DragonOS is a ready to use Linux OS image that includes many SDR programs preinstalled and ready to use. The creator Aaron also runs a YouTube channel that has multiple tutorial videos demonstrating software built into DragonOS.
In a recent video Aaron has provided a two part tutorial showing how to set up and use KerberosSDR with the RDFMapper software on DragonOS. This allows you to network multiple KerberosSDR units together and display each units radio bearing on the same map. Two or more bearings crossing can be used to determine the location of a transmitter. In the future Aaron will use this setup to have multiple mobile and fixed KerberosSDR units connected together via Zero Tier. Aaron writes:
In this first video I show how to install software to control the KerberosSDR – A 4-Channel Phase Coherent RTL-SDR for Passive Radar, Direction Finding and more onto DragonOS Focal (Lubuntu 20.04 based). A fork of the main code is required due to some changes in dependencies and packages. This fork is only meant for or at least tested on Ubuntu, Kubuntu, and Lubuntu 20.04.
I also show some issues you may experience due to poor quality USB cables, insufficient power, and/or issues with USB ports being used to power the KerberosSDR or connect to it.
In this second video I show how to install and use RDFMapper with the KerberosSDR software and Android App. I also cover some common problems I've experienced with the current KerberosSDR Android App.
Recommended to watch the first video if you are planning to run the KerberosSDR on a PC or a SBC like the Raspberry Pi. This video and setup procedure can be adapted to use the Raspberry Pi/Android App instead of a PC.
I plan to make a couple more videos on this topic. By the end, it should be possible to have multiple KerberosSDR stations, both mobile and stationary, linked to one instance of RDFMapper over Zero Tier all simultaneously performing direction finding on one frequency.
The tutorials move on to installing and using various ham radio programs like Fldigi, WSJT-X , GQRX, GNU Radio, before going on to teach some more Linux concepts. The final two PDF tutorials cover the installation and use of OpenWebRX for remote RTL-SDR use, R2Cloud for decoding weather satellites, and finally Radiosonde Auto RX for decoding radiosonde's on weather balloons.
Eric had an inverted L and T3FD antenna set up in his backyard and he wanted to test both at the same time to see which received HF better overall. Rather than relying on subjective 'by ear' measurements he decided to use the digital FT8 mode as his comparison signal. FT8 is quite useful for this purpose as the decoded data includes a calculated signal-to-noise (SNR) reading which is a non subjective measure that can be used for comparisons. It also contains information about the location of the signal which can be used for determining the DX capability of the antenna.
To perform the comparison he used two or our RTL-SDR Blog V3 dongles running in direct sampling mode, and also added an additional low pass filter to prevent excessively strong TV and FM signals from overloading the input. Each antenna is connected to it's own RTL-SDR, and a modified version of GQRX with remote UDP control is used to switch between multiple FT8 frequencies so that multiple bands can be covered in the experiment. WSJT-X is used for decoding the FT8 packets.
After logging SNR values for several days he was able to plot and compare the number of packets received by each antenna, the maximum distance received by each antenna. His results showed that his inverted L antenna was best in both regards. He then performed a relative comparison with the SNR readings and found that the inverted L performed best apart from at 14 MHz, where the T3FD performed better.
In further tests he also compared the antennas on which signal headings they were receiving best from. The results showed that Erics inverted L was receiving best from one direction only, whereas the T3FD received signals from more headings.
Eric's post includes full instructions on the software setup and also Python code which can be used to replicate his experiments. We think that this is a great way to objectively compare two types of antennas.
Android developers have a new RTL-SDR driver wrapper available to use called "RTL-SDR CP Driver". This driver by Evgeni Karalamov is designed to have an additional feature over the current Android RTL-SDR drivers in that it implements client application permission management. The overview reads:
RTL-SDR CP Driver utilises the rtl-sdr codebase and is meant to be kept in sync with the developments there. The provided interface mirrors the functionality of rtl_tcp in an Android way. Instead of via a TCP socket, the communication is carried out through file descriptors returned by a ContentProvider.
Since some potentially sensitive information could be captured through the SDR receivers, like indications of the device location, the RTL-SDR CP Driver implements permission control similar to that of the Android framework. Prior to accessing receivers, client applications have to ask the user for permission to access the driver by starting the driver's permission flow via startActivityForResult. Once the user grants access, their answer is remembered and they are not prompted again. The user has the ability to later revoke the permission from the driver's UI, accessible via the Android launcher.
Over on his YouTube channel Kalle Hallden has uploaded a video demonstrating how to perform a replay and "rolljam" attack on a wireless car key with an RTL-SDR and Yardstick One. His first experiment is a simple replay attack which involves recording the unlock signal from the car key with the Yardstick One in a place far away from the car so that it is not received, then replaying it close by.
This works well, but Kalle then explains rolling code security and how this would easily thwart any replay attack in the real world. However, he then goes on to explain and demonstrate the "rolljam" technique, which is one known way to get around rolling code security. The demonstrations are obviously not full tutorials, but are just high level overviews of how wireless security can be defeated.
Over on his YouTube channel Tech Minds has uploaded a video showing how it's possible to receive and decode GPS signals with an RTL-SDR. To do this he uses one of our RTL-SDR Blog V3 dongles and a GPS patch antenna which is powered via the bias tee on the dongle.
On the software side he uses GNSS-SDRLIB and RTKLIB to decode the GPS signal. The result of the two programs is your current GPS coordinates which can be plotted on a map. Unfortunately in the video Tech Minds was unable to get the Google Maps display to work, but you can easily type the coordinates into Google maps yourself.
A few days ago we posted about Hayati and others' work in creating a new release of the librtlsdr drivers which implemented some new interesting features. However, at the time of the post there was no GUI for actually making use of the features easily. Now Hayati has released a new rtl_tcp ExtIO interface.
The interface exposes the ability to manually adjust the filtering within the R820T tuner. This is quite useful for managing out of band interference and raising overall dynamic range especially when trying to listen to a narrowband signal. It also exposes decimation controls, tcp connection features like auto reconnect and persistent connection, manual IF gain control, the ability to choose USB vs LSB tuning, and the ability to choose the highest stable sample rate of 2.56 MSPS.
The ExtIO interface is only available for SDR programs that support ExtIO, such as HDSDR. To test the ExtIO, first download and extract the latest librtlsdr release then run rtl_tcp from the command line. Extract and run the new ExtIO dll into the HDSDR folder, then run HDSDR, making sure to select the new dll when it asks on startup. You can then set the desired bandwidth and the matching decimation settings for that bandwidth.
Over on his YouTube channel M Khanfar has put together a tutorial for an interesting idea. The idea is to use an automatic SSH connection to tell your Windows PC to run rtl_tcp whenever you open SDRTouch or RFAnalyzer on your Android device. SDRTouch and RFAnalyzer are both Android based SDR applications and rtl_tcp is a server which allows both apps to connect to a remote RTL-SDR over a network connection.
To set this up, Khanfar first sets up OpenSSH on his Windows PC which allows a secure remote connection to the PC. On his Android device he then installs MacroDroid and RaspController. MacroDroid is an app that help you automate tasks on your Android device, and RaspController is an app designed for remotely controlling a Raspberry Pi, but also works on Windows via the SSH connection. These apps are then setup so that an SSH connection to the Windows PC is automatically opened whenever SDRTouch is run. From within the SSH connection rtl_tcp is then started.
Full text instructions are available in the video description.
Automate MacroDroid with RTL_TCP through OpenSSH under Windows 10