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Can DRM Work in High Latitudes?
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Proposed Tests in Alaska, to Be Funded by the Defense
Department, Generate Curiosity |
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by Leslie Stimson, 7.02.2008
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Leslie Stimson is the News Editor and
Washington Bureau Chief for Radio World.
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DELTA JUNCTION, Alaska
It’s just one test of the Digital Radio Mondiale
technology, in one very big state. But could the results
lead to a new kind of regional radio service in which
U.S. broadcasters could use shortwave to reach listeners
within the United States?
It’s too soon to tell. However the filing of an
application for an experimental license here to transmit
a digital radio signal on three shortwave channels using
DRM technology, potentially funded by the Defense
Department, has raised the curiosity of some observers.
The president of Digital Aurora Radio Technologies has
asked the FCC to approve a two-year experimental
authorization to test statewide transmission of DRM in
the 5, 7 and 9 MHz shortwave bands.
(click
thumbnail)
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An antenna placement graphic from
Digital Aurora Radio Technologies.
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In its FCC application, Digital Aurora states: “Pending
this [FCC] authorization and funding availability,
initial tests will likely be tasked and funded by the
U.S. Government Department of Defense, Joint
Electromagnetic Technologies Program.”
Details of that program are said to be classified. An
unclassified 2002 budget document posted on the Web site
www.js.mil
said the JET Program “supports the Defense Community in
general with a particular emphasis on the requirements
of Special Forces and Intelligence in their Weapons of
Mass Destruction (WMD), Deep Underground (DUG) and
Transnational Threat (TNT) missions. This is in the form
of basic research and applied RDT&E in HF/VLF/ELF
communications and signaling, advanced forms of optical
communications, underground imaging and advancing our
understanding of the propagation of all forms of RF
communication.”
DRM is an open standard, designed for the digitization
of the frequencies below 30 MHz: long-, medium- and
shortwave. It’s used mostly on shortwave frequencies in
European and other countries.
An extension called DRM+ is in the works. The DRM
Consortium — comprising broadcasters, associations,
network operators, manufacturers, research institutions,
regulatory bodies and others — plans to expand the
system to broadcasting bands up to 120 MHz.
Application pending
On its application, the company said the goal is to
assess performance of digital terrestrial shortwave
broadcasting and serve the entire state.
“In general, the population of Alaska is underserved
with respect to the ability to have a high-quality,
reliable public radio audio service,” the company wrote.
“This is especially true for sparsely populated areas of
the state,” though that statement discounts public
stations, which cover much of Alaska.
Company President Whit Hicks declined comment for this
story, saying he did not want to “presume” FCC approval.
An Internet search turned up no prior information on the
company, which submitted the application in late April.
The application remained pending in June.
A source close to the issue said the request was not
controversial and that approval of the experimental
license could come this summer.
That timeframe is key to Digital Aurora, because many of
the submitted measurements regarding sunspots could
change as the year goes on. Also, the company needs to
build an antenna in Alaska, where severe weather allows
a short time-period for construction and accessing the
site.
It plans to construct a crossed dipole antenna with an
overall height above ground of 20 meters, roughly 66
feet.
According to the application, the DoD-funded test would
use existing 100 kW Continental transmitters designed
for an Over-the-Horizon radar transmitting system
formerly used in Cold War broadcasting and a digital
signal generator operating from the Delta Junction area,
some 130 miles southeast of Fairbanks. Other than that,
the DoD connection is unclear.
One transmitter producing output average power of 20 kW,
in concert with an antenna that sends most of its
radiated power into Alaska, should be able to be
received throughout the state, the company believes.
However, Digital Aurora needs to determine if such
reception can be accomplished during times of high and
low solar activity.
DRM has been tested extensively in latitudes lower than
those that include Alaska. This experiment, the company
said, will help to fill a gap in assessing the
performance of digital terrestrial shortwave
broadcasting in a difficult high-latitude environment.
Antenna spec
The company hopes also to determine what transmission
power levels will produce a reliable signal that can be
received on DRM radios. Digital Aurora also hopes to
determine an antenna specification to deliver a signal
statewide.
Digital Aurora proposes to perform propagation,
signal-to-noise ratio, field strength, bit rate and
audio quality measurements over a two-year period,
according to the application.
“Compared to an ordinary analog shortwave signal, the
DRM signal can operate with the same coverage reliably …
in a 10 kHz channel using a transmitter power level
approximately one-fifth of that needed for the analog
signal,” states Digital Aurora in the application. The
FCC assigned call sign WE2XRH.
DRM is designed to fit in with the existing AM broadcast
band plan, based on signals of 9 kHz or10 kHz bandwidth,
according to the Web site
www.drm.org.
It also has modes requiring only 4.5 kHz or 5 kHz
bandwidth, and modes that can take advantage of wider
bandwidths, 18 kHz or 20 kHz.
The cost of the test was not listed on the application,
which stated that utilities and space would be leased
and the existing government-provided transmitters left
in place when the experiment ends.
Digital Aurora believes it can contain most of the
signal within Alaska with little spillover into Canada.
To avoid causing interference it plans to stay at least
two adjacent channels away from any channels used by
international broadcasters into western Canada.
The two-year test proposal appears notable because it
would be the first time DRM has been tested in the
United States at such high latitudes, and because the
company is proposing to broadcast using digital
shortwave technology to an entire state.
Without knowing more about Digital Aurora’s intentions,
it’s hard to know the practical implications of the
test, observers said.
While engineering observers laud DRM technically, they
said it’s hard to make a practical business case for DRM
on shortwave in this country, noting that several
countries are abandoning shortwave and turning to less
expensive programming distribution platforms such as the
Internet and FM.
“What new audience that isn’t presently served will be
covered and at what cost per person?” asked one
observer.
Several sources raised the issue of DRM receiver
availability. Indeed, in a separate paper presented at
the NAB Show on standards and codecs for digital radio
in Europe, Fraunhofer’s Olaf Korte states that Digital
Radio Mondiale still lacks affordable mass-market
receivers. He added that the use of DRM in mass markets
like Russia and China would help to solve that issue.
In this country, shortwave broadcasters are restricted
from transmitting to listeners within the United States.
It would be interesting to see if successful results
make the case to change that rule, one observer noted,
because such a service could help “under radioed”
populations, like Alaska.
And going even further, could successful results lead
one day to testing DRM on the AM band here, considered
by some to be a logical choice to challenge IBOC?
Sources said no, that circumstances surrounding this
test are so unique they don’t support that
extrapolation.
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