[BC] Can traditional AM and IBOC co-exist?

[Phil Alexander]

On 10 Jul 2005 at 15:28, Reader wrote:

> Submitted:
> 
> OK ... with the debate raging (all right, humming) again about the future, 
> and so many of you lamenting the loss of traditional AM, why not ask the 
> question this way:
> 
> Is it possible for AM and IBOC to co-exist on the long term?

Probably not unless there is a partition of the band.  Unless the FCC
allows enough wiggle room in the rules to make DRM in the compatible
mode a viable alternative, it would require a split of the band into
digital and analog sections. The problem with that is no one would want
to be in the digital spectrum until the receiver base was established
and because there were no stations it would never happen.

> Since AM stereo is all but dead, why not have the FCC invite IBOC only 
> operation above 1600? Non-directional.

Same problem. For digital radio to get past the chicken and egg problem
IBOC, bad as it is, probably works commercially better than the alternatives.

> Slowly, the bottom of the dial (500- what, maybe  1000 or so) could be 
> maintained with the existing AM radios, and the upper channels filled with 
> hybrid, then transition to digital only.

If you are considering a rolling partition, that might work technically,
but there is the commercial competition aspect to consider. Somebody would
cry foul, and then it would be off to the courts. That would be VHF/UHF TV
deja vu.  That may happen regardless, but the way it is now the FCC can say 
all are equally affected and possibly drag the proceedings out long enough
that the result would be mooted by the shift to all digital.

> Non-directional.

No, spectrum usage is more efficient using DA's. This is true on both coasts,
but also in the middle of the country where many of the older DA's are
N-S patterns. The reason non-DA works well with FM is the LOS horizon limit.

> There really is no reason to totally kill analog AM ... White areas would 
> have traditional AM operation, wide coverage for emergencies, etc. Digital 
> would have its own area ... and the dividing point could be "dynamic" ... 
> depending upon consumer demand.
> 
> Stations remaining at the low end of the band would be required to serve 
> their region, and not just a major city.  White area coverage, too.
> 
> just a thought... or a pipe dream.....

It's worth consideration but implies a different mindset for time buying.
The trend is consolidation of most of everything into the top 25 markets.
Regional coverage is corn, wheat, and prairie coverage, but cows and pigs
don't buy groceries - they become them. LOL  So, yes, if your objective
is the PICN as stated in the Act of '34, regional coverage is important,
especially west of the Mississippi excepting three fourths of Texas
where the geography is more like the eastern states, but if you look at
it as commercial interests seem to today, there are not enough people in
white areas, or even gray areas to matter to the kids placing time buys.

It is clear that the present anemic digital power levels must increase
before the digital signals will be very useful except in the "doughnut"
of a metro. IOW digital needs power to penetrate the center cities and
to cover the far fringe. Digital, at those power levels is not
compatible with analog.

The real problem from a compatibility standpoint is digital is essentially
hash of the worst kind to an AM product detector, as is BPL, as is power
line noise, as are atmospherics. The nostalgia of playing with a cat's
whisker on a galena crystal is magical if you are about 8 years old, and
I hate to see that go away, but if we are going to overcome the 
interference problems of AM, including the ones the FCC created by 
overpopulation of the spectrum over the past 40 years, the product 
detector has to go and a - to use the current buzz - more robust method
must replace it. Or, we can leave things as they are for a few more
years and the set makers will stop including AM "because nobody wants it."

None of this considers cost of manufacture when all tech except ours 
has become digital, and we are approaching that point. My quarrel is
not with digital radio per se, but with the method of implementation 
- IOW IBOC - for the AM band. If the FCC rubber stamps NRSC-5, as they
very well may, the next generation will face similar problems again,
assuming our industry lasts that long. That's MHO.


Phil Alexander, CSRE, AMD
Broadcast Engineering Services and Technology 
(a Div. of Advanced Parts Corporation) 
Ph. (317) 335-2065   FAX (317) 335-9037





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