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'[EE] Mark and Space'
2009\04\04@224058 by Barry Gershenfeld

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Dang this newfangled Google "mail" "program". And I went and forgot to tag
the subject.


> By the way, the terms "mark" and "space" came from Morse's original
> telegraph, I believe. His original telegraph had a moving paper tape and a
> pen. When there was line current, the paper would be marked. When there
> was no line current, the paper would not be marked, causing a space. A
> telegraph operator would read the marks and spaces (forming dots and
> dashes) to read the telegram.


Few people appreciate this long legacy that started with loop currents.
Even I didn't realize it went back to the telegraph, although I knew "break"
did.  So when I read this, I thought, "Wow..."  Then I began to wonder. Folk
etymology? What bothers me is that there would be a line on the tape, broken
only when they opened the circuit and began keying.  Sounds kinda backwards.
Maybe we can research this.

2009\04\04@234815 by Harold Hallikainen

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> Few people appreciate this long legacy that started with loop currents.
> Even I didn't realize it went back to the telegraph, although I knew
> "break"
> did.  So when I read this, I thought, "Wow..."  Then I began to wonder.
> Folk
> etymology? What bothers me is that there would be a line on the tape,
> broken
> only when they opened the circuit and began keying.  Sounds kinda
> backwards.
> Maybe we can research this.


pdf page 29 of
www.unitedstatesmilitarytelegraph.org/files/ElectricTelegraph.pdf
has a picture of Morse's telegraph. The description says that when there
is current through the electromagnet, the moving paper is indented by a
stylus (marked) and not marked (space) when there is no loop current.

I'll look around some more.

Harold


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2009\04\05@175006 by Peter

picon face
Think of the continuous line current as a circuit continuity indicator that also
served as wetting current for the un-soldered (twisted together) copper wire
circuits, and kept corrosion at bay (that's why the idle signal voltage is
negative wrt. ground - it counters the natural electrochemical potential that
appears against wet things (including ground) that touch the line and this
prolongs the life of the copper wires). Later it also served other purposes
(several keys could key the circuit, when connected in series or shorting to
ground). The wetting current issue is still valid in rural areas where wires
often chaff and bounce in the wind causing bearable noises in the phone audio
circuit. Without the wetting current (pure ac coupling) tens of copper oxide
junctions created at the twisted wire splice points would oppose signal passage.

The 'key when shorting to ground' feature was used quite a lot (party line
including hooking into the line anywhere between stations using a ladder and a
hook, with a portable key that keyed to a ground point created by driving a
stake into the ground). RS232 receiver compatibility with driving to GND
(instead of going negative) may date back to those times. Phone lines (POTS) are
based on an expansion of the same principle and in the beginning they shared
wiring and switching with the then existent telegraph wires. It is still
possible to use a straight key and sounder on any POTS line that is straight
wired (static mechanical or relay switch and/or party line).

Peter


2009\04\06@065256 by Bob Axtell

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Interesting dispatch, thanks.

It reminds me of a true story told by a man I knew who was a retired
teleco executive.
He was remembering his youth as a young telephone company troubleshooter
years ago.

The complaint was that a couple's outside dog would howl whenever
their phone rang.
He went to their remote cabin and noticed a leakage on the line. The leakage was
traced to the metal dog chain. It seems that when they staked out the dog that
they drove the stake through the underground cable. A new cable, placed deeper
and well-marked, solved the problem.

--Bob A.

On Sun, Apr 5, 2009 at 2:49 PM, Peter <spam_OUTplpeter2006TakeThisOuTspamyahoo.com> wrote:
{Quote hidden}

> -

2009\04\06@162339 by Barry Gershenfeld

picon face
>
> pdf page 29 of
> www.unitedstatesmilitarytelegraph.org/files/ElectricTelegraph.pdf
> has a picture of Morse's telegraph. The description says that when there
> is current through the electromagnet, the moving paper is indented by a
> stylus (marked) and not marked (space) when there is no loop current.
>
> I'll look around some more.
>
> Harold
>

If you look up the Wikipedia article for "Telegraphy", they have a
photograph of the original "What hath God wrought?" message tape.  It is as
you say.

What surprised me is the use of the International code, which we recognize
today.  I'd heard that telegraphers all used that "click-click" stuff, the
Continental code.  Which one did Morse invent, or did he create both?

Barry

2009\04\06@175254 by Nate Duehr

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There were multiples...

Imagine, if you will, that even in the 1800's there were the same issues we
face today with patents and intellectual property rights.  Morse devised a
number of different "codes", actually, and defended them with a passion.
Competitive telegraph companies didn't use the same codes.

My grandfather (RIP) was "fluent" in Railroad telegraphy, specifically the
Union Pacific "flavor", but when we tried to see how it was similar or not
similar to my ability with so-called "International" Morse Code (Amateur
Radio) one day, they just didn't sync up at all.

I still credit his abilities and stories about learning railroad telegraphy
as one of the reasons I have an interest in International Morse Code to this
day, say -- carrying on a family tradition -- but they really aren't the
same, nor could we communicate using code when we played with it while he
was still alive.

We both seem to have a knack for typing well and fast, but he did it in his
generation on Underwood typewriters and teletype machines for the Union
Pacific, and I do it on computer keyboards... (GRIN!).

Nate

-----Original Message-----
From: .....piclist-bouncesKILLspamspam@spam@mit.edu [piclist-bouncesspamKILLspammit.edu] On Behalf Of
Barry Gershenfeld
Sent: Monday, April 06, 2009 2:23 PM
To: Microcontroller discussion list - Public.
Subject: Re: [EE] Mark and Space

What surprised me is the use of the International code, which we recognize
today.  I'd heard that telegraphers all used that "click-click" stuff, the
Continental code.  Which one did Morse invent, or did he create both?


2009\04\06@183933 by Harold Hallikainen

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As I recall, there was a Continental telegraph code, which may have been
designed by Morse. It had single dit gaps in letters. For example, as I
recall, the letter C was .. .

Radio, however, was subject to fades. So, was that a C, or was it an H
with a fade in it. I've heard the international telegraph code was
designed to get around this. There are no gaps within a character.

Harold



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2009\04\06@190424 by John Gardner

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A trove of telegraphy lore...

http://mysite.du.edu/~jcalvert/tel/telhom.htm

2009\04\06@192933 by Harold Hallikainen

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> A trove of telegraphy lore...
>
> http://mysite.du.edu/~jcalvert/tel/telhom.htm
>

Excellent! I have some reading to do!

Harold

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2009\04\06@215751 by Vitaliy

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----- Original Message -----
From: "Harold Hallikainen" <.....haroldKILLspamspam.....hallikainen.org>
To: "Microcontroller discussion list - Public." <EraseMEpiclistspam_OUTspamTakeThisOuTmit.edu>
Sent: Monday, April 06, 2009 16:35
Subject: Re: [EE] Mark and Space


>
>> A trove of telegraphy lore...
>>
>> http://mysite.du.edu/~jcalvert/tel/telhom.htm
>>
>
> Excellent! I have some reading to do!


Me too. Just printed out the Preface, to read off-line. :)

http://mysite.du.edu/~jcalvert/tel/morse/morse.htm

Thanks, looks like very good stuff.

Vitaliy

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