🚀 go-pugleaf

On Sep 30, 10:42 am, dpl...@radagast.org (Dave Platt) wrote in 
http://groups.google.com/group/uk.tech.digital-tv/msg/82ff55b36ba97dbf :

 > In article <46ff32e0$0$32538$4c368...@roadrunner.com>,
 > Green Xenon [Radium] <gluceg...@excite.com> wrote:

 > >Within physical-possibility, what is the largest amount of
 > >bits-per-symbol [assuming a baud-rate of only 1-bit-per-symbol]

 > You just made a meaningless statement.  Baud rate is measured in
 > symbols per second, not bits per symbol.  I assume that you meant to
 > say "assuming a baud-rate of one symbol per second."

Yes. I meant "assuming a baud-rate of one symbol per second."

Sorry.

F-------king typos!!!!!!!!!!!!!!!!!!!!!!!!!!


 > >                                                          that can
 > >be reached without the highest-voltage causing any clipping, generating
 > >any temperatures above 70 Fahrenheit, resulting in any harm to
 > >anyone/anything [including the equipment itself], or shortening the life
 > >of the equipment and without the lowest-voltage being lost in the noise?
 > >What is the maximum-possible amount of discrete levels between the
 > >highest and lowest voltage in such a signal?
 >
 > And, another important constraint for actual usability is this: you
 > have to make sure that the minimum-detectable difference between two
 > different symbol levels can be detected reliably and accurately at
 > _all_ levels. In the language of analog-to-digital converts this is
 > referred to as "linearity" and "no missing codes".
 >
 > [As a counterexample:  the human hearing system can hear down to 0 dBa
 >  or so... a sound level which is just barely above the noise created by
 >  the random collision of air molecules with the eardrum.  And, we can
 >  hear sounds up to around 120 decibels above that, before damage starts
 >  to result.  That's a pretty wide dynamic range.  However, it's not
 >  linear... if we're listening to a loud sound (say, at 110 dB or so),
 >  small sounds are completely lost... you can't hear somebody whispering
 >  10 feet away when you're listening to a rock concert.]
 >
 > >An 8-bit signal can have a maximum of 256 different voltage levels
 > >between the highest and lowest voltage. Right? Go too high and the
 > >signal clips, go too low and the signal will not be recognized.
 >
 > Right.
 >
 > At audio-quality sampling rates (say, 50,000 baud) you can buy
 > converters that are linear down to around 22 bits, I think...
 > marketers call them "24-bit" converters but they aren't actually
 > linear down to those levels.  At instrumentation rates like 1 baud (1
 > sample per second), with filtering and averaging being applied to
 > eliminate the noise, you can do rather better.
 >
 > I don't know quite what the state-of-the-art is for measuring signals
 > at such low baud rates as you are referring to.  I'd guess that it's
 > somewhere in the range of 28-30 bits.
 >
 > 30 bits is roughly a billion-to-one ratio between the smallest signal
 > and the largest.  Crudely put, it would mean that you might have a
 > circuit which has to handle voltages of up to 1000 volts, and has to
 > be able to generate, and then measure voltage differences of a
 > *millionth* of a volt, at all of these levels.  That's going to be
 > technologically difficult, to say the least.
 >
 > The *theoretical* limit is somewhat higher than this, but not enough
 > to help you achieve what you wish.  It'll be limited at the low end by
 > the thermal noise level (a 50-ohm resistance at room temperature
 > generates -174 dBm of noise over a 1 Hz bandwidth) and at the high end
 > by whatever voltage you think your equipment can handle without
 > damage.
 >
 > Even being extremely generous, and saying 32 bits of linear resolution
 > (and thus reliable data) per symbol, you aren't going to get video
 > across it.  32 bits per second is somewhere between "fast Morse code"
 > and "old Teletype teleprinter or ticker-tape" bandwidth.
 >
 > Note that this is the generation and measurement limit and assumes an
 > interference-free communication link (e.g. a well-shielded cable), and
 > is *not* what you can get away with in a real-world radio
 > transmission!  The background noise level on LF radio frequencies is
 > higher than this, due to both manmade and atmospheric electrical
 > noise.
 >
 > As another poster has pointed out, there's a damned good reason why
 > nobody uses very-low-baud-rate modulations to send large amounts of
 > high-speed data over a narrow-bandwidth channel, despite a century or
 > more of research and study and competition in the fields of radio and
 > electronic communication.  It just doesn't work, and the reasons why
 > it doesn't are well understood by those who practice in the field.

If 400-nanometer-wavelength coherent light was used in place of electric 
signals, would QM in this system be able to pack in more 
bits-per-symbol. AFAIK, optical signals can have a greater dynamic range 
than electric signals. That is one reason that optic fibers are 
replacing coaxial cables. Less noise.