Backers of the LimeNET Micro are set to receive a boost in computing power and storage thanks to a last-minute switch in Raspberry Pi Compute Module model, while shipping has now been pushed to the end of March.
“As you all know, there were quite a few changes to the original specification and we decided to go for USB transceiver interfacing, fully active PoE, and add camera and display LVDS interfaces, as well as a HDMI connector,” explains Lime Micro’s Zydrunas Tamosevicius in a campaign update for the project. “We also added Wi-Fi module provision, although this will not be mounted on boards as supplied.
“As you will know there is a new Raspberry Pi Compute Module around,” Zydrunas continues, “and we decided to deliver our LimeNET Micro boards with the upgraded CM3+ 8 GB, instead of the CM3 4 GB as originally planned.”
The shift means that the LimeNET Micro now has a 1.4GHz processor with improved thermal handling compared to the original design’s 1.2GHz processor and double the on-board storage at 8GB. Between this and the other changes, though, the manufacturing run slipped into Chinese New Year, leading to a short delay that will see rewards shipped at the end of March.
More information is available on the LimeNET Micro campaign page.
Radio amateur George Smart has written a piece on his experiments with transmitting to the Es’hail-2 satellite using a LimeSDR USB and SDR-Radio’s SDRConsole software.
“Let me first start by saying that I’ll be using a LimeSDR USB which has a continuous frequency range of 100 kHz to 3.8 GHz. Clearly acceptable for our requirements of 2.4 GHz,” George begins. “The bandwidth the SDR can support is staggering 61.44 MHz. Clearly the LimeSDR is nothing without some fancy software to drive it; and there are plenty of good offerings. I decided to opt for SDRConsole V3 by Simon Brown G4ELI.
“I was pretty keen to see if I could make it to the Es’hail-2 satellite. Balancing the amplifier and patch antenna on the back of a large reclining chair in the garden, I was able to align the patch antenna to the satellite’s location. Setting the TX frequency of the LimeSDR to the centre of the transponder band (2400.175 MHz), with an output power of around 1W of I was able to hear a single tone through the Es’hail-2 narrowband transponder, I quickly added a CW paddle and was able to confirm my signal by sending ‘M1GEO TEST’ several times, listening via the BATC NB WebSDR.”
George’s full write-up is available on his website.
AMSAT-DL has agreed to adopt a proposal from the British Amateur Television Club (BATC) to provide bandwidth on Es’hail-2’s wideband transponder for amateur TV coordination on an experimental basis.
“AMSAT-DL has agreed to a proposal by BATC for the use of the bottom 100KHz of the wideband transponder (10491 – 10491.1 MHz) for ATV co-ordination purposes,” explains BATC’s Noel Matthews in the announcement. “This is on an experimental only basis and stations must keep their power levels to a minimum and certainly not exceed power levels greater than 15dB above the noise floor as shown on the Goonhilly spectrum monitor.
“This is sanctioned on an experimental only basis and AMSAT-DL reserve the right to move the WB beacon towards the band edge or implement DVB-S with a wider rolloff which would render the frequencies unsuitable for this purpose. So another challenge but should be manageable and prove a useful facility although we do see the chat being the major tool for reports and contacts.”
The full announcement and resultant discussion can be found on the BATC forum.
Marty Wittrock has shared a “proof of concept” experiment in the Myriad-RF forum which pairs a LimeSDR with a wideband power amplifier and the SDRAngel software for transmission and reception on the 40m band.
“I used SDRAngel and setup a SSB modulator for USB transmit and setup all the audio path in advance using WSJT-X and it’s ‘Tune’ mode, writes Marty. “Once I felt I had things working, I took to the air for the first time with the LimeSDR. During the first WSPR transmit session, I noted that the heatsink for the PA was pretty insufficient: it got hot fast so it’ll need to be a bigger heatsink later on.
“After the first WSPR transmit session was complete, I held my breath as I watched the reports come in. First KD6RF (1075 km) and then VA3ROM (766 km) and with the setup running 2W total power output, but later adjusted to 3W of power. I allowed the Lime to transmit a couple more sessions before I declared ‘Proof of Concept’ victory and shut off the PA and allowed it to cool down. A little later on, I switched the antenna to the RxWB1 port and allowed the LimeSDR to receive and report status on the WSPR database on 40m for over 7 hours.
“At this point I’m convinced the LimeSDR, along with SDRAngel, is a viable foundation for a voice or digital modes Software Defined Station. This one just needs to be designed and built for final and then the fun can begin!”
Marty’s full write-up, and images of the setup, can be found on the Myriad-RF forum.
Elsewhere on the forum, member ‘g0dfuzz3r’ has shared a build described as “the world’s smallest BTS [base transceiver station] with LimeSDR Mini and Orange Pi Zero.”
“After testing, I can say that LimeSDR Mini works very well with Orange Pi Zero and Osmocom GSM stack,” ‘g0dfuzz3r’ writes. “With 5000 mAh powerbank and cooling fan it takes the place of 13x7x5 cm in the cardboard box from the smartphone and 13x7x4 cm without. Its just a prototype, and I think it may be smaller.”
A more detailed thread on combining a LimeSDR Mini, Orange Pi, and Osmocom software is available on Codeby.net (Russian-language, English translation), while scripts for use with the setup can be found on GitHub.
The SWLing Post has drawn our attention to a post on MacRadio DIY SDR System detailing a cheap metal mesh casing to silence noisy power supplies.
“One problem in my system is that I need to power it using cheap switched-mode power adapters. They are – well, cheap, universal, small, easy to get – and a huge source of wideband HF interference,” the post explains. “I decided to test if a cheap metal mesh would be enough. I got 60cm x 200cm roll with 0.9mm mesh size with 15 euros.
“Test results – were AWESOME! Yes yes, I know that this is the basic Faraday’s cage -sort of, but still I was very surprised about how well it was able to ‘clean the band.’ I think I found a solution to get rid of most of the HF interference caused by these yet wonderful but also very noisy power supplies.”
The full write-up is available on MacRadio DIY SDR System.
RTL-SDR has highlighted a demonstration of two SatNOGS satellite rotators, built by Massimiliano Caturegli.
“I have build two versions: a stepper motor classics and a 5:18 stepper motor version for give more force on rotator,” Massimiliano writes of his project. “They can remotely controlled by any kind of device (PC, tablet, smartphone or Raspberry Pi.)” Each is powered by a 12V solar-charged battery and is strong enough to support a large parabolic grid antenna without counterweight.
The video demonstration is available now on the max30max31 YouTube channel
Our Ham Station, meanwhile, has published a detailed guide to interfacing a Raspberry Pi with a Green Heron rotator controller for easy satellite tracking via MacDoppler.
“I have received several requests to share the image and construction details for the Raspberry Pi Satellite Tracker Interface that we use with MacDoppler as part of the Satellite Stations,” writes Fred Kemmerer in the detailed build guide. The project uses a Raspberry Pi 3 Model B+, PiTFT Plus display, and Green Heron rotator controllers to allow for easy software control and live tracking of satellites via the MacDoppler satellite tracking software for macOS.
“We wanted a compact package that did not require anything but a power supply to run the final project,” Fred explains of the hardware choices. “The setup worked on the first try using a WiFi network connection between the MacBook Air Laptop running MacDoppler and the RPi. The USB-based serial ports which control Azimuth and Elevation direction of the rotators worked as soon as they were plugged into the RPi. Also, the touchscreen interface works well with the GH Tracker App making the combination easy to use.”
The full guide has been published on Our Ham Station.
Ericsson has demonstrated a flexible antenna strip, suitable for embedding behind wallpaper or under carpet, which it claims is ideal for 5G New Radio base-station projects.
“The strip contains printed circuit boards and tiny antennas able to pick up and send 5G data,” explains CNET’s Roger Cheng of the company’s Mobile World Congress (MWC) demonstration. “Along the walls at one of Ericsson’s demos, the strip was embedded behind a thin piece of wallpaper or hidden by a thin plastic housing. Another strip was laid under a long train of carpet that was rolled up.
“‘This is how easy your network roll-out will be,’ Pal Frenger, a researcher at Ericsson, said as he placed the roll on the floor and kicked it open. He liked the joke so much, I heard him say it again a few minutes later.”
While Ericsson is positioning the technology as a potential solution to small cell deployment where traditional antennas would be an eyesore, the version on show at MWC is merely a mock-up representing an ongoing research project – which, the company admits, “doesn’t work yet, and those little antennas on the strip are fake.”
More details are available from CNET’s article.
Researchers at Delft University of Technology have created a ‘quantum chip’ which, they claim, allows the user to listen to the weakest radio signals allowed by quantum mechanics.
“Say I am pushing a kid on a swing,” lead researcher Mario Gely explains by way of introduction to the underlying concept. “In the classical theory of physics, if I want the kid to go a little bit faster I can give them a small push, giving them more speed and more energy. Quantum mechanics says something different: I can only increase the kid’s energy one ‘quantum step’ at a time. Pushing by half of that amount is not possible.”
The team’s work has resulted in the creation of a chip, measuring one square centimetre, which they claim can detect ‘quantum steps’ in radio frequency signals – providing the ability to sense radio waves at the quantum level, the very weakest possible signal changes.
While the work has potential in everything from magneto-resonance imaging (MRI) scanning and radio astronomy, the team is looking to another usage: gravity experimentations. “Using our quantum radio, we want to try to listen to and control the quantum vibrations of heavy objects, and explore experimentally what happens when you mix quantum mechanics and gravity,” Mario explains. “Such experiments are hard, but if successful we would be able to test if we can make a quantum superposition of space-time itself, a new concept that would test our understanding of both quantum mechanics and general relativity.”
The team’s work has been published in the journal Science as “Observation and Stabilisation of Photonic Fock States in a Hot Radio-Frequency Resonator.”
Virginia Polytechnic Institute and State University researchers, in partnership with Nvidia, have announced a proportional-fair (PF) scheduler for 5G New Radio networks which uses graphics processors to accelerate performance and achieve sub-100 μs scheduling.
“How can we design a scheduler for NR that provides optimal scheduling solution while working with the ~100μs time resolution,” the researchers asked themselves at the start of the project. “We tailored GPF for implementing on GPUs [Graphics Processing Units]. The basic idea: find scheduling solutions through solving a certain number of small and independent sub-problems on the GPU in parallel.
“The solution to each sub-problem is a feasible solution to the original PF scheduling problem. The output solution of GPF is then the best one among all sub-problem solutions. We use a one-dimensional grid of 30 thread blocks to generate and solve 300 sub-problems, with each block addressing 10 sub-problems. When the best sub-problem solution from each block is found, we use another thread block to find the best output scheduling solution.”
Detailed on the Nvidia Developer Blog, the scheduler is held as evidence that pushing general purpose compute to the edge of the network is going to be key in the roll-out of 5G NR and other future cellular radio technologies.
Finally, Hackaday has highlighted a modern radio build with a difference: it’s built around a vacuum tube.
“When you think of a software defined radio (SDR) setup, maybe you imagine an IC or two, maybe feeding a computer. You probably don’t think of a vacuum tube,” Hackaday’s Al Williams writes, though the build in question is more properly termed a superregenerative converter and lacks software control. “Mirko Pavleski built a one-tube shortwave SDR using some instructions from Burkhard Kainka.
“The tube acts as both an oscillator and mixer, so the receiver is a type of direct conversion receiver. The tube’s filament draws about 200 mA, so battery operation is feasible. According to Burkhard his build drifts less than 1 Hz per minute, which isn’t bad. As you can see in the video, it works well enough.”