Category: Applications

Tracking Trains: Monitoring Railroad ATCS Control Signals with an RTL-SDR

Over on his YouTube channel GusGorman402 has uploaded a tutorial which shows how he monitors ATCS (Advanced Train Control System) signals from trains. ATCS signals are found in the USA, and is used for things like communications between trains, rail configuration data, train location data, speed enforcement, fuel monitoring, train diagnostics and general instructions and messages.

In the video he first shows how to determine the frequency of trains signals in your area by using the US FCC database. He then shows how to download and install the ATCSMonitor software which is used for decoding the signals, and then walks us through configuring the correct settings within the software. The train signal audio is piped from SDR# to ATCSMonitor via VBCable, and received with an RTL-SDR and simple whip antenna.

Later in the video he shows how to fully set up the software with train databases so that the actual spotted train names show up. He also shows how to set up the dispatcher display which visually shows the current train locations and track configurations.

GusGorman402 has uploaded the tutorial in two videos. The first shows the full tutorial, configuration and demo for trains in the BNSF fleet. The second video shows how to monitor the Union Pacific fleet which uses a different protocol, which requires a slightly different set up in ATCSMonitor.

RTL-SDR Railroad ATCS Monitor BNSF Omaha

RTL-SDR Railroad ATCS Monitor Union Pacific Omaha

A Tour of Satellites in the QB50 Experiment

Over the last two weeks the QB50 experiment was launched from the International Space Station (ISS). The experiment consists of 36 cubesats built by various universities around the world, with the main science goal being to make measurements of the thermosphere (an upper atmospheric layer that the ISS orbits in). All the cubesats broadcast their telemetry in the 70cm (420 – 450 MHz) amateur band and they are expected to stay in orbit for about 3 months before falling back to earth. In a previous post we made a point to mention Lilacsat-1, which is one of the most interesting QB50 satellites due to its implementation of a FM to digital voice repeater on board.

The QB50 Experiment Launch
The QB50 Experiment Launch

Over on his blog destevez has been following these satellites, and has uploaded a post that shows him receiving and decoding several of the satellite telemetry packets. His gr-satellites GNU Radio package provides a means to decode many of the satellites in the experiment.

Some packets from QB50 and other satellites in the 70cm amateur band.
Some packets from QB50 and other satellites received by destevez in the 70cm amateur band.

YouTube Video: A Tutorial on Receiving and Decoding NOAA and METEOR Satellites

Back in March we posted about The Thought Emporium’s YouTube video that explained weather satellites and demonstrated that images could be downloaded from them using an SDR like a HackRF or RTL-SDR. Now The Thought Emporium have uploaded part two of the video series, which is a tutorial that shows exactly how to use the free software to receive, demodulate and decode NOAA and Meteor satellites.

The first part of the video shows how to use SDR#, Audacity and WXtoIMG to receive NOAA APT weather images. The second part of the video shows how to use SDR#, Audacity, LRPTrx, LRPTofflinedecoder, SmoothMeteor and LRPT processor to receive Meteor M2 LRPT images.

Receiving Images From Satellites Part 2: Decoding and Demodulating NOAA and METEOR Transmissions

Signal Reverse Engineering Tool DSpectrum Upgraded to DSpectrumGUI

DSpectrum is a reverse engineering tool that aims to make it trivial to demodulate digital RF transmissions. It is built on top of the Inspectrum tool which makes it easy to visualize and manually turn a captured digital RF waveform into a string of bits for later analysis by providing a draggable visual overlay that helps with determining various digital signal properties. DSpectrum added features to Inspectrum like automatically converting the waveform into a binary string with thresholding. RF .wav files for these tools can be captured by any capable radio, such as an RTL-SDR or HackRF.

DSpectrum has recently been depreciated in favor of the new DSpectrumGUI which builds on the success of DSpectrum by providing a full interactive GUI that helps with the reverse engineering workflow. Some interesting new features include things like automatic analysis of the binary to determine the modulation and encoding types, the ability to submit/download reverse engineering worksheet templates to/from the community and binary generation for transmitting with a RFCat.

A similar tool is Universal Radio Hacker.

DSpectrumGUI
DSpectrumGUI

Detecting Pulsars with a Circularly Polarized Yagi and an RTL-SDR

Steve Olney VK2XV is the creator and administrator of the Neutron Star Group website which collects a listing of confirmed amateur attempts at pulsar detection, many of which have been made with a humble RTL-SDR dongle. A pulsar is a rotating neutron star that emits a beam of electromagnetic radiation. If this beam points towards the earth, it can then be observed with a large dish antenna and a radio, like the RTL-SDR.

Now after more than four years of trying, Steve has finally been able make his own confirmed pulsar detection by using a 42-elment circularly polarized Yagi antenna tuned for 436 MHz and an RTL-SDR. Typically a large dish antenna is used to receive a pulsar, but Steve has instead used a fixed position circularly polarized Yagi antenna, which he writes has an equivalent aperture to a 2.8 meter diameter dish. His antenna can point directly upwards as his target is the Vela pulsar which happens to pass almost directly overhead at his location.

Detection of a pulsar involves determining its rotational period from the regular wideband noise pulses that they produce. Pulsar detections with large aperture dish antennas can easily be confirmed due to high SNR, but smaller weaker detectors require some use of some mathematical techniques to confirm a positive detection. This is especially important as it’s possible for terrestrial signals to mimic a pulsar. 

In order to detect and confirm the pulsar detection from a weak signal, Steve uses a technique called epoch folding, which makes use of the fact that the period of pulsar pulses are extremely regular. To verify the results he also makes use of techniques such as folding at the predicted period, de-dispersion and plotting daily results against the predicted results. These techniques are explained in more depth in his results post.

Steve's Results showing the detected pulsar period and his CP Yagi Antenna
Steve’s Results showing the detected pulsar period and his CP Yagi Antenna

DAB/DAB+ Decoder Software “Welle.io” Now Available on Android

Back in March of this year we posted about “Welle.io”, a DAB/DAB+ decoder that supports the RTL-SDR and other SDRs like the Airspy. It was available for Windows, Linux and Raspberry Pi 2/3.

Albrecht Lohöfener, the author of Welle.io has recently written in to announce that Welle.io is now available for Android as well. The app appears to be free, but is currently marked as beta, so there may still be a few bugs.

The only other app that we’ve seen which is capable of decoding DAB/DAB+ on Android is Wavesink. Wavesink costs $14.90 USD on the Google Play store, but there is a free trial version available with runtime limitations and no DAB+ support.

Albrecht notes that the app is fairly computationally intensive and will require an Android device with at least 4 cores and a clock speed of 1.3 GHz to run the app. He also mentions that they are also looking for any interested developers and translators to help with development of the app.

Welle.io on Android
Welle.io on Android
welle.io on Android (DAB+/DAB software radio, RTL-SDR , RTL2832U)

XRIT Decoder for GOES Satellites: Supports Airspy R2/Mini and SDRplay RSP2

Over on his blog USA-Satcom has released his XRIT (LRIT/HRIT) decoder for GOES satellites. The software requires a licence and costs $100 USD. GOES-13 (East), GOES-15 (West) and the new GOES-16 are geosynchronous orbiting satellites that broadcast very nice high resolution weather images of the entire visible disk of the earth. The transmit their LRIT/HRIT signals at about 1.7 GHz at fairly weak power, which means that a good LNA and dish set up is critical to be able to receive them. A dish size of about 1 meter, or an equivalent grid or Yagi is recommended as the lowest starting point.

GOES Full Disk Image of the Earth
GOES Full Disk Image of the Earth

USA-Satcom’s decoder is Windows based and comes with a nice GUI. Some portions of the code are based on the Open Satellite Project created by Lucas Teske. It currently supports the Airspy R2/Mini and the SDRplay RSP2 software defined radios.

The software is not free, it costs $100 USD for the licence. To help curb illegal distribution of his software which has been rampant in the past, USA-Satcom also requests that you show some proof of a working setup which is capable of receiving the GOES signal before inquiring about the software.

If you are also interested, USA-Satcom did an interesting talk at Cyberspectrum a few months ago, and he has also recently uploaded his slides.

Screenshot of USA-Satcoms GOES XRIT decoder.
Screenshot of USA-Satcoms GOES XRIT decoder.

QIRX SDR: A New MultiMode RTL-SDR Program with Built-In DAB+ Decoder

Recently Clem from softsyst.com wrote in and let us know about their new SDR software called ‘QIRX SDR’. This is a multimode receiver currently capable of receiving AM/NFM/WFM and also DAB Plus. It supports the RTL-SDR via an rtl_tcp connection, so it can be used on a local machine, or a remote networked one. The main differentiating features that QIRX has against other multimode receivers like SDR#, HDSDR and SDR-Console etc is:

  • Dual Receiver, within the bandwidth of the frontend. This is most useful e.g. for watching two stations simultaneously in busy airband regions.
  • DAB+ Demodulator, to our knowledge the first one written in C#, allowing for recordings in very good quality (some samples provided for download).

The full list of features are quoted below:

QIRX is an Open Source Software Defined Radio, written in C#, downloadable on this site as a Visual Studio 2013 Solution, offering the following features:

  • TCP/IP Based: QIRX accepts 8-bit I/Q-Data either from TCP/IP sources or from pre-recorded files containing the I/Q-data. It is designed to cooperate with RTL-SDR dongles and the widely available rtl-tcp.exe as I/Q-data server. Both QIRX and rtl-tcp may run on the same machine or on separate ones. The rtl-tcp.exe might be started automatically without additional user actions, also when used remote via a LAN.
  • Dual Receiver: Within the selected bandwidth, e.g. 2.56MHz QIRX is able to operate two independent receivers simultaneously.
  • Squelch: For each receiver, QIRX provides a digital squelch, enabling to monitor the selected stations – when not transmitting – without annoying background noise.
  • Simplest Operating Principle: QIRX – using its AM, NFM or WFM demodulators – is purely FFT-based, with a NF lowpass filter only. This might change in a future version.
  • Scanner: QIRX provides for Receiver 1 a simple scanner, being able to scan large frequency areas. This is still in an experimental state.
  • HF and NF Spectrum: For each receiver, QIRX provides a spectrum viewer being able to show the HF and the NF spectrum. No waterfall spectrum yet. For DAB+, it shows the constellation.
  • DAB+ Receiver: QIRX provides a comfortable DAB+ receiver ( Transmission Mode I ). It is -to the best of our knowledge- the first C# based SDR providing this facility. Some standard libraries like the Viterbi decoder are used as C/C++ packages, accessed via P/Invoke.
  • File Recorder: For all demodulators, the audio output can be saved to .wav files, independently for each of the both receivers. For DAB+ this allows for high-quality audio recordings.

    Additionally, the I/Q raw data can be saved to a file. It is possible to replay recorded I/Q-data files.

QIRX SDR: A new multimode receiver with DAB+ decoding
QIRX SDR: A new multimode receiver with DAB+ decoding