Hi,

why does a DRM software radio running on a PC require its sound input
from the 12 kHz intermediate frequency of a receiver? Why not just feed
the audio output of a radio to the PC?

Thanks,
Daniel

Daniel wrote:
Hi,

why does a DRM software radio running on a PC require its sound input
from the 12 kHz intermediate frequency of a receiver? Why not just feed
the audio output of a radio to the PC?

Thanks,
Daniel

A DRM signal is made up of many carriers (frequency division multiplex)
that are phase modulated, typically 200 carriers across a bandwidth of
10 kHz whose ideal spectral energy shape is rectangular. An AM or
envelope detector will generate a mishmash of products from
combinations of these carriers giving the characteristic hash sound and
so confusing the DRM decoder that it cannot possibly decode the signal.


It is possible to use a SSB reception mode with the BFO tuned off the
center of the channel by 12 kHz or thereabouts to output the DRM signal
shifted to the range that a DRM software decoder would like (uses the
computer sound card so the output spectrum must fit within its
passband). Because the 200 carriers are beat against the BFO, there is
not the distortion caused by the envelope detector. However, the
receiver must have a wide IF passband to allow such a large offset and
an audio stage designed for hi-fi, not voice communications. These are
rare.

Hence, the adaptation of most radios for DRM requires the addition of
last IF to 12kHz downconverter.

Tom

Daniel wrote:
Hi,

why does a DRM software radio running on a PC require its sound input
from the 12 kHz intermediate frequency of a receiver? Why not just feed
the audio output of a radio to the PC?

Thanks,
Daniel

If you have a PCR1000 here is one trick that works.
http://www.g7ltt.com/drm/no-mod_drmtests.html

IMO DRM is still a waste of time and and like IBOC a solution looking
for a problem.

Terry

IMO DRM is still a waste of time and and like IBOC a solution looking
for a problem.

Why? Shortwave quality is far from FM, so why not improve it with
modern signal processing silicon?

Daniel wrote:

Hi,

why does a DRM software radio running on a PC require its sound input
from the 12 kHz intermediate frequency of a receiver? Why not just feed
the audio output of a radio to the PC?

Thanks,
Daniel
too much filtering in the way. it needs that full 12 Khz to get proper
signal.