The crowdfunding campaign for the LimeSDR Mini 2.0, an upgraded full-duplex software-defined radio built around a more powerful, flexible, and easily-sourced FPGA, has drawn to a close as a resounding success – and now the work of getting the hardware into peoples’ hands begins.
The LimeSDR Mini 2.0 is based on the original LimeSDR Mini design, complete with the same Lime Micro LMS7002M software-defined RF chip, but swaps out the Intel MAX10 FPGA which has been hit by the global component shortage for a more readily-available and much more powerful Lattice ECP5; in addition to being easily sourced in the quantities needed for production of the LimeSDR Mini 2.0, it offers more resources for custom gateware and an open-source toolchain.
With the crowdfunding campaign now closed, production of the boards and accessories begins. Now that component shortages should no longer be a concern, the boards are expected to ship to backers in mid-October this year.
Meanwhile, those curious as to backwards-compatibility with existing LimeSDR-based projects can rest easy: Lime Micro’s Andrew Back has published a video demonstration of the LimeSDR Mini 2.0 running with GNU Octave via the Lime Suite plugin – requiring no modification on the software side, with only the FPGA having changed between models.
While backers wait for their hardware, some are already planning to update projects to take advantage of the LimeSDR Mini 2.0’s larger FPGA – including developer Gaspar Karm, who is to port a hardware-accelerated spectrogram to the platform.
Gaspar’s original spectrogram gateware, detailed in this Lime Micro community focus piece, took advantage of the on-board FPGA on LimeSDR devices to offer hardware acceleration for real-time spectrogram display on relatively low-end hardware – offloading what would normally be a load on the host CPU to the LimeSDR’s FGPA.
Writing on the MyriadRF Discourse forum, Gaspar confirmed that a port to the larger FPGA of the LimeSDR Mini 2.0 is planned – though no release date has been tabled. There’s also the potential that the extra capacity available in the Lattice ECP5 will allow the project to include additional functionality or offload even more compute from the host, but any such feature-creep will naturally follow a port of the base project.
Those looking to keep an eye on progress can find Gaspar’s project on GitHub under an unspecified open-source licence.
SdrGlut developer Dale Ranta has written a tool to create an all-frequency power spectrum, designed to make searching for interesting signal sources quicker and easier.
“Just run sdrReceiveWindows.exe with these options and it will sweep from 5MHz to 2.99GHz using a 10kHz step size,” Dale explains in a demonstration of the tool. “What that does is that creates about 300,000 samples, and I ran it for about 50 steps – so each of the 300,000 frequencies was sampled 50 times for a half a second each. When you’re done with that the program gives you two outputs: it gives you a CSV output and it gives you a 2D scientific data set output.
“The CSV output you could try running to a heat map, but it only handles 65,000 points and not only that if you give it something that large it’s so small you can’t see it. So instead of that I started up my program MysticPlot. Each megahertz here, there’s actually a hundred points and so there’s a hundred 10kHz points within the one megahertz range.”
A video demonstration and links to download the two Windows utilities are available on the MyriadRF Discourse thread; Dale notes that the software “should work with the LimeSDR devices,” but at the time of writing had not yet been tested.
LimeSDR user Mitch Johnson has showcased a project which bumps the bandwidth of a LimeSDR Mini – and, by extension, a LimeSDR Mini 2.0 – to 96MHz, allowing for some interesting visualisations of Bluetooth and Wi-Fi spectra.
“An intriguing discovery I made this weekend: with sufficient heat sinking (and a lot of fiddling), a LimeSDR Mini can receive 96MHz of RF bandwidth,” Mitch explains. “That’s enough to fit all of 2.4GHz Wi-Fi or Bluetooth. ‘Sufficient heat sinking”‘ here is a 60x40x20mm aluminium heatsink on the bottom of the device with two stacked cheap 67x20mm silicone thermal pads, and several stick-on heatsinks on each of the FPGA, FT601, and LimeSDR shielding can.
“If I find some free time and energy in the near future, I’m going to see if I can cram a port of SparSDR into the FPGA, which could open some interesting possibilities with lower backhaul bandwidth usage and host side processing needs.”
Video demonstrations, and a photo of the “sufficiently heat sinked” LimeSDR Mini, are available on Mitch’s Twitter thread.
Andrew Back has penned an update on the LibreCellular project, as it works its way towards a finalised CI hardware design.
LibreCellular was launched in May last year as a project to provide a fully-tested and validated hardware platform and software stack for 4G Long Term Evolution (LTE) networking. Building atop the srsRAN (formerly srsLTE) and Open5GS, OsmoGSMTester, the LimeSDR family, and LimeRFE projects, the aim is to make entry into cellular networking as easy as possible.
“We have made a number of improvements to the CI hardware platform design and the largest being a change from each subsystem having its own mains PSU, to using a common DC power supply which will provide in total 12V at 50A and 5V at 12A,” Andrew explains of the progress made so far. “Benefits of this change will include better efficiency and hopefully reduced potential for noise/EMC issues.
“The second major change is that the RF distribution network which connects the SDR base stations to modem banks will now feature a digitally controlled step attenuator. This should prove useful for testing performance and further down the line, handover between base stations.”
An alternative approach for the enclosure has also been found, following the original supplier’s shuttering as a result of the pandemic: in-house machining. “We’re aiming to complete the first phase of the CI hardware platform build within the next month or so,” Andrew writes. “As we make further progress and subsystem builds are completed, we’ll be adding more detailed documentation to the website, while 3D CAD models and the corresponding bill of materials etc. will be published to GitHub.”
Developer Luigi Cruz is working on a cross-platform accelerator for GNU Radio, designed to offload processing onto a host system’s GPU to improve performance.
“Enjoying some coding time by the pool after a conference to integrate my GPU accelerated frequency sink on GNU Radio,” Luigi writes in a sunny update to his latest project. “It uses Metal on Macs and CUDA/OpenGL on Linux. I’m planning to release a complete OOT [Out Of Tree] block in the next few weeks.”
This won’t be Luigi’s first look at how radio work can be boosted through GPU acceleration: he’s scheduled to speak at next month’s SciPy Conference on a CUDA-accelerated multi-channel FM demodulator. “My talk,” Luigi says, “will share several optimization tips and tricks I used to achieve good DSP performance on the GPU.”
Interested parties should keep an eye on Luigi’s Twitter account for updates and code release.
Job Geheniau has written up the successful detection of a pulsar using a homebrew radio telescope dubbed JRT, or Job’s Radio Telescope.
“A pulsar is the rapidly spinning and pulsating remnant of an exploded star,” Job explains. “SR B0329+54 is a pulsar approximately 3,460 light-years away in the constellation of Camelopardalis. It completes one rotation every 0.71452 seconds and is approximately 5 million years old.
“Everything indicates that I may have been able to detect the pulsar B0329+54 with JRT. This dish has a diameter of 1.9 meters, which would make it the first time this pulsar has been detected with a dish of this size as far as I can tell. This result was obtained thanks to the good help and software of Michiel Klaassen.”
In addition to the dish and a software-defined radio, Job’s telescope includes two low-noise amplifiers and a dedicated interdigital bandpass filter. It also includes a computer running Windows XP, despite being long out of support. “This due to the fact that Windows 10 does too many tasks behind the scenes,” Job explains, “and that is just not the intention when I’m downloading data from a weak signal.”
Job’s full write-up is available on his website.
Engineers at the Massachusetts Institute of Technology (MIT) have developed a quantum sensor capable of detecting signals of any frequency at all – by using a “quantum mixer” to shift them in either direction.
While quantum sensors have proven their worth for the sensitivity required for ultra-precise measurement, they have a problem: they’re tuned to a particular frequency. If you decide you want to sense a different frequency, you need a different sensor – unless, that is, you use a quantum mixer.
The quantum mixer injects a second frequency alongside the frequency to be measured, creating a new signal with the difference between the two – and by adjusting the injected frequency it’s possible to down-shift or up-shift the target signal to whatever frequency is required by the quantum sensor.
To demonstrate, the team took a 150MHz signal and measured it using a qubit detector tuned to 2.2GHz. “The same principle,” first author Guoqing Wang claims, “can be also applied to any kind of sensors or quantum devices.”
The team’s paper has been published in the journal Physical Review X.
The GNU Radio project has received a grant which will be used to fund work on improving the software’s accessibility, helping to bring new blood into the software-defined radio fold.
“GNU Radio developers have identified several improvements that will make the software more accessible and easier to maintain,” the grant announcement explains. “These improvements include: easier installation of GNU Radio on Windows and MacOS computers; easier installation of out-of-tree modules (OOTs); better documentation to make GNU Radio easier to use; and usability features for GNU Radio Companion (GRC).”
Work on those laudable improvements will now be funded, courtesy of the grant from the Amateur Radio Digital Communications (ARDC) foundation. “This grant from ARDC will allow GNU Radio to hire developers with the expertise needed to push these developments forward,” the group says. “For example, hiring a usability expert will give GNU Radio Companion, the project’s graphical user interface (GUI), a much-improved user experience.
“For each improvement project, one or more mentors (who will be volunteers from the GNU Radio leadership or core developers) will guide the work. These mentors will help the contractors stay aligned to project goals and offer feedback at periodic intervals.”
More details are available on the ARDC website.
Per Vices’ Brendon McHugh has waxed lyrical on the benefits of integrated FPGA technology with software-defined radio, as in the LimeSDR family – explaining how it allows devices to adapt to “an unlimited number” of scenarios.
“The main reason for integrating FPGAs in SDRs is that latency can be controlled on the order of clock cycles,” Brendon writes. “DSP functions such as digital downconverters (DDCs) and digital upconverters (DUCs) using coordinate rotation digital computer (CORDIC) algorithms, filtering, interpolation, decimation, etc., are done on FPGA devices incredibly quickly. Furthermore, sample buffers and the framing/de-framing of data of Ethernet packets also are performed on the FPGA.
“Wideband spectrum monitoring and recording is another one of the many applications that benefit from FPGA integration. FPGAs provide computationally intensive features and are much more powerful than standard CPUs when performing processing in real-time. They’re low-latency devices due to the hardware’s parallel architecture and deterministic nature, making them ideal for low-latency links.”
Brandon’s full article is available on Electronic Design now.
Finally, Jock Elliott has written a guest blog for the SWLing Post on a practical application of amateur radio: the Commuter Assistance Network.
“About 40 years ago, a Citizens Band operator named Ed Barnat started a loose-knit group called Tri-County Assistance. Its purpose was to detect problems on the roadways and report them in real time,” Jock explains. “In time, Ed got his ham license – N2RKA – and added a 2-meter section to the Tri-County net. Somewhere along the line, I got my ham license and participated in both sides of the net. Then change of jobs forced Ed to stop running the Commuter Assistance Net as it was now known.
“A couple of hams tried to continue the net, but struggled and ran into trouble. One day, I had just checked in when the repeater owner came on the air, because of a problem, he forbid the two hams from using his repeater to run the net and added, ‘Jock, if you want to run the net, you can.'”
Now, the Commuter Assistance Network runs under Jock’s auspice – including crack-of-dawn announcements when the repeater is open and a coverage area reaching across the Capital District of New York. “The net has just two rules,” Jock explains. “The PRIME DIRECTIVE is: don’t cause anything! Rule two: when in doubt, report anyway.”
Jock’s full write-up is available on the SWLing Post now.