The LimeSDR-powered Portsdown digital TV transmitter project has been featured in the latest issue of The MagPi Magazine, showcasing how low-cost software-defined radio is being used by the British Amateur Television Club (BATC).
“Now Dave [Crump, chair of the BATC] has completed Portsdown 4, using the more powerful Raspberry Pi 4 Model B [and] a Raspberry Pi 7-inch touchscreen and strong case have made a complete travel-ready unit suitable for outdoor transmission,” PJ Evans writes of the project, which aims to provide an easy route into digital TV experimentation for radio hams.
“The power and frequencies are heavily regulated by Ofcom and you’ll need a licence to operate a Portsdown 4, but such licences have been granted to those as young as ten years old. Amazingly, you can add a powerful enough antenna to relay your DTV signal to a satellite that has transponders available to amateur radio enthusiasts. It’s estimated that over 500 hobbyists have built their own Portsdown transmitter.”
The full feature is available in The MagPi Issue 118, available for free download from the magazine’s website; additional information on Portsdown is available in a community highlight piece on the Lime Micro website.
Tomasz “SP5LOT” Błażej, of the Space Balloon Club, has shared details of a stratospheric mission which saw a LimeSDR Mini beaming live video from an altitude of 31km (around 19 miles) on the 70cm band.
“The transmitter was based on a Raspberry Pi 3B+, a LimeSDR Mini, a preamplifier and amplifier made in the Far East, and an external H.265 encoder,” Tomasz explains of the balloon’s payload. “Inside the capsule were two GoPro3 cameras and a [Raspberry Pi] Cam HQ. The amplifier power was 1W fed to a QFH type antenna made by Robert SQ5RB. The software used was dvbsdr by F5OEO.
“The signal was broadcast with a variety of parameters, ranging from low resolution images to HD, so that anyone with even a simple SDR receiver could receive and decode the transmission from the stratosphere. Many colleagues, even using a simple omnidirectional antenna, received and decoded the DVB signal. The reception record was set at a distance of 370km from the balloon. We also had a receiver from outside the country, from Slovakia.”
More details on the mission are available on the Space Balloon Club’s Facebook page.
Radio software developer Charles “G4GUO” Brain has shown off a work-in-progress project to feed audio received by a LimeSDR to Nvidia’s Riva speech-to-text engine for GPU-accelerated automated transcription, while also celebrating an M17 transmission to space and back again.
“I have been experimenting using AI speech decoding and GNU Radio,” Charles explains of the transcription project. “I am using Nvidia’s Riva speech tools running on a [GeForce] RTX 3090 [graphics card] being fed with audio samples generated by GNU Radio.
“I tried using it on a RTX 2080 Super card, but it gave loads of out of memory errors, so the above example is running on a RTX 3090 with 24G[B] of memory.”
The project uses a LimeSDR to receive the radio signals, which are decoded into audio by GNU Radio and fed into the Riva speech recognition system. Based on deep learning technology, the Riva engine runs on the graphics processor to provide real-time transcription – and can also work in reverse for text-to-speech.
In another project, Charles successfully transmitted an M17 voice signal, using the M17 Project’s open-source digital radio protocol designed for both voice and data and a LimeSDR, “36,000km into space” – and received it back intelligibly.
Developer Dale Ranta has announced a new version of the SdrGlut software-defined radio player, v1.30, bringing with it an audio window with customisable equalisation settings.
“It now saves audio in WAV format,” Dale explains of the software’s latest release, “and it has a new audio window that reads and plays all of the audio types that the libsndfile library handles. It was amazing how simple it was to create a 7-channel audio equaliser using the filter design routines in SdrGlut.
“With the GLUT interface,” Dale notes, “you need to right click in a window to bring up its menus.”
The new release also fixes a few bugs, and comes pre-built in Windows and macOS variants – the former as an installable package or stand-alone build in a compressed archive, and the latter for Intel or Apple M1 based systems. Compilation instructions are also provided for Linux-based systems, including the Raspberry Pi family of single-board computers.
Pseudonymous Redditor “physical_kid” raised the question of how to reduce noise on SDR dongles when connected to a mains-powered computer via USB – and received a wealth of advice from other users.
“Try to understand if the noise is from the USB cable, antenna, or SDR,” one user replies. “Connect the SDR to the laptop and move it close to the PC. If the noise is not there, the problem is the USB, either via the power lines or the grounding.”
“Is the laptop plugged in when you do this? If not, then it’s probably that the PC is poorly grounded (old wiring in your home),” adds another. “It could also be components inside the PC like the graphic card. You could also try a different USB port, turning off the monitor and seeing if that affects it, any number of trial and error changes.”
“A snap-on [toroid] on both ends of the PC power cable might help,” says a third, “but odds are, your PC is radiating RF ‘hash.’ I can’t use my Baofeng HT within 20 feet of my workstation, for example. I suspect your SDR also suffers from a similar lack of shielding.”
The full thread is available on Reddit now.
A tunable metasurface built using common crafting supplies and costing mere pennies per unit has been proven capable of redirecting a “pencil-beam” point-to-point 6G signal to an eavesdropper, in a project from Brown and Rice University researchers.
“Awareness of a future threat is the first step to counter that threat,” claims co-author Edward Knightly, professor at Rice, of the work, which focuses on 150GHz transmissions planned for use in next-generation 6G communications systems. “The frequencies that are vulnerable to this attack aren’t in use yet, but they are coming and we need to be prepared.”
Dubbed “Metasurface-in-the-Middle,” the attack redirects a point-to-point signal to a remote attacker using a low-cost flexible metasurface – made using a printer with standard office paper, a foil transfer sheet, and a hot laminator and costing just pence per metasurface.
“People have been quoted saying millimetre-wave [mmWave] frequencies are ‘covert’ and ‘highly confidential’ and that they ‘provide security,'” Shaikhanov claims. “The thinking is, ‘If you have a super narrow beam, nobody can eavesdrop on the signal because they would have to physically get between the transmitter and the receiver.’ What we’ve shown is that [the attacker] doesn’t have to be obtrusive to mount this attack.”
The team’s work is available in the Proceedings of the Association for Computing Machinery’s WiSec 2022 conference under open-access terms.
Electronics engineer and vintage computing enthusiast Steve Chamberlin has written up some experimentation with antenna gain directionality on the 20m and 40m bands, concluding that it “matters far more than the radio” used when it comes to success.
“With the right radio, antenna, and weather conditions, these frequencies can support direct communication with someone halfway around the world,” Steve writes. “I haven’t managed to do that yet, but I’m having fun experimenting with what’s possible. I’ve discovered that the antenna matters far more than the radio: its design, size, height, and physical location.
“There’s a peculiar directionality to the contacts. On the 40m band, most of the people I can hear are within a few hundred miles of my San Francisco location. On the 20m band, I don’t hear very many local people, but I hear strong clear signals from Seattle, Vancouver, Calgary, Idaho, and western Montana. I also hear people in Arizona and Texas, but not as clearly. Occasionally I can hear people from Europe, Russia, New Zealand, and Australia. But I hear virtually nothing from Utah, Colorado, the midwest, or eastern USA.”
Steve then goes on to offer a rough map showing a windmill-like coverage pattern, and goes into explanations of radiation lobes, gains, orientation, and how the two different frequencies are treated by the same antenna.
The full write-up is available on Steve’s website, Big Mess o’ Wires.
Pseudonymous developer “veso266” has written a plug-in for SDR# which finds and decodes Subsidiary Communications Authorization (SCA) sub-carrier signals on FM – revealing “hidden” audio.
“In this example, I demodulate a radio reading service for the blind from a broadcast FM radio station,” says YouTuber Adam A. of Double A Labs in a video showcasing the new plug-in. “This broadcast is ‘hidden’ to normal FM radio receivers, originating from WITF-FM in Harrisburg, Pennsylvania.
Compatible with the latest SDR# builds, and older versions from v1785 downwards with the manual inclusion of a “magic line” to point the software at the plugin, the open-source plug-in automatically decodes SCA signals and, in its latest release, includes a sample rate display.
Binary releases plus source code under an unspecified open-source licence are available on the project’s GitHub repository.
Hackaday has brought our attention to a neat project for automatically switching antennas depending on what you’re trying to receive, using an Espressif ESP32 microcontroller module on a custom circuit board.
“Recently I built a 405MHz tuned ground plane antenna for weather balloon tracking using the rdzsonde ESP32 firmware,” writes pseudonymous project creator “g3gg0” of the inspiration behind the switcher. “Later I added a 6 m long copper tape dipole antenna for the other bands. Having some antennas in my attic now, I wanted a comfortable solution to switch between them.
“Of course I have chosen an ESP32 for the brain, switching multiple antenna inputs between two outputs. This and a WS2812 for the obligatory RGB colours. I had the idea to use one MXD8636 SP3T switch per input channel to choose between two RF outputs or a 50 Ω termination. As this switch also has an open position, it is also possible to disconnect the antenna with 25-35 dB isolation.”
A paper authored by Daniel “EA4GPZ” Estévez, Mario “DL5MLO” Lorenz, and Peter “DB2OS” Gülzow, brought to our attention by Southgate Amateur Radio News, walks through a successful effort to receive, store, and decode telemetry from the Tianwen-1 Chinese Mars mission using GNU Radio.
“This paper describes the reception of the Tianwen-1 Chinese Mars mission carried out by AMSAT-DL with the 20 metre antenna at Bochum Observatory (Germany),” the trio write. “A real-time GNU Radio decoder has been used to receive and store telemetry almost every day over the course of 10 months. Some of the telemetry variables, such as the trajectory information, have been successfully interpreted and used to track the progress of the mission.
“Over a period of 313 days, a total of around 5.9×10⁹ bytes of telemetry data have been received. At a rate of 7040 bps, this represents around 232 hours of successful telemetry reception. As of writing this paper, at the beginning of September 2021, Bochum Observatory is still decoding successfully signals from Tianwen-1 at a distance of 393 million km.
“This distance keeps increasing every day,” the authors note, “and is already quite close to the maximum distance between Earth and Mars, which is 401 million km. To our knowledge, this constitutes a record of the farthest digital communication being decoded in real-time with GNU Radio.”
The full paper is available as a PDF download from AMSAT-DL.
The US National Institute for Standards and Technology (NIST), working to assist the Telecom Infra Project (TIP) with its goal of deploying 60GHz Wi-Fi access points on streetlamp poles, has verified a model determining optimum attachment heights.
“In general, the NIST team found that the optimal height depends on transmission frequency and antenna design,” the organisation explains. “Attaching equipment at lower heights of around 4 meters is better for traditional wireless systems with omnidirectional antennas, whereas higher locations 6 or 9 meters up are better for the latest systems such as 5G using higher, millimetre-wave frequencies and narrow-beam antennas.”
“We verified the model we developed and used measurements from downtown to prove this point further,” explains Derek Caudill, electronics engineer at NIST. “This work shows that by using our model, someone like a cell provider can account for various advantages and disadvantages of 60 GHz access points and signals on light poles in urban environments.”
The team’s work has been published in the journal IEEE Antennas and Wireless Propagation Letters under closed-access terms.
The Telecom Infra Project (TIP) itself, meanwhile, has announced a partnership with Accenture to launch the TIP Academy – a platform for “upskilling the telecoms industry.”
“TIP Academy fulfills two industry needs that are currently unaddressed: impartiality in terms of content, and breadth and depth in terms of scope and relevance of learning across open and disaggregated network solutions,” claims TIP’s Vishal Mathur of the launch. “TIP Academy is that necessary solution to a global industry need and will be an important catalyst towards accelerated deployment of open and disaggregated network solutions.
“TIP has established itself as a coalescing force in the industry – bringing the world’s operators together with vendors and other connectivity stakeholders to accelerate the development of new and innovative disaggregated technologies,” says Yago Tenorio, TIP’s chair. “The momentum behind the development of these technologies is undeniable.
“The commercial reality of these technologies means that the industry now needs to upskill its workforce to fully leverage these new solutions. That’s where TIP Academy fits in. The mission and vision of the TIP Academy is to be a referral point in the ecosystem of organizations who share the common goal of closing the knowledge and skills gap related with open disaggregated solutions.”
More information on TIP Academy is available on the official website.
Martin Ossmann, writing for Elektor Magazine, has put together an ultra-affordable software-defined radio for the MSF timing transmissions – using a Raspberry Pi Pico microcontroller board.
“This SDR project shows how a receiver and decoder for these (and other) time signals can be implemented quite simply and, above all, inexpensively,” Martin writes. “For the hardware you really won’t need much more than a low-cost Raspberry Pi Pico to receive, decode, and display MSF time signal information.
“In Germany the DCF77 transmitter in Mainflingen transmits an encoded long-wave time signal. Its equivalent based in the UK is the MSF signal formerly known as ‘The Rugby Clock.’ It sends out time signals using a 60kHz long-wave carrier signal. In the early days, it served as a frequency standard, and sent out a five-minute pulse train twice a day.
“The ‘transmission protocol’ of the signal has changed several times over the decades, but it was not until 1977 that the encoding included time-of-day and date information that could be evaluated by the receiver.”
The full project, which receives the signal, decodes it, and displays the time and date data, is available on Elektor’s website.
Finally, orders have opened for the LimeSDR Mini 2.0, which offers a higher-specification Lattice ECP5 FPGA.
Designed to work around shortages of the original LimeSDR Mini’s FPGA while simultaneously shifting to a higher-specification chip featuring many more logic resources, the LimeSDR Mini 2.0 has now launched on Crowd Supply, with the first boards scheduled to ship in October of this year. To find out more and to place orders, please visit the LimeSDR Mini 2.0 Crowd Supply page.