BBC local radio on DAB - transmitter information
BBC local radio services on DAB digital radio are transmitted by commercial broadcasting operators. This is because the BBC's digital multiplex is already used to full capacity for BBC national services.
Some BBC local radio services are not yet available on DAB because they are in areas where a commercial licence has not yet been awarded so there is no commercial operator. Commercial licences are awarded by the regulator, Ofcom.
More details
http://www.bbc.co.uk/reception/transmitters/radio/digital_local_radio.shtml