Tagged: kerberossdr

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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Locating a Radio Transmitter with Direction Finding Techniques 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 post. Please 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 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, for use during fox hunts and more.

KerberosSDR pinpointing a transmitters location
KerberosSDR pinpointing a transmitters location
KerberosSDR Prototype
KerberosSDR Prototype

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KerberosSDR Running RF Direction Finding on a Tinkerboard

KerberosSDR (formerly HydraSDR) is our upcoming 4-input coherent RTL-SDR. It's designed for coherent applications like RF direction finding, passive radar, beam forming and more, but can also be used as a standard 4-channel SDR for monitoring multiple frequencies. In this post we demonstrate the direction finding application running on the TinkerBoard. 

Reminder: If you have any interest in KerberosSDR, please sign up to our KerberosSDR mailing list. Subscribers to this list will be the first to know when KerberosSDR goes on preorder, and the first 100 sales will receive a discounted price.

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Please select all the ways you would like to hear from RTL-SDR Blog:

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KerberosSDR Updates

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