On Jul 24, 9:41 pm, RHF wrote:
On Jul 24, 2:51 pm, dxAce wrote:





Steve wrote:
On Jul 24, 3:41 pm, (Jim Haynes) wrote:
I happen to have the July 18, 2007 issue of Radio World, which says
it is a special issue on Shortwave and U.S. DRM. See it online ashttp://radioworld.comwhileit lasts. Mentions that there are some
HD radio receiver reviews on their site, and also on the site ofwww.nprlabs.org

--

jhhaynes at earthlink dot net

DRM...are they still doing that? I thought they'd abandoned that old
fossil.

No, it still exists, QRM'ing the SW bands.

dxAce
Michigan
USA

Anyone Know for sure - How far does the Shortwave DRM
Side Band Hash extend out from the Carrier Frequency ?

IIRC - About 25kHz on both Sides ? - Right or Wrong ?

i want to know ~ RHF
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DRM and IBOC are different in that AM-IBOC adds digital sidebands
outside the spectrum occupied by the AM signal (otherwise the station
would interfere with itself) and thus increases interference to
adjacent AM stations. There is a variant of DRM that similarly
coexists with AM in a wider channel and would be as bad as IBOC at
interfering with adjacents but SW DRM used so far is purely digital
and (usually) confined to the standard channel width.

Most SW DRM transmission use 10kHz total bandwidth; some went to 20kHz
bw for higher quality and stereo but I think this was done mainly for
demonstration and/or only at upper HF, e.g. 26MHz. The SW analog 5kHz
channeling plan is based on 10kHz wide channels so, on the surface,
10kHz DRM is compatible. However, the energy distribution of DRM is
uniform throughout the channel (rectangular) while DSB-AM is sort of
triangular (high at carrier, medium at sideband bass and mid-voice
frequencies and tapering off at higher frequencies) but varies with
modulation. A DRM signal with center-channel 5kHz away from the
carrier of an AM DSB signal will put a uniform energy across the whole
of one of the latter's sidebands. This will create a constant
interference and sound profoundly more interfering to the desired AM
signal than an adjacent AM signal would unless the AM adjacent was
modulated with something like white noise (or certain electronic or
rock music compositions) and its carrier power produced a sideband of
equal energy to the DRM.

One of the arguments in favour of DRM is that lower power levels are
needed than for DSB-AM and that mitigates interference. But you would
need controlled A-B testing to witness the advantage. Instead, we just
hear the interference to AM signals and, because of its constancy,
think it's worse than if there was an AM signal there instead.

Tom