OTA: TIP Summit, Aircraft Reflections, 3D Printed Communications, and More

University of Washington's 3D printed transmitters

The team from Lime Microsystems will be at the Telecom Infra Project (TIP) Summit in London next week, with a range of LimeNET and CrowdCell demonstrations.

Part of the cross-vendor Telecom Infra Project (TIP), founded to encourage openness and disaggregation in access, backhaul, and core & management of a modern telecommunications infrastructure, the TIP Summit will play host to everything from open-source cellular communications systems to millimetre-wave backhaul and edge computing – and Lime, with the LimeSDR-powered LimeNET and CrowdCell base station hardware.

Anyone interested in seeing the LimeNET and CrowdCell in action, or just looking to say hello to the Lime Micro crowd, can find ticket options on the Summit’s official website.

The LimeSDR Mini-powered MarconISSta project continues to run on board the International Space Station, though not without a few hiccups – this time rooted in an apparent under-voltage scenario.

The MarconISSta project, detailed in earlier OTAs, has been receiving quality data from its LimeSDR Mini – including its first confirmed reception of deliberately-targeted amateur radio traffic. “A successful transmission was received from UNSAM students and radio amateurs in Buenos Aires,” the team explains in its status update. “Although the peak is not that big, we were still able to identify the source and wait for future transmissions!”

The project continues to have issues with recovering from power outages, however. “After September 20th we did not receive any recordings,” the team confirms. “Ground control found out about this after they were not able to contact the Astro Pi during the nominal commanding window on September 27th. A hard reboot by Alex Gerst could solve this issue, however afterwards the LimeSDR was not recognised anymore. After a lot of testing with the lab model we think this happened due to an unde-rvoltage condition. Today Alex Gerst plugged the LimeSDR off and on again and we hope that the system is now working nominal again.”

The project’s status can be monitored on the official website, while Lime Micro has a detailed case-study on the project for more background information.

GNSS engineer and radio amateur Daniel Estévez has shared a work-in-progress project to build a transmitter for work on the Es’hail-2 geostationary communications satellite, tying a LimeSDR into a BeagleBone Black and a 125W S-band amplifier.

Created by the Qatar-based Es’hailSat, Es’hail-2 is designed to be the first geostationary communications satellite for amateur radio use covering hams from Brazil to Thailand from a 25.5 degrees East position. The satellite includes two Phase 4 amateur radio transponders, operating in the 2400 MHz and 10450 MHz bands, along with a 250 kHz linear transponder and 8 MHz transponder for experimental digital modulation schemes and amateur DVB broadcasts.

“Transmitter for Es’Hail 2 work in progress. LimeSDR, BeagleBone black and 125W S-band amplifier,” Daniel writes of his project on Twitter. “Probably the amp will go directly to the antenna. A power meter would be interesting, but since this will be operated remotely, it adds some complexity. More than enough [headroom] for narrowband, but I also want to use this for somewhat high-speed digital tests and DATV.”

More information can be expected to appear on Daniel’s blog as the project progresses, while details on Es’Hail-2 can be found on AMSAT-UK.

Daniel is also behind a project to detect aircraft reflections from a 2.3 GHz radio beacon using a LimeSDR, brought to our attention by RTL-SDR.

“A couple months ago, Andrés Calleja EB4FJV installed a 2.3GHz beacon in his home in Colmenar Viejo, Madrid. The beacon has 2W of power, radiates with an omnidirectional antenna in the vertical polarisation, and transmits a tone and CW identification at the frequency 2320.865 MHz,” Daniel explains. “On July 8 I did a recording of the beacon from 10:04 to 11:03 UTC from the countryside just outside Tres Cantos. In this post I will examine the aircraft reflections seen in the recording and match them with ADS-B aircraft position and velocity data obtained from adsbexchange.com. This will show the locations and trajectories which produce reflections strong enough to be detected.”

Daniel’s post details a receiver based on a LimeSDR connected to a 2.4 GHz small-form-factor antenna originally designed for Wi-Fi use. The signal was recorded via GQRX, then Doppler traces for each aircraft – calculated from ADS-B data – overlaid onto the waterfall. “We see that how likely is an aircraft to produce a reflection obviously depends a lot on the route that the aircraft has taken,” Daniel explains of his results. “This leads us to study the aircraft routes more in detail.”

That detail, and more, can be found in Daniel’s blog post.

Researchers at the University of Washington have demonstrated 3D-printable devices capable of tracking and storing details of their own use, despite having no built-in electronics, through backscatter radio.

“We’re interested in making accessible assistive technology with 3D printing, but we have no easy way to know how people are using it,” explains co-author Professor Jennifer Mankoff. “Could we come up with a circuitless solution that could be printed on consumer-grade, off-the-shelf printers and allow the device itself to collect information? That’s what we showed was possible in this paper.”

Building on the team’s previous work of 3D-printable objects capable of communicating via Wi-Fi without electronics, including a detergent bottle which can transmit how much liquid is poured out at each use, the new techniques are capable of monitoring bidirectional motion. “This time we have two antennas, one on top and one on bottom, that can be contacted by a switch attached to a gear,” explains lead author Vikram Iyer. “So opening a pill bottle cap moves the gear in one direction, which pushes the switch to contact one of the two antennas. And then closing the pill bottle cap turns the gear in the opposite direction, and the switch hits the other antenna.”

Using specifically-sequenced gears, an encoded message – described as being like Morse code – can be transmitted. The team’s work bwent further still with a 3D-printed insulin pen capable of storing data when outside of the range of an active receiver, encoding its data in a spring which unwinds – triggering the transmission – when back in range again.

More information is available on the University of Washington website.

Antenna Test Lab, brought to our attention by Hackaday, has also used 3D printers in a project to create metallised horn antennas – and has tested their performance in a professional anechoic chamber.

“What RF engineer has not thought about 3D printing an antenna? It’s a natural combination of RF curiosity and and basic 3D printing capabilities,” the antenna testing specialist explains. “You have probably even seen social media photos and posts about this achievement. But do these antennas work? Has anyone properly tested them? Is it even practical with simple materials and processes? We decided to give it a try ourselves, and also to add some value to the conversation.”

The Antenna Test Lab’s project saw a family of 15 dBi horns printed, smoothed, then metallised with shielding spray paint – costing around a dollar a piece in materials, the company claims, compared to $500 upwards for their commercial, metal counterparts. The result: the discovery that a smoothing step is absolutely necessary for decent performance, and the higher the frequencies in which you’re working the smoother the surface needs to be.

“Yes, you can 3D print your own working microwave antennas using common materials and your ‘handyman’ skills,” the company concludes. “Just smooth the active surfaces with solvent, sanding, or filing then use our recommended conductive paint. If you can check the shorted aperture return loss/VSWR and verify that it has at least some frequencies of low return loss (less than 1 dB), you can reasonably expect the same antenna performance as a solid metal antenna.”

The full report can be found on the company website.

Software engineer Chris Lam has written up a project to create a speech recognition system for amateur radio communication, capable of recognising callsigns and creating a timestamped log of everything each ham has said on a monitored frequency.

“I speak to a Baofeng handheld radio transceiver, the DIY [copper wire] antenna picks up the radio wave, SDR demodulates the radio signal to standard audio signal, Google speech-to-text performs the speech recognition, Smith-Waterman algorithm performs sequence alignment to find the most probable call sign in a database and AJAX is used in a local http server to output the text,” Chris explains of the project. “It successfully finds the most probable call sign from a database and captures the message ‘monitoring.'”

Chris explains that SDRSharp was used for signal processing and conversion, a simple Python script linked to Googe’s speech-to-text application programmming interface for the actual speech recognition, then the clever Smith-Waterman algorithm – again, programmed in Python – attempts to recognise key words associated with aircraft and radio amateur traffic. The result: a webpage that provides both a transcript of what was said and a log of which callsign said it and when it was received – all performed automatically.

Full details of Chris’ project can be found on Towards Data Science.

ARRL, the US national association for amateur radio, has taken exception at the Federal Communications Commission over an enforcement advisory which suggests that uncertified radios imported into the US as amateur radio equipment cannot be sold if capable of operation on non-amateur frequencies – even if never used on such.

The ARRL’s statement comes following the publication of an Enforcement Notice (PDF warning) by the FCC in late September, detailing the importation and sale to the general public of radios capable of operation on both amateur and non-amateur frequencies. “In several places, the Enforcement Advisory makes the point that ‘anyone importing, advertising or selling such noncompliant devices should stop immediately, and anyone owning such devices should not use them,'” the ARRL explains of its complaint.

“The Advisory broadly prohibits the ‘use’ of such radios, but our view is that there is no such prohibition relative to licensed Amateur Radio use — entirely within amateur allocations — of a radio that may be capable of operation in non-amateur spectrum, as long as it is not actually used to transmit in non-amateur spectrum.”

The ARRL and FCC are said to be in discussions regarding the matter, though no decision has yet been announced as to whether the Enforcement Notice should stand. “We will keep our members informed as our discussions with FCC on this subject continue,” the ARRL has stated.

Radio amateur Scotty Cowling’s talk on the pros and cons of nine single-board computers (SBCs) when it comes to their suitability for use with software defined radios has been uploaded to Jason Johnston’s Ham Radio 2.0 YouTube channel.

In the presentation, filmed at the TAPR Digital Communications Conference 2018, Scotty walks through the best practices for using SBCs with SDRs, the reasons for choosing SBCs over larger traditional personal computers and workstations, and discusses the pros and cons of nine boards in particular: the Raspberry Pi 3 Model B, the Hardkernel Odroid C1 and XU4, the Asus Tinker Board S, the 96 Boards Mediatek X20 and HiKey 960, the FriendlyElec NanoPC-T4, the Pine64 RockPro64, and the UDOO X86 Ultra.

A summary of the presentation written up by RTL-SDR explains that Scotty finds that the popular Raspberry Pi 3 Model B may not be the best choice for SDR use, instead recommending the Odroid X84, Asus Tinker Board S, FriendlyElec NanoPC-T4, and Pine64 RockPro64.

The full video is available now on YouTube.

Mozilla and the National Science Foundation have announced the winners of the NSF-WINS grant programme, and the grand prize has been given to a project designed to provide off-the-grid communication over short-wave radio.

“We launched NSF-WINS in early 2017 with the goal of bringing internet connectivity to rural areas, disaster-struck regions, and other offline or under-connected places. Currently, some 34 million Americans lack high-quality internet access. That means 34 million Americans are at a severe economic, educational, and social disadvantage,” explains Mozilla’s Mark Surman. “Now — after months of prototyping and judging — Mozilla and NSF are awarding $1.6 million to the most promising projects in the competition’s two categories. It’s part of Mozilla’s mission to keep the internet open and accessible, and to empower the people on the front lines of that work.”

The grand prize winner, walking away with a $400,000 grant, is HERMES, the High-frequency Emergency and Rural Multimedia Exchange System, developed by Rhizomatica. Fitting into a suitcase, HERMES ties together GSM and shortwave communications to provide emergency communications to disconnected areas. “In an emergency, you want to be able to tell people you’re okay,” explains Rhizomatica. “HERMES allows you to tell anyone, anywhere with a phone number that you’re okay. And that person can respond to you over text or with a voice message. It also allows someone from a central location to pass information to a disaster site, or to broadcast messages. We can now send a text message 700 miles through HERMES.”

More information on the other winners is available on the Mozilla blog, while more details on HERMES can be found on the Rhizomatica website.

Finally, OsmoCon 2018, the technical conference for Osmocom users, operators, and developers, is now only one week away, taking place in Berlin, Germany, on the 18th and 19th of October.

“For the second time, the Osmocom Conference brings together users, operators and developers of the Osmocom Open Source cellular infrastructure projects, such as OsmoBTS, OsmoBSC, OsmoSGSN, OpenGGSN and others,” the event’s organisers explain. “OsmoCon 2018 is your opportunity to deepen your understanding of Osmocom technology and to meet other people in and around the Osmocom Ecosystem. Join us for two days of presentations and discussions with the main developers behind Open Source Mobile Communications, as well as commercial and non-profit users of the Osmocom cellular infrastructure software.”

The event schedule has been published on the sysmocom website, while information about the event and the venue can be found on the Osmocom website.

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