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Ofcom publishes Technical Feasibility Study for DAB digital radio coverage improvements

last updated 22:51

Ofcom has published a technical feasibility study for the Goverment containing a DAB digital radio coverage plan to support any future potential digital radio switchover.

The report covers the definition of geographical areas, based on the editorial coverage areas of existing FM radio services, within which DAB coverage should be replicated as well as technical planning parameters used to predict acceptable levels of FM and DAB indoors, outdoors and in cars. The report also shows an illustrative example of how Manchester's local DAB multiplex coverage could be increased by adding additional transmitter sites around the "Manchester editorial area".

The BBC and Arqiva provided supporting documents for the report showing how national BBC and Digital One multiplexes would increase coverage. The BBC's national DAB network now covers over 90% of the population, however the BBC admitted that it was struggling to increase coverage beyond this because of the self-interference that a DAB single frequency network (SFN) causes when transmitters more than 74km apart cancel each other out. This technical constraint of DAB continues to be a problem in East Anglia, where the BBC proposes to launch new DAB transmitters in carefully selected sites where transmitters more than 74km away cause the least interference. The BBC says that it is looking at possible ways in which interference could be mitigated.

Arqiva/Digital One does not have such a problem, as coverage is well below the BBC's, so that there are fewer transmitters covering less of the population producing less DAB self-interference issues. The Arqiva annex to the report revealed that there was more commercial resistance to expanding DAB coverage of the national multiplex carrying Classic FM, Absolute Radio, Talksport and others, stating "It should be noted that several of Digital One’s customers believe the current main network of 133 transmitters includes sites which, according to the radio station’s business criteria, are already non-economic." 

According to the proposals for coverage expansion, only around 5% more of the population would come under the coverage of Digital One. It would seek to improve Classic FM digital coverage in urban areas and along major roads, but would not commit to replicating FM coverage on sparsely populated hillsides, stating that some of that type coverage is a by-product of having to deliver a strong robust signal in the direction of  urban areas, with Classic FM never having intended to cover these remote areas.

Ofcom admitted that if "Government decides to proceed with digital radio switchover a more detailed planning exercise will be needed, in collaboration with multiplex operators and other stakeholders, to optimise the exact number, location and power of additional DAB transmitters needed to replicate FM coverage in the most practical and cost effective way."

Recommended reading:
Read the full report, see all the charts and the annexes at the above Ofcom website link.
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