Tagged: passive radar

Creating a Passive Traffic Radar with DVB-T Signals and KerberosSDR our 4-tuner Coherent RTL-SDR

KerberosSDR is our upcoming low cost 4-tuner coherent RTL-SDR. With four antenna inputs it can be used as a standard array of four individual RTL-SDRs, or in coherent applications such as direction finding, passive radar and beam forming. More information can be found on the KerberosSDR main postPlease remember to sign up to our KerberosSDR mailing list on the main post or at the end of this post, as subscribers will receive a discount coupon valid for the first 100 pre-order sales. The list also helps us determine interest levels and how many units to produce.

In this post we'll show KereberosSDR being used as a passive traffic radar. Passive radar works by using an already existing transmitter such as a FM, DAB, TV or GSM and listening to the reflections of those signals created by moving objects like aircraft, boats and cars. A simple passive radar consists of two directional antennas. One antenna points at the 'reference' transmitter (the transmitting tower), and the other towards the 'surveillance' area that you want to monitor. The result is a speed vs distance plot that shows all the moving objects.

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). 

Highway Passive Radar Traffic Monitor with DVB-T and KerberosSDR a 4x Coherent RTL-SDR

DVB-T Antennas In Car
DVB-T Antennas In Car

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.

In the future we'll be working on optimizing the code so that the display updates much faster and smoother. It may also be possible in the future to use the third and fourth tuners to obtain even greater object resolution.

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KerberosSDR Preview: A 4x Coherent RTL-SDR for Direction Finding, Passive Radar and more

Over the last few months we've been working on a 4-input coherent RTL-SDR called 'KerberosSDR' (formerly known as HydraSDR) that is designed to be a low cost way to get into applications such as RF direction finding, passive radar, beam forming and more. It can also be used as a standard 4-channel SDR for monitoring multiple frequencies as well.

Phase coherent RTL-SDRs have been worked on and demonstrated several times over the past few years, but 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 KerberosSDR we aim to change that by making phase coherent applications easier to access and run by providing ready to use hardware and software.

Thanks to our developer Tamás Peto, a PhD student at Budapest University of Technology and Economics whom we hired via the ad in our previous post, and the Othernet (formerly Outernet) engineering team who are our partners on this project, we've been able to build a working system, and demonstrate coherent direction finding and passive radar working as expected (demo videos below). We plan to eventually release Tamás' code as open source so that the entire community can benefit and build on it. Also if KerberosSDR turns a profit, we plan to reinvest some of the profits into continually improving the software and expanding the list of use cases.

KerberosSDR will be usable for coherent applications from ~80-100 MHz up to 1.7 GHz (as a standard receiver it will work down to 24 MHz like a regular RTL-SDR). The lower coherent limitation is due to the phase calibration board, and could be improved by custom creating a larger calibration PCB.

At the moment we are finalizing our prototype, and plan to begin final production within the next 2-3 months.

If you have any interest in KerberosSDR, please sign up to our Kerberos mailing list. This will help us gauge how many units to produce and will affect the final pricing. If you've already signed up to our weekly posts list, please sign up to this list too as it's a different list. Subscribers to this list will be the first to know when Kerberos goes on preorder, and the first 100 sales will receive a discounted price. We expect to begin taking preorders in within a month and to ship 2-3 months after preorders begin.

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Direction Finding

KerberosSDR can be used to find the bearing towards a signal using it's coherent direction finding capabilities. The software by Tamás currently implements several direction finding algorithms such as Bartlett, Capon, Maximum Entropy (MEM) and MUSIC. In the video below we show a quick test of the direction finding system working with a HackRF being used as a signal source, and four dipole antennas connected to KerberosSDR in a linear array. The MUSIC algorithm is used.

KerberosSDR Direction Finding Test

In the image below we also attempted to find the direction towards a known TETRA transmitter. We were able to confirm the direction with an Android compass app that points towards the known transmitter location. As the two angles match, we can be confident that Kerberos is finding the correct direction to the transmitter.

Finding the direction of a TETRA Transmitter
Finding the direction of a TETRA Transmitter

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.

Below is an example time lapse video of KerberosSDR being used for passive radar. The reference antenna points towards a DVB-T transmitter at 588 MHz, and the surveillance antenna overlooks a small neighborhood, with aircraft sometimes flying over. The antennas we used were two very cheap TV Yagis.

You can constantly see the reflections from vehicles at small doppler values (low speeds), and every now and then you see an aircraft reflection which shows up at much higher doppler (speed) and further time delay (distance) points. 

KerberosSDR Passive Radar Timelapse Test 1

More information about KerberosSDR

KerberosSDR includes:

  • 4x Coherent R820T2 based RTL-SDR dongles with standard 24 MHz - 1.7 GHz frequency range
  • On board GPIO switched wide band noise source for sample sync and phase calibration
  • Special phase calibration PCB for 4x inputs. Required to make the Kerberos phase coherent.
  • On board USB Hub, so only one USB port is required on the PC
  • Shielded metal enclosure

KerberosSDR can also be extended to 8x receivers by daisy chaining two boards together, so that their clocks and noise sources are connected. We've also taken into account undesirable effects such as heat related PLL drift which can be an issue for phase coherence.

At the moment we are also investigating whether singleboard computers like the Raspberry Pi 3 or Tinkerboard can be used, and there will be a header available for powering them via the Kerberos PCB. In the future we also plan to work on optimizing the code and potentially using CUDA/OpenCL GPU optimizations for passive radar so everything runs smoothly.

Once released we plan to have extensive tutorials and documentation that show exactly how to set up and replicate direction finding and passive radar experiments with low cost antennas.

Screenshots of KerberosSDR software:

Screenshots of each KerberosSDR software screen
Screenshots of each KerberosSDR software screen

Remember, if you're interested please sign up to the KerberosSDR mailing list for announcements and the chance to get in early with the cheaper first 100 units.

Be on the look out for more interesting demos that will be posted in the coming weeks!

Update: Please note that due to a Trademark complaint, we have changed the name of this unit from HydraSDR to KerberosSDR.

KerberosSDR Updates: 27 August 18

This week we've managed to get the KerberosSDR demo software made by Tamás Peto functioning on a TinkerBoard. The TinkerBoard is a US$60 single board computer. It's similar to a Raspberry Pi 3, but more powerful. We've also tested the app running on the Raspberry Pi 3 and Odroid XU4. The Pi 3 is capable of running the software but it is a little slow, and the Odroid XU4 is a little faster than the TinkerBoard. In the future we hope to further optimize the code so even Raspberry Pi 3's will be smooth.

In the video below we used a circular array of four whip antennas connected to KerberosSDR. The TinkerBoard is connected to KerberosSDR and is set up to generate a WiFi hotspot, which we connect to with an Android phone and a Windows laptop. The Windows laptop connects to the TinkerBoard's desktop via VNC, and the Android phone receives an HTML/JavaScript based compass display via an Apache server running on the Tinkerboard. With this setup we can wirelessly control and view information from KerberosSDR and the TinkerBoard.

We've also tested the KerberosSDR system on a real signal, and have found it to work as expected. More demo's of that coming later.

For more info on KerberosSDR please see our previous announcement post.

KerberosSDR Direction Finding Test 2: Tinkerboard + Circular Array

KerberosSDR Prototype
KerberosSDR Prototype with TinkerBoard Running Computations

KerberosSDR Updates: 4 September 2018

In this post we'll show an experiment that we performed which was to pinpoint the location of a transmitter using KerberosSDR's coherent direction finding capabilities. RF direction finding is the art of using equipment to determine the location of a transmitting signal. The simplest way is by using a directional antenna like a Yagi to try and determine the bearing based on signal strength. Another method is using a pseudo-doppler or coherent array of antennas to determine a bearing based on phase information.

For the test we tuned the KerberosSDR RTL-SDRs to listen to a signal at 858 MHz and then drove to multiple locations to take direction readings. The antennas were set up as a linear array of four dipole antennas mounted on the windshield of a car. To save space, the dipoles were spaced at approximately a 1/3 the frequency wavelength, but we note that optimal spacing is at half a wavelength. The four dipole antennas were connected to KerberosSDR, with a laptop running the direction finding demo software. 

Low cost direction finding array mounted to vehicle windshield.
Low cost direction finding array mounted to vehicle windshield.

Our open source demo software (to be released later when KerberosSDR ships) 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. 

KerberoSDR SDR Directing Finding DOA Reading
KerberoSDR SDR Directing Finding DOA Reading

In the image below you can see the five bearing measurements that we made with KerberosSDR. Four lines converge to the vicinity of the transmitter, and one diverges. The divergent reading can be explained by multipath. In that location the direct path to the transmitter was blocked by a large house and trees, so it probably detected the signal as coming in from the direction of a reflection. But regardless with four good readings it was possible to pinpoint the transmitting tower to within 400 meters.

In the future we hope to be able to automate this process by using GPS and/or e-compass data to automatically draw bearings on a map as the car moves around. The readings could also be combined with signal strength heatmap data for improved accuracy.

This sort of capability could be useful for finding the transmit location of a mystery signal, locating a lost beacon, locating pirate or interfering transmitters, determining a source of noise and more.

KerberosSDR pinpointing a transmitters location
KerberosSDR pinpointing a transmitters location

KerberosSDR Updates 7 September 2018

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). 

Highway Passive Radar Traffic Monitor with DVB-T and KerberosSDR a 4x Coherent RTL-SDR

DVB-T Antennas In Car
DVB-T Antennas In Car

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.

In the future we'll be working on optimizing the code so that the display updates much faster and smoother. It may also be possible in the future to use the third and fourth tuners to obtain even greater object resolution.

Information on Time Correlating Signals with RTL-SDRs

In a previous post back in September 2017 Stefan Scholl (DC9ST) treated us to a very interesting write up about how to localize transmitters to within a few meters using time difference of arrival (TDOA) techniques with multiple RTL-SDR dongles spread out over an area.

Stefan has recently added to his post now with some additional information on how to properly correlate signals received between multiple RTL-SDR dongles, which is one of the key parts to TDOA. He writes that he covers the following questions:

- What signal parameters influence the quality of the correlation?
- Which type of correlation calculations are available (four)
- Which are suitable with RTL-SDRs, considering noise and phase and frequency offset?

Stefan writes that his findings could be interesting to people interested in the following techniques:

- TDOA localization
- Synchronizing several RTL-SDRs
- Passive Radar

Comparing various bandwidth sizes on correlation quality
Comparing various bandwidth sizes on correlation quality

Real Time Passive Radar Running Native on the ADALM-PLUTO ARM CPU

The ADALM-Pluto (aka PlutoSDR) is a US$149 TX/RX capable SDR that we have posted about several times in the past. It has a tuning range from 70 MHz to 6000 MHz with a bandwidth of up to 56 MHz (with software hack applied). One additional useful feature on the PlutoSDR is it's built in ARM CPU, which can be used to run programs on board the SDR itself. 

Over on his blog Mike has shown how he implemented simple passive radar code on the PlutoSDR's ARM processor. This means that no PC or other hardware is required to process the data, the entire script can be run via a SSH connection to the PlutoSDR. Mike doesn't seem to have shared his script anywhere, but one of his previous posts explains the process. The script creates the video in real time on board the PlutoSDR's ARM CPU, which is then streamed via ffplay to a PC with a screen. On his second post Mike shows some extra videos of passive radar working with FM Broadcast and DVB-T signals.

Passive radar is a radio technique allows you to detect and track RF reflective objects such as aircraft using strong signals from already existing transmission towers, such as broadcast FM or DVB-T signals.

Feedback Request: New RTL-SDR Product, Ideas and Interest Check

We are considering building a new multi-purpose RTL-SDR product. The idea is to make several difficult to achieve applications and projects much more accessible. We are looking to implement the following ideas:

  • 3x on-board coherent RTL-SDRs built into the PCB
    • 4x SMA inputs: 3x individual inputs, 1x common input (switched between the two). 
    • All RTL-SDRs connected to the same clock source – enables coherent experiments
    • All RTL-SDR feature sets and performance equivalent to RTL-SDR V3 or better
  • On-board noise source and directional coupler
    • Useful for correlation with rtl_coherent
    • Measure filter characteristics, and get rough SWR antenna readings.
  • Noise source able to be switched in and out via silicon switches
    • Useful with rtl_coherent and other coherent experiments for cross correlation timing correction. This allows for accurate direction finding.
  • Ability to mount onto a Raspberry Pi 3, and provide an ESD protected, buffered and filtered output for RpiTX transmissions. (a PCB plugin filter specific to the transmission frequency would need to be installed onto PCB to use this feature)
    • With a filter installed the board can be connected to an antenna and used with RpiTX for simple transmissions.
    • Go portable with an Raspberry Pi 3 compatible HDMI LCD screen and a battery pack. Possible HackRF portapack alternative.

Possible applications:

  • Multi-band RTL-SDR applications
    • One RTL-SDR receiving NOAA, one receiving ADS-B, one scanning the air band.
    • Easy trunk tracking with 2x RTL-SDR. Third RTL-SDR used for something else.
    • One streaming NOAA weather, one scheduled to receive NOAA/Meteor sats and weather balloons, one receiving Outernet weather updates.
  • Coherent applications
    • RF direction finding
    • Passive radar
    • Possible radio astronomy applications?
  • Noise source applications
    • Characterize filters
    • VSWR meter with directional coupler
  • Raspberry Pi mount applications
    • Replay attacks and security analysis of ISM band devices with RpiTX and an ISM band filter.
    • Transmitting WSPR with WSPRpi.
    • Portable if used with a small HDMI screen and battery pack.
    • Possible control of board via an Android app.
    • Similar applications to the HackRF Portapack idea.
    • Multi-band noise locator if a GPS is added to the Pi. e.g. See Tim Havens’ ‘Driveby’ concept.

The idea is still in the concept stages so we’re looking for any feedback from the community to see if this is even something that people would want.

Would a receiver board like this interest anyone? We would also work on providing basic ready to go software on a downloadable image file for the Raspberry Pi 3 so starting an app would be as easy as using a launcher. We would also provide various tutorials as well.

The target price would be $99 USD. If you think this is too much, please let us know what you would expect to pay in the comments.

Are there any additional features that anyone requests? Please let us know in the comments.

Would you pay $99 USD for a 3-input RTL-SDR coherent receiver with built in noise source, antenna switcher and filtered RpiTX output?

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Real Time RTL-SDR Passive Radar with Clutter Supression and Target Acquisition

Marcus Herber is a 4th year electrical engineering student at the University of Queensland, Australia. For his final year thesis he set out to build a real time RTL-SDR based passive radar with clutter suppression and automatic target acquisition. On YouTube he’s uploaded a video that gives a quick overview and demonstration of his project. The description reads:

For my final year electrical engineering thesis, I developed a real-time passive radar system with clutter suppression and target acquisition. This was mainly able to be achieved through the use of GPU computing, with CUDA. With any slight improvement of the following hardware (especially the GPU), the system would be able to perform much faster, and increase the number of frames per second. Choosing a slightly better GPU would also allow for a better SDR, with a faster sampling rate.

All the signal processing and the algorithm was done in Python 3, with the Anaconda distribution.

Hardware used:
-RTL-SDR Dongle
-GTX 950 Graphics card
-DAB+/DVB-T LPDA Antenna
-Intel Core i7 6700 Quad Core 3.4GHz CPU
-16GB RAM

Passive radar works by looking for signals being reflected off objects such as aircraft. Strong signals from broadcast towers can easily be reflected off an aircraft towards a directional antenna, then correlated with the broadcast signal received from another antenna. Then with some clever processing the relative speed and distance of the object can be determined.

Real-time RTL-SDR Passive Radar w/ Clutter Suppression + Target Acquisition

A Multi-Channel Coherent RTL-SDR Product: For Passive Radar, Direction Finding and More

Coherent-receiver.com is a company which is a customer of our RTL-SDR V3 dongle and they have been working on creating a multi-channel coherent receiver product based on the RTL-SDR. An RTL-SDR multi-channel coherent receiver is at its most basic, two or more RTL-SDR dongles (multi-channel) that are running from a single clock source (coherent). A multi-channel coherent receiver allows signal samples from two different antennas to be synchronized against time, allowing for all sorts of interesting applications such as passive radar and direction finding.

The team at coherent-receiver.com have used the new expansion headers on our V3 dongles to create their product. In their receivers they attach a control board which has a buffered 0.1 PPM TCXO (buffered so it can power multiple RTL-SDR’s). They also added an 8-bit register and I2C connection capabilities which allows for control of future add-on boards. The I2C capability is useful because it means that several RTL-SDR dongles can be controlled and tuned from the same control signal. More information on the registers and build of the receiver control board can be seen on their technical support page.

A ten channel RTL-SDR coherent receiver.
A ten channel RTL-SDR coherent receiver.
The Coherent Receiver block diagram.
The Coherent Receiver block diagram.

One example application of a multi-channel coherent receiver is passive radar. Coincidentally, we’ve just seen the release of new GUI based Passive Radar software by Dr. Daniel Michał Kamiński in yesterdays post. Passive radar works by listening for strong signals bouncing off airborne objects such as planes and meteors, and performing calculations on the signals being received by two antennas connected to the multi-channel coherent receiver.

A second example is direction finding experiments. By setting up several antennas connected to a multichannel coherent receiver calculations can be made to determine the direction a signal is coming from. An interesting example of direction finding with three coherent RTL-SDRs can be seen in this previous post. A third example application is pulsar detection which we have seen in this previous post

Coherent-receiver.com sent us a prototype unit that they made with four of our V3 dongles. In testing we found that the unit is solidly built and works perfectly. We tested it together with Dr. Kamiński’s passive radar software and it ran well, however we do not have the correct directional antennas required to actually use it as a passive radar yet. In the future we hope to obtain these antennas and test the coherent receiver and the software further.

Currently they do not have pricing for these models as it seems that they are first trying to gauge interest in the product. If you are interested in purchasing or learning more they suggest sending an email to [email protected] It seems that they are also working on additional RTL-SDR ecosystem products such as filters, downconverters, antennas and LNAs.

We hope that the release of this product and Dr. Kamiński’s software will give a boost to the development of coherent multi-channel receivers as we have not seen much development in this area until recently.

SDRDue running on the coherent-receiver.com unit.
SDRDue running on the coherent-receiver.com unit.

SDRDue: New Software for Passive Radar with Two Coherent RTL-SDR Dongles

Dr. Daniel Michał Kamiński, author of two SDR# plugins has recently released a new passive radar program for the RTL-SDR called “SDRDue”. Passive radar is a technique that makes use of signals from strong distant transmitters. The idea is that these signals can be reflected off the fuselage of aircraft or other flying objects, and the reflection can be observed by a passive radar receiver. By correlating data from two receivers and two antennas, more accurate positional data can be obtained.

For passive radar to work properly the receivers should be coherent, meaning that they run from the same clock and have synchronized samples. The RTL-SDR can be made coherent by connecting two dongles to a single clock source.

The software runs on multi-threaded C# code, and uses Microsoft XNA 4.0 for the graphical operations. It also supports GPU parallel calculations if you have OpenCL and an AMD graphics card.

Please note that we attempted to run the program, but it would not even open on our PC. We’ve contacted the author to ask if there is any known problems. If anyone gets it running please report back in the comments section of this post. EDIT: Daniel has updated the software and it appears to be functioning normally now. You will need to install it into a SDR# folder, and run SDR# first with both dongles before the software will recognise the dongles in SDRDue. We also had better luck with using the rtlsdr.dll_ file, rather than the default rtlsdr.dll file. Just delete the original rtlsdr.dll and rename rtlsdr.dll_ to rtlsdr.dll.

For more information on passive radar we recommend looking at this previous post where we showed the work of Juha Vierinen who used RTL-SDR’s to build a passive radar.

The SDRDue Passive Radar Software
The SDRDue Passive Radar Software