I tend to view most technologies as either emerging or breakthrough.
Emerging technologies form the basis for, and typically address, a new
approach to a problem. In some cases, an emerging technology could also
represent a replacement solution to an existing situation. While the
complex technical aspects of IBOC qualify it as a true technology, it
is hardly a breakthrough.
Breakthrough technologies change the way we do things, possibly even
causing a complete paradigm shift in our lives. One example of a
breakthrough technology might be something as simple as the creation of
wireless Ethernet hardware. Supported by the 802.11 standard, wireless
Ethernet permits the connection of PCs to a network without wires
— this changes the way that people work. Users are no longer
tethered to a location where a connection is present.
The changes that IBOC brings to radio affect stations owners, managers
Breakthrough technologies also need to address a social problem or
need—I'm not sure IBOC addresses this either. Why? Let's consider
exactly what we are accomplishing.
IBOC is considered a viable method to move radio into a fully
digital terrestrial service. It seems to do this well, through its
ability to operate within a station's assigned allocation, gradually
moving from a hybrid mode to a fully digital mode.
The IBOC digital encoder provides two possible digital streams. The
core stream and the enhanced stream, which provide higher bit rates
respectively. The IBOC system assigns the respective streams to
different parts of the spectrum.
IBOC systems have the ability to scale back to a lower bit rate in
locations with poor signal. In the case of hybrid implementations, the
digital streams will blend into the analog. In practice, if the station
has enabled the enhanced stream, the receiver should switch from
enhanced to core and ultimately to analog, as a listener moves away
from the transmitter site. How will this blending ultimately affect the
listener? Will phase delays and other artifacts produced by this
blending end up causing listener fatigue?
Perhaps the largest issue surrounding IBOC presently is the NRSC's
recent announcement that it is temporarily suspending its IBOC
standards-setting process due to concerns over the quality of the
36kb/s PAC coding technology. Actually, the statement left little room
for interpretation: "DAB subcommittee members...do not consider the
audio quality demonstrated by the Ibiquity 36kb/s PAC technology to be
suitable for broadcast." The original demonstrations of this technology
by Ibiquity used the MPEG-2 AAC encoder, which by all accounts sounded
measurably better than the present analog technology used over the past
several decades. Will this ultimately be resolved? Possibly, but it may
slow the initial deployment of IBOC.
Another issue is the reality that most broadcast transmission
systems are less than perfect. In my experience, few station owners
have been willing spend the extra time and money necessary to optimize
the transmission system. Generally, transmission system problems are
dealt with as a result of a failure, and even then the expectation is
to address the specific problem only.
In general, the performance of the current generation of FM antennas
ranges from good to excellent, however, that performance can be
degraded by a number of factors, including reflections and coupling
from the mounting structure, mismatches, element damage, ice build-up
and damage to the transmission line.
Despite the recent NRSC announcement, receiver manufacturers still plan
to release production units later this summer.
Another issue I have not heard discussed is the effect of poor axial
ratio (unequal amplitudes and phase between horizontal and vertical
polarization). IBOC uses the fully allocated spectrum—either
along with the analog signal or in fully digital mode. These problems
may go unnoticed using the traditional analog system, however, it is
not clear whether they have an effect on the ODFM subcarriers that are
located away from the center carrier frequency, particularly in an
urban environment where multipath is common. Let's not forget the
bandwidth limiting effects of poorly tuned final cavities.
Another concern I haven't seen addressed are the results of RF
intermodulation products that can be a problem at locations that host
multiple stations using separate antennas. Tests were performed on a
station operating through a master antenna system with reasonable
results, however, there are a variety of master antenna systems
presently in operation that may not perform as well due to the type of
design, filtering scheme, station frequency separation or antenna
system bandwidth limitations.
Finally, whether IBOC can live satisfactorily with analog
subcarriers will be yet another potential obstacle. Tests performed by
Ibiquity and the NRSC indicate that the IBOC subcarriers should be able
to operate with minimal interference to subcarriers, but acknowledge
the potential for problems. The FCC has also recognized this problem
and stated with its rulemaking that in the event IBOC interferes with
subcarriers, the licensee of the station needs to work toward a
remediation. One of the main concerns of the FCC is the potential
interference to SCA broadcast reading services that target blind
I would suspect that the implementation of AM IBOC would present a
major challenge to engineers for many of the same reasons I stated
earlier regarding the FM system. The ultimate effects of improperly
tuned phasing systems and network components will become apparent
quickly. At least IBOC is not being permitted to be used in nighttime
operation yet and you can scrap that AM stereo exciter. Also, what will
happen when the AM listener is traveling near power lines or a
multitude of other noise sources? Does the IBOC receiver blend to
So is IBOC a friend or foe? I think a fully digital terrestrial
service is certainly in our future, but the path will be rocky at best.
Radio has always had the advantage of being local and of serving that
local area better than a network. The ability to broadcast a fully
digital signal may seem to put radio at parity with satellite-delivered
services and CDs, however, without exploiting that unique local
position from a programming perspective, I doubt IBOC or any other
approach will keep radio viable.
McNamara is president of Applied Wireless, New Market,