Due to various human activities causing the environmental destruction of it's habitat, the Orangutan is now classed as a critically endangered species. In addition to being endangered, Orangutans face another problem in that they are often captured and sold as pets due to their intelligence and cuteness.
To combat these problems, NGOs, charities and rescue centers have been using RF tags on rehabilitated Orangutans that have released back into the wild. The RF tag regularly transmits a data-less pulse at VHF frequencies which is then typically tracked using direction finding equipment such as a directional Yagi antenna. The range is only approximately 200-400m.
In order to try and alleviate the range issue Dirk Gorissen has been working on creating a drone based system that could detect the VHF transmission and create a heatmap of Orangutan positions. The first iteration of his system uses an RTL-SDR, Odroid and lightweight loop antenna. A simple Python script then monitors the spectrum and logs the drones current location, altitude, speed and heading when a pulse is detected. Tests confirmed that the signal was able to be detected from the sky, but unfortunately the drone was eventually crashed and lost before it could be properly used.
In his second try a few years later, Dirk used a larger drone and switched SDRs to an Airspy Mini with preamp. The pulse detection code was also improved by using GNU Radio to create a DSP algorithm combining peak detection, cross correlation with a known template of the signal, and a phase locked loop. Visualization and data transfer is achieved through react.js and a Flask web server running on the drones WiFi hotspot. This time with the new drone and system Dirk was able to successfully detect and locate several Orangutan's on various flights, despite noting that some RF tags appeared to be glitchy.
Most readers of this blog are probably familiar with the more commonly received APT images that are broadcast by the NOAA satellites at 137 MHz, or perhaps the LRPT images also broadcast at 137 MHz by the Russian Meteor M2 satellite. HRPT signals are a little different and more difficult to receive as they are broadcast in the L-band at about 1.7 GHz. Receiving them requires a dish antenna (or high gain Yagi antenna), L-band dish feed, LNA and a high bandwidth SDR such as an Airspy Mini. The result is a high resolution and uncompressed image with several more color channels compared to APT and LRPT images.
In his video Tysonpower shows how he receives the signal with his 3D printed L-band feed, a 80cm offset dish antenna (or 1.2m dish antenna), two SPF5189Z based LNAs and an Airspy Mini. As L-band signals are fairly directional Tysonpower points the dish antenna manually at the satellite as it passes over. He notes that a mechanised rotator would work a lot better though. For software he uses the commercial software available directly from USA-Satcom.com.
The Airspy Mini is a software defined radio with a tuning range of 24 MHz to 1800 MHz, 12-bit ADC and up to 6 MHz of bandwidth. It usually costs $99 USD and is the younger brother of the $149 USD Airspy R2.
Currently the manufacturer iTead is running a Christmas sale on the Airspy Mini. The sale price is $80 USD, which is a 19% saving. To get the sale price you need to click on the “Get coupon code here” link and then share the promotion to your Facebook, Twitter or LinkedIn account.
Update: They have given us a special blog coupon code “AS-RTLSDR-BLOG“. Just use this code at the checkout and it will apply the discount without the need to share.Edit: The blog coupon appears to have stopped working, an alternative one that is still working is “as3“.
The sale lasts from December 20, 2016 – January 3, 2017.
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
24 - 1800 MHz
24 - 1800 MHz
Maximum Bandwidth (Alias Free Usable)
6 MHz (5 MHz)
10 MHz (9 MHz)
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
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.
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 has similar high performance specifications to the Airspy R2, but comes in a USB dongle sized enclosure and only costs $99 USD – half the price of the $199 USD Airspy R2. The only difference in specification appears to be that the Airspy Mini has 6 MHz of spurious free bandwidth, versus 9 MHz in the Airspy R2, and that it lacks the external clock input and some of the expansion headers which are mainly useful only for advanced experimenters. The other features including its 24 – 1800 MHz operation, 12-bit ADC and 0.5 PPM TCXO all remain the same. The Airspy team also write that the Mini still supports a 20 MSPS mode for ADS-B decoding with the ADSBSpy decoder, which should place its ADS-B decoding performance at an identical level to the Airspy R2, which is very good.
To receive the HF frequencies the Airspy team are also releasing an Airspy Mini + SpyVerter bundle which will cost $149 USD. The SpyVerter is an upconverter designed to work with Airspy products, but has also been found to work well with the RTL-SDR.
In the future we hope to review the Airspy Mini and check to see if its performance is similar to the Airspy R2. If its RX performance is at least the same as the R2, then it probably will be the best value SDR for those wanting to upgrade from an RTL-SDR.