Category: Digital Signals

TETRA-Kit: A New Open Source TETRA Decoder

Thank you to Larry for submitting information about his latest project called TETRA-Kit. TETRA-Kit is an extensible open source TETRA downlink decoder for Linux that makes use of GNU Radio as the first stage, so it should be compatible with any SDR supported by GNU Radio, including the RTL-SDR. Larry writes:

[TETRA-Kit] is inspired by a lot of existing stuff (see 'Previous work' in the project page) but started from scratch with those following ideas:

  • Stays as close as possible to TETRA specification layers defined in ETSI EN 300 392-2 v3.4.1 (2010-08)
  • Transmit downlink informations (including speech frames) in Json plain text format to be recorded or analyzed by an external program
  • Reassociate speech frames with a simple method based on associated caller id and usage marker (save messages transmitted simultaneously in separated files)
  • KISS

The decoder implements a soft synchronizer allowing missing frames (50 bursts) before loosing synchronization.

It consists in 3 parts:

  • A physical layer transforming PI/4 DQPSK rf signal to bits (RF frontend is NESDR at 2MBPS)
  • A decoder, which is the actual TETRA stack reading bits and transforming it to Json text
  • A recorder, which read Json stack output and reorder speech frames into separate files

The ETSI codec is also provided so unencrypted speech can be played.

Software is written in C++ and licensed under GPLv3 and use few external softwares with compatible licensing.

TETRA is a type of digital voice and trunked radio communications system that stands for “Terrestrial Trunked Radio”. It is used in many parts of the world, but not in the USA.

TETRA-Kit Screenshot
TETRA-Kit Screenshot

Techminds: Testing out the new Plugins Feature on SDRuno V1.4 RC1

Earlier in the month SDRplay released SDRuno V1.4 RC1. This is a beta version that amongst other changes now has the capability to run "plugins". Plugins allow developers to easily create modules that extend the functionality of the SDRUno software. For example right now there is a plugin included with V1.4 RC1 that allows users to listen to DAB audio. Up until recently plugin functionality has only been available in Airspy's SDR# software, so it's good to see SDRuno finally including this feature too.

Over on the Techminds YouTube channel Matthew has uploaded a short video where he tests out the new plugins feature. First he tests out the DAB decoder, noting that the CoreAAC codec needs to be installed first separately. Later he tests the second plugin which is an audio recorder that allows users to record audio to MP3.

SDRPlay SDRuno Plugins Feature - NEW!

Tutorial on Using xrit-rx to Receive Weather Images from Geostationary Satellite GK-2A

Over on his website VKSDR has recently released a tutorial about his Linux based xirt-rx software which allows RTL-SDR and other SDR owners receive weather images from the geostationary satellite known as GEO-KOMPSAT-2A (GK-2A). GK-2A is a Korean satellite, hence it is positioned over the Asia-Pacific region, covering Asia, Eastern Russia, Australia and New Zealand. 

To receive images from GK-2A you'll need an RTL-SDR, 2.4 GHz WiFi grid antenna and an L-band LNA. We have an earlier tutorial about receiving GK-2A and GOES geostationary L-band satellites that goes into more detail about the hardware required. 

VKSDR's xrit-rx software decodes the Low Rate Information Transmission (LRIT) signal from GK-2A which provides a 64kbps data stream and full disk images of the earth every 10 minutes. His tutorial explains the various image types that are transmitted, shows a few example images, and shows that some smooth animations can be created with the 144 images received over a day. The rest of the tutorial goes into the software setup, and explains the installation and configuration procedure.

We note that the latest version of xrit-rx now also comes with a nice web based dashboard that allows you to view the latest image, as well as the upcoming image schedule.

Full Disk Images Received from GK-2A via XRIT-RX
Full Disk Images Received from GK-2A via xrit-rxThe new web based dashboard for xrit-rx

The new web based dashboard for xrit-rx

TechMinds: Detecting HF Interference from a VDSL Internet Connection

Over on YouTube user Tech Minds has uploaded a video showing how you can determine if you are getting HF interference from a VDSL internet connection going to your house or neighbors. VDSL or Very High Speed Digital Subscriber Line is an internet connection technology that runs over old copper phone wires allowing for a fast broadband connection. The frequencies used by VDSL are between 25 kHz to 12 MHz, and for VDSL2 up to 30 MHz. Unfortunately the frequencies used can result in high amounts of radio interference from RFI radiating from the copper phone lines which is a major problem for HF amateurs and short wave listeners.

In his video Tech Minds uses an SDRplay RSPdx to record a short IQ file of the VDSL interference that he experiences in his home in the UK. He then opens the IQ file in a piece of software called Lelantos, which was developed by a member of the UK amateur radio organization RSGB. If a VDSL signal is present, this tool will determine various bits of information about the interference, and will give you enough information to make a complaint to OFCOM, the UK's radio communications regulator.

VDSL RFI Detection and how to report it to OFCOM

TechMinds: Demonstrating the QT-DAB Digital Audio Broadcast Decoder

Over on YouTube TechMinds has uploaded a video where he explores the QT-DAB software (formerly known as SDR-J), which is a program capable of decoding Digital Audio Broadcast (DAB) signals. QT-DAB is compatible with several SDRs including the RTL-SDR, HackRF, Airspy and SDRplay units. 

DAB stands for Digital Audio Broadcast and is a digital broadcast radio signal that is available in many countries outside of the USA. The digital signal encodes several radio stations, and it is considered a modern alternative or future replacement for standard analog broadcast FM.

In the video TechMinds explains how to download, install and use the software on a Windows machine. He goes on to demonstrate some DAB decoding in action with various SDRs and then shows how to connect QT-DAB to a remote RTL-SDR via rtl_tcp.

DAB Radio Decoder For SDR (RTL_SDR - HACKRF - AIRSPY)

OpenEar Now Supports TETRA, DMR, POCSAG, ADS-B

Back in March we posted about "OpenEar" which was a newly released Windows TETRA decoder for RTL-SDR dongles. Back then the author "moneriomaa" noted that he planned to add several new modes. In the release that is currently available, OpenEar now supports TETRA, DMR, Pocsag, ADS-B as well as standard AM and NFM modes. We tested the software, and all modes appear to decode as advertised. In the future the author plans to add more modes such as MPT-1327 and AERO.

In the previous post we added an update noting that OpenEar appeared to be violating the GPL licence of OsmocomTETRA, and the author noted that he would remove the TETRA functionality until licencing was resolved. As TETRA decoding is back in the recent releases we assume these legal issues have been solved.

In the current release you also need to provide your own rtlsdr.dll file, which can be obtained from your SDR# folder, or directly from the Osmocom windows release (rename librtlsdr.dll to rtlsdr.dll).

Latest OpenEar Version
Latest OpenEar Version

OpenEar: An Easy to Use Windows TETRA Voice Decoder

A new TETRA voice decoder called "OpenEar" has just been released. The program is a standalone Windows app that directly connects to an RTL-SDR. Decoding a TETRA voice signal is as simple as opening the program, tuning to the TETRA frequency and clicking on the signal. With good signal strength voice comes through very clearly. CPU usage on our PC is also minimal. 

The program source is currently not available as the author notes that he only intends to release it as open source in the future once the project is completed, and right now this is only the first early release. Right now the program is just an .exe with a few .dlls. You'll need to first install the Microsoft Visual C++ Redistributable Package linked in the Git readme. Just in case, we virus scanned the exe and tested the program in Sandboxie. It appears to be clean, and it works as intended.

In the future the author hopes to support many more protocols such as DMR, MPT1327, ACARS, AIR, GSM and more. In order to support his work he is asking for Bitcoin donations, and the donations link can be found on the Git readme.

UPDATE 1: If you're getting missing dll errors and you already installed the Visual C++ Redistributable, try downloading the missing dll's from dll-files.com. There should only be about 5 missing.

UPDATE 2: As pointed out in the comments by Steve M. from Osmocom, this software may be in violation of several GPL licences as no source code has been released and it appears to rely on GPL code and libraries. Please take this into account.

UPDATE 3: As per update 2, the author has decided to temporarily disable the TETRA functionality pending a rewrite of the code that he will complete within one to two months). Instead he has added DMR decoding.

OpenEar TETRA Voice Decoder Screenshot
OpenEar TETRA Voice Decoder Screenshot

OpenWebRX Version 0.18.0 Released: New Decoders for Digital Voice, Digital Ham Modes and More

Back in early January we posted about how the popular web based SDR and RTL-SDR compatible receiver software known as OpenWebRX was officially discontinued by the original author. However, thanks to it's open source licence, code contributor Jakob Ketterl (DD5JFK) has been able to continue developing the code and is taking over as the lead developer on his own fork of the code.

Recently he released version 0.18.0 of OpenWebRX which includes a few major upgrades including the much needed shift to Python 3, and the inclusion of multiple new decoders for DMR, D-Star, YSF, NXDN, FT8, FT4, WSPR, JT65, JT9, APRS and Pocsag.

Hello fellow radio enthusiasts,

with great excitement I would like to announce the availability of OpenWebRX Version 0.18.0 as public release. This is the first release of the project in some time, and the first release since I started working on it, so I’m more than happy to bring this to you.

What’s new? Quite a lot, actually. For those that haven’t had the chance to follow the progress of the project in the past months, here’s a quick overview:

    • Most of the server code has been rewritten for better flexibility, stability and performance. The project is now fully based on Python 3.
    • Large parts of the frontend code have been updated or polished.
    • The new core now supports multiple SDR devices simultaneously, as well as switching between multiple profiles per SDR, allowing users to navigate between multiple bands or frequencies.
    • Added support for demodulation of digital voice modes (DMR, D-Star, YSF, NXDN).
Added support for digital modes of the WSJT-X suite (FT8, FT4, WSPR, JT65, JT9).
  • Added support for APRS.
  • Added support for Pocsag.
  • Bookmarks allow easy navigation between known stations.
  • Background decoding can transform your receiver into an automatic reporting station, including automatic band scheduling.
  • The integrated map shows digimode spots as well as APRS and YSF positions.
OpenWebRX 0.18.0 is available via the following channels: Please check out our updated Setup Guide along with the rest of the documentation on the Wiki!

Questions, ideas, problems? Get in touch with the community at [email protected]!

Best regards and vy 73s

Jakob DD5JFK

We're so glad to see that this excellent software isn't dead in the water and is in fact thriving. We will continue to follow the Jakob's and the OpenWebRX communities' future developments. If you are interested, you can follow OpenWebRX development on the OpenWebRX groups.io forum.

OpenWebRX Screenshot
OpenWebRX Screenshot