switched on. Initially, this occurred four weeks after stage one, but starting with the switchover at Mendip in April 2010 onwards, this gap was reduced to two weeks. Three multiplexes (BBC A, D3&4, BBC B) are for public service broadcasting and are broadcast from all transmitter sites. They contain around 25 TV channels, half a dozen radio stations and half a dozen text/interactive services. These include all the television channels from the BBC, some from ITV and Channel 4, Channel 5 and S4C (in Wales only). The other three multiplexes (SDN, Arqiva A, Arqiva B) are broadcast from main transmitter sites only and are operated by their respective commercial licence-holders. To reflect the slightly changed roles, the multiplex names were also changed: Post-switchover The adoption of the technically superior DVB-T format occurred in each region at the date of switchover. This resulted in no reception for viewers with older '2k' only equipment, such as former ONdigital/ITV Digital boxes, and other incompatible IDTVs and set top boxes. In the Meridian and Anglia regions, transmitters formed a single-frequency network when they were converted to all-digital operation. Alternative post-switchover multiplex designations were used on internal documentation by the BBC switchover contractor Arqiva, but changing the designations of the multiplexes requires changes to legislation and to the multiplex licences issued by Ofcom and is not in the current draft. When digital switchover was complete, two new sub-bands of the UHF spectrum were clear (frequencies corresponding to channel ranges 31–40 and 63–69), leaving only channels 21–30 and 41–62 for digital television multiplexes. This "digital dividend" required millions of homes to upgrade their aerials to the wideband type to receive some or all of the Freeview multiplexes. This spectrum is useful because of its trade-off between bandwidth and range. Following a consultation, in September 2011 Ofcom stated that an auction for the 600 MHz band will most likely lead to channels 31–37 being used for three new TV multiplexes; a reference transmission plan assumes two frequencies would be multiple-frequency networks, and channel 36 would be used as a national single-frequency network. The remaining reallocated frequencies can be re-used for other services, for example the provision of: Mobile Television services wireless (mobile) broadband services wider coverage for advanced services in remote and rural areas more multiplexes carrying more channels high definition (HD) services The clearing and re-allocation of these channels of the spectrum for other services caused