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.
Aerial landmine detection using SDR-based Ground Penetrating Radar and computing vision
John required a wideband antenna that could cover the cellphone bands, WiFi, Bluetooth up to 6 GHz and the new USB band from 5 GHz to 10 GHz all in a single antenna installation. He also needed the impedance to be as flat as possible to reduce signal pulse distortion. First he looked into classic discone and sphere antenna designs, but found that while a sphere had the required bandwidth, it did not have the desired impedance characteristics, and a discone had the desired impedance characteristics, but not the ultra wide bandwidth required.
To get around this John combines the sphere and discone designs together to create a sort of icecream with cone looking shape. This results in the ultra wide bandwidth required, and a relatively flat SWR that stays below 2.
The design is easily reproducible by anyone with a metal 3D printer. The antenna's top hemisphere and cone are printed in brass, whilst the radome and supporting structure are printed in plastic.
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.)
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]
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
Aleksey Smolenchuk (lxe) has recently uploaded a step-by-step guide to setting up a GOES weather satellite receiver with an RTL-SDR dongle, Raspberry Pi and the goestools software. GOES 15/16/17 are geosynchronous weather satellites that beam high resolution weather images and data. In particular they send beautiful 'full disk' images which show one side of the entire earth. Compared to the more familiar and easier to receive low earth orbit satellites such as NOAA APT and Meteor M2 LRPT, the geosynchronous GOES satellites require slightly more effort as you need to set up a dish antenna, use a special LNA, and install Linux software.
Aleksey's tutorial first shows where to purchase the required hardware and notes that the total cost of the system is around $185. Next he goes on to show the hardware connection order, and then how to install and configure the goestools decoding software onto a Raspberry Pi.
Over on YouTube, Alexander from the Russian channel РАДИОБЛОГ с Александром Никитенко has uploaded a video review of a Russian USB filter product, designed for USB SDR dongles. The video is narrated in Russian, however you can use the YouTube auto-translate feature to get somewhat understandable subtitles. The actions he takes in the video are also easy to understand.
The USB filter is designed by Maxim who runs a small company called ExpElectroLab. Back in August we posted about another ExpElectroLab product which was the SDR# tuning knob. Since then we've seen that a few people outside of Russia have been able to order the product by contacting him at [email protected], and have been happy with it.
When using USB SDR dongles, the USB cable can pick up lots of interference from the PC and monitors, providing a direct path for this interference to enter the RTL-SDR. A USB filter can be used to remove this interference. There are several USB filters on the market designed for improving USB audio devices, but this is the first one we've seen designed for SDRs in particular.
In the video Alexander tests an RTL-SDR with and without the USB filter connected. With the USB filter not connected, the SDR# display shows several spikes of interference in the spectrum, and once the filter is connected these spikes disappear. He also tests it on a USB powered shortwave radio, and the filter appears to remove the hiss caused by the power supply.