The South Indian SDR User Group (SI-SDR-UG) have recently held their fourth live stream conference. This conference included some interesting talks such as:
"Introduction to GNU Radio Series, Part 2" by Neel Pandeya
"Silice, a Language for Hardcoding Algorithms into FPGA Hardware" by Dr.Sylvain Lefebvre
"RF Geo-Location for Everyone" by Corey Koval
"Overview of Wireless Channels, Part 1" by Aditya Arun Kumar
In particular we were interested in Corey's talk which starts at 1:27:40 and talks about DF-Aggregator, an open source mapping program he's written for KerberosSDR, KrakenSDR and any other radio direction finding hardware that can be adapted to the software. In the talk Corey explains what DF-Aggregator is and how the clustering algorithm works.
South Indian SDR User Group (SI-SDR-UG) Live Stream Event-4
KrakenSDR is our 5-channel coherent RTL-SDR product that we have successfully crowdfunded for over on CrowdSupply. KrakenSDR is the successor to our previous 4-channel product called the KerberosSDR and will begin shipping to initial supporters within the next few months. Along with the new hardware developments, KrakenSDR comes with a new opensource codebase that is also compatible with the KerberosSDR.
With a coherent SDR like KrakenSDR or KerberosSDR, interesting applications such as radio direction finding and passive radar become possible.
Unlike the newer KrakenSDR, the KerberosSDR is unable to automatically calibrate without manual intervention on the hardware. However, it is possible to upgrade the KerberosSDR with some third party hardware switches provided by Corey Koval of Lakeshore Labs. With these switches and the new software the KerberosSDR can be made to automatically calibrate like the KrakenSDR.
Corey also has created DF-Aggregator, which is open source software that allows users to plot bearing data from one or more KerberosSDR, KrakenSDR or other radio direction finding devices on a map.
Recently, Corey has demonstrated some changes to our codebase that allow the new KrakenSDR software to directly upload to DF-Aggregator. Over on his YouTube channel, Aaron who runs the DragonOS channel has uploaded a video that shows exactly how to set this up. In the future we plan on integrating support for DF-Aggregator directly into our core code.
Mark Jessop (@vk5qi) has recently been experimenting with a LED based hardware vehicle heads up display (HUD) that he has created to be used together with our KerberosSDR. The KerberosSDR combined with four antennas in a circular array determines the bearing towards a transmitter, and then the HUD displays this bearing visually on a circle.
The HUD is cleverly designed so that the LEDs reflect on the windshield of the car, allowing for the lights to be safely seen on the windshield while driving. More videos of the HUD being developed and used can be seen on his Twitter feed.
In the video below Mark also shows how he combines KerberosSDR bearing data with his Chase Mapper software, which he uses for tracking down radiosonde weather balloons.
For the last few months I've been piecing together a radio direction finding (also known as 'fox-hunting') system using a RTLSDR-Blog Kerberos-SDR, a custom-made antenna array, and my 'ChaseMapper' software. I have also recently added a 'heads up display' (HUD) box which displays the direction-of-arrival and SNR data from the Kerberos-SDR software.
I hope to put together a longer video showing how the system goes together sometime in the future, but this short clip shows how the system is used in the final approach to a radio transmitter (in this case, a 144 MHz transmitter from one of the Amateur Radio Experimenters Group organised night fox-hunts).
The antenna array consists of two 4-element nested arrays, one with 200mm antenna spacing for the 70cm band, and another with 425mm antenna spacing for the 2m band. The array is mounted to my car roof-racks, with phase-matched coax entering the car through a window-mounted bulkhead.
The red lines on the map indicate a bearing line produced by the Kerberos-SDR software. As we drive around the fox location, bearings are plotted, and we look for where they cross. There are always some inaccurate bearings due to multi-path issues, and misalignment between bearing acquisition time and the position/heading of the car, but it works well enough to be able to allow navigation to the transmitter location. The display can get fairly busy, so there are options to threshold by signal quality, and to 'age out' bearings over time.
The beeping noise you hear in the video is the signal from the radio transmitter, in this case a 144.390 MHz beacon which transmits short CW 'pips'. We were listening to the signal with an Icom IC-705 attached to an omnidirectional antenna so we knew when the transmitter started and stopped (and hence when to trust any bearings produced by the DoA system).
Towards the end of the video you can see the HUD in action, with the blue lights showing the estimated signal arrival direction, relative to the front of the car. As I slowly drive past the transmitter location (which I could see out the side of the car), the bearings swing to the right, and the SNR shows as being very strong. This is exactly what the display was intended for - it's not about getting hyper-accurate bearings, but more knowing when you need to turn left/right, or get out of the car!
Thanks to Will Anthony for capturing the video while I was driving!
Finding a Radio Fox using a Kerberos-SDR + ChaseMapper
KerberosSDR is our 4-channel phase coherent capable RTL-SDR unit that we previously crowdfunded back in 2018. With a 4-channel phase coherent RTL-SDR interesting applications like radio direction finding (RDF), passive radar and beam forming become possible. It can also be used as four separate RTL-SDRs for multichannel monitoring.
KerberosSDR is soon to be replaced with the upgraded KrakenSDR, which will begin crowd funding on Crowd Supply later this year. Be sure to sign up on the Crowd Supply page to be updated once the campaign releases as due to long supply chain crisis related lead times, only a limited amount of stock will be initially available.
If you weren't already aware KerberosSDR is our 4-channel phase coherent capable RTL-SDR unit that we previously crowdfunded back in 2018. With a 4-channel phase coherent RTL-SDR interesting applications like radio direction finding (RDF), passive radar and beam forming become possible. It can also be used as four separate RTL-SDRs for multichannel monitoring.
KerberosSDR is soon to be replaced with the upgraded KrakenSDR, which will begin crowd funding on Crowd Supply later this year. Please note that we have had some pandemic related delays finalizing the design, but progress is being made.
Recently we came across a brief demonstration video on YouTube where it appears that students have embedded a KerberosSDR into an RC boat. The boat carries four direction finding antennas connected to the KerberosSDR and autonomously navigates towards a signal source.
Back in October we first posted about the release of DF-Aggregator, a program by Corey (ckoval7) which can be used to receive and plot data from multiple KerberosSDR direction finding units.
If you weren't already aware KerberosSDR is our 4-channel phase coherent capable RTL-SDR unit that we previously crowdfunded back in 2018. With a 4-channel phase coherent RTL-SDR interesting applications like radio direction finding (RDF), passive radar and beam forming become possible. It can also be used as four separate RTL-SDRs for multichannel monitoring.
In one of his latest DragonOS videos, Aaron has been testing out DF-Aggregator. In his test he had two vehicles driving around each with a KerberosSDR and antenna array, with both using a mobile data connection to send data to a remote PC running DF-Aggregator. The results were successful, with the team being able to determine the location of a broadcast FM transmitter to within a few meters after a short drive.
DragonOS Focal KerberosSDR x2 Mobile w/ DF-Aggregator Direction Finding Attempt 2 (Better Results)
If you weren't already aware KerberosSDR is our 4-channel phase coherent capable RTL-SDR unit that we previously crowdfunded back in 2018. With a 4-channel phase coherent RTL-SDR interesting applications like radio direction finding (RDF), passive radar and beam forming become possible. It can also be used as four separate RTL-SDRs for multichannel monitoring.
A single KerberosSDR combined with an antenna array is able to determine a bearing towards a signal source. By using multiple KerberosSDR units spread over a large area it is possible to triangulate the location of a transmitter and display it on a map. Corey's software uses a modified branch of our open source KerberosSDR code in order to generate a modified XML page that the mapping software polls for updated data. Some instructions on it's use are available on our forums and on the GitHub.
The image below shows three KerberosSDR stations on the map, and two transmitter locations that have been triangulated using the bearings from the three distributed KerberosSDR units.
Over on GitLab Josh Conway has released a design for an automatically adjusting antenna array which can be used with radio direction finding capable SDRs like our KerberosSDR. KerberosSDR is a SDR consisting of four RTL-SDRs connected to the same oscillator, a USB hub, a built in noise source and calibration hardware which allows software to use the four RTL-SDRs coherently. Coherent operation of SDRs enables interesting applications such as radio direction finding, passive radar and beam forming.
With coherent antenna array based direction finding, the optimal spacing between the antenna elements is proportional to the wavelength of the frequency being received. If you want to do RF direction finding on different frequencies, either multiple antenna arrays with different element spacings, or manually adjusting the antenna array with each frequency change is required.
Josh's design automates this problem with an antenna array that can adjust the spacing automatically. The design puts the antennas on an extending pantograph arm whose length is controlled via a threaded rod connected to a stepper motor. An Arduino microcontroller controls the stepper, thus allowing the spacing to be adjusted automatically.
A Pantograph Antenna Array for Direction Finding
A full description of the build is provided in the document on GitLab titled "provisional_patent_application.pdf". From Twitter it appears that Josh (@CrankyLinuxUser) was unable to secure a patent for this design, so he has released the design for free under AGLP3. Most of the parts are 3D printed, and the CAD stl files all appear to be available on the GitLab. The Arduino microcontroller firmware is also available.
If you weren't aware KerberosSDR is our 4-channel phase coherent capable RTL-SDR unit that we previously crowdfunded back in 2018. With a 4-channel phase coherent RTL-SDR interesting applications like radio direction finding (RDF), passive radar and beam forming become possible. It can also be used as 4 separate RTL-SDRs for multichannel monitoring.
In previous posts we've shown some interesting experiments performed with the KerberosSDR. For example:
We note that V2 of our KerberosSDR demo software is also on the way but a little delayed. We are aiming to release a beta around the end of the year, or early next year at the latest. The new software will have better handling of bursty intermittent signals, and paves the way for new developments coming in 2021 such as combined passive radar direction finding.
The KerberosSDR: 4x Tuner Coherent Capable RTL-SDRKerberosSDR Android App for Direction FindingAn Example of KerberosSDR Passive Radar Display Peak Hold Displaying Aircraft and Road Tracks
