OTA: New LimeSuite, RISC-V LimeNET, ‘Minecraft’ Video, and More

LimeNET RISC-V Prototype

There’s a fresh new version of the Lime Suite software stack out, version 18.03.0, which brings with it full support for the LimeSDR Mini.

Released earlier this week on the Lime Suite GitHub repository, Lime Suite v18.03.0 brings with it full support for programming and controlling the LimeSDR Mini as well as the existing models in the LimeSDR family. Other changes and tweaks include additional controls for the SPI panel in the LimeSuite GUI, fixes for a range of bugs, and updated gateware – which runs on the field-programmable gate array (FPGA) – for both the LimeSDR Mini and LimeSDR USB.

Lime Suite v18.03.0 is available in packaged form in the official Personal Package Archive (PPA) repository now for Ubuntu Linux and other PPA-compatible distributions, and in source code form from GitHub. Builds for Windows and macOS will follow in due course.

The first experiments on building a truly open LimeNET basestation, combining the LimeSDR with a SiFive Freedom U500 RISC-V processor platform, started earlier this month with promising results.

Based on the LimeNET platform, which traditionally combines a LimeSDR board with an Intel-based PC running the Ubuntu Linux distribution, the proof-of-concept prototype replaces the Intel portion of the LimeNET design with SiFive’s Freedom U500. Based on the open RISC-V architecture, the Freedom U500 is capable of driving the LimeSDR – and, given its openness, can potentially be used to design all-in-one basestation hardware using a customised application-specific integrated circuit (ASIC) at an extremely low cost.

“The combination creates a platform where wireless systems are implemented via software-defined radio, with the ability for custom hardware accelerators to be integrated in FPGA, before progressing to a customised ASIC once their design has been validated,” explains Andrew Back of the team’s work. “This fundamental flexibility across both baseband processing and RF will make it possible to bring high-performance radio access network solutions – e.g. for LTE, NB-IoT, and 5G – to market far quicker than ever before and at greatly reduced cost.”

More information, and a video of the current prototype, is available over on Crowd Supply.

Over in the forums, LimeSDR Mini user Adrian has been working on the transmission of low-resolution “Minecraft style” video in as low a bandwidth as possible.

“Last year I set myself a goal to transmit low resolution digital video with the LimeSDR Mini,” Adrian explains. High resolution video using DVB-T / DVB-T2 has been done, as Evariste showed us a while ago. Myself I went for the other end of the spectrum. How much RF bandwidth is it really necessary to broadcast a digital video signal that can still be usable (larger than a post stamp)?

“So my software uses a 250 kbit/s DQPSK modem which fits the radio signal in 150 KHz, about the same bandwidth as commercial FM. The video size is not great, 320 x 240 upscaled to 640 x 480 which is why it resembles Minecraft. Seems to be enough to at least show a face. As a bonus fits well in the 433 MHz ISM band should you lack an amateur radio licence.”

A demonstration of the transmission is available on YouTube.

For further inspiration, Electronics 360 has published a piece on interesting things to do with a software defined radio, penned by Daniel Franklin.

Starting at, arguably, the most basic use – monitoring unencrypted radio traffic from the emergency services – Daniel’s piece runs through a range of possible uses for an SDR including receiving and decoding pager signals, satellite signals, tracking aircraft and ships, ham radio, TV reception, radio astronomy, and smart meter monitoring.

While aimed firmly at the beginner, anyone looking for inspiration for their next project may well find something to tickle their fancy.


The Jupiter Research Foundation (JRF) Amateur Radio Club has been issuing updates on its HF Voyager project, a seafaring research vessel carrying an autonomous 20 meter band station operating in PSK-31 and FT8 modes.

Launched earlier this year as a piggybacked payload on a mission to locate a ‘missing’ population of humpback whales in the low northern latitudes, the JRFARC station has had a few periods of downtime caused by inclement weather resulting in a power shortage from the solar panels, but its statistics are impressive: as of the 27th of March the station had received 1,116 total contacts from 752 unique callsigns across 17 countries.

Those who have successfully contacted the HF Voyager will, the JRFARC has confirmed, receive a certificate of recognition.

The US Federal Communications Commission (FCC) has voted to exempt small-cell radio deployments from federal environmental and historical preservation reviews, a move which will make it considerably easier for small-scale SDR deployments to take place.

“5G networks will look very different from the networks of today. Those tall, 100-foot towers that we associate with current generations of wireless service will be supplemented by new small cell facilities, many of which will be no larger than a backpack,” says Commissioner Brendan Carr in support of the new regulation. “Going forward, upwards of 80% of new deployments are expected to be small cells.

“We will exempt small cells from NEPA [environmental] and NHPA [historical] review, given their much different size and footprint than large towers. This will extend the same regulatory treatment to those deployments that the Commission has always applied to other types of infrastructure, including Wi-Fi routers and consumer signal boosters.”

More information on the change in regulation is available from the FCC website (PDF warning).

EE Times has published an first-hand account from the DARPA SDR hackfest held late last year, written by DARPA’s Tom Rondeau.

“Out of the many decades of work on free and open source software (FOSS) projects have come debugged and optimised software that now is helping us address technical challenges more quickly and effectively that we could before these tools became available,’ Tom writes. “Although this remains true, we learned from our hackfest experience in California that there still are many hard problems to solve.

“FOSS and SDR have helped us come a long way in solving problems in the cyber-physical world but, as we learned from the hackfest, there is still much more to do. Based on my experience, hackfest-like contexts, and the way they concentrate innovative energy, could be effective means for getting us there.”

Open Electronics has published the design for an open-source frequency meter and clock generator, based on a Xilinx field-programmable gate array.

Based on a design for an earlier LED matrix controller, the project is primarily designed to showcase the flexibility of FPGA platforms while also providing a functional and useful tool. “It is a bivalent tool, since it both acts as frequency meter and clock generator, very useful in this era where logics and digital devices are extremely commonplace,” explains Boris Landoni of the design. “You can surely find ready-to-use tools on the market, however it makes sense to create our own.”

Once flashed onto a suitable FPGA, the design can operate from between 100kHz to around 400MHz while also generating a four-frequency clock signal.

RTL-SDR has alerted us to a new SDR# plugin from coder Eddie MacDonald, which adds a handy toolbar to the software.

Following on from his three previous plugins – a tuning dial, night mode, and Fast Fourier Transform (FFT) capture – detailed in an earlier OTA, Eddie’s latest plugin provides quick access to a range of SDR# functions from a single central toolbar – meaning that users no longer need to keep opening and closing the plugin panels.

All Eddie’s plugins are available for free download from SDRPlugins.com.

Elsewhere on RTL-SDR is a write-up of a video demonstrating how to protect an SDR using a transmit/receive switch, originally published by HamRadioConcepts.

Designed primarily with receive-only devices in mind, the video shows how to use a transmit/receive switch to connect an SDR to a transmission-capable amateur radio in such a way as to not risk damaging the SDR – a real problem with using standard splitters. HamRadioConcepts’ solution is an automatic relay switch, which does away with the problem of forgetting to flip a manual control while using the radio to transmit.

Finally, SWLing’s Tom Lebryk has published an update on the status of his Backpack Shack 2.0 portable loop antenna following the completion of some in-the-field testing.

Highlighted in an OTA back in February, the Backpack Shack 2.0 is Tom’s second attempt at making a highly-portable loop antenna for general listening use, and his testing shows that it does indeed work as promised. “It is not the most powerful antenna,” Tom writes, “but in the right location it can be useful, especially with using an SDR. It was used during February in two Forest Preserve (County Park) locations outdoors and once from my usual Grocery Store parking lot!”

Tom has said that he will be working on two new designs, a larger build for car transportation and a small VHF loop antenna, with mroe updates expected in the coming months.

Focus On: Chuck Swiger

Chuck Swiger

OTA’s Focus On is a series of interviews with notable members of the Myriad-RF and wider software defined radio community. If you’d like to nominate someone to be interviewed, or would like to be interviewed yourself in a future OTA, send your proposal to ota@myriadrf.org.

System administrator Chuck Swiger’s entry into electronic radio projects came a number of years before software defined radio was anywhere close to mainstream. “My first DSP [digital signal processor] project was long ago,” he explains. “Byte Magazine had an article on creating music with an 8080 2MHz box, using a resistor ladder digital-to-analogue converter on an Altair, and I went crazy over that.

“That was in my early college days. Got it to play Bach Invention #8, created waveform tables with FORTRAN using punch cards, way back. Then many years with computers on one hand and ham radio, and college electromagnetics, and DSP courses on the other, until the GNU Radio ATSC project broke on Slashdot in 2003.

“I went gaga over what Eric Blossom was doing with SpectrumWare and how you can use a scripting language – Python – to wire up high-performance, boosted C++ modules like filters, multipliers, FFT displays and so on in flowgraphs. After a life change and stuff I had to get a USRP from Matt Ettus – got a board s/n 00000000 that has a couple of wires patched on it – with basic TXRX and a TVRX.

“Then I did a bunch of stuff with those for years, mainly in HF with the basic boards that work up 30MHz, and enjoyed going on field trips to record 2MHz-wide bands of AM or shortwave then playing them back later, and also using splitters and directional couplers to measure amplitude and phase response of devices and antenna. Basically, re-doing college courses on RF in SDR. That actually worked well, and I was amazed it could correctly report, say, the value of a capacitor at the end of a coax so many feet long, plot smith charts, etc. That was not too hard in HF where you can work with lumped values and ignore the strays.”

Soon, though, Chuck’s needs outgrew his equipment. “I was intrigued by the OpenBTS project and wanted to do that, but the ol’ USRP1 would need some expensive daughter boards plus a clock upgrade,” he recalls. “So when the LimeSDR came out and was able to get an early bird price I jumped on that. I remember well, we were on vacation at the beach the Monday the crowdfunding was ending and they still hadn’t quite reached the goal, so I sat outside an ice cream shop sending out tweets to get people interested and they blasted through!”

Asked what attracted him to software defined radio technologies in general, Chuck answers: “Probably what attracts a lot of people – the flexibility and possibilities it opens up to hobbyists. It’s astounding all the niches people have filled with the affordable RTL-SDR, for example. I can quickly build software packages to track aircraft going overhead or read my neighbours’ electric meters. It’s just amazing what people are doing, like contacting lost satellites, amazing.

“My current work-in-progress is the OpenAirInterface LTE project,” Chuck reveals. “I’m trying to comprehend that currently and get it working with a Galaxy S4 Mini (GT-i9195), and I just got some of the sysmocom SIMs and a card read/writer, so I’m playing with those. I don’t really achieve anything just copy other peoples work,” he jokes. “Maybe the biggest was working on the gr-atsc project to get it all in GNU Radio 2.0 python blocks, that was challenging. Eric mostly set it up and made it easy to finish off. Lots of talented people contribute to GNU Radio. I was working the night shift and remember finding the last bug around 4AM, when actual MPEG media popped out of my RF data!”

The majority of this work takes place on off-the-shelf consumer-grade hardware. “I mostly use a Toshiba laptop with an Intel Core i7-3610QM CPU at 2.30GHz with an SSD,” he explains of his workstation arrangement, “and recently added a Dell Core i7-3770 at 3.40GHz box – inexpensive eBay stuff. I just recently got a Trimble GPSDO clock working, so the LimeSDR sits on that by the window. Software is all Ubuntu Linux, mostly 16.04, and I build all components from source so I can explore – put print debug statements in, recompile and learn how it works. The Dell mostly runs OsmoBTS using the NITB and the GPRS parts. That works great with the LimeSDR, so I can play games on cheap 2G watches.”

“Get started inexpensively,” Chuck offers by way of advice to those looking to break into SDR themselves. “Two things: get a basic book on DSP, and learn as much as you can – at least know Nyquist! The Lyons book [Understanding Digital Signal Processing by Richard G. Lyons, ISBN 8601400037980] is good. Electromagnetics theory can help too, I think. Then pick up an RTL-SDR and explore the plethora of projects available there. Build antennas and decode signals from space – that’s still on my bucket list!”

Asked, as is Focus On tradition, for a ‘learning experience’ from his past, Chuck racks his brain. “I’m actually really careful, especially with dangerously powerful things – physically and legally,” he explains. “All I can think of is poofing a $60 2W blue laser diode a few year ago when trying to rewire the power: a wire briefly slipped and it was gone, man.”

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