The question asked what difference can we expect with the downconverter compared to just using an LNA, like the LNA4ALL.

In the video Adam shows that L-Band reception with the LNA4ALL can be as good as with the downconverter. The main problem with L-band reception on the RTL-SDR is that some units tend to fail to receive properly at around 1.5 GHz. The downconverter bypasses this problem by receiving L-band at around 200 MHz instead. Though we believe that this problem is solved on the units we sell as we heatsink to a metal enclosure, and if that is not enough, it can be solved further by using this modified driver. The other advantages of the downconverter is that it includes filtering, an LNA, and allows you to use much longer runs of lossy cable, which is useful if for instance you want to put a permanent L-band antenna on the roof.

LNA4ALL & RTL SDR @ L band

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Monitoring Ionosondes and Creating Ionograms with a USRP and GNU Chirp Sounder

In the HF region between about 0 – 30 MHz it is common to see and hear “chripers” – signals which quickly sweep through the HF frequency band and produce an audible chirp. These chirps are actually signals from Ionosondes which is a type of radar system used to monitor the Ionosphere. The Ionosphere exists about 50km above the surface of the earth and is the atmospheric layer responsible for a large part of long range HF communications. In a previous post by Mario Filippi we also discussed Ionosondes.

Usually it is scientists who transmit and monitor these Ionosondes, however if you have wide band radio that can cover a majority of the HF spectrum then you can also monitor these chirpers yourself. Over on his blog Fabrizio Francione has created a post showing how to use a USRP, together with a GNU Radio Program called GNU Chirp Sounder to create his own amateur Ionogram monitoring station. The USRP is a fairly expensive SDR with a bandwidth of 25 MHz, but we add that we think that next generation of low cost wide band SDRs like the up and coming LimeSDR should also be able to do the same job.

The Ionograms show at what frequencies HF propagation is currently optimal for a specific distance (or number of signal bounces from the Ionosphere). Below is an example Ionogram animation showing the reception of Ionosondes taken over time. Video from the GNU Chirp Sounder page.

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