The MarconISSta mission, which saw a LimeSDR and Raspberry Pi installed on the International Space Station (ISS), has successfully completed its first phase and has been safely deinstalled and stowed.
“MarconISSta was deinstalled on Saturday, February 9th 2019, by NASA astronaut Anne McClain,” writes project lead Martin Buscher in what is the last live mission update from phase one. “The system is stowed in a safe location and waits for MarconISSta phase II, which we currently plan for not earlier than the end of this year.
“Since no data was downloaded before deinstallation, we only have the data that has been published already. From this data, we will try to identify all successful transmissions. If you see your transmission in the plots, comment accordingly. Some people noted that they are not able to comment, but we could not figure out why. Please just try again, maybe with another browser, commenting is enabled without login.”
Those who participated in the MarconISSta transmission experiments can find waterfall plots on the mission website, and also apply to receive a limited-edition mission sticker to celebrate the attempt.
Radio amateur Dave Robinson has written of his success in transmitting amateur analogue television over a 35 kilometre signal path, using an unamplified barefoot LimeSDR Mini.
In an experiment confirmed and posted to the forum by British Amateur Television Club chair Dave Crump, Dave Robinson succeeded in sending an ATV signal 35km (21.8 miles) using an unamplified LimeSDR built into a BATC Portsdown ATV Transmitter system – part of an ongoing ‘LimeSDR Challenge’ run by members of the BATC.
“The transmit antenna was a 23 element Yagi, mounted in my roof space,” Robinson detailed in a brief interview published on Lime Micro. “The LimeSDR Mini was mounted via a low pass filter directly on the antenna to reduce feeder loss. A low pass filter is imperative to comply with the licence conditions: the second harmonic is only 20 dB down on the fundamental. The controller for the LimeSDR Mini was the BATC [Portsdown] controller with the Raspberry Pi; my Pi runs off a 5.2V 5A switcher to avoid trouble powering all the devices and the components on the USB ports. The receive antenna was a PCB log periodic.
“It wasn’t really a surprise that the 35km path worked,” Robinson concluded. “The same path had previously worked with DATV signals on 47 GHz, and I can see the target out of my apartment window.”
Telecoms engineer Bouras Abdennour has written of his successful effort to create an ultra-low-cost open-source cellular base station, combining a LimeSDR Mini with a Raspberry Pi running the Osmocom Cellular Network Infrastructure (CNI) stack.
“Running a full open source Cellular Network Infrastructure on Raspberry Pi using LimeSDR Mini, with only $169 [of hardware],” Bouras wrote on Twitter. “I am using this open source GSM system because I’m fed up deploying the big closed proprietary expensive black boxes manufactured by the multinational companies during my job career as wireless engineer.
“I wanted a real time protocol stack analysis using Wireshark and verbose logs, [to] get a solid knowledge and better understanding. This opportunity was made possible by awesome brilliant guys from the Osmocom project.”
Colin Richardson has shared a low cost homebrew housing for the LimeSDR Mini, which cleverly repurposes military-grade BNC and SNA connectors taken from decommissioned hardware.
“Simple Boxing idea for a LimeSDR Mini,” Colin writes on Twitter, alongside images of his creation. “Cost less [than] about £20, case, USB 3.0 conn[ector] and cable from RS Components UK. BNC – SMA mil spec – Ex equip, good to 4GHz.”
Those with access to 3D printing capabilities will find plenty of other options for LimeSDR family housings on sites like Thingiverse, with many including additional extras such as ventilation and fan mounts.
Simon Brown, the developer of SDR-Radio, has confirmed he is continuing to improve LimeSDR support in the software, and has now implemented the LMS7002M’s built-in digital low-pass filter (LPF).
“So, revisiting the Lime support and have implemented the digital low-pass filter (LPF) built into the chip,” Simon writes in the latest update on LimeSDR support in the SDR-Radio package. “In the screenshot below the sample rate is 40 MS/s (40 MHz bandwidth) with the digital filter set to 55% (22MHz). You now see this filter in action.”
The LPF support has not yet made it to a public build, but is expected to arrive in the next release of the SDR-Radio package.
The European Space Agency’s David Honess has published a slow-scan television (SSTV) decoder designed to run on a Raspberry Pi, designed primarily for use in education.
“Have you ever wanted to receive a radio signal from space? It’s fun and actually a lot easier than you might think,” David writes in his detailed instructions for SSTV reception. “These instructions show you how to set up a ground station and receive SSTV pictures using just a Raspberry Pi computer and an RTL-SDR USB dongle.
“Why use a Raspberry Pi? This could be done using a desktop PC or Mac however you often need to leave the receiver running overnight, waiting for the ISS to fly over your location, and it’s usually easier to tie up a Raspberry Pi with this task than your main utilitarian computer that you use all the time.”
The instructions, Python decoder, and example SSTV audio capture can be found on David’s GitHub repository.
Amateur radio enthusiast John Brier has begun publishing a series of videos detailing the creation of a satellite ground station, including the acquisition of hardware and surveying for antenna installation.
Highlighted in a post on the eHam.net forum, John’s videos differ from the usual in that they are livestreams – though recorded for posterity. “I am building a Yaesu G-5500, M2 LEO pack, Icom IC-910H based ground station,” he writes. “Nothing exotic at all but I thought it would be cool to make simple videos/livestreams as I progress through the process.
So far, John has posted three videos in the series: the first with background information, the second with the hardware purchases, and the third surveying the roof for antenna installation. More are promised to follow.
Finally, Hackaday has brought to our attention an interesting project o build a low-cost ground-penetrating radar (GPR) system for around £530 – considerably below commercial offerings.
Detailed in a presentation first given at the National Institute of Telecommunications of Poland in 2017, the design by Vincenzo Ferrara, Margarita Chizh, and Andrea Pietrelli is based around a controlling Arm Mbed development board connected, via suitable custom-built amplifiers, to receiving and transmitting antennas. Impressively, the total cost is said to be under €600 (around £530) while being possible to build with reduced bandwidth for under €400.
“The developed software and firmware programs,” the trio conclude, “allow interactive control of the GPR [functionality], the implemented GUI program is user-friendly and will facilitate students’ interaction with the radar system.”
Full details are available in the presentation documentation (PDF warning).
Focus On: Michelle Thompson and Phase 4 Ground
Photo copyright MustBeArt, used with permission
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 email@example.com.
“Phase 4 Ground is a multiple-access digital broadband microwave communications system for amateur radio,” Michelle Thompson explains, by way of introduction to the project for which she serves as team lead. “The design is fully open source and members of the volunteer team are from around the world. In our system, many users are supported through a central station, such as a satellite payload. When we talk about uplinks, those are the links from the user to the payload. The downlink is the shared link from the payload to all users.
“Phase 4 Ground came about due to a fundamental change in the direction of space communications. Amateur radio has a satellite service, where amateur radio operators are allowed to communicate through satellite resources. The amateur satellite service has a long and storied history. In general, amateur satellite communications have been in the VHF/UHF bands and the ground side is accomplished with off the shelf commercial gear. The modes used on these bands are legacy modulations, such as FM and SSB. Digital modes are very limited on amateur VHF/UHF for a variety of reasons. This satellite allocation is increasingly crowded. Our goal is to provide an advanced open source implementation of DVB-S2/X for amateur use, to share all our progress, and to find and collaborate with anyone else working on open source satellite communications.
“My involvement began in 2008 when I was invited to work with AMSAT-NA Eagle,” Michelle recalls. “That rapidly developed into working on a ground terminal project for a geosynchronous payload for AMSAT-NA. That payload did not launch, but the work was so interesting that I kept at it after the cancellation. When the geosynchronous Phase 4B Payload project kicked off in 2015, Bob McGwier N4HY asked if I would lead the ground station team. I said yes and began working hard to build a team, define requirements, and start experimenting. I have spent between 20 and 40 hours a week on Phase 4 Ground ever since.
“I also worked on ARISSat, the Fox program – I co-designed Data Under Voice telemetry downlink – Microwave Engineering Project, and had some involvement with GOLF. When AMSAT-NA lost interest in Phase 4B and Phase 4 Ground in March of 2018, I co-founded Open Research Institute, a non-profit dedicated to open source and open access work in amateur radio. Phase 4 Ground moved to ORI.
“Phase 4 Ground has accelerated development and collaboration since then, and is pursuing a variety of launch opportunities, funding, and collaborations. We currently work with a wide variety of organisations, individuals, schools, and groups in amateur radio and open source, and have participated in numerous conferences and events. All our work is published on GitHub. We have several space and terrestrial projects going on. News is distributed through our mailing list and daily engineering coordination happens on Slack and over the phone. Our team is international, positive, and enthusiastic. It’s a great honour to have such wonderful people to work with.”
Software defined radio is, of course, key to projects like Phase 4 Ground. “SDRs are powerful tools for Phase 4 Ground,” Michelle explains. “We are taking a broadcast television standard, that assumes that receivers – paid subscribers – are controlled and authorised, and we are implementing it in a fundamentally different way. In amateur radio, anyone can (and should always be able to) receive a signal. The transmitter is the licensed and controlled entity in amateur radio.
“Once you start challenging the basic assumptions of a standard or protocol, you need to have the flexibility to engineer, adapt, experiment, and test in order to get the most out of the opportunity. SDRs fill this need. With an SDR, customized DVB-S2/X test signals can be easily generated. With the flexibility of SDR, the broadcast MPEG stream can be replaced with GSE and amateur-centric communications can be designed. Algorithms for adaptive coding and modulation, authorisation and authentication, queueing up different types of data, handling multiparty conversations, and all sorts of other complexities are best researched with a capable SDR.
Amateur radio projects like Phase 4 Ground have an unusual advantage over their commercial equivalents, too: “When financial motivations are removed from a protocol generally used in commercial settings, then all sorts of interesting aspects can be explored. For example, we have a mantra and it is ‘No Crappy CODECs.’ Amateur radio voice quality does not have to be dialled down to the lowest tolerable level in order to extract the maximum amount of subscriber money,” Michelle explains. “We can ‘afford’ to have high voice quality. and we can ‘afford’ to carry out experiments that commercial communications may not be motivated to do.
“We believe one of the biggest mistakes of amateur radio digital systems has been settling for proprietary low data rate CODECs. There are substantially better alternatives to the ones used by existing amateur radio digital radios and there is a lot of interesting work still to do with respect to digital voice quality. While the choice of CODEC is not built into our standard, having an SDR makes CODEC work and experimentation much easier and more successful than it otherwise would be. For voice communications, the voice is the product. Getting digital voice done right is vital.”
While SDRs, including a number of LimeSDR Mini boards donated to the project by the European Space Agency (ESA), are key, they’re not the only hardware you’ll find in a Phase 4 Ground system. “A wide variety of hardware and software are required for a complex communications system. Forward error correction coding, synchronisation, channelisation, queueing, RF transceivers, dual band feeds, enclosures, dish pointing, user interface, accessibility innovations, and peripheral devices, like our hackable Trans-Ionospheric wearable conference badge,” Michelle lists off. “This is designed to be able to report uplink and downlink health and alert the operator when they have a message or alert. There is a universe of possibilities. SDRs enable a very large fraction of research and development across the project. A typical user station may be an SDR, a 5 GHz amplifier, a dual-band feed – we have a working design in our repository – an inexpensive microwave dish, a quality clock source, 10 GHz LNA, and a web browser for the interface.
There’s a home for the new LMS8001 Companion Board< too. “The frequency-extending Companion Board has dramatically reduced prototype complexity in our lab,” Michelle explains, “and has given everyone on the project a glimpse into the near future, where we won’t necessarily have to have a transverter to reach 10 GHz.”
For Michelle, the collaborative and open-source nature of the project is key. “This is extremely important to me for two major reasons. First, it’s how I best work,” she explains. “If I’m going to volunteer a very large amount of my time and energy on an ambitious high-risk project, given all the other demands on my time, then it needs to be how I most strongly prefer to work.
“Things worth doing are rarely easy, and that’s true of collaboration. It takes consistent, patient, optimistic, and creative effort to get far-flung, diverse, and busy people to work together on a common goal. When things progress, it’s magical and totally worth it! When it doesn’t work, then you dust things off and try again the next day. Learning along the way, recognising the contributions of everyone, meeting volunteers where they’re at, finding out what they want to achieve, and helping them achieve that are fundamental motivations for doing this work. I want to be the leader I did not have when I started volunteering in open source software, way back in 1992.
“Second, the best possible way forward for working on communications satellite technology is to take full advantage of the open source carve-outs in ITAR and EAR. The International Traffic in Arms Regulations (ITAR) and the Export Administration Regulations (EAR) are United States export control laws that affect the manufacturing, sales and distribution of technology. In order to comply with ITAR and EAR, our work is public domain, no exceptions. We are fully supportive of and happily work with Libre Space Foundation, a global leader in open source space communications, and we strongly encourage all AMSAT organizations to fully embrace open source as the way forward. The benefits of selecting open source as the framework for amateur radio space communications is substantial, enduring, and clear.”
As with any complex endeavour, ‘learning experiences’ are inevitable – and Michelle can recount a number. “Just this week I unnecessarily reconfigured a 10 GHz receive station four times because I assumed it wasn’t working. Beacons on amateur radio frequencies are used in contesting and experimenting. When you don’t hear a beacon, it’s because your station is not receiving it,” she explains. “At least, that’s almost always the case. It’s so ingrained that making fun of the novice operator complaining about the beacon being down is a recurring meme. So when the beacon suddenly vanished from my LNB-on-a-Stick waterfall display, I spent weeks tormenting a completely innocent SDR, embedded processor, and codebase. I did all of this when I could have simply turned on a known-good amateur 10 GHz transceiver in the next room and confirmed the beacon was present. Fortunately, someone else in the community (finally) noticed the beacon was truly off. It’s now back on the air.
“I have de-soldered and then re-soldered correctly constructed boards, delaying critical lab tests that affected an expensive production line. This cost money that could have been saved if I had double-checked the three ring binder that was open to the correct page and lying on the bench next to the boards in question. I have blown up expensive high voltage test equipment. Twice. In the exact same way. Physics works! Who knew? I have caused a fire in a lab by using temporary alligator clips for a permanent power supply solution. Of course, it didn’t start out being a permanent solution, but the schedule pressure was immense, it worked, so I procrastinated and didn’t replace with better wiring when I should have.
“If you’re doing something ambitious, then you are necessarily doing something risky,” Michelle continues. “Taking risks means that you will fail. Being successful, to me, doesn’t mean eliminating risks. It means being able to successfully deal with the mistakes. Dealing with mistakes means being able to recognise them, react to them, predict them, learn from them, and avoid them. Dealing with mistakes means that they don’t derail you. You learn to keep your wits about you. Open source means that if that knowledge should be shared, you advise others about dealing with mistakes. Open source should not be only about victories.
“The question of where these mistakes are documented is a good one. No one wants to have to hunt past long and potentially boring war stories to find the register definition file or a minimum voltage. In our current hardware documentation pantheon, the Adventures of BlunderGod or the Parables of Princess Pedantic don’t have a dedicated spot. But, they should! The first time I encountered anything close to a post-mortem or lessons-learned was reading Success through Failure by Henry Petroski. I was embarrassed enough by the title that I made a book cover for it out of post-its. Now, this reaction seems quaint and silly. The idea of post-mortem and lessons-learned is common enough and reading a book about it is no cause for shame.
“However, these activities happen after the product is sold, has hit the streets, has failed, and something “must be done”. This is usually demanded from above. Opening up the design process to critique earlier, not to vandalism or theft, but to honest and positive feedback, is not a post-mortem, because the product, code, or idea hasn’t died yet. Open source communities have a big role in showing how comment and critique can be better incorporated in the engineering process. This is evident from the very structure of revision control systems like GitHub, to the changes in the language surrounding coding and hardware design, to the number and type of people demanding a place at the table from all sorts of businesses and institutions. There has never been a better time to be an engineer, and many of the most vibrant engineering communities are open source.”
There are failings in the wider world of SDR that Michelle would like to see addressed, too. “The software! The state of SDR software is dire,” she laments. “In general, we need usable and non-proprietary solutions for heterogeneous computing, detailed API level documentation on every module or block we use, and better debug tools. Very often the hardware is great and the software is terrible.
“There’s two areas where SDR software implementation causes the most pain. First, is how to get started. Software on-boarding, when it exists, generally consists of blinking an LED or tuning in an FM broadcast radio station. These are simple useful Hello World projects that get you up and running. Then, right after that, there is too often a vast dark abyss. If one is lucky, then there’s great documentation and a forum or community with people that can give some advice or direction. If one isn’t so lucky, then sometimes the only lighthouse visible in the distance is, say, something like a master’s thesis using the same architecture. It looms up from the fog in the distance, but unless you can recreate the conditions of the thesis or get a copy of the source, which was not necessarily published by the author, then you have only the reassurance that it’s possible. Building a bridge from blinking an LED to experimenting with, say, SC-FDMA multi-path in a lab can be quite daunting.
“Second, the educational and experience level of SDR enthusiasts is very diverse. The people that come from the hardware or amateur radio side know what an antenna is, know it’s essentially a filter, and know it needs to be matched to the frequency, bandwidth, and application in order to give the best results. People that come from the software side into SDR may assume that the stock antenna that came with their RTL-SDR will work pretty much the same over the entire range of their radio. The repercussions of selecting a sample rate are well known for someone with communications background, but Nyquist rates may be completely counter-intuitive to someone that has only analogue circuit experience.
“Serving a diverse community with quality software and documentation is a very difficult challenge, but it would make future SDR implementations much better suited for projects like Phase 4 Ground. We draw upon a wide variety of volunteers with a very large range of experience and expertise. I believe that there has to be better design pattern for progressing through SDR competence than leaping from tuning in 98.1 FM to debugging complex synchronisation work. I think we lose too many people along the way that fall into the abyss and can’t climb out as easily as we expect them to.”
The future for the Phase 4 Ground project, though, looks bright. “There are a lot of moving parts and plenty to do. The next big milestone for receive is an open source implementation of LDPC on FPGA, but there’s also some big decisions on uplink protocol and waveform that need to be made,” Michelle explains. “The next big milestone for payload is working polyphase filter bank, but the quality of service and queueing implementation needs to be fully specified and tested too. The next big milestone for the user interface is an HTML interface prototype. A revision of the air interface, which is the documented protocol between payload and ground station, is urgent too. There isn’t one milestone in front of us. There are a multiplicity.”
Anyone looking to get involved in the project can start right away, Michelle explains: “Join the mailing list and Slack – send me your preferred email for a Slack invite to our project – start asking questions, read the DVB-S2, DVB-S2X, and GSE specifications from DVB.org, build microwave hardware and start coding, even if it’s messy! Reach out to us or your local amateur radio microwave group for help. Bravely experiment, be ready to fail, and know that we have your back when it comes to learning.
“This stuff is hard, but can be mastered one step at a time. Traditional sources of some of this type of engineering have grown accustomed to being gatekeepers. SDRs are a very effective tool to cut down the challenges and make rapid progress. Things are changing very rapidly in digital microwave scene, and SDRs really do give you superpowers. Controlling those powers is where we can give some help and support.”
More information can be found on the Phase 4 Ground GitHub documentation site.