🚀 go-pugleaf

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"SFTV_troy" <SFTV_troy@yahoo.com> wrote in message 
news:1191108136.459409.212620@50g2000hsm.googlegroups.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