Tagged: Software-defined radio

An Intro to RTL-SDR: Technical DSP Concepts Explained

Over on his blog Ajoo has posted a very comprehensive introduction to the technical concepts behind RTL-SDR, as well as any other SDR in existence. His post first goes through the basic communications theory and mathematical concepts required to understand the technical concepts behind software defined radio. He then goes on to specifically discuss the RTL-SDR and how it works internally, mentioning what the major components do and providing useful block diagrams.

In part II of his introduction he moves on to the software. Here he starts to explain a bit about librtlsdr and how the RTL-SDR drivers and codebase is put together. Further on he explains higher level software such as rtl_test, rtl_fm, rtl_sdr, the pyrtlsdr wrapper and how it could be used to demodulate FM.

If you're looking at diving deeper into SDR theory then Ajoo's posts are excellent starting points. Note that the theory explanations come at about an undergraduate University level of complexity, and thus these posts are mostly for people wanting a deeper understanding of SDR. To simply use an RTL-SDR to receive signals such a deep level of understanding is not required.

In a future post which is not yet available, Ajoo will introduce GNU Radio and show how to demodulate FM signals. It appears his goal is to work his way to an understanding of how GPS L1 signals work.

One of Ajoo's block diagrams explaining the RTL-SDR behavioral model.
One of Ajoo's block diagrams explaining the RTL-SDR behavioral model.

Uniden Announce the SDS100: A Software Defined Handheld Scanner

The Uniden SDS100 Handheld SDR Based Scanner
The Uniden SDS100 Handheld SDR Based Scanner

Radio manufacturer Uniden have just released news about their latest product called the SDS100 which is a handheld software defined radio scanner specifically for digital voice and trunking modes. The scanner will retail for USD699, and aims to be released in the 2nd quarter of 2018 pending FCC approval. Note that certain software decoders will require paid upgrades, but it will be capable of all the major digital voice modes such as P25 Phase I and II, DMR, NXDN and trunking modes. It doesn't seem to support TETRA since it's marketed at the American consumer, however, it seems plausible that simple software update could enable this feature in the future.

As far as we know this is the first handheld scanner to incorporate SDR and is probably one of the bigger leaps in scanner technology to date. Compared to hardware based scanners, the SDS100 should provide significantly better decoding capabilities, even in weak signal and simulcast conditions. Simulcast is when multiple overlapping base stations transmit a signal at the same frequency. This can cause multi-path distortion problems, but an IQ based radio like an SDR is able to overcome these issues.

Uniden creates another first with the SDS100 True I/Q Scanner, the first scanner to incorporate Software Defined Radio technology to provide incredible digital performance in even the most challenging RF environments. The SDS100’s digital performance is better than any other scanner in both simulcast and weak-signal environments.

The SDS100 is also the first scanner that allows you to decide what to display, where, and in what color. Custom fields put the information important to you right where you need it.

And, one more first, the SDS100 meets JIS4 (IPX4) standards for water resistance.

For more information you can check out this discussion thread on Radio Reference. In the future there should also be some videos of it in action available on the Uniden YouTube channel. The owners manual is also available here and all their promo material including many more demonstration videos can be found on their Google Drive.


Nexmon SDR: Turning a Broadcom 802.11ac WiFi Chip into a TX Capable Software Defined Radio

Over on GitHub we've recently seen the release of some interesting code called "Nexmon Software Defined Radio" which demonstrates a discovery that allows a Broadcom 802.11ac WiFi chip to be used as a transmit capable software defined radio. This means that it can be used to transmit (within the 2.4 GHz and 5 GHz WiFi bands) any arbitrary signal from IQ data. The specific WiFi chip used in their experiments is the US$10 BCM4339 which has been found in smartphones such as the Nexus 5. It's not clear if other Broadcom 802.11ac WiFi chips could also work.

To begin with Nexmon SDR you'll need a development environment set up on a Nexus 5 smartphone. Then it's a matter of downloading the dependencies, installing the Android NDK, and compiling Nexmon. IQ data can then be transmitted in code using from special system commands.

The Nexmon team have indicated on Twitter that they plan to present a paper with more information on Nexmon SDR at the MobiSys 2018 conference which will be held in June.

FOSDEM 2017/2018 SDR Conference Videos: Passive Radar, Radio Telescopes, SatNOGS and Wireless Traffic Lights

Fosdem 2017 and 2018 were conferences on software development that occurred on 4 & 5 February 2017 and 3 & 4 February 2018. The conference features several software defined radio and RTL-SDR based talks which appear to have recently been uploaded to YouTube. Below we're posting some of our favorite SDR related talks, but the full video list can be found here, and here is the SDR playlist from Fosdem 2018.

(Yet another) passive RADAR using DVB-T receiver and SDR

by Jean-Michel Friedt @ FOSDEM 2018

In this presentation Jean-Michel shows a GNU Radio passive radar implementation utilizing two coherent RTL-SDR dongles. During the talk he demonstrates his results with RTL-SDR passive radar operating on planes, boats and cars.

Slides: http://jmfriedt.free.fr/fosdem2018.pdf
Paper: http://jmfriedt.free.fr/URSI.pdf

Intro to Open Source Radio Telescopes

by Martin Braun and Sue Ann Heatherly @ FOSDEM 2018

In this talk Martin and Sue discuss how amateur radio astronomy can be performed using lost cost software defined radio tools such as an RTL-SDR. They show how to receive solar flares and detect the 21cm hydrogen line and focus on showing how easy it can be to do these projects in a classroom environment.

Claim Space, the Libre Way, using SDRs

by Manolis Surligas @ FOSDEM 2018

In this talk Manolis from the Libre Space Foundation and SatNOGs discusses how they use RTL-SDR's and other SDR's in their volunteer run network of satellite ground stations to create an online database of received satellite data.

Receiving Wireless Mobile Traffic Lights

by Bastian Bloessl @ FOSDEM 2017

Wireless mobile traffic lights are often used to secure construction sites when roads are partially blocked. Some day, when a pair of them was placed close to our home, I set off to explore how they are working. In this talk, I will describe how I used a cheap RTL-SDR together with GQRX, Inspectrum, and GNU Radio to reverse engineer the modulation and frame format of different types of wireless traffic lights. With some patience, I could also make some sense out of the bits. In particular, I was able to extract the signal state and display it in a web interface, mirroring the traffic light. A closer look at the frame format and the apparent absence of any authentication might leave one with a bit of a worrying impression regarding the security of those systems.

Building an IcoBoard FPGA based Software Defined Radio

The IcoBoard is an FPGA IO board that is compatible with the Raspberry Pi. An FPGA (Field Programmable Gate Array) is a silicon chip that can implement custom digital circuits (such as DSP processors) and be reconfigured with different circuits many times. Other silicon chips are ASICs (application specific integrated circuit) which have circuits that are set in stone.

Over on YouTube OpenTechLab has been trying to create a software defined radio with his IcoBoard FPGA. To do this he's combined it with an audio A2D/D2A (analog-to-digital/digital-to-analog) converter board and a Raspberry Pi. The video goes through the entire design process, including A2D/D2A selection and purchasing, PCB adapter design in KiCad, soldering the PCB, as well as 3D printing a frame.

In the last part of the video he does a simple test where a signal is input into the A2D converter, converted to digital and processed by the FPGA. The circuitry programmed into the FPGA then simply outputs the received data to the D2A which converts it back into an analog signal. In the next steps of the project OpenTechLab hopes to work on the software and turn it into a full SDR. Show notes for the video are available here.

Building a Software Defined Radio from Scratch

Over on his blog Lukas Lao Beyer has uploaded a post that shows his journey with designing and building a software defined radio from scratch. Lukas’ finished SDR design is called the FreeSRP and is based on the Analog Deviced AD9364 transceiver and a Xlinx FPGA.

In his post Lukas describes how he designed the PCB with Altium Designer, routing the traces carefully to ensure the shortest path was used, and to ensure impedance matching was correct. Then after producing the PCB’s with OSH park he writes how he assembled the board by carefully placing the components down by hand and using his reflow oven. This was no easy task due to the manual nature of the operation and the high possibility for undetectable solder problems to arise. Despite the difficulties he found that the SDR powered up as expected.

His next steps were to start work on the FPGA controller design, however he discovered that he had failed to properly route some clock pins on the FPGA. On his third revision of the PCB he was able to fix this. Finally he was able to program the FPGA and get his SDR to work.

Designing an SDR from scratch is no easy task, especially if you have little design experience like Lukas did. However, in the end despite some mistakes he was able to build a working SDR that interfaces with GNU Radio. 

Lukas' FreeSRP SDR.
Lukas’ FreeSRP SDR.

Demonstrating the ARM Radio

Back in November 2015 we posted about the ARM Radio, a minimalist direct sampling software defined radio that runs almost entirely on an ARM processor on a STM32F429 discovery board. It can tune from about 8 kHz up to 900 kHz, which covers the VLF, LF and some of the MF bands. 

Now over on YouTube amateur radio hobbyist W9RAN has uploaded a video where he demonstrates an ARM Radio that he built. He shows the radio in operation with it clearly receiving some NDB’s and some AM broadcast stations.

An online Software Defined Radio training course

We’ve recently found what looks to be a new online video based course that uses the RTL-SDR to teach basic software defined radio topics. The course is not free, it is priced at $29.99, but the first three videos are free. Judging from the first three videos the content appears to be quite basic, but is presented in a very clear way that may be useful for beginners. Currently the lessons include:

  1. Course Overview 

    Welcome to the exciting world of Software Defined Radio. In this video, we’ll discuss what SDR is, and why it’s such a hot button topic right now.

  2. Setting up the environment

    In this module, we’ll setup our environment for development. If you’re already very comfortable with Ubuntu, you might want to just follow the guide below.

  3. Browsing the spectrum 

    In this module, we’ll cut our teeth on GRQX, and learn a little about the radio spectrum.

  4. Signals Intelligence

    In this module, we’ll learn how to find transmissions in the frequency domain, and capture them to disk for offline analysis.

  5. Modulations

    In this module, we’ll learn how to identify two types of basic digital transmissions, and talk a little about the history of radio.

  6. Demodulation – Part 1

    In this module, we’ll practice capturing signals in the wild, identifying the modulation, and demodulating the signal with GNU Radio.

  7. Demodulation – Part 2

    In this module, we’ll learn about clock recovery. And we’ll pull out packets from the garage door remote.

It also appears that they plan to have some live classes in the future.

We note that there are also alternative SDR training courses available such as Micheal Ossmanns lessons at greatscottgadgets.com/sdr.

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