Software Defined Radio Talks from the Friedrichshafen Ham Radio Convention

Several new software defined radio talks have been released on YouTube this week from the big European 2018 Friedrichshafen Ham Radio Convention which just finished this month. The full list of 14 new videos can be found on the Software Defined Radio Academy YouTube channel. Below are two of our favorites:

The OVI40 / UHSDR Project, Developing An Open Standalone SDR

OVI40 is an Open Source standalone homewbrew SDR TRX project (VLF to 2m), developed with the aim of being modular and future-proof. The talk describes the hardware and the UHSDR software including a discussion on the evolution from the "single-system" software used for the well-known mcHF (initially written by Chris, M0NKA and Clint KA7OEI) to the multi-SDR approach in the UHSDR software project.

DF8OE, DB4PLE, DL2FW, DD4WH: The OVI40 / UHSDR Project - Part 1 and 2
DF8OE, DB4PLE, DL2FW, DD4WH: The OVI40 / UHSDR Project - Part 1 and 2

András Retzler, HA7ILM: Let's code a simple receiver in C

For using SDR in amateur radio applications, it is easier to use existing receiver software, or create GNU Radio flowgraphs with pre-build blocks. On the contrary, in the do-it-yourself spirit of amateur radio, this talk will guide you through the steps of implementing a simple AM/FM/SSB receiver from scratch, in plan old C, in order to get a deeper understanding of what happens actually under the hood in popular SDR software. The talk builds on the author's learning experience of creating the open source CSDR command line tool, which is used for DSP in the OpneWebRX web based SDR receiver.

András Retzler, HA7ILM: Let's code a simple receiver in C
András Retzler, HA7ILM: Let's code a simple receiver in C

Software Defined Radio for Engineers: Free University Level Text Book with PlutoSDR Examples

Analog Devices has recently released a new text book for free called "Software-Defined Radio for Engineers, 2018". This is an advanced university level text book that covers communication systems theory as well as software defined radio theory and practice. The book uses the PlutoSDR as reference hardware and for practical examples. The PlutoSDR is Analog Devices $150 RX/TX capable SDR that was released about a year ago.

The objective of this book is to provide a hands-on learning experience using Software Defined Radio for engineering students and industry practitioners who are interested in mastering the design, implementation, and experimentation of communication systems. This book provides a fresh perspective on understanding and creating new communication systems from scratch. Communication system engineers need to understand the impact of the hardware on the performance of the communication algorithms being used and how well the overall system operates in terms of successfully recovering the intercepted signal.

This book is written for both industry practitioners who are seeking to enhance their skill set by learning about the design and implementation of communication systems using SDR technology, as well as both undergraduate and graduate students who would like to learn about and master communication systems technology in order to become the next generation of industry practitioners and academic researchers. The book contains theoretical explanations about the various elements forming a communication system, practical hands-on examples and lessons that help synthesize these concepts, and a wealth of important facts and details to take into consideration when building a real-world communication system.

The companion site for the book which contains links to complimentary online lectures, slides, and example MATLAB code can be found at https://sdrforengineers.github.io. MATLAB is a very powerful programming language and toolset used by scientists and engineers. MATLAB is not a cheap tool, but there is a home user licence available for a more reasonable price. To do some of the exercises in the book you'll probably at least require the core MATLAB plus the Communications System Toolkit which is an extra add on.

The full book can be purchased as a Hardcover from Amazon, or downloaded freely online as a PDF.

If you're interested in a similar book, there is also the free DesktopSDR book which uses RTL-SDR dongles for the practical examples.

SDR For Engineers Book
SDR For Engineers Book

Using a LimeSDR to Implement Software Defined Optoelectronic Systems

Back in January of this year we posted about PhD student Lucas Riobó's work that about about using an RTL-SDR to create a low cost optical "high-speed real-time heterodyne interferometer". In that work he used an RTL-SDR as a data acquisition tool for an optoelectronic front end sensor (opto = visual light). This allowed him to translate optical data into an RF signal, which could be received by the RTL-SDR, and then easily processed in a PC.

In his latest work Lucas has published a paper titled "Software Defined Optoelectronics: Space and Frequency Diversity in Heterodyne Interferometry" in the IEEE Sensors Journal. Note that the paper is behind an IEEE paywall, but Lucas notes that if you're interested in discussing his work that you can contact him at [email protected] The research is similar to the work published in January, but uses a LimeSDR which can take advantage of TX capabilities. Lucas writes:

In this work, a general architecture for the implementation of software-defined optoelectronic systems (SDOs) is described. This concept harnesses the flexibility of software-defined hardware (SDH) to implement optoelectronic systems which can be configured to adapt to multiple high speed optical engineering applications. As an application example, a software-defined optical interferometer (SDOI) using the LimeSDR platform is built. The system is tested by performing high speed optical detection of laser-induced photoacoustic signals in a concentrated dye solution. Using software modifications only, conventional single carrier and also multicarrier heterodyne techniques with space and frequency diversity are performed.

A main difference with the other article described in this post, is that we could also use the transmission path of the LimeSDR to perform many modulation waveforms of the electromagnetic fields which will interfere, to provide a noticeable performance improvement in single-shot interferometric measurements.

PC: Programmable controller, SDH: Software-defined hardware platform, E/O: Electrical-Optical block, O/E: Optical-Electrical block, OS: Optical System.
PC: Programmable
controller, SDH: Software-defined hardware platform, E/O: Electrical-Optical block, O/E:
Optical-Electrical block, OS: Optical System.
A Software Defined Optical Interferometer
A Software Defined Optical Interferometer

SDRplay Spectrum Analyzer Alpha Version Released

Steve Andrew has just released an alpha version of a Windows Spectrum Analyzer app for SDRplay SDRs that he's been working on. The app is currently still in alpha, meaning that all the features are not yet implemented. In particular, scans larger than the SDRplay's maximum bandwidth of 10 MHz are not ready yet. In the future the app will be able to scan swath's of bandwidth up to 2 GHz wide, similar to what SpectrumSpy for the Airspy and rtl_power for the RTL-SDR does.

We are pleased to announce the availability of the first cut of Spectrum Analyser software developed by Steve Andrew specifically for the RSP line of products. Please note that this is first alpha software and so it is still very much in development and some features are still to be added. Currently supported are:

RSP1
RSP2/RSP2pro
RSP1A

This first alpha release gives a good idea as to the look and feel for the software. The main functional limitation is that sweeps of greater than 10 MHz are not currently supported. Steve is currently re-working the algorithms for providing wider sweeps than 10 MHz to improve sweep time and remove the issue of the DC spike in ZIF mode, so please bear with him.

We recommend using the software with AGC turned off and use manual control of the gain for better display stability.

Please use this forum thread to post any issues. Read the issues already raised and only post if the issue you have found hasn’t been raised. This will help Steve in his development.

Further development information can be found on the forum.

Click here to download the 0.9a Alpha release.

SDRplay Spectrum Analyzer Alpha
SDRplay Spectrum Analyzer Alpha

Browsing the UHF Satcom Band via SpyServer

Over on YouTube Corrosive has published a video of him browsing through the UHF Satcom band with a remote Airspy SDR being streamed via SpyServer. The UHF-Satcom band is anywhere between 243 - 270 MHz and contains fairly strong signals from many several US satellites that can be received with a simple antenna. Some of the satellites are simple repeaters without security, and pirates from Mexico and South America often hijack the satellite for their own personal use. So it can be quite interesting to look for pirate conversations and sometimes SSTV images. Reception of these satellites is generally available in Canada, US, Mexico, South America, Europe and Africa.

UHF Satcom Transponders Close Up on the Airspy SDR
UHF Satcom Transponders Close Up on the Airspy SDR

CrowPi: Raspberry Pi Experimenters Kit Review (With RTL-SDR and RPiTX Tests)

CrowPi is a Raspberry Pi all-in-one experimenters kit that is currently crowd funding on Kickstarter. The idea behind CrowPi is to combine a touchscreen, various sensors, actuators and interfaces into a clutter free kit mounted on a PCB in an easy to carry hard shell case. It's mostly intended to be used in STEM learning environments, however it could also be used for rapid prototyping of Raspberry Pi based ideas, or simply as a portable computer. 

The CrowPi
The CrowPi

The kit has 4 days left on Kickstarter and has already met its minimum goal. Pledging $1,169 HKD (~USD $150) gets you the basic kit which does not include a Raspberry Pi. Higher pledge levels (up to US$250) get you models that include a Raspberry Pi as well as extras such as a 5V power supplies, earphones, heatsinks, keyboards, game controllers etc. Shipping of the units is expected to commence in July.

Elecrow, the Shenzhen based company behind CrowPi kindly sent us a free kit for an honest review. While not directly related to RTL-SDR or RF, we thought that there might be several applications that might make the CrowPi kit useful for prototyping some simple low cost RF based ideas. For example:

  • Prototyping IoT based modules that use the RTL-SDR as a receiver. For example receiving a 433 MHz ISM signal and writing received information to the LCD/LED array or activating the relay.
  • Similarly, using FL2K-SDR or RPiTX to transmit a signal when a sensor is activated, or to transmit telemetry from that sensor (e.g. distance data from the ultrasonic sensor, humidity levels from the DH11 sensor, or light levels from the light sensor)
  • Using an RTL-SDR to prototype an ADS-B plane camera tracker using the two servo module interfaces.

To get an idea of what's packed into the CrowPi, the kit includes the following modules:

  • Everything that came with our CrowPi Demo Kit (Except the Raspberry Pi)
    Everything that came with our CrowPi Demo Kit (Except the Raspberry Pi)
    1920 x 1080 Capable HDMI 7" Touch Screen
  • LCD Module
  • 8x8 Matrix LED
  • Breadboard
  • 4 character 7-seg LED
  • Vibration motor
  • Light Sensor
  • Buzzer
  • Sound Sensor
  • Motion Sensor
  • Ultrasonic Sensor
  • Servo Interface
  • Step Motor Interface
  • UART
  • Tilt Sensor
  • IR Sensor
  • Touch Sensor
  • DH11 Humidity Sensor
  • Relay
  • Matrix of buttons
  • RFID Module

With our kit we also received:

  • 2x GPIO Flex Cables
  • 1x Stepper Motor
  • 1x Servo
  • 1x Charger
  • 1x IR diode
  • 1x NFC Tag
  • 1x Mini HDMI for the Raspberry Pi Zero
  • 1x IR Remote control

Setup, Initial Testing and Thoughts

Setup: Setup was simple and consisted of downloading their customized Raspberry Pi image onto an SD card, connecting the Raspberry Pi to the HDMI, USB and GPIO pins, and then powering it up using the power jack on the CrowPi Board. A user manual is available for download.

Initial Testing: CrowPi provide a set of lessons that show how to use each of the modules on the board. All modules also have Python code examples that are ready to run as soon as you boot up. Immediately after booting up we were able to run their demo code which allowed us to test all the various sensors, print text to the LCD module, activate the 7-seg display, and actuate a servo and stepper motor. 

The tutorials are easy to understand and provide a good basic rundown of the sensors. You will need to have some basic Python skills to understand the Python code however.

Thoughts: The CrowPi is built sturdy, and is definitely easy to use. The touch screen is bright and clear. It is capable of running in 1080P mode, but is a bit too small and hard on the eyes to use at this resolution. We kept the screen in 720P mode. In order to use the Raspberry Pi, you'll need to plug in a USB keyboard and mouse which is not included in the basic kit. A wireless keyboard/mouse combo is ideal. There appear to be speaker holes next to the monitor, but it seems that our demo model is the basic model which does not include built in speakers. The kit is impressive looking and appears to be priced reasonably for what you get.

RTL-SDR and RF Testing

Unfortunately when it came to run the RTL-SDR we instantly ran into a problem. With the one 5V 3A power supply running the Pi, HDMI Screen and modules, it seems that there just isn't enough power budget left over to run the RTL-SDR which draws about 270 - 290 mA current. The RTL-SDR connects fine, but when trying to run GQRX, the Pi 3 shuts down. To get around this problem we have to connect a second power supply directly to the Raspberry Pi 3's input. After doing this the board and kit runs smoothly with the RTL-SDR. Using a powered USB hub would also work.

RPiTX is software for the Raspberry Pi that allows you to transmit RF signals directly via PIN12 or PIN7 from the GPIO ports. On CrowPi PIN12 is already connected to the buzzer, and PIN7 is connected to the humidity sensor. Using PIN12 causes the buzzer to sound, so we tried PIN7. Even though it's connected to the humidity sensor, it doesn't seem to mind the GPIO bit flipping going on. The traces within the board and cable radiate sufficiently to transmit signals strongly enough to use within a room, so no external antenna is needed. Use of PIN7 can be activated in RPiTX by using the "-c 1" flag.

Using our Replay Attacks with an RTL-SDR, Raspberry Pi and RPiTX tutorial, we copied  the signal from the remote control of a 433 MHz alarm/door bell, and used RPiTX to replay the signal. Then by modifying some of the supplied CrowPi Python code we were able to get the doorbell to sound on a touch of the touch sensor, activation of the sound sensor and via activation the RFID sensor. We could see the CrowPi being used as a general tool for learning how to prototype simple IoT or home automatic devices. The video below shows a brief demonstration. 

It would have been nice if these RPiTX GPIO pins could have been exposed, and not connected to a sensor, but the developers of the board had probably not heard of RPiTX as the goal is for a more general classroom application.

CrowPi Demo
CrowPi Demo

Conclusion

If you're looking to get kids or STEM students/hobbyists interested in what Raspberry Pi's can do, then this kit couldn't make it simpler. The single board and briefcase design makes the whole thing very tidy and portable and the kit looks and feels sturdy and professional. If you know a kid interested in electronics, then this kit would make a great present.

You could probably purchase all the components cheaper individually, but at the end of the day an all-in-one kit just makes sense as it is a lot tidier, and much easier to get up and running quickly.

For RF experiments, it's possible to use the RTL-SDR with the minor annoyance of having to connect two power supplies or use a powered USB hub. RPiTX also functions fine on the device and can be used to transmit an RF signal on activation of any one of the sensor modules. This could easily be used to prototype simple home automation or IoT ideas.

Osmocom now accepting Donations

Osmocom, the team behind the original RTL-SDR driver project, the Osmo-FL2K discovery, OP25, gr-osmosdr, gr-gsm and various other open source cellular phone projects is now accepting monetary donations. If you weren't already aware, it was the efforts of Antti Palosaari and Eric Fry who made the original tests on DVB-T dongles, and then Osmocom who wrote the first RTL-SDR driver and software that is still currently used in the RTL-SDR project today. If you're interested, there is a full write up on the history or RTL-SDR at the bottom of rtlsdr.org.

Recently Osmocom have begun accepting donations via Open Collective. They write

The Osmocom project (if you count its predecessor OpenBSC) have been running for close to 10 years, creating a large number of Open Source projects related to mobile communications. We have never needed nor wanted any legal entity for it. It's a pure/classic FOSS project, open to contributions from anyone.

Until today, you could only contribute in one of the following forms:

  • by writing code (bug fixes, new features, etc) and submitting it (which means you need to be a developer)
  • by writing documentation / improving the wiki
  • helping other users on the mailing lists, IRC, or in other forums
  • donating cellular equipment (which many don't have)
  • hiring a freelancer or a company to write code and contribute to Osmocom on your behalf 
  • buying products or services from companies who dedicate lots of work to Osmocom

However, we've repeatedly getting requests from some individuals who wanted to contribute to the project in an easy way, even if they are not a developer, and/or don't have time, and/or don't have the size of a budget to fund development of entire new features or sub-systems.

Today, Osmocom announces that we have joined Open Collective in order to enable you to make financial contributions, either one-off or recurring.

We'll be using the funds (if we get any!) according to our funding policy outlined at https://opencollective.com/osmocom/expenses/new# in order to pay for expenses such as hosting costs for our servers / IT infrastructure, travel funding for the annual developer conferences, etc. Any and all expenses paid from those funds will be visible on the OpenCollective website. You cannot ask for more transparency than that :)

Thanks in advance for your kind assistance!

So if you've ever enjoyed the RTL-SDR project, and how much it's improved your access to the RF spectrum, please consider donating via Open Collective or contributing back in other ways. Donations may help Osmocom to continue making new and interesting discoveries, such as Steve M's amazing FL2K-SDR discovery that was released back in April this year.

Controlling moRFeus over a Network Connection

Thank to LamaBleu for submitting news about his new software for the moRFeus signal generator and frequency mixer called moRFeus_listener. The software allows you to remotely control a moRFeus device via Telnet, TCP/UDP or HTTP. This could be used to control the moRFeus in a similar way to the short script that we used for generating a tracking tone in our previous tutorial on using measuring filters and antenna VSWR with the moRFeus.

LamaBleu also shared his results with using the harmonics of the moRFeus to generate a signal well past it's upper frequency limit of 5.4 GHz. He writes that by using the third harmonic is was able to generate a CW signal at 10.8 GHz and that tones up to harmonic 11 seem to work well.