INSTRUCTIONS FOR THE PREPARATION OF A FINAL TYPESCRIPT

HD-RADIO: REAL WORLD RESULTS IN ASIA
Charles W. Kelly, Jr.
Broadcast Electronics, Inc., USA
ABSTRACT
Digital FM Radio is going on the air worldwide – throughout the Americas as well as in Europe
and Asia. Since radio is a mobile media, what are the results in terms of mobile listening? How
does HD Radio perform in heavy multi-path areas, and in weak signal areas? What are the
ramifications of adjacent channel interference and in conditions of serious over-modulation as is
sometimes practiced in Asia?
INTRODUCTION
HDRadio is the only current digital radio solution which operates in the existing FM band. It allows
the transmission of the existing unchanged FM analog signal along with digital subcarriers which
provide CD quality audio – as well as the possibility of multiple digital channels. Both the
conventional FM analog signal and the digital sidebands fit within the typical spectral mask
allocated for FM stations.
As of July 2006 – Digital HD Radio has been on the air in over 900 stations throughout the US,
Mexico, Brazil, France, Australia, New Zealand, Philippines, Thailand and Indonesia.
FM TECHNICAL DESCRIPTION
FM IBOC is an OFDM (Orthogonal Frequency Division Multiplex) system which creates a set of
digital sidebands each side of the normal FM signal. The combined FM and IBOC signal fits in the
same spectral mask as is specified for conventional FM. The system allows for growth towards
eventual full utilization of the spectrum by the digital signal in three steps: Hybrid, Extended
Hybrid, and Full Digital.
FIGURE 1 – FM HDRADIO HYBRID MODE
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The Hybrid mode provides 100kbps data throughput, 96kbps for audio, and 4kbps for ancillary data
(song title/artist). This allocation is adjustable. This mode supports Stereo Analog and SCA / RDS.
Digital subcarriers are 20dB below analog.
FIGURE 2 – FM HDRADIO EXTENDED HYBRID MODE
The FM Extended Hybrid Mode provides 151kbps data throughput, 96kbps for audio, and 55kbps
for ancillary data (song title/artist). This allocation is adjustable. This mode also supports Stereo
Analog and RDS. Again, the digital subcarriers are 20dB below analog.
FIGURE 3 – FM HDRADIO FULL DIGITAL MODE
In the FM HDRadio Full Digital Mode, no analog signal remains. This mode provides 300kbps data
throughput, which may be allocated as desired.
REAL WORLD RESULTS
While specifications and drawings are useful, what’s most important is results, what the listener
hears through the wide range of signal environments and receivers in use. What follows then, is
results of coverage tests in many different environments.
JAKARTA, INDONESIA
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Radio Bahana / Prambors recently hosted HD Radio tests in their station in Jakarta. The main
station was broadcasting with 5kW, and the digital was operating with a lower antenna with less
gain – at 100W.
Here is the actual coverage as measured with a JVC car receiver driving around Jakarta:
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Bangkok, Thailand
RNT Television in Bangkok has purchased and HD Radio transmitter, and it operates in association
with an existing 5kW analog transmitter. Here is the approximate coverage with the 50W of HD, 8
element CP antenna at 140M:
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ADELAIDE, AUSTRALIA
Tests were performed in Adelaide, Australia recently – on a 10kW FM station. Here is a plot of the
measurements:
The hill leading into Victor Harbor,
over 50KM south of Adelaide was
the first spot where digital coverage
was lost. Bear in mind that the digital
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power feeding the antenna was only 100 watts. Digital coverage was also noted in an underground
parking known for poor analog FM reception for the host station.
AUCKLAND, NEW ZEALAND
Tests were performed in mid-2005 in Auckland, New Zealand. The station was given a test licence
and installed on the Skytower.
The transmitter was operating at 37 watts analog and 0.37 watts of digital power to a single bay
antenna mounted part way down and on the side of the Skytower.
Here is a map of the greater
Auckland area. The red colored
area is the approximate metro
area, encompassing 900,000
residents, and the yellow line is
the measured digital coverage.
The white dot at the center is the
Skytower.
OVERMODULATION
During the tests in Auckland,
questions were raised regarding
the tolerance of the digital
sidebands to overmodulation of
the host analog station. The
analog modulation was increased
for a few minutes to 200%
modulation, and there was no
noticeable impact on the digital
reception.
Later, more conclusive tests were
performed in a closed
environment, with a variety of analog modulation levels including 75kHz (100%), 150kHz (200%),
188kHz (250%), and 225kHz (300%) modulation. No errors could be detected at up to 188kHz, but
block errors were detected at 225kHz.
Here is a plot of the measured spectrum of HD Radio when the analog FM signal is modulated at
188kHz (250%).
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CONCLUSIONS
HD Radio FM is both robust and efficient in the difficult mobile environment. Digital coverage
extends beyond -45dBu contour, even with an average digital power of 1/100th (-20dB) of the
analog power. While analog overmodulation is a serious problem in Asia, even the most severe
cases are unlikely to affect HD Radio digital reception.
REFERENCES
1.
iBiquity Digital Corp., White paper archive: http://www.ibiquity.com/technology/papers.htm
3.
Broadcast Electronics Inc., HDRadio References: http://www.bdcast.com/HDRadio/
4. Radio World HDRadio Reference Room:
http://www.radioworld.com/reference-room/iboc/index.shtml
ACKNOWLEDGEMENTS
The author would like to thank Mr. Richard Hinkle and Mr. Tim Bealor of Broadcast Electronics,
Trevor Harwood of TJH Systems, Geoff Durrant of Cobalt Technologies, and Jeff Detweiler and
Perry Priestley of iBiquity Digital Corporation for their assistance with this article.
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