Category: Other

Creating a Drone Based Synthetic Aperture Radar

Synthetic Aperture Radar (SAR) is a technique that can generate high-resolution imagery through the use of radar microwaves on a moving platform. Placing the radar system on a moving platform allows the system to simulate a very large aperture. Combined with some clever algorithms, the result is very high resolution imagery available in all weather conditions.

Typically, SAR implementation is the domain of high-level military spy and commercial satellites such as ICEYE and Sentinel-1. However, on his blog, Henrik Forstén has shown that it's possible to create a homemade SAR system using an FPGA, ADC, and custom 6 GHz radar antennas mounted on an FPV drone. Henrik's blog explains his setup in detail, discussing the radar and RF design, link budget, FPGA, his custom PCB, focusing, and more.

The results are rather stunning images that look almost like a photograph. And not only was Henrik able to take images, but a video too, which can be seen on his blog post.

A Synthetic Aperture Image from Henrik's Drone

An RTL-SDR/LoRa/GPS/RTC/USB-Hub Extension Board for the uConsole

The uConsole is a handheld computing device developed by ClockworkdPi that costs US$189. Its computing power is based on a Raspberry Pi Compute Module 4, but other CPU options are also available. The uConsole comes with a 5-inch 1280x720 HD screen, keyboard, and battery module that takes two 18650 lithium-ion batteries.

The uConsole is also modular, allowing for expansion. We wanted to thank RTL-SDR.COM reader Sunny for sharing the news that a RTL-SDR/LoRa/GPS/RTC/USB Hub All-In-One Extension Board for the uConsole will be available from HackerGadgets soon. This board includes a full RTL-SDR module, an SX1262 LoRa chip, a GNSS chip, a real-time clock chip, and a USB hub. The expansion board is currently advertised as being priced at US$78.99.

The expansion board is not yet available for sale, but you can join their waiting list to be notified of its release.

Over on YouTube 'Symbiiote' has released an early review video showing how to build the module into the uConsole and then showing it running SDR++ and receiving some broadcast FM stations.

This uConsole accessory changes EVERYTHING!

A Handheld Cyberdeck with RTL-SDR

Over on his YouTube channel and Hackaday.io blog page, Nicholas LaBonte has shown his "Cyberdeck Handheld" which is a portable computer consisting of a Raspberry Pi 5, LCD screen, custom CNC'd keyboard, UPS module, and an RTL-SDR. All the components are placed in an aesthetically pleasing custom enclosure, made of some interesting premium materials like Sepele hardwood and Richlite. Nicholas writes:

Having been inspired by the uConsole and similar projects, I wanted to try my hand at building my own with off-the-shelf components. Richlite and Sepele hardwood would be used for the housing, materials that I have worked with furnishing yacht interiors. Combined with a bronze heatsink, I wanted to merge cyberpunk and nautical aesthetics. Since the keyboard was the biggest challenge, I started there by combining concepts from both Bobricius and the Ello 2M keyboards, settling on tabbed keys atop PCB-mounted microswitches.

Cyberdeck Handheld

ESPARGOS: An ESP32 Phased Array for Seeing WiFi

Recently, Florian Euchner, a research assistant at the Institute of Telecommunications at the University of Stuttgart, has released information about a project called ESPARGOS that he has been working on. ESPARGOS is a phased array of many patch antennas, each connected to an ESP32 WiFi microcontroller. Phased arrays enable interesting things like radio direction finding.

Combined with a bit of code, Florian can not only determine the direction of arrival of WiFi signals but, with enough patch elements, also create a live heatmap of the WiFi source overlayed on top of the video. We note that ESPARGUS is not based on software-defined radio, however, the overall concept and implementation are quite similar to KrakenSDR.

In the video embedded below, Florian explains the system and demonstrates it in action. He shows how the WiFi signal from a device can be visualized, how it can be used to track movement of the device behind a wall, how reflections from a directional antenna can be seen, how a device can be triangulated with multiple arrays. Finally Florian also shows how a device can be located with a single array, even in a high multipath environment after a neural network is trained on the environment.

Florian writes:

More information is available on the project website of the ESP32 antenna array "ESPARGOS": https://espargos.net/

Source code for Python library + demos: https://github.com/ESPARGOS/pyespargos (directory "demos/camera" for "WiFi camera" demo)

As a research assistant at the Institute of Telecommunications at the University of Stuttgart, I work on multi-antenna systems like (distributed) massive MIMO, with a focus on wireless channel measurement platforms and algorithms for processing channel measurements (classical and deep learning-based).

One day, my (incredibly talented) colleague Marc Gauger suggested to use ultra low-cost ESP32 chips instead of software defined radios for channel measurements. I was highly sceptical at first, but when he showed me a minimalistic prototype he had soldered together, I was intrigued by the idea of being able to demonstrate my algorithms in real time using WiFi signals. In a series of Bachelor's / Research theses, my excellent students Tim Schneider, David Engelbrecht and David Kellner helped me develop the ESP32 antenna array "ESPARGOS".

Measured CSI dataset used for AoA / TDoA visualization: https://espargos.net/datasets/data/espargos-0005/
AoA / TDoA localization source code (needs some minor modifications to be applied to espargos-0005 dataset): https://github.com/Jeija/ToA-AoA-Augmented-ChannelCharting/
Channel Charting source code for the animation in the video: 
https://github.com/Jeija/Geodesic-Uncertainty-Loss-ChannelCharting
Tutorial on Channel Charting: https://dichasus.inue.uni-stuttgart.de/tutorials/tutorial/dissimilarity-metric-channelcharting/

This ESP32 Antenna Array Can See WiFi

We note that while the software is open source, the array hardware itself is not. Florian has noted in a comment on his YouTube video that he is preparing a manufacturing run for ESPARGOS.

I am now preparing a manufacturing run for ESPARGOS. This involves some PCB redesigns to make the design more mass-manufacturable and to get the cost further down, and to get it certified. This will obviously take some time, but I will make sure to keep you updated. You can use the button on the website https://espargos.net/ to sign up for email updates, and I will also post updates via YouTube community notes.

Creating a Software Defined Radio from Tiny Tapeout Chips

Tiny Tapeout is a project that allows anyone to design and fabricate custom open ASIC silicon at a low cost by combining hundreds of projects from different people on the same chip. Each design on the the chip is freely available to use by others.

Over on Hackster.io, we've seen a post where Sylvain Munaut used two of these Tiny Tapeout chips to create a software defined radio.

On the Tiny Tapeout 6 chip, Sylvain discovered that Tiny Tapeout customer Carsten Wulff had implemented an 8-bit ADC on the chip. Then, on the Tiny Tapeout 7 chip, Sylvain found that Kolos Koblász had implemented an RF mixer. So, he decided to combine the two Tiny Tapeout chips together to build a software defined radio.

The entire build consists of the two Tiny Tapeout chips, a Glasgow Interface Explorer (USB interface), and a GNU Radio flowgraph to demodulate and display the signals received.

In his YouTube video, Sylvain demonstrates the software defined radio in action, showing that it has 2 MHz of bandwidth and is capable of receiving FM signals.

SDR with custom silicon ! Combining TinyTapeout projects.

Using an EFR32 IoT Microcontroller Transceiver as an SDR

Thank you to Joshua R. for writing in and sharing some links on how an EFR32 microcontroller can be used as a software-defined radio. The EFR32 is a microcontroller designed for IoT applications such as Zigbee, Z-Wave, Thread, Bluetooth. Of interest to us is that the EFR32 has a special mode that allows for the demodulator/modulators to be switched off and instead allowing for raw IQ data to be transferred from the chip.

An example of the EFR32 being used as an SDR has been provided by OH2EAT/tejeez and can be found in this write-up and in his 'geckokapula' GitHub repo. This MIT-licenced repo provides hardware schematics and software for creating a full handheld FM, AM, USB, LSB, and CW receiver with FM, CW, USB, and LSB transmit capabilities. It also supports a 12 kHz waterfall display. The tuning range is nearly 13.2 MHz to 2.9 GHz, but there are some gaps.

This Knowledge Article by Silicon Labs also explains the SDR mode of the EFR32.

This is an interesting low-cost chip, but the limiting factor appears to be the small bandwidth.

An EFR32 SDR by Tejeez/OH2EAT
An EFR32 SDR by Tejeez/OH2EAT

SignalSurge – An open source bandpass filter with selectable LNA for the VHF and UHF bands

Thank you to Rodrigo Freire for writing to us and sharing his project called 'SignalSurge'. The SignalSurge project started when Rodrigo discovered that adding an RTL-SDR Blog FM Bandstop filter to his Yaesu FT-991A significantly improved his reception in the 2-meter band.

An FM bandstop filter can improve reception by reducing the power of strong broadcast FM signals, which can overload the front end of radios, causing the desensitization of signals on other bands.

This finding led Rodrigo to design SignalSurge, a bandpass filter for VHF and UHF bands, with a selectable LNA. The design includes selectable 2m and 70cm bandpass filters, a selectable 15dB LNA, automatic LNA shutdown when the radio is transmitting, and ESD protection. A 50W relay gives the ability to select between filters and switch the LNA in or out.

The design is entirely open source and available on the SignalSurge GitHub.

SignalSurge Schematic
SignalSurge Schematic

Creating an SDR from a TEF6686 Car Radio FM/AM Chip

A recent IEEE Spectrum article details how hobbyist PE5PVB has repurposed an NXP TEF6686 automotive FM/AM tuner chip into a software-defined radio with a tuning range of 65 MHz - 108 MHz and 144 kHz - 27 MHz.

PE5PVB developed custom open-source firmware for TEF6686 dev boards, allowing them to tune beyond their original design frequency range. He then went on to develop a version that included a screen. Eventually, the Chinese manufacturers caught on to the potential of the design and are now producing a full handheld version that is available on Aliexpress at a current sale price of US$61.26.

Reviews of the product are all positive, and it appears to be one of the best choices for a portable handheld DXing radio.

A TEF6686 based SDR available on Aliexpress.
A TEF6686 based SDR available on Aliexpress.