Digital TV Radio scanning and measurement



DAB Explanation (Digital Audio Broadcasting)



Frequencies :

DAB/DAB+ can use VHF frequencies in VHF band around 50Mhz and 200Mhz. There is also some frequencies available around 1450Mhz.
As DVBT multiplex, each frequency can support many Radios at the same time.
It uses synchronous technology, which allows to use same frequency for transmitter sending same multiplex in the same area. These frequencies are named "Blocks" and are named like "2A". Here is the list of blocks:

2A47.936 MHz2B49.648 MHz2C51.360 MHz2D53.072 MHz
3A54.928 MHz3B56.640 MHz3C58.352 MHz3D60.064 MHz
4A61.936 MHz4B63.648 MHz4C65.360 MHz4D67.072 MHz
5A174.928 MHz5B176.640 MHz5C178.352 MHz5D180.064 MHz
6A181.936 MHz6B183.648 MHz6C185.360 MHz6D187.072 MHz
7A188.928 MHz7B190.640 MHz7C192.352 MHz7D194.064 MHz
8A195.936 MHz8B197.648 MHz8C199.360 MHz8D201.072 MHz
9A202.928 MHz9B204.640 MHz9C206.352 MHz9D208.064 MHz
10A209.936 MHz10B211.648 MHz10C213.360 MHz10D215.072 MHz
11A216.928 MHz11B218.640 MHz11C220.352 MHz11D222.064 MHz
12A223.936 MHz12B225.648 MHz12C227.360 MHz12D229.072 MHz
13A230.784 MHz13B232.496 MHz13C234.208 MHz13D235.776 MHz
13E237.488 MHz13F239.200 MHz



DAB block


One DAB block can handle many Radios, each radio is independent. The total capacity of a DAB block is 864 "capacity units".
The provider of the block need to ensure that the summ of each radio capacity is not higher than 864 CU.
Each Radio choose its audio bitrate. The radio can add some datas (for ex traffic datas) on a new PID channel.
The DAB can also add datas on special reserved and normalized part, as for ex "radiotext (DLS)" with the current title and the "slideshow" who can transmit pictures.

The radio need also to choose it's transmit level protection. This protection is adding some datas on transmit part, to allow reception error cancelation in receiver.
The more highest is the protection, better will be the reception. Each radio in a DAB block can have different protection level.

The number of "Capacity units" of one radio is related to the audio bitrate, data bitrate, datas radiotext and slideshow and also by the protection level.
The DAB tables of Digitalbitrate have all these informations, and a multiplex graph is displaying the room used by each radio in term of capacity units.




AUDIO Encoding


The DAB is using MPEG1 layer 2 for audio encoding.
The DAB+ is using AAC to decrease bitrate needed and to increase sound quality.
The AAC has some audio encoding optimization features:
SBR: spectral band replication
PS: Parametric stereo
The Digitalbirate table is showing id SBR and/or PS are enabled.