RTÉ WILL cease broadcasting on medium wave (MW) next Monday just as it expands its digital radio service to cover almost half the population.

This week the State broadcaster extended its trial of digital radio technology to Cork and Limerick, making it available to 44 per cent of the population.

Based on the Digital Audio Broadcasting (DAB) standard, the trial broadcasts include seven new RTÉ digital radio services including a children's radio service and a dedicated news headline channel, as well as content from commercial broadcasters.

However, some industry observers have wondered if the State broadcaster is backing the right technology, particularly in light of its statutory obligation to broadcast to the Irish abroad.

Brian Greene, a digital media consultant, says "killing MW to fund DAB is a crazy move by RTÉ" because DAB has a short range while MW can be picked up by listeners in the UK.

For its part, RTÉ maintains that its services are available on the Sky Digital platform and over the web.

According to JP Coakley, RTÉ Radio's head of operations, the broadcaster will save €1.5 million in annual running costs by shutting down MW, of which €1 million relates to electricity costs.

Coakley says the MW infrastructure had "an immediate need to inject circa €2.4 million in capital as the installation is reaching the end of its natural life".

The savings will not just fund DAB but a number of online projects, improvements to FM broadcasting and additional programming resources, according to Coakley.

"That said, national DAB has to stand as a separate business and rationale - it's about an industry moving together to provide the next generation of radio to the listener, rather than just what RTÉ can fund on its own," says Coakley.

The replacement that RTÉ is proposing for MW is long wave (LW). RTÉ installed a new LW transmitter in 2007, which also supports broadcasting in a newer digital technology called Digital Radio Mondiale (DRM).

However, Greene maintains that because DRM is more efficient, it has to be broadcast at a lower power. As a result, an Algerian radio station also broadcasting on LW252 is causing interference with RTÉ's signal.

Coakley concedes Tipaza in Algeria interferes with LW252 at night in London and parts of southeast England, but points out that MW is not available at all in London.

This month Greene wrote to Cathal Goan, director-general of RTÉ, raising questions about the broadcaster's transmission planning and move to digital.

He also questions just how successful DAB has been in the UK, despite the fact that well over five million receivers have been sold there and the format dominates sales of kitchen, portable and clock radio sales.

He says DAB is now 23 years old, having first been demonstrated in 1985. It uses lower quality MPEG-2, compared to the more efficient MPEG-4 used by DRM and newer digital standards such as DAB+, and has yet to be a "roaring success" in the rest of Europe.

In many ways RTÉ has made a pragmatic choice by choosing DAB given its installed base in our largest neighbour and the spill-over of retailers from Britain that are selling DAB receivers in Ireland.

"We see DAB and DRM as complementary in the same way that we see FM and LW as complementary," explains Coakley. "They do different things. One gives a good quality domestic service, the other is poorer quality but has a greater reach."

Coakley believes, however, that DRM is still unproven. "It is still very difficult to find reasonably priced sets and there's no new content available."

Digital radio primer: the facts

RTÉ is one of the main players in an industry grouping giving trials to Dab (digital audio broadcasting) in Ireland.

RTÉ began a public digital audio broadcasting trial in the first half of 2007 and the broadcasts are now available to 44 per cent of the population.

An independent industry group, digitalradio.ie, has been formed to smooth the transition to digital radio and to promote its uptake.

Dab receivers automatically tune into available stations and there is much less crackle and hiss compared to FM.

Additional information such as the artist and song title can be embedded in the Dab broadcast and displayed on the receiver's screen.

Companies such as Virgin are giving trials to Dab for multimedia services including the delivery of TV and music downloads to mobile handsets.