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're showing some more passive radar demos. The first video is a time lapse of aircraft coming in to land at a nearby airport. The setup consists of two DVB-T Yagi antennas, with KerberosSDR tuned to a DVB-T signal at 584 MHz. The reference antenna points towards a TV tower to the west, and the surveillance antenna points south. Two highlighted lines indicate roughly where reflections can be seen from within the beam width (not taking into account blockages from mountains, trees etc).
The second video shows a short time lapse of a circling helicopter captured by the passive radar. The helicopter did not show up on ADS-B. On the left are reflections from cars and in the middle you can see the helicopter's reflection moving around.
We are expecting to receive the final prototype of KerberosSDR within the next few weeks. If all is well we may begin taking pre-orders shortly after confirming the prototype.
Over the last few years researchers at Universidad Javeriana Bogotá, a University in Colombia, have been looking into using SDRs for aerial landmine detection. The research uses a USRP B210 software defined radio mounted on a quadcopter, together with two Vivaldi antennas (one for TX and one for RX). The system is then used as a ground penetrating radar (GPR). GPR is a method that uses RF pulses in the range of 10 MHz to 2.6 GHz to create images of the subsurface. When a transmitted RF pulse hits a metallic object like a landmine, energy is reflected back resulting in a detection.
Recently they uploaded a demonstration video to their YouTube channel which we show below, and several photos of the work can be found on their Field Robotics website. We have also found their paper available here as part of a book chapter. The abstract reads:
This chapter presents an approach for explosive-landmine detection on-board an autonomous aerial drone. The chapter describes the design, implementation and integration of a ground penetrating radar (GPR) using a software defined radio (SDR) platform into the aerial drone. The chapter’s goal is first to tackle in detail the development of a custom designed lightweight GPR by approaching interplay between hardware and software radio on an SDR platform. The SDR-based GPR system results on a much lighter sensing device compared against the conventional GPR systems found in the literature and with the capability of re-configuration in real-time for different landmines and terrains, with the capability of detecting landmines under terrains with different dielectric characteristics.
Secondly, the chapter introduce the integration of the SDR-based GPR into an autonomous drone by describing the mechanical integration, communication system, the graphical user interface (GUI) together with the landmine detection and geo-mapping. This chapter approach completely the hardware and software implementation topics of the on-board GPR system given first a comprehensive background of the software-defined radar technology and second presenting the main features of the Tx and Rx modules. Additional details are presented related with the mechanical and functional integration of the GPR into the UAV system.
Drone with USRP Ground Penetrating Radar Setup
Aerial landmine detection using SDR-based Ground Penetrating Radar and computing vision
Spektrum is a popular spectrum analyzer program that is used with RTL-SDR dongles. It is based on the command line rtl_power software and is compatible with both Windows and Linux. Thanks to it's easy to use GUI it is an excellent piece of software for scanning and determining where active signals exist, or for measuring filters and antenna SWR with a noise source.
Recently SV8ARJ (George) and SV1SGK (Nick) have been working on extending the original open source Spektrum code. Their improvements focus around the UI and making it more functional and easier to use. Currently the updated branch is in alpha, and they are hoping that any testers could help report bugs, issues and wishes to them. The code is available on their GitHub and the latest Windows test build can be downloaded from their DropBox.
The changelog reads:
2 Cursors for Frequency axis.
2 Cursors for Amplitude axis.
Absolute and differential measurements with cursors.
Zoom functionality of the cursors's defined area (gain + frequency).
Mouse Wheel Gain adjustment on graph (Top area for upper, low area for lower).
Mouse Wheel Frequency adjustment on graph (left area for lower frequency, right for upper).
Mouse Wheel in the centrer of the graph performs symetric zoom in/out.
View/settings store/recall (elementary "back" operation, nice for quick zoomed in graph inspection).
Right click positions primary cursors.
Right Double Click positions primary cursors and moves secondary out of the way.
Left Double Click zooms area defined by cursors (Amplitude + frequency).
Left Mouse Click and Drag on a cursor moves the cursor.
Middle (mouse wheel) Double Click resets full scale for Amplitude and Frequency.
Middle (mouse wheel) Click and Drag, moves the graph recalculating limits accordingly.
Reset buttons to Min/Max range next to Start and Stop frequency text boxes.
Cursor on/off checkbox now operate on all 4 cursors.
ZOOM and BACK buttons.
Filled-in graph option (line or area).
Display of frequency, Amplitude and differences for all cursors.
Modified: Button layout.
Fixed: Save/Reload settings on exit/start. IMPORTANT : delete the "data" folder from the installation location if you have it.
Thank you to Josh for submitting news about his project called GammaRF. GammaRF is an client-server program that is used to aggregate signal information via the internet from distributed SDRs. Currently the RTL-SDR and HackRF SDRs are supported.
ΓRF (“GammaRF”, or “GRF”) is a radio signal collection, storage, and analysis system based on inexpensive distributed nodes and a central server. Put another way, it is a distributed system for aggregating information about signals, and a back-end infrastructure for processing this collected information into coherent “products”.
Nodes utilize inexpensive hardware such as RTL-SDR and HackRF radios, and computers as small and inexpensive as Intel NUCs. Each node runs modules which provide various radio monitoring functionality, such as monitoring frequencies for “hits”, watching power levels, keeping track of aircraft (through ADS-B), and more. Nodes are distributed geographically and their data is combined on the server for hybrid analysis.
A web-based system allows users to view information from and about each station in its area. Below shows the server landing page. Markers are placed at each station’s last known location (stations can be mobile or stationary.)
GammaRF Server Landing Page
From the currently implemented modules it appears that you can monitor ADS-B, scan and monitor the power of a set of frequencies, forward the output from trunk-recorder (a P25 call recorder), scan the spectrum and monitor power levels, monitor a single frequency for activity, take a picture of a swath of RF spectrum, and collect 433 MHz ISM data. Some example applications might include:
Monitoring ham radio activity on repeaters in a city
Creating timelines of emergency services activity in an area
Distributed tracking of satellites and other mobile emitters
Monitoring power at a frequency, for example as a mobile node traverses an area (e.g. signal source location)
Building direction finding networks (e.g. for fox hunts)
Spectrum enumeration (finding channels and guessing modulation) [under development]
Monitoring Activity of an Amateur Radio Repeater via the 'scanner' Module
Over on YouTube user aonomus has uploaded a video showing how he's used an RTL-SDR to observe and listen to the radio signal generated via a chemistry lab's nuclear magnetic resonance machine. To do this he simply taps the RF output of the NMR machine which allows the RTL-SDR to listen to the signal and play it as audio. In the video he shows the sound of a sample of chloroform in acetone-d6. The demo has no real scientific purpose other than to hear the sound of the molecule. Normally the RF output goes straight into a spectrum analyzer for visual analysis.
Nuclear magnetic resonance is a technique used in chemistry for the analysis of chemicals, as well as in MRI medical imaging machines. Very basically, it works by applying a chemical sample to a strong magnetic field, exciting it with a strong pulse of RF, and listening to the echo. An echo will only occur when the radio waves are transmitted at the chemicals resonant frequency. The frequencies used are typically between 60 to 800 MHz.
A few years ago I came up with a demonstration for some high school students interested in chemistry. This demo is a modern take on a classic NMR experiment, using a low cost software defined radio to observe the FID signal as audio. In short, this demo allows you to hear the proton FID echo from the liquid sample inside the NMR magnet.
Nuclear Magnetic Resonance Demonstration Using Software Defined Radio
FPV stands for 'First Person View', and is a term used to describe the hobby of flying remote controlled aircraft entirely via the view from a wireless camera that transmits live video to the pilots screen or video goggles.
Part of the FPV hobby is to not only enjoy flying, but also to tweak the wireless video equipment for maximum range and reliability. This involves measuring the SWR characteristics of FPV antennas. SWR is a metric that describes how well the impedance of an antenna is matched with the receiver at a certain frequency. Poor SWR results in additional signal loss on top of cable and connector loss. We note that SWR is only one antenna metric, and doesn't take into account radiation pattern and antenna gain which is often more important, but it is the easiest metric to measure and control, and should give you some idea as to if an antenna was designed and tuned properly.
As FPV hobbyists are often not hams or radio professionals, most don't have access to the equipment required to measure SWR. So over on his YouTube channel bonafidepirate shows how he's been using a cheap RTL-SDR, noise source and RF Bridge to measure the SWR of his FPV antennas. The process is similar to the one shown in our tutorial, but he uses the Spektrum software which allows you to measure SWR entirely within the software itself.
In the video bonafidepirate goes over the required hardware, software and the setup, and then demonstrates several SWR scans of different FPV antennas.
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 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).
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.
Othernet (formerly known as Outernet) are a providers of a free data service broadcast from satellites. They hope to build a system and low cost satellite receiver products where people can easily stream free daily data such as news, videos, books, and live audio down to a computer or phone from anywhere in the world via a device called a Lantern. It is a one way download only service, but may be useful for those in areas with limited internet, disaster preppers, or people in countries with internet censorship. The describe their mission as:
Othernet's mission is to build a universal information service; a truly pervasive multi-media service that operates in the most remote places and functions even when nothing else does.
In the past they ran a trial service on L-band satellite frequencies and used RTL-SDR dongles as the receiver. They have since discontinued that service in favor of a new Ku-band LoRa based service which can provide much more data - up to 200MB a day. The update released today was sent to Lantern backers, which was the receiver they crowdfunded for in their Kickstarter back in 2014. The update notes that the final iteration of the Lantern is close to being ready.
Broadcasting Khan Academy 24/7
Hello Backers,
Yes, we are still here. It’s been a long while since the last update, but that does not mean we have stopped–or even slowed–working on Lantern. We have been making progress, though it has been much, much slower than what everyone wants. Fortunately, we are in the final stage of development.
The last update described the new network technology we had developed. Our original goal was to broadcast 20 MB of content per day, which is what we were doing with our previous network. The new system is operating at 10-times that speed, which is a little over 20kbps and 200 MB of content per day. Some of the work we’ve been doing over the past few months is related to tripling our current download speeds. Our target is 60kbps, which results in over 600 MB per day. The size of the device will be similar to a standard flashlight.
At our current download speed of 20kbps, we are broadcasting both data and a 24/7 audio stream. I know many of you were interested in the educational applications that were highlighted during the campaign, which is why I’m very pleased to share that we are currently broadcasting the entirety of Khan Academy as a 24/7 audio stream. The Khan Academy library consists of over 900 separate lectures, which we’ve turned into a giant audio playlist. Now we just need to get Lanterns into everyone’s hands.
The next update will include a picture of our final antenna design. The antenna that is currently included in our DIY kit is 2-inches/5-cm across and the shape of a cone. We are trying to flatten the cone and also increase the size to about 4-inches/10-cm, which is what allows for greater download speeds. Since we are operating at microwave frequencies (12 GHz), both the design of the antenna and the parts to convert the high frequency to a lower one are pretty tricky. Microwave engineering is widely considered black magic, which is the main reason for the long break since the last update. We are close to turning the corner and are targeting the end of the year for our initial production run.
Unrelated to our technical work is our recent name change. We had been fighting a trademark issue for the past four years. We recently decided that it made more financial sense to change our name, rather than continue spending legal fees to defend our position. We are now Othernet (http://othernet.is). This name change does not mean we are going away, nor does it mean we are not delivering Lanterns. It’s just a legal hiccup.
Thanks for your patience and support while we get through the final stage of building what you all backed several years ago. I know it’s been a long time and we are making every possible effort to deliver something that exceeds everyone’s original expectations. Although it’s taking three times longer to develop and ship the product, what we now have will be ten-times more useful.
