[A-DX] Digital medium-wave test runs into trouble after dark

[Erik <erkubs@xxxxxx>]

Hier ein Bericht des Guardian über die BBC DRM-Tests auf Mittelwelle:

Year-long BBC trial positive on extra digital radio technology, but warns of problems with signal at night
Comments (2)
Buzz up! 
Digg it 
John Plunkett 
guardian.co.uk, Friday 22 May 2009 07.20 BST 
Article history


The BBC's year-long test of digital medium-wave radio proved
a hit during daylight hours but was a serious turn-off for its
band of volunteer listeners after sunset.

Digital medium wave, or digital radio mondiale (DRM) can offer
a more robust signal than digital audio broadcasting (DAB) radio
and can be broadcast for much longer distances. It was thought
that DRM could be used to fill some of the gaps in the existing
UK DAB transmitter network.

The trial, held in the south-west of England with a frequency
used by BBC Radio Devon and codenamed Project Mayflower, revealed
that the area covered by the DRM signal was much bigger than the
one covered by analogue AM.

Reception during daylight hours was good and most panellists
rated the audio quality as comparable to FM, but not as good as DAB.

However, at night there were serious problems with reception, with
the signal breaking down entirely in some cases. The BBC said the
problem could be solved, but would require it to replan its
transmission network or build more powerful transmitters.

"For the most part, the panel's reaction to DRM was positive,"
said Tom Everest, the senior distribution manager at BBC Distribution,
writing on the BBC's Radio Labs blog.

"We found that the area we were able to cover during the day was
very much bigger than the area we could cover with the old AM
signal that had been there previously.


"But, on the downside, some of our panel experienced problems at
night ? and we saw these effects in our measurements as well. The
problem will be familiar to many listeners to medium wave ? at
night, changes in the atmosphere mean that signals from distant
transmitters reach our shores more easily. On medium wave, you
might hear this as cross-talk: a foreign voice underneath what
you're trying to listen to, or the occasional 'splat' of another
transmission.

"The issue we came across with DRM is that this interference
causes the radio to stop decoding the signal: sometimes only
momentarily, sometimes for a while longer. So rather than listening
through the interference, it's like all digital systems: you either
get it (and so get it at a consistently high quality) or you don't
get it at all.

"So while most of the panel continued to listen without experiencing
any problems, some of them found they were only served during the day
and had patchy coverage at night. And of course this problem became
worse as the hours of daylight shrunk during the autumn; so by winter,
some were beginning to experience poor reception in the late afternoon."


DRM is used by the BBC World Service on some of its European medium

wave and short wave transmissions but there are no plans at the moment
to extend its use in the UK beyond the 12-month trial.

The radio industry, the media regulator Ofcom and communications
minister Lord Carter have thrown their weight behind DAB as the broadcast
transmission technology of choice for digital radio in the UK.

But a switchoff of the analogue radio signal still appears some way off,
with the Ofcom chief executive Ed Richards warning yesterday that DAB
had to become financially viable before talking about a digital switchover
date, which he said would be "meaningless" if the industry was not ready for it.

Everest said: "DRM still has potential: indeed, considerable potential
where it remains of great interest to our colleagues at the BBC World
Service and others, and it might have an application at home as well.

"But our trial has shown that the migration from analogue to digital
at many of the frequencies which are currently allocated to the UK
has its own set of challenges that would need to be addressed."


direkter Link zum Artikel:

http://www.guardian.co.uk/media/2009/may/22/bbc-trial-digital-radio-mondiale-medium-wave



73

Erik

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