I recently bought an AirSpy mini SDR (Software defined radio) dongle. Understand, it is a radio scanner you connect on your computer able to analyze radio communications on a large frequency range from 24MHz to 1,7HGz. The main difference between this SDR and the low cost one based on RTL 2832 + R820T is the spectrum view up to 6Mhz, the TCXO working with 0,5ppm and globally the quality of the solution and the availability of libraries. What is presented here is also valid for RTL based dongle.
With this tool you can see what is happening on the radio frequencies in real time, compare power, listen radio … This post is presenting how to install it and use it on windows & Mac Os X.
Getting the dongle
The dongle can be obtained from the list of reseller available on airspy.com website for about $100. The delivered version does not contains any antenna and you have to think about getting one having a SMA connector. The delay for getting it from Hong-kong was about 2 weeks.
Getting start on MacOsX
As surprising as it is it was more easy to make it working on MacOsX than on Windows. The scanner immediately start working on MacOsX by using the open source software GQRX.
You need to plug the dongle on an usb port and run the GQRX software. On the first run it will ask for hardware configuration :
The device is automatically identified. The input rate is 6M (10 will crash). You can select different Decimation depending on your compromise between precision and sampling throughput. Adding decimal will give you a better SNR.
Bandwidth can be up to 10MHz. I assume we have no LNB LO (Low Noise Block)
Once configure the UI starts and you can see signal like FM radio if you want :
Basically if you center on one of the signal spike you should listen FM radio.
Getting start on Windows 7
The dongle on windows requires a WinUSB driver. According to the documentation it is supposed to be found automatically but in my experience I had to find another way. I spent a long time finding the solution as AirSpy is not the most used device. So once found it is simple : you have a packaged solution provided by zadig. The airspy website also propose the Windows compatibility driver (Sound I should wear my lens..) You run this software and choose on install WinUSB driver. Now your dongle will be recognize and you can run the software delivered by Airspy on the website like SharpSDR looking like the previous one but having more options and spectrum spy allowing you have a large and realtime view of what is happening in a large spectral range. The plus of airspy is to be able to track 10Mhz in real time.
Taking a look to SigFox signals
For watching sigfox signal you simply have to center on 868,15 and request one of your device to emit.
You will see a spike during each of the 3 consecutive communications. You can also see that the spike is really concentrated on the frequency center due to the UNB communication.
Each communication uses 3 different (pseudo) random channels (eq 3 different frequencies).
The following screen capture will demonstrate it :