Indiegogo Crowdfunding Has Now Ended.
New Ordering Information:
KerberosSDR - A 4x Phase Coherent RTL-SDR for Passive Radar, Direction Finding and More!
The RTL-SDR software defined radio phenomenon has changed the world by unlocking low cost access to the radio spectrum. Whilst RTL-SDR is now a relatively mature commodity item that almost everyone whose tinkered with electronics has played with, there is still so much more potential to be unlocked.
A phase coherent RTL-SDR can be made out of two or more RTL-SDR dongles that share a common clock. With a bit of help from a noise source, the RTL-SDRs can be synced together. Once synced interesting applications become available, such as direction finding, beam forming and passive radar.
Phase coherent RTL-SDRs have been worked on and demonstrated several times over the past few years, but at RTL-SDR.com we've been disappointed to find that so far there hasn't been any easy way to replicate these experiments.
The required hardware has been difficult to build and access, and the software has been kept as unreleased closed source or has been too complicated to install and use.
With the Kerberos SDR we aim to change that by making phase coherent applications easier to access and run by providing ready to use hardware and good demo software with an open source DSP code base that can be extended.
Please note, although we are aiming to make KerberosSDR as easy to use as possible, at least a basic to moderate level of computer and radio technical knowledge is required, or you must be willing to learn. This is an experimental product and some willingness to experiment and explore solutions is required. The demo software that we provide is capable of doing direction finding and 2-RX passive radar. Your own custom code or applications will be required for custom applications.
What's Included?
If you back our campaign you'll receive one KerberosSDR set. This includes:
- The KerberosSDR Board which has:
- 4x RTL-SDR R820T2 Receivers
- A wideband noise source that can be switched in software
- USB Hub so only one USB connection is required
- A calibration board for synchronizing samples with the noise source
- A shielded metal enclosure
- Cables for connecting the two boards and noise source
What you'll need to provide: You'll need to provide your own antennas for your application (e.g. four magnetic whips for direction finding, two directional antennas for passive radar), a 5V USB power supply, and a microUSB USB cable, and a Linux computing device like a PC/laptop or single board computer like a Raspberry Pi 3, Tinkerboard or Odroid XU4. (Must run Linux natively - VMs have too much USB lag for coherency).
Please Note: Images are of prototype hardware - subject to change slightly. The actual product will come in a metal enclosure with SMA antenna connectors.
KerberosSDR Hardware Specs
Each RTL-SDR on board the KerberosSDR is based on the R820T2 and RTL2832U chips, which are the same chips used in the most common RTL-SDR dongles.
-
Frequency Range: 24 MHz - 1.7 GHz
-
ADC Sample Rate: 2.4 MSPS
-
Bit Depth: 8 Bits
KerberosSDR connects it's RTL-SDRs to the calibration board via four u.FL cables. The calibration board then has four u.FL -> SMA cables that can be used to connect to antennas.
Please note that antennas are not included with the KerberosSDR. For direction finding applications you'll need four omni-directional antennas (e.g. magnetic whips). For passive radar you'll require two directional antennas.
Power Requirements
The KerberosSDR takes a USB power input. Any 3A supply should be sufficient. On some modern PCs you may even be able to directly power the board without any additional power supply.
Applications
Some applications might include:
- Using passive radar to monitor aircraft that do not transmit ADS-B
- Monitoring vehicle or marine traffic with passive radar
- Pinpointing the source of VHF/UHF noise, pirates, interference, jammers, unknown signals etc using radio direction finding (RDF)
- Direction finding for amateur radio fox hunts
- Determining the location of rescue or stolen asset beacons
- Combining multiple small dishes to create a large dish for radio astronomy via beam forming.
- Using the four tuners as standard RTL-SDRs. e.g. two for trunking, one for ADS-B and one for weather satellites.
KerberosSDR Demo Software
For KerberosSDR we have hired Tamás Peto, a PhD student at Budapest University of Technology and Economics. He has developed an excellent open source Linux demo application that can be used for direction finding and passive radar. The DSP and synchronization code could easily be extended to implement other applications, or extend features.
The code can be found at https://github.com/rtlsdrblog/kerberossdr, and a guide to installing it can be found at www.rtl-sdr.com/ksdr. A support forum is available at https://www.rtl-sdr.com/forum/viewforum.php?f=9.
PC/Laptop Requirements
Any modern PC should be able to run the software fine. The PC will need to be able to run Linux. Single board PCs like the Raspberry Pi 3 and Tinkerboard also work.
KerberosSDR Demo Applications
Radio Direction Finding
Our open source demo software developed by Tamás Peto gives us a graph and compass display that shows the measured bearing towards the transmitter location. The measured bearing is relative to the antenna array, so we simply convert it by taking the difference between the car's bearing (determined approximately via road direction and landmarks in Google Earth) and the measured bearing. This hopefully results in a line crossing near to the transmitter. Multiple readings taken at different locations will end up intersecting, and where the intersection occurs is near to where the transmitter should be.
UPDATE 8 August 19: New Kerberos Android App updates make radio direction finding and pinpointing the source of a transmitter significantly easier. Please watch the videos below for a demonstration of it in action.
UPDATE 1 May 19: Our new KerberosSDR direction finding with Android app tutorial and demo video shown below
New updates to the Android software to be released before the end of July will make direction finding significantly easier.
In this experiment we located an 858 MHz TETRA transmit tower. Initially the app will navigate you to the edge of the grid, in the direction that most DoA lines are pointing to. When there is sufficient data to be able to confidently pinpoint the TX location, it will begin navigating you to the estimated location.
Below is screenshots from a 415 MHz DMR tower that we located with KerberosSDR. The antenna array was purposely kept small, with a diameter of only 12cm. Even with the small antenna array we were able to pinpoint the transmitter down to about 100 - 200 meters.
Older Original Videos from early development in 2018:
KerberosSDR can be used to find the bearing towards a signal using it's coherent direction finding capabilities. The demo software by Tamás currently implements several direction finding algorithms such as Bartlett, Capon, Maximum Entropy (MEM) and MUSIC. The demo videos below show this in action.
Passive Radar
KerberosSDR can also be used for passive radar. Normal radar systems work by transmitting a pulse of RF energy, and listening to the reflections from objects like planes, cars and ships. Passive radar works by using already existing transmitters such as those for FM/TV and listening for reflections that bounce of objects.
With a simple passive radar system you need two directional antennas and two coherent receivers. One antenna points at the transmitting 'reference' tower, and the other at the 'surveillance' area where you want to listen for reflections. It's important to try and keep as much of the reference signal out of the surveillance antenna as possible, which is why directional antennas like Yagi's are used.
The result is a doppler vs time delay graph, where the reflection of aircraft, cars, ships and other objects can be seen. The doppler gives you the speed of the object relative to your antenna and the transmitting tower, and the time delay gives you the distance relative to your antenna and the transmitter tower.
We've also tested KerberosSDR with vehicles in traffic. For this test we parked our car to the side of a highway and pointed a cheap DVB-T Yagi antenna towards a DVB-T transmission tower, and another cheap Yagi down the road. The video shown below displays the results captured over a 5 minute period. The blips on the top half of the display indicate vehicles closing on our location (positive doppler shift), and the blips on the bottom half indicate objects moving away (negative doppler shift).
The resolution of each individual vehicle is not great, but it is sufficient to see the overall speed of the highway and could be used to determine if a road is experiencing traffic slowdowns or not. When larger vehicles pass by it is also obvious on the display by the brighter blip that they show. The display also shows us that the highway direction coming towards us is much busier than the direction moving away.
Who is KerberosSDR For?
Anyone who has an interest in RTL-SDRs, radios, SDRs, ham radio or electronics could have some fun with KeberosSDR. It might also find use in commercial applications such as for detecting unlicenced radio stations, detecting asset beacons, or for monitoring traffic speeds/volume etc.
Please note that while we are attempting to make everything as easy as possible to setup and use, this is still a technical product which will require some skill to use. The open source software is considered as alpha, so anyone hoping to use it in a particular application may want to extend it. At this stage it is not considered as a plug and play commercial product, although we aim to hopefully reach that stage at some point.
To use KerberosSDR in coherent applications you should be comfortable with installing software in Linux (full copy and paste instructions will be provided), and you need to be willing to learn the basic physical concepts on how direction finding and passive radar works (simple concepts like antenna spacing, wavelength etc, and we'll provide tutorials on this too). The current state of the demo software allows you to determine a bearing towards a signal in direction finding mode, and to create a 2-input passive radar.
Future Work
If KerberosSDR sells successfully we will be able to pay developers to continually improve and extend the open source software alongside open source contributors.
Extended Tuners - KerberosSDR currently runs four tuners, but it should be possible to extend it up to eight tuners by daisy chaining two boards together. Eight tuners will allow for increased direction finding and beam forming capabilities.
Direction Finding Map Integration - For direction finding we would like to integrate the compass with Google Maps and GPS/compass data. This has now been completed via the Android App.
Processing Speed - It should be possible to significantly improve processing speed (especially for passive radar) with GPU acceleration and C code optimizations.
We have just tested our final prototypes and have confirmed that it is working as expected. As with any manufacturing run there are risks, however Othernet.is and RTL-SDR.com have several years experience with manufacturing in China.
The demo software application is approximately 95% complete at this stage (excluding future work).
Who are We?
RTL-SDR.COM and Othernet.is have collaborated to create KerberosSDR. RTL-SDR.COM is a blog about low cost SDRs such as the RTL-SDR, and also the manufacturer of the popular RTL-SDR V3 dongle. Othernet is a satellite service bringing free satellite data to the world. They have several years experience in developing SDR hardware. Othernet is the team behind the hardware, manufacturing and shipping. RTL-SDR.COM is handling the software development, overall design and support.
UPDATE 1: BATCH 1 MANUFACTURING
We are now manufacturing the boards, see images below. Please see the Updates tab for more information.
UPDATE 2: BATCH 1 SHIPPING
We are now shipping units out, and expect all shipments to have been completed by the end of March. Thank you all for your patience! For information about setting up the unit, please visit www.rtl-sdr.com/ksdr, and for support and discussion visit our forums at https://www.rtl-sdr.com/forum/viewforum.php?f=9