Open formats point way for small-scale DAB

Small-scale DAB stations could be a way ahead for community and smaller local radio station transmission, according to an Ofcom report. It is based on findings from trail that ran in Brighton between September 2012 and January 2013.
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Small-scale DAB stations could be a way ahead for community and smaller local radio station transmission, according to a report published by UK broadcast regulator Ofcom. The research document was based on findings from an experimental multiplex that ran in Brighton between September 2012 and January 2013. The trial was set up and funded privately by Rashid Mustapha, senior associate with Ofcom's Spectrum Policy Group, who worked on it in his spare time. In the opening summary to the report, Small Scale DAB - The potential for lower-cost transmitting stations in support of DAB rollout (http://stakeholders.ofcom.org.uk/binaries/research/radio-research/Software-DAB-Research.pdf), Mustapha writes that "As no similar study had previously been carried out, the test was a valuable exercise to inform policy makers of the practicalities of low cost DAB solutions when used to serve small areas, particularly from a single transmitter." The UK government is currently considering a switchover to digital radio but retaining some analogue FM frequencies for smaller-scale local and community services. Mustapha argues that after the remaining patents for the Eureka 147 standard for DAB (digital audio broadcasting) expired in January this year it is now the first free and open digital radio format. This, combined with the growing trend for Software Defined Radio (SDR), Mustapha says, gives the potential for engineers to develop their own lower-cost modulators and use them in conjunction with open source audio source encoders and ensemble multiplexers. The test transmissions ran under an Ofcom Non-Operational Test and Development licence and were based on an experimental multiplex running from a PC with a custom version of xubuntu, which is derived from the Debian Linux operating system. A major concern was Adjacent Channel Interference (ACI) involving existing DAB transmissions. Five different digital radios were used to receive the signals but no ACI was detected. The transmission was further tested using a Radioscape DAB field monitor (pictured), which measures field strength and signal to noise ratio. The report concludes that small-scale DAB could be way of transmitting local and community stations in the future, with SDR for multiplexing and transmission able to produce good coverage and quality "at costs that are near to parity with a FM transmitter system carrying a single service". An Ofcom spokesman commented that it was still "early days" for this technology and no regulatory framework had been discussed. Similarly, he added, it was not yet clear if changes in legislation would be necessary. www.ofcom.org.uk

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