The title is the basic premise of the recently completed Extreme
Digital Road show, a joint informational and sales seminar co-presented
in six major U.S. cities by Harris, Ibiquity Digital and Impulse Radio.
I attended the presentation in Chicago. Present at the all-day sessions
was a good representation of the engineering talent in the Chicago area
and some management.
The day began with an informational, but mostly sales-oriented,
presentation by Harris representatives on the history and current state
of the art for the proposed IBOC digital standard. Emphasis was placed
on the company's heavy commitment to the development of a system that
will give the standard broadcaster the ability to compete with the
parallel emerging technologies of satellite delivered digital radio.
Another recurring theme was that this technology is not another
high-tech means with no end, in the way that AM stereo and RBDS became.
Presentations then followed by Ibiquity on the projected rollout of
IBOC, and by Impulse radio on some exciting uses for the data bandwidth
that is imbedded in the IBOC standard.
How do you convince broadcasters to spend, on average, a quarter of a
million dollars per station on infrastructure changes for a digital
standard that is not yet a standard, or a requirement?
It’s digital so it has to sound better, right?
Yes and no. A couple of clips were played to compare the digital
reception and analog reception in a mobile environment. The digital
signal at the sample points was free from the effects of multipath in
the FM test, and in the AM test had superior audio fidelity compared to
the 3.5kHz bandwidth of a typical auto receiver. There is no doubt that
the digital signal makes the delivery of the product more robust. But
what does the heavy digital compression (96kb/s) do to the product
itself? Let’s just say that you wouldn’t want an audiophile
to do a direct A-to-B comparison. This might be a real issue for some
formats like classical, jazz or new age. On the other side of the coin,
the popularity of the MP3 format, and the even lower bit-rate of the
satellite delivered services, doesn’t seem to have been perceived
by the bulk of the consumers as anything other than CD quality audio.
Subjective listening tests have proven that most people cannot hear
what the test equipment tells us is missing from the original source
Where are the receivers?
It’s the chicken and the egg relationship. The goal of the
seminars is to get enough broadcasters in these six major U.S. markets
to invest in the transmission side to provide 50 percent market
saturation. Simultaneous rollout of the receivers at major retail
outlets is expected to seed the market and develop consumer interest.
Projected growth beyond the initial rollout is rapid.
What is the benefit to me as a broadcaster?
This is not the business of radio as usual. The digital IBOC signal
contains not just the audio of the main product, but a significant data
stream. Impulse Radio has developed a standards-based system to allow
the broadcaster to use that data to sell more advertising product,
something that will get the interest of station management. There is
great potential to this aspect, and more information can be found at www.impulseradio.com. This technology gives the
broadcaster the ability to market directly to the listener in a
high-tech format he is already using on his cell phone, PDAs and on the
Internet. The key is non-traditional revenue.
Another incentive to motivate the cost conscious broadcaster is the
early-adopters incentive program. There is a license fee associated
with the IBOC technology. That fee is based on a multiple of the annual
FCC regulatory fee, and will average about $20,000. For a higher
multiple, a 10-year payment option is available that will average about
$3,7000/year. Royalty on the wireless data portion of the signal is
waived until 2005. As an incentive, fees will be waived for life if a
commitment is made to purchase the IBOC system before Dec. 31,
In the question and answer session that followed the morning
presentations, several questions were raised.
What is projected target date for completion of AM nighttime
studies? Due to the onset of winter propagation models, at least
six months out.
What is the data rate for the ancillary data channels? From
115b/s–400b/s. The main channel is 96kb/s.
Will XM and other satellite-delivered systems be integrated into the
final product? No, not at this time, but the receivers will be
marketed as XM ready. The technical reason for this is that XM requires
a different receiver front end. IBOC is seen as the base radio, and XM
is seen as an accessory, much the same as a CD changer.
What are the possibilities of cross promotion and sharing resources
to maximize data channel usage in a group-owned cluster of
stations? This prompted a lengthy discussion of the possibilities
of putting dual tuners in IBOC receivers so that a cluster could use
the data channels in a soft key configuration to tune the second
channel to data of another cluster station. This would allow one
station to use their entire allocated data channel for weather, another
for traffic, another for emergency services and yet another for direct
marketing. The main tuner would stay on the audio of the desired
What type of audio processing is recommended for IBOC? Due to
the heavy digital compression already in the transmission standard, it
is recommended that less aggressive processing be used on the digital
The afternoon session dealt with the technical side of IBOC. Impulse
Radio presented the details of their interactive data stream standard,
and Harris presented their product line and reviewed the three
different ways a station can implement the technical facilities.
For the AM side, any of the modern digital transmitters should be able
to pass the IBOC signal. Being that this was a Harris show, the focus
was naturally on Harris transmitters, including the DX and DX Destiny
series, as well as the soon-to-be-released DAX series of 5kW and under
transmitters. An IBOC exciter is required, and that is used in a manner
similar to AM stereo where the digital signal phase modulates the
carrier, and the analog passes thru the regular audio stages. It should
be noted that IBOC will not work on a plate-modulated transmitter or on
progressive series modulation (PSM) designs. Single-phase 75kHz PDM
transmitters will work with difficulty.
For FM, the IBOC transmitter must be capable of linear power
amplification. This does not mean that a new transmitter is required in
all cases. The Harris Z series of FM transmitter can be re-biased to
operate in Class A or AB, and depending on the power level, the
existing transmitter can pass the analog and the IBOC signals. There
are two methods of transmitting the IBOC FM signal: combined
amplification and separate amplification. Which to use depends on the
station's power, available floor space and budget. In the combined
amplification method, a single transmitter (or combined transmitters
for high power) passes the analog and digital. In the separate
amplification method, an external high power combiner is used to
combine the existing analog transmitter and a new IBOC transmitter into
a common transmission line and antenna. Due to the losses in the
combiner, the analog transmitter must operate at 110 percent of the
analog only power level, and the digital transmitter looses 90 percent
of its power in the combiner and must be sized accordingly. The
additional transmitter and combiner require floor space, and both
systems will generate additional heat load for the HVAC and possibly
require larger service from the power company.
A third method for FM discussed briefly, uses separate amplification
and a separate transmission line and antennas. For this to work
successfully it is necessary to have sufficient bay-to-bay isolation in
the antenna, and it is best if the actual digital and analog elements
are interleaved and matched. This is so the radiated signal maintains a
consistent phase and amplitude relationship after leaving the
The question and answer session following the technical discussion was
surprisingly brief. Here are some of the questions that were
Has the system been tested successfully through a multistation
combiner? Yes, using two different methods. Recently in Seattle,
IBOC transmitters were injected into the existing Cougar Mountain
combiner using circulators in place of the reject loads on each
stations combiner module. The wideband port was then used to feed a
separate transmission line and digital antenna.
Can a single IBOC exciter be used to drive two AM transmitters, for
example a main and an aux? Yes, if both main and aux can pass the
digital component. As an example, the Harris Dexstar IBOC exciter
supports eight group delay setups that should accommodate the
multitransmitter and multipattern configuration.
Is the data text display on the IBOC receivers capable of multiple
languages? Not yet. It is currently the English subset of ASCII
only. The European subset with accent letters is in the works.
What is the audio latency of the system? Six to seven
Overall, I was glad I attended the day’s sessions. Yes, it was
clearly a sales pitch for IBOC, but the information gleaned was useful.
Comments from other engineers afterward were mostly positive. There is
still a real concern of the AM nighttime restrictions, and most were
disappointed that the early-adopter incentive was of no value because
budgets for 2003 are already done.
I fear that unless the FCC mandates the IBOC standard, or significant
incentives are given to the broadcasters to invest in the technology,
adoption will be much slower than anticipated. It will probably become
reality because there is too much invested in the project thus far, but
when is the question.
Wright is a senior studio engineer for Clear Channel Communications'
Chicago Radio Group.