Tutorial DAB DABplus

Tutorial: DAB and DAB+ digital radio

What it is. DAB and DAB+ are the digital radio standards of Europe, Australia and other regions. One transmission, called an ensemble, carries many stations (DAB uses MP2 audio, DAB+ uses AAC) together with station names, scrolling text (DLS), slideshow pictures, announcements, Journaline text pages and a transmitter identification. In OnAir you pick a channel, the ensemble locks, and you play a station.

What you need

• A radio that tunes Band III (about 174 to 240 MHz). An RTL-SDR works; an ensemble is 1.536 MHz wide, so 2 Msps is enough (the source field shows the rate). See Supported radios.
• A Band III antenna (a telescopic whip trimmed for about 200 MHz works; a proper DAB or VHF antenna is better).
• A channel. The frequency database lists all 38 Band III blocks: 5A at 174.928 MHz, 5B at 176.640, 5C 178.352, 5D 180.064, 6A 181.936 ... up to 12D at 229.072, 13A 230.784, 13B 232.496, 13C 234.208, 13D 235.776, 13E 237.488, 13F 239.200 MHz (1.536 MHz wide). Many countries use blocks 10 to 13 only; the Scan tab finds the ones that carry an ensemble.

Before you start

• Keep the gain moderate. An overloaded Band III front end, often from nearby FM and TV transmitters, produces dropouts that look like a weak signal.
• A short clean cable and an antenna in the clear matter more than gain.

Step by step

1. In the mode list open Broadcast radio and choose DAB / DAB+ (second line Digital radio).
2. Open the Scan tab and press the scan button. It tunes through the 38 Band III channels (5A to 13F) and lists the ensembles with their stations. About a minute.
3. Pick an ensemble, or choose a channel from the Channel drop-down in the tuner, and press Start.
4. When the ensemble locks, the Ensemble tab lists its services and sub-channels.
5. In the Radio tab click a station to play it. The Player section shows the station name, the text (DLS), the logo and the slideshow picture, and has Volume.

What you should see

• A wide, flat block 1.536 MHz across.
• The status bar shows the lock state and signal quality.
• The Stations list fills in as the FIC arrives (a second or two).

Reading the screen

Tab	What it shows
Radio	Stations, the player, the recording controls, announcement handling.
Ensemble	Services and sub-channels with bit rate, protection and codec.
Map	Transmitters identified by their TII code (see below).
Analyzer	The ensemble as a tree, an audio spectrum, the latest picture and the main service channel allocation (how many of the capacity units are used).
Journaline	Text and menu pages (ETSI TS 102 979) when the ensemble carries it.
FIC	The fast information channel: every FIG, with a tree and a type list.
Scan, History	The ensemble scanner and the signal log.

Options and settings

• Record: save the audio of the playing station; choose a format and tick Label log to write a log of the text labels. Press Stop to finish.
• Switch to announcements: lets an announcement (traffic, news, etc.) interrupt the station; types... picks which; Back to the station returns.
• Follow to other frequencies: follow a service to another ensemble or FM frequency when the signal drops (check the panel for the exact options).
• Station logos from the service information are shown.

The transmitter map

Every transmitter of a DAB network sends its own identification (TII: MainId / SubId) in the null symbol. OnAir lists the transmitters you receive with their relative strength. With a transmitter list (dab-transmitters.csv in the data folder: eid,main,sub,lat,lon,name,country,power_kw), or after pressing download in the Map tab for your country, they appear on a map with distance and bearing; set your antenna position in the ADS-B tuner for distances.

Troubleshooting

• No ensemble found. Wrong band or antenna. Run the scan; check the antenna; try other positions.
• Locks, drops out. Overload or a weak signal. Reduce gain; improve the antenna.
• Audio breaks up in bursts. Reed-Solomon and the error-corrected DAB+ superframes need a minimum SNR. Watch the counts.
• A station stays silent. Check the codec in the Ensemble tab: DAB (MP2) and DAB+ (AAC-LC/HE-AAC) are both decoded; HE-AAC with SBR/PS depends on the audio library in your build.
• No Journaline tab. It only appears when the ensemble carries Journaline.

Tips

• Used and checked on real broadcasts.
• The same ensemble can be on different channels in different regions; use the Map and Analyzer tabs to learn your area.

Legal and privacy notes

Listening to broadcast radio is legal almost everywhere. The transmitter database is community data; the app does not upload your position unless you choose the opt-in server (see Privacy).

Under the hood

DAB (ETSI EN 300 401): transmission mode I (1536 carriers, 1.536 MHz), DQPSK, a null symbol and phase reference for synchronisation, the fast information channel (FIC) for multiplex configuration, and the main service channel (MSC) with convolutional coding and time interleaving. DAB+ (ETSI TS 102 563) uses AAC audio in super-frames with Reed-Solomon coding. Text is carried in PAD (DLS); pictures use MOT (slideshow).

Related

Mode page: DAB / DAB+ | DAB+ digital radio (short version) | FM | Supported radios | Troubleshooting