A Better Way to Implement AM IBOC
by Guy Wire
 Like
a small snowball slowly rolling from the top of a hill, IBOC conversion
in the United States seems to be getting underway.
Will the controversial invention now called HD Radio steadily grow
and gather more speed as it courses down the slope of radio technology
history? Or will it break apart encountering too many obstacles
and fall by the wayside with earlier contestants like FM Quad and
AM stereo?
The FCC has just issued the long-awaited initial R&O authorizing
deployment of HD. Radio aficionados in the six rollout markets have
a ringside seat for this one.
We're glad CEO Bob Struble and the Ibiquity brain trust took our
advice and waived the licensing fees for early adopters through
the end of this year. It just had to happen if deployment is going
to be jump-started. And it reassures the industry that Ibiquity
has more patience and caring for the long-term future of radio than
many had given them credit for.
Thanks Bob. I hate to ask again, but could you possibly extend
this?
Impressive in Seattle
The NAB Radio Show in Seattle unveiled a few more clues on how
the rollout is likely to fare.
One group owner stepped up to the plate and announced purchasing
IBOC transmission gear from Harris at the convention. Urban specialist
Radio One was the first major market group to jump on the bandwagon
and commit money to add HD. Ibiquity, along with Harris and other
manufacturers are betting heavily that others will climb aboard
soon.
Over-the-air comparisons have confirmed in all tested markets that
HD Radio on FM "sounds better" and clearly outperforms
analog in mitigating noise and interference, plus adding the potential
of expanded data services. Seattle NAB HD demos on Entercom's KISW
and Infinity's KBKS played very well, as expected. Every FM IBOC
demo in a fixed setting or moving vehicle I've heard over the past
three years have delivered impressive results. HD FM clearly is
ready.
Whether data will become the "killer-app" for HD and
make broadcasters significant revenue is the big unanswered question
in this entire proceeding.
If it were only about the FM band, HD Radio would likely have an
easier task picking up converts and convincing consumers that the
new radios will be worth buying.
HD for AM, on the other hand, has emerged as a much more problematic
and challenging proposition. Saddled with painfully narrow bandwidth
and a compromised allocations scheme that allows neighboring adjacent
channels to interfere with each other, HD on AM may be a snowball
rolling uphill.
The promise and the pain of AM
The Ibiquity digital solution developed for AM has long held the
promise of 15 kHz stereo and noise-free reception - a giant leap
forward for all stations on the venerable low-fi band that would
give them parity with today's FM stereo. While such extraordinary
improvement appears to be mostly real, it will come at the expense
of creating some new interference to analog listeners. That's the
disconcerting part for many with vested interests in existing AM
stations and those who are worried about being able to hear weaker
signals.
The interference will come in two flavors. The NRSC sounded the
initial concern about nighttime coverage for HD and skywave interference,
withholding endorsement of the system for FCC approval until more
studies could be completed. Ibiquity's "final" report
on this is expected shortly.
The more overlooked scenario is daytime interference involving
suburban and rim-shot stations trying to cover a nearby larger market
served by a powerful second- or third-adjacent-channel signal. Much
of this new perceived interference will be receiver induced.
We've heard about a few over-the-air tests that are attempting
to characterize what happens to the nighttime listenability of one
station when subjected to HD noise from a first-adjacent station
via groundwave or skywave. Several well-known engineers recently
evaluated the impact of HD interference using WOR 710 and WLW 700
as test cases. We understand that measurements and qualitative assessments
were made for skywave interference to groundwave reception and groundwave
interference to skywave reception for all typical scenarios of desired
to undesired signal strength ratios. Skywave interference to skywave
reception was even considered. Does anyone besides members of AM
DX clubs even do that anymore?
Ibiquity's summary report on this has not been released yet, but
it will likely say that only one of these modes is going to pose
a real problem. Interference will be noticeable and objectionable
only when someone tries to listen to a skywave or weaker groundwave
signal in the presence of a stronger first adjacent interferer -
like when a WLW skywave listener in northern New Jersey tries to
hear the Reds ballgame with WOR bearing down with a signal stronger
than about 2 mV/m. Is this scenario going to be a problem for significant
numbers of AM radio listeners?
Understanding the NIF
Nighttime service coverage largely is determined by the NIF or
nighttime interference free contour. The FCC calculates this number
based on RSS summing of all predicted skywave signals arriving into
the coverage area of a given station.
Skywave signals reflected from the ionosphere generally achieve
received levels of only 2 mV/m or less. Few stations nowadays have
NIFs close to 2 mV/m - mostly the 50 kW clear channels and some
of the very old regional channel stations.
The majority of AM stations have NIFs higher than 5 mV/m. They
lose a ton of meaningful nighttime service outside their primary
5 mV/m contour. NIFs of even 10 or 15 mV/m are common. Pity those
above 20 mV/m. There are quite a few. The only silver lining in
this ionospheric cloud is that much of the time, useful coverage
extends to about half the NIF for many stations.
Ibiquity figures that with skywave signals rarely exceeding 2
mV/m, little meaningful coverage will be lost. Using an extensive
computerized study of existing AM signal coverage across the entire
United States, they project the overall loss of service at less
than 1 percent. If that's true, it's more of a confirmation of the
sad fact that not too many folks listen to weaker signals at night
on AM radio. It's mostly because they can't.
You can't please 'em all
The daytime interference issue for HD on AM is only beginning to
be heard.
Sandusky's nostalgia station KIXI demonstrated HD Radio for the
Seattle NAB show, using an older Harris DX-50 transmitter. We understand
Harris engineers encountered significant difficulty getting HD to
work and keep it working for reasons not fully disclosed.
Various broadcast.net radio-tech participants mention hearing noise
interference beyond the first-adjacent channels throughout the KIXI
coverage area. Similar comments followed the IBOC testing on AM
1140 in Las Vegas during recent conventions.
I didn't hear anything significant on my rental car radio while
cruising Seattle beyond the KIXI first adjacents. But depending
on the design of the radio, perceived interference appears to vary
considerably. Those with wider IF bandwidths and better high-end
frequency response performance appear to be more vulnerable.
I did think the KIXI on-air HD signal heard on several receivers
in the Harris NAB booth sounded impressive compared to the analog.
It's hard to argue otherwise with the high end opening up from 3
or 4 kHz all the way to FM-like 15 kHz response. In spite of minor
compression artifacts, the average listener would almost certainly
agree.
Meeting the mask
It's not really a matter of whether HD AM transmissions can meet
the existing NRSC mask. Ibiquity has maintained in their considerable
testing that they can.
In fact, Ibiquity is saying the existing NRSC mask will be made
even more restrictive than it is now, to afford better adjacent-channel
and host analog protection. I guess that's reassuring, but many
in this industry are still worried about HD AM digital interference
to the millions of analog radios out there during the hybrid phase.
Ibiquity engineers spent considerable effort making this work for
the demos. But it may prove to be difficult to keep many existing
transmitters within the mask when setup for HD AM by others.
For several extended periods over the past year, WTOP 1500 in Washington,
D.C., has been running HD to enable both day and night HD coverage
and interference evaluation. Most of Ibiquity's concern has been
focused on first adjacent interference. The digital sidesaddles
sit 20 dB down, squarely in the middle of the first-adjacent passbands.
They may have under-estimated how many radios respond to the second
adjacents. Most existing radios seem to fare better suppressing
interference from analog modulation limited by the NRSC mask than
from HD digital.
Suburban DC foreign language stations WPWC 1480 and WTRI 1520 are
not too happy with all the new digital hash coming from WTOP. We've
heard that it's made it almost impossible for many of their listeners
to hear those less than 5 mV/m signals in the DC area. Such stations
were bought and sold based on values supported by their ability
to serve part of the larger metro area with the analog signal.
Protecting the weak
This might become a thorny problem for the FCC. Do daytime signals
less than 5 mV/m deserve any protection with the advent of HD and
the use of wider bandwidth radios? There are perhaps more than 1,000
stations licensed to bedroom communities trying to serve larger
nearby markets.
Some would suggest the FCC let the suburban genie out of the bottle
long ago and it's now coming back to haunt them. The concept of
city of license and maintenance of premium signal levels to ensure
reliable service has taken a beating over the years. Blame some
of that on greedy and opportunistic broadcasters.
Many HD AM naysayers are predicting the band will become a sea
of hash rendering all weaker signals unusable when most stations
in every market convert. We may be seeing only the tip of the iceberg
on this issue. As more HD AM signals come on the air, many more
complaints will likely be heard.
Even though the vast majority of AM listeners will benefit by HD,
should the FCC pay any attention to these concerns before writing
the final rules for HD AM?
It could get messy.
Skipping the AM hybrid mode
A few consultants and industry observers, including yours truly,
think there might be a better way to implement HD AM.
Let the FCC authorize the standard for receivers now, but skip
the AM hybrid mode entirely and delay conversion for transmission.
The benefits of all-digital, similar to those being implemented
for Digital Radio Mondiale, are dramatic and impressive. HD FM would
deploy on schedule as proposed, allowing HD receivers for both AM
and FM to begin filling the marketplace.
In less than 10 years, the majority of all radios in use would
be HD-capable, making it feasible for all stations in the AM service
to make a one-time complete conversion to all-digital. Dropping
analog has been the ultimate goal from the beginning. The FCC would
set the date perhaps five years in advance, giving all parties with
a vested interest plenty of time to prepare for the heralded event.
FM could also convert to all-digital at the same time unless LPFMs
and smaller stations needed more time. Certainly that could be negotiated.
The precedent for mandating the end of the old service has already
been established for TV. But no, this would not be another HDTV
boondoggle. It's comparatively cheap and easy to add HD transmission
to most AM stations and only a bit more challenging for FM.
Something for everybody
This proposal accomplishes several vitally important goals. First,
it eliminates the messy hybrid transition phase for AM and all of
the concerns about interference.
Most important, it forces the issue of industry wide acceptance
for all parties and guarantees the entire industry that HD Radio
will be adopted. No more "let the marketplace decide"
uncertainty. Stations will know well in advance they will have to
make the conversion.
Receiver manufacturers will know well in advance that analog radios
will no longer be necessary and can focus on building HD and all
digital designs. They have made it clear that it's more expensive
to build and market both HD and analog-only radios. Prices for HD
receiver chips would drop more rapidly enabling affordable Walkman
and tabletop versions.
Finally, it allows more time to further develop and enhance the
HD AM system with software improvements that would later be conveyed
to all the smart receivers already out there. No telling what technology
breakthroughs might be uncovered and discovered in this arena over
the next ten years.
Protecting the present, enabling the future
Some might argue that delaying HD conversion for AM would only
cripple it more and give FM yet another technological advantage
for many years. The percentage of radio listeners using AM has finally
stopped eroding and has leveled off in 2002 at about 19 percent.
Most of that is concentrated on the lucrative news/sports/talk formats
and is not going to change because FM has HD.
Our proposal effectively protects AM from any further loss of listening
caused by interference until all stations convert to HD together.
The most radical and unnerving realization here is that all existing
analog radios would be rendered instantly useless. Lots of collectables,
paperweights and throwaways would be created by the flick of a switch.
While many of you might view this as unthinkable, it would just
be another event in the long history of technological evolution
that has relegated the hardware of old obsolete inventions to the
scrap heap.
Anybody who wants to keep using radio would have plenty of time
and forewarning to acquire a new HD model. The analog-only radio
just might become the next 386 DOS computer.
Guy Wire is the pseudonym for a veteran broadcast engineer with major-market radio credentials. His opinions are his own and do not necessarily reflect those of Radio World. RW welcomes other points of view.
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