Category: Amateur Radio

FOSDEM 2024 Videos now Available: Synthetic Aperture WiFi RADAR, GPU DSP Acceleration and more

FOSDEM (Free and Open Source Developer’s Meeting) is a yearly conference that took place in Brussels, Belgium on 3 - 4 February 2024. This conference featured a room on Software Defined Radio and Amateur Radio.

Recently the videos of most the talks have been uploaded to their website. Some interesting talks include:

Covert Ground Based Synthetic Aperture RADAR using a WiFi emitter and SDR receiver

Link to Talk Page

Using a WiFi emitter as radiofrequency source illuminating a scene under investigation for slow movement (e.g. landslides), a Ground-Based Synthetic Aperture RADAR (GB-SAR) is assembled using commercial, off the shelf hardware. The dual-channel coherent Software Defined Radio (SDR) receiver records the non-cooperative emitter signal as well as the signal received by a surveillance antenna facing the scene. Spatial diversity for azimuth mapping using direction of arrival measurement is achieved by moving the transmitter and receiver setup on a rail along a meter-long path -- the longer the better the azimuth resolution -- with quarter wavelength steps. The fully embedded application runs on a Raspberry Pi 4 single board computer executing GNU Radio on a Buildroot-generated GNU/Linux operating system. All development files are available at

Synthetic Aperture RADAR with WiFi and USRP SDR

Using GPU for real-time SDR Signal processing

Link to Talk Page

GPU processors have become essential for image or AI processing. Can they bring anything to real-time signal processing for SDR applications? The answer is yes, of course, but not all classic algorithms (FIR, DDC, etc.) can be used "as is", sometimes a different approach must be taken. In this presentation, I will share the solutions that I implemented to achieve multi-channel DDC on NVIDIA Jetson GPU and will make a comparison with "classic CPU" approaches.

Using GPU's for Real Time Signal Processing

Maia SDR: an open-source FPGA-based project for AD936x+Zynq radios

Link to Talk Page

Maia SDR is an open-source project with the main goal of promoting FPGA development for SDR and increasing the collaboration between the open-source SDR and FPGA communities. Currently it provides a firmware image for the ADALM Pluto and other radios based on the AD936x and Zynq. This firmware can display a real-time waterfall at up to 61.44 Msps in a WebSDR-like interface using WebGL2 rendering, and record IQ data in SigMF format in the SDR DDR. The FPGA design is implemented in Amaranth, an Python-based HDL, and the software stack is implemented in Rust, targetting the embedded ARM CPU and WebAssembly.

The first firmware version was released in February 2023, and the project was presented in June in the Software Defined Radio Academy. In this talk we cover the progress since the summer, including the addition of support for devices such as the Pluto+ and AntSDR. We focus on the technical details of the project and the possibilities for re-using some of the components in other projects.

Maia SDR

DAPNET: Bringing pagers back to the 21st Century

Link to Talk Page

When talking about pagers, most of us will think about an object of the past, often seen in TV shows from the 90s, used by medical staff and businessmen. However, they're an interesting way to get simple data broadcast over amateur radio frequencies, with receivers that can be built for less than 20€. We'll explore this and understand how an extensive network can be deployed with simple equipment and using open source hardware and software.


An HF Ham Radio SSB/AM/FM/CW Transmitter made from a Raspberry Pi Pico and not much more

Over on Hackaday we've seen a story about a Raspberry Pi Pico based software defined radio transmitter that is capable of transmitting SSB, AM, FM and CW anywhere between 0.5 - 30 MHz.

The design generates an oscillator signal using the Pico's Programmable IO. For AM/SSB it uses the PWM output pins to generate an RF envelope which gets mixed together with the oscillator using an analog multiplexor. A small microphone is also connected to the Pico for voice transmissions. The designer notes that the output power is far too low to be used on the air, but adding an output amplifier would help.

The software is all open source and provided on GitHub, and more information about the design can be found on the designer's '101things' website.

The Raspberry Pi Pico is a low cost microcontroller board, and we note it cannot run Linux like standard Raspberry Pi boards. This means that software like RpiTX cannot be used.

Build a Ham Transmitter with a Raspberry Pi Pico

Tech Minds: Testing a High Impedance Amplifier for Software Defined Radio

Antenna impedance matching is important for antennas and software defined radios as impedance mismatches can result in poor reception. For transmitting SDR's the situation is more dire because impedance mismatches can actually damage the transmitting hardware or at least cause high power efficiency losses.

Over on his YouTube channel Tech Minds has uploaded a video where he tests out a battery powered HF high impedance amplifier for software defined radios. The amplifier is designed to be used with long wire antennas on the HF bands as these antennas typically have high impedances which don't match the 50 Ohm impedance that most SDRs expect to see. This device is an amplified alternative to using a passive unun.

The results in his video show that the signal to noise ratio is indeed boosted when the impedance matching amplifier is used. Later the device is opened to show the battery, charging management chip and amplifier chip.

High Impedance Amplifier for Software Defined Radio

Radio Field Mixed Reality Visualization with the Quest 3

The Meta Quest 3 is a recently released mixed reality headset from Meta. Recently Manahiyo has ported his RadioFieldAR software to the Quest 3. The RadioFieldAR software allows you to use a radio field probe together with an RTL-SDR or TinySA Ultra, and have the readings visualized in augmented/mixed reality. This could have several real world use cases, for example, probing an electronic PCB and mapping out the RF noisiest parts. Or for visualizing sources of RF signals.

Previously we posted about Manahiyo's work where he used a smartphone to visualize the augmented reality space, and also an older VR headset. Manahiyo writes:

MetaQUEST3, which was recently released, has a color pass-through function and features MR (Mixed Reality). Thanks to this, this software was made possible.

With a smartphone, We took measurements while looking at the antenna through the display, but with QUEST3, we can take measurements in MR (Mixed Reality) using color pass-through features.

In addition, the hand tracking function allows various settings and FFT to be displayed.

It is now possible to take measurements in a more natural and comfortable way.

There are still many bugs, so I'm considering distributing the executable file as before after fixing them.

Manahiyo has not released the software yet, but it appears he is willing to personally distribute the software for testing first. If we receive any further details about software  distribution we will update this post.

UPDATE 29 November 2023: Manahiyo has released the software on Github. He notes:

This software now supports both RTL-SDR and tinySA-ULTRA. Of course, Quest3 is also required. I have provided instructions in the on the GitHub page, which should help you understand how to use it. Currently, only the APK file is available for download. I do not have a plan to open the source code at this time.

RadioFieldMR with the QUEST3 -Measuring noise on FPGA board-

RadioFieldMR with the QUEST3 -Measuring the FM transmitter signal-

Creating a Multicarrier Base Station Transceiver For DMR, YSF, M17 and more with MMDVM and LimeSDR

Thank you to Adrian, creator of the QRadioLink software for writing in and sharing with us his post about how he uses a LimeSDR as an Multi Mode Digital Voice Modem (MMDVM) for various modes including DMR, YSF and M17. 

A MMDVM is usually a computing device running multiple radios, each of which is used for a separate channel with it's own filters and power amplifier hardware. Each channel can run a separate protocol if desired. 

However in order to save on radio hardware, Adrian wanted to use his LimeSDR as the radio hardware in his MMDVM system. The LimeSDR is a transceiver which has enough bandwidth to implement several channels just by itself. To do this Adrian uses his MMDVM-SDR software.

His implementation runs multiple instances of MMDVM-SDR, one instance for each channel. Then a GNU Radio flowgraph with LimeSDR block connects to each of these instances, transferring data between GNU Radio and MMDVM-SDR via ZeroMQ or TCP sockets. The bulk of Adrian's post explains the architecture in detail. Adrian writes:

The setup can transmit 7 digital carriers in 200 kHz occupied spectrum, and each radio channel can be assigned to a different mode or digital voice network as configured in MMDVMHost.

This is based on the work of Jonathan Naylor G4KLX and Rakesh Peter (r4d10n).

Adrian also notes that this is still a work in progress and there are still several limitations including high latency and issues with filtering, overload and poor channel rejection. 

Multi-Channel MMVDM LimeSDR Architecture Overview

Testing the ATS25 Max-Decoder Receiver

Thank you for Manuel Lausmann for submitting his videos where he tests out and upgrades an ATS25 Max-decoder receiver. The ATS25 Max-decoder is a low cost portable HF receiver which has a large number of decoders built in such as RTTY, Hell, FT8 and FT4. Manuel notes that more decoders are still to come, such as SSTV. The built in decoders make it superior to it's predecessors the x1 and x2.

We note that the ATS25 Max appears to be around US$75 on Aliexpress, but these appear to be Max units without the "-decoder" add on. So if you are looking at purchasing one, please make sure to check that you are getting one with the text "max-decoder".

Manuel also notes that older models of the ATS25 can be retrofitted with a decoder PCB and converted into an ATS25 Max-decoder with a firmware update written by Bernhard Binns.

Note that Manuel's videos below are narrated in German, however the YouTube subtitle auto-translate feature works well enough to understand what is being said. In the first video Manuel demonstrates and reviews the ATS25 Max-Decoder, showing off some of the decoding features.

In the second video Manuel shows how to update an old model ATS25 in to the ATS25 Max by soldering on the decoder board.

Alter ATS25 umbauen zum max Decoder Teil 1 Die Hardware

Fox Hunting with the KrakenSDR

Over on his YouTube channel Mark Jessop has uploaded some dash cam footage showing him using a KrakenSDR and a custom LED display to hunt down three amateur radio transmitters during a fox-hunt.

An amateur radio fox-hunt is an activity where someone will hide a transmitter within a defined area, and it is up to the hunters to use radio direction finding equipment to find it. The KrakenSDR is our 5-channel coherent radio based on RTL-SDRs, and it can be used for applications like radio direction finding.

Mark uses a custom four element array on the roof of his car, which is connected to his KrakenSDR. Instead of the KrakenSDR app, Mark prefers to use his custom LED HUD to displays the bearings and signal power directly.

Some annotated and sped-up dash-cam footage captured during the July 2023 Amateur Radio Experimenters Group Fox-hunt. We run these monthly, and usually have three transmitters hidden around the Adelaide (South Australia) area.

I run a KrakenSDR with a custom-built 4-element antenna array mounted to the roof of my car. This gives me direction estimates to the target transmitter, at least when the signals are strong enough!

I've also build a heads-up-display which helps me safely make use of the KrakenSDR's output data while driving. The source code for this is here:

The display is shielded so it's not visible from outside the car - Red & Blue lights on your dashboard can give the wrong impression!

AREG Fox-hunt - 14th July 2023

André shares his QO-100 Ground Station and HF/VHF/UHF Station

Thank you to reader André for submitting and sharing with us his QO-100 ground station setup. The setup also includes antennas and equipment to receive HF and VHF/UHF. His setup can serve as an example of a well set up permanent installation.

André's set up consists of a 1.8 meter prime focus dish, Raspberry Pi 4, GPIO connected relay, Airspy R2, Ham-it-up upconverter, coaxial relay for switching between Mini-Whip and Discone Antenna, and FM bandstop filter and a power terminal rail block. The Airspy R2 is used for HF/UHF/UHF reception and the antennas and upconverter are all controlled via a web connected relay system. All equipment is enclosed in an outdoor rated box, and André notes everything has been working well from temperatures range from -10C to 35C.

Inside the satellite dish feed is housed an Adalm Pluto SDR, and a wideband LNA and a USB to LAN converter with power over Ethernet. A small log periodic Yagi serves as the feed. In order to work the wideband DATV band on Qo-100, André' swaps out this feed for a custom feed and brings the PlutoSDR indoors where it is connected to a 120W Spectran Amplifier and modulator.

For the full writeup of his setup, we have uploaded André's document here.

André's ground station setup for QO-100 and HF/VHF/UHF