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From: Mel on 11 Mar 2010 17:40
Dombo wrote:

> The problem is that what comes out of the cable is quite different than
> what you put into the cable, especially at high signaling rates.

A few months ago, Circuit Cellar Ink ran a lovely article by Robert Lacoste
that showed what happens when a signal hits off-impedances in a transmission
line. ISTR in one of his examples you could see the reflections from the
co-ax connectors. I can't seem to find that issue, but in the December 2009
issue the same author has written "Digital Modulation Demystified." Imagine
that!

Mel.


From: langwadt on 11 Mar 2010 18:37
On 11 Mar., 21:41, RalfM <r...(a)invalid.invalid> wrote:
> Grant Edwards wrote:
>
> > Nobody with more than five firing neurons would think they could send
> > 4 billion different DC levels down a cable and correctly discriminate
> > them at the far end.
>
> And, what about just 256 levels? Would that be impossible too?

go look up the Shannon–Hartley theorem

-Lasse
From: Paul Carpenter on 11 Mar 2010 20:17
In article <hnbkki$5bh$2(a)speranza.aioe.org>, rm(a)invalid.invalid says...
> Grant Edwards wrote:
> >
> > Nobody with more than five firing neurons would think they could send
> > 4 billion different DC levels down a cable and correctly discriminate
> > them at the far end.
>
> And, what about just 256 levels? Would that be impossible too?

Down a few inches of cable between a DAC and ADC well tuned, in
a shielded box, preferably with its own battery supply, driving the
signal at least +/-10V signalling levels.

Forgetting all other aspects, get 100m of cable, lay it out on
the ground (to avoid coil effects), put a DC level in one end
and put a receiver circuit on the other end and try putting
a 5V triangle wave in.

On the receiver place an ADC on the far end and using same clock
feed it into a DAC, and scope the signal from the DAC and see
how many missing codes and lack of amplitude you have.


--
Paul Carpenter | paul(a)pcserviceselectronics.co.uk
<http://www.pcserviceselectronics.co.uk/> PC Services
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From: Paul Keinanen on 12 Mar 2010 01:07
On Thu, 11 Mar 2010 21:54:15 +0100, Hans-Bernhard Br�ker
<HBBroeker(a)t-online.de> wrote:

>
>Better yet, stop writing for a while and use the saved time to read up
>on the subject before you embarrass yourself any further. For starters
>let me suggest you look up, and _understand_ all of the following
>transmission standards:
>
> 56kbit/s analog modem over POTS
> ADSL/SDSL technologies
> QAM-256 modulation used for digital cable TV
> Gigabit Ethernet

This is the best response I have seen in this thread.

Those systems also highlights the problems with transferring multiple
bits on a symbol.

A transmission path with non-linear frequency and phase response will
quickly kill any simple multilevel signaling.

QAM256 seems to be the most that you can get through a transmission
path (8 bits/symbol) with reasonable quality on a single carrier.
Splitting the signal into several carriers will help avoiding those
propagation problems. The DVB-C2 standard allows up to 12 bits/symbol
over the cable-TV network and ADSL2+ theoretically up to 12-14
bits/symbols over the telephone wire.

On multi mode fibers, the transmission speed over long distances is
limited by the dispersion. Using several colours will allow a much
larger throughput.

With single mode fibers, the limiting factor is the throughput of the
electronics, but running signal on different wavelengths, the typical
throughput for a single transatlantic fiber is 800 Gbit/s (80 colours
x 10 Gbit/s).


From: Hans-Bernhard Bröker on 13 Mar 2010 12:25
Glenn wrote:

> No he is not a troll,

Well, if he is not _trying_ to be one, he's doing an awfully good job of
being one anyway.

> he is just a bright person that is starting to think about how to
> improve data transmissions.

No, he's bright only in the sense that Jack Nicholson's character in
"The Shining" was a shining example of humanity. One of the things that
distinguishes bright people from others is that they're willing to
actually learn something. This guy hasn't shown the least sign of that.

> Theoretically he is right,

No, he isn't. In particular, he's completely wrong about what the state
of the art in this field is, and he presents that "knowledge" in a
pretty offending style.

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