'White' paper on Digital TV, details, more or less

Archived from groups: alt.video.digital-tv (More info?)

Would someone please point me to a link where I will find an ad-free
document describing digital-TV, from the camera to the display.

For instance, at what point is the analog-scanned image converted,
digitized?

Transmission is then purely MPEG'd digital riding on an analog subcarrier?

At the TV, is the digital stream riding on an analog subcarrier then split
out and decoded?

Know a bit (maybe) but not enough to be comfortable.

Pls advise.... and thank you!

Wayne

'The Gutenberg galaxy is being eclipsed by the constellation of Marconi.'

Archived from groups: alt.video.digital-tv (More info?)

"Doug McDonald" >

Doug, that - below - is what I do not understand. And what is it that
emerges out of the cable-supplier's spicket? i.e. piped into the TV?

Wayne


>
> When transmitted to the actual home viewer, there are no
> "subcarriers". Each station sends all its programs as bits in
> one pot. Some systems (satellite and cable) have no carrier at all
> (it is suppressed, but regenerated at the receiver),
> one over the air system has only one carrier, and another over the
> air system has thousands of carriers, but they don't carry a program
> each, just "bits" each.
>
>
> >
> > At the TV, is the digital stream riding on an analog subcarrier then
split
> > out and decoded?
>
> At the TV the digital signal is amplified and converted to a baseband
> analog signal which is then decoded into the bits. This can be
> exceedingly complicated, especially the part where the bits are
> reassembled into an MPEG stream that a computer would recognize as
> an MPEG file. At teh transmitter the bytes are all split up and the
> bits shuffled all over the place in both time, and for the multicarrier
> systems, over the carriers. This is done for error correction purposes
> (to paste over impulse noise.)
>
> Doug McDonald

Archived from groups: alt.video.digital-tv (More info?)

Doug: Thank You!

Wayne


"Doug McDonald" <mcdonald@SnPoAM_scs.uiuc.edu> wrote in message
news:csbdld$1ag$1@news.ks.uiuc.edu...
> Wayne G. Dengel wrote:
>
> > "Doug McDonald" >
> >
> > Doug, that - below - is what I do not understand. And what is it that
> > emerges out of the cable-supplier's spicket? i.e. piped into the TV?
> >
> > Wayne
> >
> >
>
> Well, from a cable it is easily explained.
>
> Cable digital works exactly like the color subcarrier
> of NTSC. It is QAM, quadrature amplitude modulation,
> suppressed carrier.
>
> At the cable head end the string of bits is split in half.
> At each instant in time 8 bits are transmitted. There are
> two signals, each carrying four bits, that is, one of 16
> possible levels. Each of the two signals modulates
> a carrier plain AM. The two carriers are 90 degrees out of phase.
> The two signals are added and the carrier removed. This is
> exactly like the R-Y and B-Y signals of NTSC. Except that
> digital TV isn't a "subcarrier", its a plain ordinary
> RF carrier (which is of course removed).
>
> The receiver has to regenerate the carrier. There is no pilot
> carrier. You can't do this with the NTSC color carrier because the
> possible set of signals, if plotted on a vectorscope, is a
> circle ... whereas for digital it is a square. Because it is
> a square, there are only four possible orientations, and only
> for one does the error correction work, so it is easy to choose.
>
> The receiver regenerates the carrier, and demodulates the
> two phases. You get back the two signals each with
> 4 bits at each instant in time. The bits are then
> put back into the original 8 bit word order.
>
>
> Over the air digital in the US doesn't use QAM, but what's called
> VSB: it's the same as ordinary B&W TV, except the carrier
> is reduced, but not totally removed.
>
> Satellite is effectively phase modulation, with
> either 4 or 8 phases, for either two or three bits at
> each instant in time.
>
> Over the air digital is Europe is very different.
>
> Doug McDonald

Archived from groups: alt.video.digital-tv (More info?)

Thank You Kirk

Wayne


"K. B." <hotmail.com@lis2lis2> wrote in message
news:41ea2d34.11050161@netnews.worldnet.att.net...
> On Thu, 13 Jan 2005 14:04:06 GMT, "Wayne G. Dengel"
> <wgd.roaming@verizon.net> posted:
>
> >Would someone please point me to a link where I will find an ad-free
> >document describing digital-TV, from the camera to the display.
>
> <http://electronics.howstuffworks.com/dtv.htm>
>
> Kirk Bayne
> alt.video.digital-tv Home Page
> <http://www.geocities.com/lislislislis/avdtv.htm>