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/replacement for standard analog broadcast FM.
The tutorial is split into four parts. The first part simply explains what SDRs are and in particular discusses the LimeSDR and how it can be used with ODR-mmbTools. Part two discusses what hardware you need, and explains what each component of the ODR-mmbTools software does. Part three gets into the actual setup of the software on Linux. Part four finishes with actually transmitting the signal and decoding it with an RTL-SDR and the Welle.io DAB decoder.
The end result is a DAB radio station with three stations being broadcast.
QIRX SDR is a multimode SDR program compatible with the RTL-SDR. One of its defining features is that it has a built in DAB+ decoder. Recently beta version 2.01 of QIRX SDR was released which has some scanner, recording and spectra display improvements. We note that the beta version appears to be a DAB decoder only, with no multi-mode features. The new features and improvements include:
Configurable w/r to the Muxes to be scanned and/or included in the usual set of Muxes being used.
New algo, considerably faster
"Scan forever" feature, interesting for DX-ers wishing to observe Muxes over a longer time, particularly together with TII logging.
Selectable waiting time after recognition of a Mux, for TII logging.
TII Recorder: File structure improved, now directly importable into Excel, with TAB as separator.
Audio Recorder (DAB+ only): Format selectable between WAV (as usual) and pure AAC (with ADTS headers). The latter allows for high-quality recordings compressed by at least a factor of 10 compared to WAV. The popular Foobar2000 app is able to play these files. Not seekable yet though, because embedding in a suitable container is not yet implemented.
CIR with different scales (Samples, Distance, Time)
Indication of the correlation peaks used for the "FFT Window" determination in the CIR spectrum.
Welle.io is a Windows/Linux/MacOS/Android/Raspberry Pi compatible DAB and DAB+ broadcast radio decoder which supports RTL-SDR dongles, as well as the Airspy and any dongle supported by SoapySDR. It is a touch screen friendly software which is excellent for use on tablets, phones and perhaps on vehicle radio touch screens.
Thank you to Albrecht Lohofener, the author of welle.io for writing in and sharing his news about the release on welle.io version 2.
welle.io 2.0 Beta 1 released
I’m happy to announce the version welle.io 2.0 Beta 1. Since the first rtl-sdr.com post roughly two years ago (Mar 2017) welle.io became the leading open source DAB/DAB+ SDR. Many people are using welle.io in their daily life and gave a lot of feedback.
With all this feedback we started developing the version 2.0. Apparently, the biggest change is the complete redesign of the user interface (GUI). It changed from a dark design to a bright design and handles easily different screen resolutions and orientations.
Many users asked for a favorite list, automatic playing of last station and a mute button. Now these features are ready to test with the 2.0 Beta 1!
Another new feature is the settings menu where users can set the hardware receiver with all the necessary settings. This is more user friendly than the command line parameters.
For people with a deep technical interest we improved the expert mode a lot. In addition to the spectrum users can also view the impulse response, null symbol and constellation diagram, even at the same time! An experimental I/Q RAW file recorder as well as a debug output window is available for systems without a text console.
In the back-end we improved the multi-path behavior and started a source code refactoring to allow the code to be easily maintained. Great thanks to the people from the Opendigitalradio association (http://www.opendigitalradio.org/) which are actively contributing to this project.
Now it is possible to build a complete DAB/DAB+ system (transmitter and receiver) with open source!
As a result from this collaboration welle-cli is available. The main use case is to monitor DAB/DAB+ transmitters networks over the internet. Thus it has a HTTP API and includes a basic Web page which shows the features.
Over on GitHub user jj1bdx has just released a new tool called rtl_power-fm-multipath which can be used for estimating broadcast FM multipath distortion with an RTL-SDR. Broadcast FM multipath is caused when a signal is received from multiple directions due to it reflecting off and refracting through physical objects like buildings and terrain. As the reflected/refracted signals will be delayed it can cause echo like distortions in the RF signal which can cause issues like poor digital decoding, poor FM audio reception and ghosting in analogue video.
The multipath distortion estimation method works by measuring the ratio of the strength of direct/reflected radio waves which results in the desired/undesired (D/U) ratio. This measurement method was proposed by Komiya87 and JushinFM who both wrote papers in Japanese describing the method. In summary the methodology is:
Measure the maximum peak strength for +-50kHz spectrum of the target FM station
Obtain the maximum value (Lmax) and minimum value (Lmin) within the spectrum
Obtain the ratio of the maximum and minimum values L = Lmax / Lmin (note: Lmax and Lmin are real values (not in dB), and L must be > 1)
The estimated D/U ratio R = (L+1) / (L-1) (in the real value, not in dB)
The rtl_power-fm-multipath program is based on rtl_power and works by using rtl_power to record power measurements for 5 minutes, then sending the data to a peakhold function which computes the maximum power value for each frequency, and then calculations the distortion ratio.
Broadcast shortwave radio is not always archived for long at the station, so finding sound bites from interesting historical events can be difficult. We know that songs are of course recorded, but talk back radio, discussions in between music, news readings, weather updates, ads and pirate radio are all lost over time. Although these things may seem mundane now, future historians may be interested in listening in on this little slice of life.
Thomas' idea is to create a database of shortwave radio IQ recordings so that they can be archived for historical purposes. The project is called "The Radio Spectrum Archive" and has a website set up at spectrumarchive.org. To do this modern software defined radios like the RTL-SDR can be used to record a large bandwidth, however the problem is with data storage as IQ recordings can take up extremely large amounts of disk space.
Interestingly, it turns out that people have actually been making IQ recordings since the 1980's by connecting their shortwave radios to VCR tape recorders. In the modern day these VCR recordings can be digitized into an IQ file, and played back in software like HDSDR. In the video below Thomas demonstrates the playback of a digitized VCR radio recording from May 1 1986. You can hear some interesting news tidbits on the soviet cover-up of Chernobyl, the Challenger disaster and the launch of a new hurricane tracking satellite. If recording was more popular it would have been interesting to hear soviet radio during this time too.
In addition to archiving IQ files, Thomas has been releasing a podcast of curated historical audio recordings from VCR tapes, as well as modern recordings that may be of interest over at shortwavearchive.com.
We envision a future where one day these recordings could be automatically turned into text logs via advanced speech to text software, so they could easily be searched through.
The PantronX Titus II is a yet-to-be-released portable Android tablet based SDR that we've been following since 2016. The device will feature a 100 kHz - 2 GHz tuning range, and software that focuses on HF digital DRM decoding, as well as DAB on VHF.
As you might be aware, we have joined up with Fraunhofer to include their MMPlayer app standard on Titus–what a difference a professional decoder, for both analog, DRM(+), and DAB(+), makes! MMPlayer is full featured even including reliable one way file downloads with DRM.
We are attempting also to license HD to include on the app for North America, making a truly worldwide receiver. Some deficiencies in our version of Android have caused issues as well as MMPlayer. All of which have caused delays leading to some serious business decisions – as you can imagine. You are correct that broadcasters have made large orders that will be fulfilled first. There are units in the field testing and such and continuing resolution of the software issues.
One of the issues that folks seem to have a hard time understanding is that we can not just build a few hundred or even thousands of units. Our minimum run is 10,000pcs! To do that everything has to be 100% – including the software. We simply will not ship units that are not 100%. Titus works, MMPlayer works – its that last 5% that takes the most time to resolve. These facts preclude any incremental production attempts. All that being said, we are very hopeful that the first production run is ready by last quarter of this year.
Over on YouTube the web show Hacker Warehouse have created a video explaining wireless pagers and how RTL-SDRs can be used to sniff them. In the video host Troy Brown starts by explaining what pagers are and how they work, and then he shows how to decode them with SDR# and PDW. We have a tutorial on this project available here too.
Later in the video he shows some examples of pager messages that he's received. He shows censored messages such as hospital patient data being transmitted in plain text, sports scores, a memo from a .gov address claiming allegations of abuse from a client, office gossip about a hookup, a message about a drunk man with a knife, a message from a Windows server with IP address and URL, a message from a computer database, and messages from banks.
In the past we've also seen an art installation in New York which used SDR to highlight the blatant breach of privacy that these pager messages can contain.
Over on YouTube user Rob Fissel has uploaded a nice video that demonstrates the iBiquity HD Radio decoder working with an RTL-SDR. HD Radio is a terrestrial digital broadcast signal that is only used in North America. It is easily recognized by the two rectangular blocks on either side of a broadcast FM station signal on a spectrum analyzer/waterfall display.
For a long time it was thought impossible to decode due to the closed and proprietary nature of the signal format. But thanks to Theori who was able to reverse engineer and create an HD Radio decoder it has now become possible to decode this into actual audio that you can listen to. In some areas it is even possible to extract the weather and traffic data encoded into some broadcasts from iHeartRadio.
Rob's YouTube video demonstrates him downloading and setting up the HD Radio decoder, then receiving, decoding and listening to some HD Radio stations in his area.