News story about an admission by UK media regulator Ofcom that the transmitter powers of DAB digital radio multiplexes had been set too low to ensure robust reception, a problem requiring significant investment in additional transmitters to correct, written by Grant Goddard in July 2006 for The Radio Magazine.

1. NEWS: OFCOM ADMITS DAB
DIGITAL RADIO TRANSMITTER
POWERS WERE SET TOO LOW
FOR ROBUST RECEPTION,
REQUIRING MORE INVESTMENT
by
GRANT GODDARD
www.grantgoddard.co.uk
July 2006

2. Significant additional investment will be required from DAB digital radio
multiplex owners in order to improve the quality of reception for listeners to an
acceptable level, particularly in cities. Ofcom has admitted that the transmitter
strengths originally allocated to DAB radio stations by its predecessor, The
Radio Authority, have proven insufficient to provide reliable reception in
buildings and on portable devices. As a result, the powers of existing DAB
multiplexes will have to be increased, and new repeater transmitters will need
to be added within cities to improve reception in homes and offices.
Grae Allen, manager of digital distribution at EMAP Radio, explained that “[the]
Wiesbaden 1995 [radio conference] and all the other DAB planning dealt with
mobile reception – in-car and portable outdoors. It made assumptions about
aerial heights being just above ground level and, to provide good service to
99% of locations, the conclusion was that it required 58dbųV per metre to
maintain that quality of service, and it made some assumptions about the
performance of receivers and aerials.”
In practice, he said, “some receivers do not quite live up to expectations –
some have lossy aerial systems and suffer from self-noise.” Allen said that this
year’s European Regional Radio Conference “is moving DAB to become a truly
indoor medium. The new planning model has around 10dbųV higher field
strength than was envisaged in the original plan.”
With DAB now also being used to carry TV services, Allen said: “That raises a
question. We are seeing increasing numbers of hand-held receivers, such as
the BT Movio receiver, that do not have an aerial of any significant size. So, in
some areas, we may have to go to higher field strengths to deliver to
handhelds indoors. So how are we going to improve the coverage?
Unfortunately, the people who fill in RAJAR diaries don’t tend to live in large
numbers alongside the sheep in the fields [where DAB transmitters are mostly
located]. They live in the cities and the urban sprawl, and that’s where we need
to deliver the high field strengths that are required for the types of receivers
that are becoming popular, and the level of service that is expected. In the
future, as I envisage it, we will see a need to put more and more [transmitter]
sites inside the cities in areas where we actually need significant power where
people are living and working.”
Mark Thomas, head of broadcast technical policy at Ofcom, admitted that the
original power allocations had proven too low: “The Radio Authority had no
data of how [DAB] receivers performed, so it had to make some very broad-
brush assumptions. More recently, now that we have a lot of receivers in the
market and we can see how they behave, an industry group has been working
under Ofcom’s chairmanship for the last two years to look into the issue in
more detail and come up with some modus operandi for new transmitter sites.”
Thomas explained that it had become evident to the group that DAB receivers
suffer Adjacent Channel Interference [ACI] not only from the immediately
adjacent channel, but also from several channels above and below the one
being listened to. He admitted: “This means that the issue is more pervasive
for the industry in developing new transmitters than we might have hoped for.”
News: Ofcom Admits DAB Digital Radio Transmitter Powers Were Set Too Low For Robust Reception, Requiring
More Investment page 2
©2006 Grant Goddard

3. News: Ofcom Admits DAB Digital Radio Transmitter Powers Were Set Too Low For Robust Reception, Requiring
More Investment page 3
©2006 Grant Goddard
Allen added: “ACI is a very regrettable feature [of DAB] and, if it had just been
[one channel] adjacent as a problem, we could have managed it more readily.
When it’s a multiple adjacency problem, it gives us a much greater challenge.
However, it’s one we just have to live with. The Ofcom approach is that the
industry co-operates between commercial operators with each other, and with
the BBC, in identifying the sites that will improve field strength of DAB services
to consumers and will also avoid the issues surrounding ACI. ACI also adds to
the investment challenge that all of this spectrum development is building.”
[First published in 'The Radio Magazine' as 'More DAB Investment Required', #746, 26 July 2006]
Grant Goddard is a media analyst / radio specialist / radio consultant with thirty years of
experience in the broadcasting industry, having held senior management and consultancy
roles within the commercial media sector in the United Kingdom, Europe and Asia. Details at
http://www.grantgoddard.co.uk