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The "Radio Crazy" Well-earned demise of AM IBOC.

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July 16th 04, 06:45 AM

Robert Orban

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In article , says...

Mark Roberts wrote:

If AM IBOC is such hot stuff, why is it restricted to daytime hours only?

Because the group delay that is the result of the uneven ionosphere prevents
it from being decoded properly when the signal is received on skip, and the
amount of stuff coming over the horizon on skip prevents it from being
properly received when it's being received on groundwave at night.

I do not believe that this is correct. The modulation scheme of iBiquity's
IBOC system is basically multiple carrier COFDM, and is quite similar to the
modulation scheme used in Digital Radio Mondiale (DRM), which is known to be
robust in the face of selective fading. It all depends on the symbol spacing
used in the COFDM carriers. If the multipath period is shorter than the
symbol spacing, then the various reflections will reinforce. Because there
are multiple narrowband carriers in COFDM, the data rate on each carrier can
be very low (allowing long symbol spacing), yet the presence of multiple
carriers still allows the overall system to deliver a high data rate.

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