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"SFTV_troy" wrote in message
ups.com...

Tom wrote:

...So, too, does DRM benefit from said development, making it
possible to provide a digital carrier within LW,MW and SW channeling
plans. Thast said, I find it much less fatiguing to listen to a
program on an analog AM carrier than to the same program over DRM.

I've never heard DRM. How does it sound, and why is it "fatiguing" to
hear?



DAB...because of a concerted government, broadcaster and
manufacturing industry push, the likes of which we have not seen in
other countries. A stronger parallel can be drawn to the sizable
takeup of XMRadio and Sirius satellite services in the US and Canada -
the quality stinks but the program choice and wide ranging coverage
are unique.

The quality stinks? Really? I listen to XM streams via the internet,
and they sound just fine. Is there really that huge of a difference
between Internet and Mobile Receiver?



I've been more impressed by synchronous AM demodulation of AM signals
than by a digital equivalent. It's a pity we could not get mass
manufacturing of synch AM radios and ultimately convert all AM
stations to USB with reduced carrier for power savings and reduced
interference.


What's USB? What's synchronous AM demodulation? Thanks.


I think the USB to which Tom refers is upper sideband. Converting AM stations would mean
they'd transmit only one set of sidebands, the upper set, reducing the bandwidth to almost
half. More stations could be licensed in the same band. A small amount of carrier would
remain, to give the receiver something to lock on to for use in recovery of the audio.
Analog video uses something similar called vestigial sideband, and we could be talking about
that for AM. Conventional radios with envelope (diode) detectors wouldn't work well at all.
When there's only one set of sidebands, with or without the carrier, the envelope of the
composite RF signal doesn't look much like the original audio, and large amounts of
distortion occur.

As a side issue, the loss of fidelity for which AM is notorious is largely in the receivers,
with their narrow bandwidths, resulting in audio that is rolling off pretty fast around the
5 KHz point. (AM stations actually transmit a fairly high-fidelity signal.) This narrow
bandwidth reduces the noise (including the 10 KHz whistle from the carriers of
adjacent-channel stations) that results largely from many distant stations all coming in on
the channel. AM radio, with its low frequencies, travels very far, particularly at night,
so lots of distant stations come roaring in. Converting AM stations to only one sideband
with a reduced carrier would reduce all of that noise. I doubt it will happen.
--
Regards from Virginia Beach,

Earl Kiosterud
www.smokeylake.com