OTA: LimeSDR Cases, HDSDR and GNU Radio Support, SDR Hacks, and More

LimeSDR Minis in Cases

Fulfilment of the LimeSDR Mini pre-orders continues, with the optional aluminium cases for the bundles having gone through assembly and testing ready for Crowd Supply to send them on.

Delivered late last week and pictured in a campaign update, the LimeSDR Mini aluminium cases are designed to provide protection for the LimeSDR Mini without obstructing any of the ports – including the reference clock input/output connectors on the underside of the printed circuit board, which remains accessible through an access port in the case.

Those who ordered the assembled LimeSDR Mini and aluminium case bundles can expect to receive their devices in the very near future: following receipt last week, the cases and LimeSDR Mini boards have been going through assembly and testing before being shipped to Crowd Supply for fulfilment.

All LimeSDR users with access to Microsoft Windows can also now benefit from support in High Definition Software Defined Radio (HDSDR), the popular freeware SDR application.

Using HDSDR’s ExtIO interface, which allows for hardware support to be quickly added using dynamic-link libraries (DLLs) rather than requiring modification of the underlying software itself, and building on work carried out by community member Jocover, support has been added for both the LimeSDR USB and LimeSDR Mini. Configuration for these boards is as simple as copying the specific ExtIO library – ExtIO_LimeSDR.dll – into HDSDR’s library folder and then using the ExtIO button to configure antenna input selection and reception gain.

At present, the HDSDR ExtIO DLL only supports receive operation; transmission is planned for a future release. For now, interested parties can read full instructions on the wiki or browse the source code on GitHub.

Support for LimeSDR boards has also been added to GNU Radio, doing away with the need to have an intermediate software layer such as SoapySDR between the two.

While GNU Radio is a popular method of operating a LimeSDR device, it has previously required the use of Osmocom or UHD blocks to act as an intermediary between GNU Radio and the LimeSDR hardware itself. Now, it’s possible to install GNU Radio blocks which allow for direct operation and configuration – though its creator, Zack, warns that the plug-in is to be considered beta status at present.

Instructions on installing and using the blocks with GNU Radio and a LimeSDR USB or LimeSDR Mini can be found on the wiki, with support provided for GNU/Linux at present and additional operating systems to follow. Both transmission and reception are supported at launch.

The Canadian Centre for Experimental Radio Astronomy (CCERA) has published a memorandum on the creation and testing of a simple FX correlator for amateur and open-source radio telescopes, using a LimeSDR and GNU Radio.

“During the beta-testing phase of the LimeSDR, in the summer of 2017, David Lonard worked on an FX correlator for LimeSDR, without benefit of GNU Radio,” the team explain of the inspiration behind the design. “From the available design discussions, it appears that the system required a PC with a GPU card for some of the bulk computations, and that it didn’t execute in real-time. Our effort distinguishes itself in running on very cheap ARM-based single-board computers, and executing in real-time.

“Both a USRP B210 and LimeSDR have been used with the FX correlator, with similar results,” the team notes, while warning that the LimeSDR exhibited a band-edge spur when operating at 6Ms/s but not 5Ms/s; operating at 5Ms/s, it is noted, caused “only a very minor loss in sensitivity.”

The experiment, the memo notes, was a complete success. “An FX correlator for small-scale or amateur interferometer experiments is clearly feasible without significant expenditure on exotic hardware,” the conclusion reads. “Very modest computational resources can be brought to bear on the problem, at least for sample-rates up to 10 to 12Msps, without any ‘store and compute’ architectural requirement.”

The memo can be read in full on the CCERA website (PDF warning).

RTL-SDR has written of two new graphical user interfaces for the Outernet moRFeus wideband signal generator, created by Ohan Smit and Lama Bleu.

Available from Crowd Supply, the low-cost moRFeus is a 30MHz to 6GHz field-configurable Fractional-N wideband frequency converter and signal generator. An on-board LCD panel and buttons offers on-the-go modification of settings, but it can also be controlled via software though a pair of new GUI applications written specifically for the device.

Lama Bleu’s moRFeus_GUI, published under the GNU General Public Licence v3, allows for full control over the moRFeus from any Linux machine. Ohan Smit’s moRFeus_Qt, by contrast, offers control from both Linux and Windows, and is available under the same licence. In both cases, the tools allow for control over the moRFeus’ various functions without the need to use the physical interface on the device itself – something previously restricted to text-based utilities.

Radio enthusiast Thomas ‘N1SPY’ Cholakov has published a short video demonstrating how a low-cost SDR device and a plain wire antenna can be used to receive slow-scan television (SSTV) video signals from the International Space Station.

During the five-minute introductory video, Thomas explains how to find and track the ISS as it orbits the Earth, receive, and decode the SSTV signals present on 145.8MHz using the MMSSTV software package. Those wishing to repeat his experiment, though, are advised by a write-up on RTL-SDR to monitor information sources for transmission times as the signal is not always present in the ISS broadcasts.

Thomas’ video is available now on YouTube.

Steve Markgraf has released osmo-fl2k, a tool which demonstrates that software defined radio hardware can sometimes be found in unusual places – such as a USB-to-VGA video adaptor.

The low-cost SDR community received a shot in its arm when it was discovered that cheap USB dongles designed for digital TV reception could be used as general-purpose receive-only software defined radios. Now, Steve has found a way to convert even-lower-cost USB-to-VGA adaptors into software defined radios – though for transmission only.

“After reverse-engineering the USB protocol of the FL2000 [Fresco Logic USB video chip] in 2016, Steve Markgraf discovered through experimentation that it is possible to operate the FL2000 in a way that both horizontal and vertical synchronisation are disabled, thus creating a continuous stream of samples,” the osmo-fl2k project page explains. “This work resulted in osmo-fl2k, which so far was used to transmit low-power FM, DAB, DVB-T, GSM, UMTS and GPS signals.

“The raw, unfiltered DAC output contains lots of harmonics at multiples of the base frequency. This is what is creatively (ab)used if you use osmo-fl2k to generate a signal much higher than what you could normally achieve with a ~165MHz DAC without up-conversion,” the page explains. “However, this means that the frequency spectrum will contain not only the one desired harmonic, but all the lower harmonics as well as the base frequency. Before transmitting any signals with an FL2000 device, it is strongly suggested that you check the resulting spectrum with a spectrum analyser, and apply proper filtering to suppress any but the desired transmit frequency.”

Full source code for osmo-fl2k is available on the project’s git repository.

The team behind the postmarketOS smartphone operating system has announced the progress of an OsmocomBB port to the Mediatek-based Fernvale development board – which, if successful, would create a fully open GSM client device for pairing with open GSM basestations built on SDR technology.

“There is already a free software implementation of a GSM baseband called OsmocomBB. But it is only compatible with phones based on the TI Calypso chipset, such as the Motorola C138,” the postmarketOS explains of the inspiration for the project. “Given that the Motorola C138 came out in 2006 and is no longer produced, OsmocomBB’s use is limited unless it gets ported to newer platforms.

“After the entire layer one firmware of OsmocomBB is ported to Fernvale, it would be possible to do 2G voice calls, send SMS and access the Internet from a laptop via tethering (just like it is possible with old Motorola phones today). @unrznbl [the developer porting the software] is also involved in creating layer one as a library for use in NuttX, bringing full userspace phone functionality to it,” the team continues. “With this, in combination with an oFono or RILD compatible interface added to the code, postmarketOS and friends, would be able to talk to the cellular modem inside the phone. All without the rather inconvenient laptop in between.”

More information is available on the postmarketOS blog.

Laird Connectivity Solution’s Carl Turner has published an interesting analysis of the clever ground-plane antenna of the Raspberry Pi Zero W microcomputer, in place of the more common chip antenna of its predecessor the Raspberry Pi 3.

“As an antenna enthusiast, I was drawn to the Zero W model of the Raspberry Pi because of its tiny and sleek antenna design used for Wi-Fi and Bluetooth,” Carl explains in his piece for Embedded Computing Design. “How did the engineers behind the Raspberry Pi Zero W tackle antenna design, given its compact size, its low cost, and its mission of being usable by even novice computer science students?

“Given its small size and interesting shape of the Pi Zero W antenna, I had my doubts on how well the antenna actually worked. Luckily, as an antenna design engineer, I have access to an antenna chamber so I can measure it in the lab. With this clever trapezoidal antenna design, the Zero W only concedes 2.25 dB of antenna efficiency while reducing the maximum antenna dimension by 8x compared to a Wi-Fi router antenna. That is remarkable. Remarkable not simply because of the small size of the Zero W’s antenna, but because the design adheres to the strict cost and simplicity objectives behind every aspect of Raspberry Pi. This is a great example of how those kinds of constraints can spark elegant engineering solutions.”

The full analysis can be found on Embedded Computing Design.

Radioworld’s Davide Moro has published a summary of the goings-on at RadioHack, an annual event run by the European Broadcasting Union during its Digital Radio Week schedule.

“The European Broadcasting Union’s RadioHack event, which takes place each year during the EBU Digital Radio Week, brings together hardware and software developers from various organizations, including non-EBU members, to share projects and ideas,” Davide explains. “The event aims to push technology a step further by modifying it. Radio is traditionally ‘live,’ but it is safe to say that during each RadioHack, radio becomes ‘lively!’ It is a place where coders, solderers and thinkers collaborate and innovate together, working on new ideas and technologies and exploring how existing ones can be linked together.”

Highlights of this year’s RadioHack include a look at the Open Digital Radio project, a presentation on Audi’s in-car hybrid radio receiver platform, the UK regulator Ofcom’s approach to small radio stations, smart speakers, and next-generation audio by Bayerischer Rundfunk.

More information is available over on Radioworld.

Matthias Schulz has announced that his NexMon software is now capable of taking control of the Broadcom Wi-Fi, Bluetooth, and FM radio module on the low-cost Raspberry Pi 3B+ microcomputer to turn it into a functional transmit-only software defined radio.

“This projects demonstrates our discovery that turns Broadcom’s 802.11ac Wi-Fi chips into software-defined radios that transmit arbitrary signals in the Wi-Fi bands. In this example, we patch the Wi-Fi firmware of BCM4339 devices installed in Nexus 5 smartphones and BCM43455c0 devices installed in Raspberry Pi B3+ computers,” the project’s documentation explains – meaning that it’s possible to transmit arbitrary signals using no additional hardware, albeit currently restricted to the 2.4GHz and 5GHz spectrum bands in which the module was designed to operate.

At present, the tool is only capable of transmitting arbitrary signals; its creators explain that raw signal reception has been proven to work in principle, but warn that “sometimes we get only noise, so we have to get a better understanding to enhance stability” before making the functionality generally available.

More information, and the NexMon software itself, is available on the project’s GitHub repository under a custom licence which allows for use, copying, modification, merging, publication, distribution, sublicensing, and sale providing the copyright notice is kept intact and that the project is cited in any and all publications.

Engineer Russ Garrett has launched the Wireless Telegraphy Register, a browsable interface to the register of business radio licences published by UK communications regulator Ofcom.

“Ofcom has recently (?) released the full dataset of UK business radio licenses, so I made a little site to browse them,” Russ explains in a Twitter post announcing the site. “Made in a few hours with @simonw’s lovely Datasette, a very efficient system for turning CSV files into Docker containers.”

Demonstrations of its use include the creation of a map showing all microwave high-frequency trading (HFT) links owned or operated by Viliant Global and all active microwave links on London’s landmark BT Tower. In an update following its initial publication Russ also added the ability to visualise transmission and reception frequencies and directions, though warns that “it gets a bit confusing when there are lots of licences at the same location, tough.”

The Register is available for use now on its official website.

Finally, Hackaday’s Christian Trapp has written of a valuable ‘learning experience’ in how not to build a differential GPS (DGPS) base station using a Raspberry Pi and a USB GPS dongle.

“A RasPi with a USB GPS dongle in a known location should be able to act as a DGPS over IP base station, right,” Christian writes in his introduction to what turned out to have been a weekend of pain. “In theory, yes. In practice… fail.

“This is a ‘Fail of the Week’ so I’m sure you already guessed that my location data from this test was completely unreliable. The positions showed the same amount of spread as the raw data that I had used earlier to locate the base station,” Christian explains. “Something clearly was not working as expected. I checked my code for errors, then tried some random modifications, hoping to infuse correctness by accident and finally took a break to do what should have been the first step of this project: testing my assumptions about the working principle of DGPS.

“To achieve this, an hour of position were measured by both the GPS dongle and the hand-held while both receivers were placed right next to each other. NMEA provides a timestamp for each fix and so it was easy to correlate the measurements of the two devices. And it turned out, even if the GPS error is locally constant, the way it affects individual receivers may be different.”

The full write-up, where Christian is requesting help to create a functional DGPS base station, is available on Hackaday.

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