FACTS AND FIGURES
Some of the latest technical facts and figures about Digital Swichover...
After analogue switch off there will be six multiplexes (muxes), just as there are today, but they will be designated slightly differently, as follows:
These will roughly equate to the six current muxes, the main exception being that Ch5 and (in Wales) S4C will move into a shared PSB mux with the BBC.
It is now "anticipated" that the post-switchover transmission mode for all six multiplexes will be 64QAM modulation (2/3 rate) with an 8k FFT size.
RE-ENGINEERING THE NETWORK
It is understood that most main TV sites will be fitted with new main transmitting aerials, feeder cables and transmitters. In addition, most main sites will also have fully redundant reserve DTT aerials.
Most visibly at Blackhill, Caldbeck and new replacement masts will be constructed. Some other sites - including Wenvoe, Sutton Coldfield and Divis - require mechanical strengthening work. To this end, work on a temporary mast began in Autumn 2008 at Wenvoe to allow the existing mast to be modified 'cold'.
MORE ROBUST SIGNALS
In order to maintain reception protection 99% of the time, some digital transmitters might ultimately run at just 4dB below current analogue levels. (Post-DSO most services will be at -7 or 10dB below current analogue levels).A likely contender is Rowridge, it suffers interference from the continent during 'lift' conditions. To povide more robust reception two ideas are under consideration.
Other south east sites are under consideration for a similar scheme, notably Dover and Sudbury.
All muxes will be 64QAM, probably at 8k. 8k working is necessary for SFN (single frequency networks) and this use will be brought in at DSO from 2011 in East Anglian and Southern areas where new sites will be built and SFN will be necessary to reduce the effect of interference from European transmitters.
2-4 weeks before analogue shut down day at a given site, one of the 4 analogue transmiters will be shut down resulting in the closure of the BBC2 analogue service, which would be replaced by the high power BBC-A digital multiplex.
2-4 weeks later BBC1, ITV, C4 and if applicable, Ch5 will also shut down, along with the low power DTT muxes 2, A, B, C and D and would be replaced overnight by PSB-2, PSB-3, and COM-4, COM-5 and COM-6.
The night each main station is switched over, all of its dependant relays will also be switched.
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