On Aug 17, 8:46*pm, "Max Power" wrote:

CODFM (as DRM uses it) in the SW bands is a PSUDO-CODFM; the audio of the
CODFM signal is imposed on an AM waveform for transmission.

Sorry, but that's simply not the case. It is true that DRM can be used
along with AM, or along with FM, exactly the same as HD Radio does. In
a simulcast, where the DRM COFDM spectra can be placed on either side
of the analog spectrum. But the DRM signal per se is COFDM, modulated
either QPSK, 16-QAM, or 64-QAM. Not AM.

All of this is readily available information:

http://www.drm.org/uploads/media/ETS...980_v2.3.1.pdf

Check out in particular Annex K, which I think is what's confusing
you.

PSUDO-CODFM aka AM-CODFM
-- CODFM signal is of Audio bandwidth, 10 kHz or 20 kHz

DRM can use 9, 10, 20, 50, or 100 KHz bandwidth. Maybe more. The
bottom three are when it's used in the LW, MW, or SW bands. The upper
two are for the new extension of DRM into the VHF band (up to 120
MHz). Those bandwidths are chosen specifically so that DRM can coexist
with analog spectra in those RF bands.

The bandwidth of the signal is not directly related to the max audio
frequency here, as it is in AM. It's related to the max bit rate, at
different levels of robustness, like any other digital transmission.
In turn, that max bit rate can be related to the max audio frequency.
But with digital, you can trade off the audio frequency limit against
the bits used in quantizing each sample.

In short, DRM could have been used as the basis for the new HD Radio
service in the US, instead of the Ibiquity system we have here.
Functionally, they are similar.

Bert