The Morkrum Printing Telegraph Typewheel Page Printer, was also known as the Blue Code
and Green Code Page Printers, referring to variations on the design. The design was
derived from a Blickensderfer typewriter, which used a typewheel printing method.
"The Morkrum Printing Telegraph is a direct acting keyboard
system; that is, the operation of the keyboard at the sending end
actuates the printing mechanism at the receiving end directly,
without any intermediate operations." [such as punching and reading a tape]
[1]
The "Blue Code Printer" was first sold in 1910 to the Postal Telegraph Company, whose
company color was blue. This printer had three rows of symbols on the typewheel,
like the Blickensderfer typewriter that was the basis for the design.
There were three cases of type: CAPITALS, FIGURES and LOWER.
Printing was by a typewheel mounted on a vertical shaft, and having
three rows of type on its periphery. The wheel was raised to match the
desired "case", and rotated to the selected character position. It was
then swung toward the paper, contacting an inked felt roller which put
ink on the typeface. The roller was then pushed out of the way as the
wheel impacted the paper, printing the character.
[5]
The Blue Code printer was the first [?] to use "Start-Stop" character synchronization,
which used just one polarity of signaling, and one strength of current.
Code impulses were contiguous, not separate as in earlier systems, and the
"no-current" condition was used as a START signal, causing the receiving device
to look for received code impulses as they were being generated by the transmitter.
The character would end with a "current" condition, called STOP. Thus absolutely
precise timing would not be required, since corrections were being made with each
character.
[5]
In 1912, the printer was refined to become the "Green Code Printer," which had only
two rows of type, CAPITALS and FIGURES (dispensing with lower-case).
The Green Code Printer was developed for
Western Union, which used an olive-drab green color, hence the name.
[5]
The Associated Press adopted Morkrum Green Code printing telegraph
equipment in 1914 to provide simultaneous service to competitive newspapers
in New York City. [3]
[Note: In the above discussion by Slayton, he indicates that the Blue Code
and Green Code machines both used uni-polar signalling (current-on/current-off).
In the 1911 paper (believed to be) by Krum and Krum (who ought to know their machines),
they discuss a polar signalling technique (negative/positive polarity).
The Krums' paper also
describes a two-case typewheel. Since the 1911 paper date is between the Blue and
Green Code versions, it is unclear to me whether the polar signalling was an
experiment, or was actually used in either the Blue or Green Code machines. It is
also unclear whether the Blue Code machines for the Postal Telegraph installation
used a three-case or two-case typewheel.
The Krums' paper explains more below -- Gil Smith.]
Thirty-two selections are made over the line, and by using a
shift of the type wheel, fifty-three letters, figures and
characters are printed.
The current is of single strength, with the battery always
connected to the line, and the signals are transmitted by reversals
of polarity. This system gives the advantages of the Morse polar
duplex, in its ability to work successfully over long lines, and
also makes it possible to repeat through direct point repeaters.
The negative pole of the battery is normally connected to the line
between signals, and it is accordingly essential that a signal be
started by connecting the positive pole to the line.
The transmitted signal is divided into six time intervals.
The first interval is known as the starting interval.
The [next] four intervals control a mechanical selecting
device, which interposes the proper stop pin in the path of the
typewheel arm, and the [last] interval governs the direction of
rotation of the typewheel, and completes the operation of printing
the letter.
[1]
[Note: Another inconsistency arises in the Nelson/Lovitt paper, which describes
start/stop synchronization as being "first embodied (for commercial purposes) in
the Green Code Printer." Did the Blue Code machine use start/stop? Polar signalling?
Two-cases or three? -- Gil Smith.]
The Morkrum Printing Telegraph was produced from 1910 to 1925? under the Morkrum Company.
