Digital modulation!!

Clay S. Turner wrote:
> Hello Steve,
> 
> Heinrich Hertz (who discovered radio waves) would switch his apparatus on
> and off and notice the comings and goings of a spark in a spark gap on the
> other side of the room. This predated Marconi and he didn't have a narrow
> carrier per se. He just let sparks excite a resonant circuit which used huge
> amounts of spectrum, but since nobody else was using it - it didn't matter.

This would be what we now term UWB, I think :-)

As I understand it, Hertz just noticed an interesting effect. He didn't 
try to use it as a communications tool. Therefore, Marconi migh be a 
more appropriate person to tag with inventing interrupted carrier 
modulation.

Regards,
Steve

> 
> Digital modulation is described in the New Testament (Matthew 5:37)
> which
> specifically recommends binary signaling (instead of M-ary signaling
> with M > 2),
> and coding with a (2, 1, d = 2) block code, presumably for error
> detection.  The
> verse in question says (in the King James Version)
> 
>     "But let your communication be, Yea, yea; Nay, nay: for whatsoever
> is more
>       than these cometh of evil."
> 
> and is part of the Sermon on the Mount....


Your wounds dont heal very fast. Right, professor ?   :=)

Good to see u back. Hope u were not ill or something.

             shankar

> 
> Hmmm.  Digital modulation is older than analog.   The Morse telegraph is
> older than the Bell telephone.    Digital modulated radio transmission is
> older than analog (voice) radio.
> 
> The reason is that it is easier to do.
> 
> Be sure to credit the newsgroup and/or Google (tm) on your homework paper.
> 
> -- glen


I think this needs clarification. If the source is generating "discrete
information" ( letters of alphabet etc ), then "digital modulation"
naturally follows.  ( How/why would u use "analog" modulation to
transmit letters ? )

I think what op wants to know is who discovered that it is good to
send analog info using digital techniques, ie PCM .

I think it is Reeves and team.
Read "philosophy of PCM" by Shannon , Oliver, Pierce. If anybody has
it, please send to me  at

jkv567  at  yahoo.com

Advantages initially contemplated were :
1) preventing noise accumulation using repeaters
2) concept of tdm to mux/demux.  ( lesser hardware than fdm. )
3) easier to do switching

Transmultiplexers got invented to convert between fdm and tdm.

                shankar

"kbc" <kbc32@yahoo.com> wrote in message
news:a382521e.0307092250.2c2d570b@posting.google.com...
> >
> > Hmmm.  Digital modulation is older than analog.   The Morse telegraph is
> > older than the Bell telephone.    Digital modulated radio transmission
is
> > older than analog (voice) radio.

(snip)

> I think this needs clarification. If the source is generating "discrete
> information" ( letters of alphabet etc ), then "digital modulation"
> naturally follows.  ( How/why would u use "analog" modulation to
> transmit letters ? )

I suppose so.  Actually, it was an ISDN book I had from the library some
years ago that mentioned this.  For people used to the digital is new,
analog is old idea, I thought I should remind them that it isn't true.

> I think what op wants to know is who discovered that it is good to
> send analog info using digital techniques, ie PCM .
>
> I think it is Reeves and team.
> Read "philosophy of PCM" by Shannon , Oliver, Pierce. If anybody has
> it, please send to me  at

Just to continue the discussion, the problem Nyquist was working on was not
sampling analog signals, but sending digital signals (telegraph pulses)
through a band limited analog system.  He wanted to know how close together
the pulses could be and still be distinguished at the other end.  (I have a
copy of the paper around somewhere.)

-- glen

"Steve Underwood" <steveu@dis.org> wrote in message
news:beid6r$1no$1@hfc.pacific.net.hk...
> Clay S. Turner wrote:
> > Hello Steve,
> >
> > Heinrich Hertz (who discovered radio waves) would switch his apparatus
on
> > and off and notice the comings and goings of a spark in a spark gap on
the
> > other side of the room. This predated Marconi and he didn't have a
narrow
> > carrier per se. He just let sparks excite a resonant circuit which used
huge
> > amounts of spectrum, but since nobody else was using it - it didn't
matter.
>
> This would be what we now term UWB, I think :-)
>
> As I understand it, Hertz just noticed an interesting effect. He didn't
> try to use it as a communications tool. Therefore, Marconi migh be a
> more appropriate person to tag with inventing interrupted carrier
> modulation.

I wasn't kidding earlier about Black's mention of Marshall in the 1700's.
Claims to the contrary he *was* attributed to having described the first
practical telegraph system.  Apparently it was based on using a wire for
each character in the alphabet.  So, binary to be sure.  That the modulation
is on "dc" instead of a carrier is immaterial in asking the question about
"modulation". Hertz and Marconi came much later.....

Much, much later Marshall and Cooper in an unpublished work performed
experiments with a spark gap transmitter (courtesy of the Ford Motor Co. for
the spark source) which succeeded in sending morse code over a distance of a
mile or so without using a resonant circuit or antenna tuner.

I liked the mention of smoke signals!
This is a bit like the question we dealt with regarding "when did DSP start"
and finding that things like interpolation go way, way back.

Fred

Actually using the word "digital" to describe the modulation as it is
has confused a lot of people. When I was a student, my teacher spent
almost two hours to explain why the modulation was called "digital". I
cannot recall the most stuff he was talking about, but still remember
his final statement that the "digital" modulation was in deed no
digital, because the modulating and the modulated signals are both
analog or time continuous.

Now I realized how difficult to find a word to define the DSP-based
implementation of the "digital" modulation and demodulation. I
sometimes use the "sampled digital" and some other times the
"discrete-time digital" modulation and demodulation. Both are still
not satisfying. A similar confusing terminology is CDMA people use to
describe the digital modulation scheme that includes a kind of (direct
sequence) spreading spectrum. Why CDMA? The modulation is nothing to
do with the medium accessing. Sigh�


santosh.nath@ntlworld.com (santosh nath) wrote in message news:<6afd943a.0307071009.1dc4432c@posting.google.com>...
> Hello all,
> Can anybody tell the key motivation of  the inventor (who is the
> genius behind it?) to use digital modulation instead of its analog
> counterpart and how did it happen historically and experimentally?
> 
> Regards,
> Santosh

"Ying Xiong" <ying@omnexcontrols.com> wrote in message
news:56b54115.0307101136.6846b862@posting.google.com...
> Actually using the word "digital" to describe the modulation as it is
> has confused a lot of people. When I was a student, my teacher spent
> almost two hours to explain why the modulation was called "digital". I
> cannot recall the most stuff he was talking about, but still remember
> his final statement that the "digital" modulation was in deed no
> digital, because the modulating and the modulated signals are both
> analog or time continuous.

I suppose paper tape is really digital, but for magnetic tape, or most
transmission systems analog electronics is very imporant.  Pulses are stored
or transmitted with finite width, and must be carefully detected.  It is
hard not to call that modulation.

I was once in a discussion on DSL, with someone claiming that it wasn't a
modem as digital signals were transmitted.  Especially for the DSL case,
where baseband is used for the regular phone line, it is definitely
modulated.

Ethernet is either Manchester coded or phase modulated with two allowed
phase values, depending on which side you are on.

For any long distance communications link, it takes analog electronics to
get the bits back out again.

-- glen

Glen Herrmannsfeldt wrote:
> "Ying Xiong" <ying@omnexcontrols.com> wrote in message
> news:56b54115.0307101136.6846b862@posting.google.com...
> 
>>Actually using the word "digital" to describe the modulation as it is
>>has confused a lot of people. When I was a student, my teacher spent
>>almost two hours to explain why the modulation was called "digital". I
>>cannot recall the most stuff he was talking about, but still remember
>>his final statement that the "digital" modulation was in deed no
>>digital, because the modulating and the modulated signals are both
>>analog or time continuous.
> 
> 
> I suppose paper tape is really digital,

Hanging chad?

  but for magnetic tape, or most
> transmission systems analog electronics is very imporant.  Pulses are stored
> or transmitted with finite width, and must be carefully detected.  It is
> hard not to call that modulation.
> 
> I was once in a discussion on DSL, with someone claiming that it wasn't a
> modem as digital signals were transmitted.  Especially for the DSL case,
> where baseband is used for the regular phone line, it is definitely
> modulated.
> 
> Ethernet is either Manchester coded or phase modulated with two allowed
> phase values, depending on which side you are on.
> 
> For any long distance communications link, it takes analog electronics to
> get the bits back out again.
> 
> -- glen
> 
> 

Glen Herrmannsfeldt wrote:
> 
  ...
> 
> I suppose paper tape is really digital, but for magnetic tape, or most
> transmission systems analog electronics is very imporant.  Pulses are stored
> or transmitted with finite width, and must be carefully detected.  It is
> hard not to call that modulation.
> 
  ...

Is a mercury delay line, a memory that stores bits, digital? I once had
to build sense amplifiers and line drivers for a core memory. They were
analog, believe me!

Jerry
-- 
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������

ying@omnexcontrols.com (Ying Xiong) wrote in message news:<56b54115.0307101136.6846b862@posting.google.com>...
> Actually using the word "digital" to describe the modulation as it is
> has confused a lot of people. When I was a student, my teacher spent
> almost two hours to explain why the modulation was called "digital". I
> cannot recall the most stuff he was talking about, but still remember
> his final statement that the "digital" modulation was in deed no
> digital, because the modulating and the modulated signals are both
> analog or time continuous.
> 
> Now I realized how difficult to find a word to define the DSP-based
> implementation of the "digital" modulation and demodulation. I
> sometimes use the "sampled digital" and some other times the
> "discrete-time digital" modulation and demodulation. Both are still
> not satisfying. A similar confusing terminology is CDMA people use to
> describe the digital modulation scheme that includes a kind of (direct
> sequence) spreading spectrum. Why CDMA? The modulation is nothing to
> do with the medium accessing. Sigh?
> 


There are only 2 defining notions for digital modulation 
1) the notion of a symbol
2) a finite-set of waveforms , each typically of same ( symbol ) duration.

We sent symbol after symbol.  Each symbol takes a 'value' from the
finite-set.

The elements in the set should be as far away from each other by
some criteria.

(We are now operating in a finite-dimensional vector space. This 
helps.)

Until sampling theorem came, this was useful only for discrete sources
of info.

Dont confuse this with any discrete-time processing that u may do ( but
that is also being possible due to sampling theorem. )