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The Telecom Digest for March 13, 2012
Volume 31 : Issue 68 : "text" Format
====== 30 years of TELECOM Digest -- Founded August 21, 1981 ======
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Date: Mon, 12 Mar 2012 10:38:53 -0400
From: Reed <reedh@rmi.net>
To: telecomdigestmoderator.remove-this@and-this-too.telecom-digest.org.
Subject: Re: Did anyone ever figure out where "E&M" came from?
Message-ID: <SridnXh6OOwcl8PSnZ2dnUVZ_hidnZ2d@giganews.com>
On 3/11/12 12:28 PM, Bill Horne wrote:
> I was at a lunch for ham radio operators yesterday, and the sea of
> grey hair that I saw has put me in a reflective mood.
>
> I've been searching through various archives this morning, without
> success, trying to find out if anyone ever figured out the origin of
> the "E& M" signalling lead designations. When I took the D-18 course
> at New England Telephone, I read that the designations might have come
> from old circuit diagrams for telegraph equipment, but that nobody
> knew for sure.
>
> Bill
>
FWIW, here is what is posted on Wikipedia at
http://en.wikipedia.org/wiki/E_and_M_signaling#Origin_of_.22E.26M.22
"The most likely explanation is that E&M comes from "earth" and
"magneto" from the very earliest days of telephony. An actual magneto
(coil) was used to apply -48 volts to the M lead through mechanical
relay switches, while the E lead is normally held to ground (earth)
unless acknowledging the signaling from the M lead."
This is in addition to the "Ear & Mouth" possibility.
Date: 13 Mar 2012 02:18:54 -0000
From: "John Levine" <johnl@iecc.com>
To: telecomdigestmoderator.remove-this@and-this-too.telecom-digest.org.
Subject: Re: Did anyone ever figure out where "E&M" came from?
Message-ID: <20120313021854.87857.qmail@joyce.lan>
>
>http://en.wikipedia.org/wiki/E_and_M_signaling#Origin_of_.22E.26M.22
>
>
>"The most likely explanation is that E&M comes from "earth" and
>"magneto" from the very earliest days of telephony.
Seems pretty unlikely unless either you think that telephones were
invented in the UK, or that Bell used British terminology because he
was Canadian.
As far as I know, what's called earth in the UK has always been ground
in the US, and I believe the thing that the crank turned was usually
called a generator or a ringer generator.
I'll leave my 25c on Ear and Mouth.
R's,
John
Date: Mon, 12 Mar 2012 18:19:23 -0400
From: Fred Goldstein <fgoldstein.SeeSigSpambait@wn2.wn.net>
To: telecomdigestmoderator.remove-this@and-this-too.telecom-digest.org.
Subject: Re: Did anyone ever figure out where "E&M" came from?
Message-ID: <20120312221919.705485468@mailout.easydns.com>
On Sun, 11 Mar 2012, Bill Horne wrote,
>I was at a lunch for ham radio operators yesterday, and the sea of
>grey hair that I saw has put me in a reflective mood.
Hey, but we kept the riff-raff out with that Morse Code requirement! ;-)
(In this case, almost anyone born after, say, 1955. It was dropped too late.)
>I've been searching through various archives this morning, without
>success, trying to find out if anyone ever figured out the origin of
>the "E & M" signalling lead designations. When I took the D-18 course
>at New England Telephone, I read that the designations might have come
>from old circuit diagrams for telegraph equipment, but that nobody
>knew for sure.
I'd put this into one of those "lost to history", but I tend to give
some credence to the story told in various sources, including David
Talley's "Basic Telephone Switching Systems" (1969), which said,
"The E and M system received its name from historical designations
found on old circuit drawings. The E refered to the middle "e" in
received and the M from the m in transmit."
But it's also possible that those were just mnemonics. The drawings
of some circuit or other at sone point in time may have simply
labeled the leads A,B,C,... and those two happened to be E and
M. Then somebody came up with the mnemonics. After all, if I wanted
to name the two signaling (not bearer) leads, ear and mouth would not
be the first things that come to mind.
--
Fred Goldstein k1io fgoldstein "at" ionary.com
ionary Consulting
http://www.ionary.com/
+1 617 795 2701
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