Re: [IRCA] NAB wants it both ways

["Craig Healy" <bubba@xxxxxxxxxxxxxxxxxxxx>]

>> Right now digital power is 1% of analog...
>
>The digital power is not 1% of analog, though everyone seems to think it
is.
>You're thinking of the FM system, which is a different breed of cat.  In
the
>AM system, the digital power is either 5.8% or 6.8% of the analog power,
>depending on a power setting that is part of the NRSC-5 standard.  So, if
>your theory about coverage was correct, you would need roughly equal
digital
>power to get the same coverage as analog.  However, you can't really
compare
>the hybrid digital and all-digital systems in that way, since they are
quite
>different in their characteristics (bandwidth, power spectrum, etc.).

Hmm.  So, that 16% gets multiplied by 5.8 or 6.8.  92.8% or 108.8%.  As you
say, roughly equal.  That really doesn't bode well, considering that the
interference potential is greater for the digital signals.  How much
different is the comparison for hybrid mode vs. all digital?  A digital
carrier is a digital carrier.  Plus, don't the dual carrier sets provide a
sort of diversity reception?

That makes the case for using the analog allocation system much more of an
issue.  Consider the WYSL-1040 matter.  Having a 3400w station with a two
tower array gain aimed right at them a few hundred miles away would *never*
be allowed under analog allocation rules.  That makes this much worse than
the 500w I had written earlier.  If they allow it, then it really voids the
whole allocation procedure.

>All that said, it would still be interesting to try some all-digital tests
at
>some power level, and see how it shakes out.  In theory, all HD receivers
and
>exciters should support the all-digital mode, though reality may differ.
:-)

Given the earlier Harris IBOC exciters don't support all-digital - or so I'm
told - I have to wonder if the receivers do.  I've never seen it mentioned.
With the all-digital at least a decade away, why would they bother?

>Of course, if an all-digital mode is actually used, it should be DRM, which
is
>greatly superior to the iBiquity all-digital system.

Even more superior if they put it on another band.  No matter how good
Digital Radio Mundial is compared to IBOC, it still has to battle the
inherent problems of the frequency range.  Added noise, inability to
penetrate buildings, skywave propagation.  Those three difficulties along
are enough to kill it.  And no amount of blather and bluster from iBiquity
will change the physics.

Thanks for the info.  I probably have it right at hand and missed it.

Craig Healy
Providence, RI

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