Light Weight Teletype Unit for Mobile Use

Smaller than standard typewriter, equipment uses regular keyboard and keying code—Control converts code to frequency shift signals (TeleTech Feb 1947)

New teletypewriter with associated converter-control unit Interior view of converter-control used with radio circuits

Smaller than standard typewriter, equipment uses regular keyboard and keying code—Control converts code to frequency shift signals

• Teletype equipment, rapidly
coming into wider use in many
communications fields, has been
somewhat restricted in usefulness
due to the relatively great weight
and bulk of the units and the
space needed for their operation.
Now, however, Teletype Corp. has
developed a printer unit that actually
is smaller and lighter than a
standard typewriter, thus greatly
extending the field of usefulness of
the equipment which now becomes
available for operation in airplanes
and in earthbound vehicles where
space is at a premium. An associated
converter-control unit to
operate with the new printer has
been developed by Bell Telephone
Laboratories; R. A. Vanderlippe,
supervisor responsible for the development
of radio teletype systems
for the Laboratories, tells of
both units in the November issue
of "The Record".

The new printer uses the reg-
ular teletype keyboard and keying
code. The converter-control unit
at a station which is sending
changes this code into frequency shift
signals in the audio frequency
range for transmission over existing
radio telephone equipment. At
the receiving station, the converter control
unit changes the frequency shift
signals into impulses for operating
the receiving-typing part of
the printer.

The new instrument will work
with any existing radiotelephone
installation capable of carrying on
satisfactory two-way voice communication.

This, of course, means
that by the simple addition of the
radio teletype equipment, weighing
less than thirty-five pounds, and
without any modification of the
radiotelephone equipment, two-way,
typed communication, with all
its advantages, may be achieved.
The normal use of the radiotelephone
equipment is in no way
affected by the installation of the
radio teletype.

Frequency Shift
Circuits in the converter unit
provide an automatic closure to
condition the radiotelephone equipment
for transmission when the
first teletype character is sent. This
function is disabled when a message
is being received. Other control
circuits provide for holding the
selector magnet circuit of the teletype
printer in a marking condition
during idle periods of the circuit,
so that radio noise will not
cause false characters to be printed,
and to light lamps to indicate
whether the terminal is in a transmitting
or a receiving condition.

Openings and closures of the
printer transmitting contacts which
occur as the keyboard is operated
are applied to the sending circuit
and shift the frequency of an oscillator
between 1,615 and 1,275 cycles
as required by the marking and
spacing elements of the character
to be transmitted. The output of
the sending circuit modulates the
radio transmitter in the same
manner as a voice signal. A small
amount of energy from the sending
circuit is applied to the receiving
circuit in which it functions in
the same manner as a signal received
from a distant station. In
this way, a local copy of the teletype
characters being transmitted
is obtained. During transmission,
the auxiliary contacts of the teletypewriter
close during each character

and, operating through the
control circuit, cause the press-totalk
control circuit of the radio
transmitter to close at the beginning
of transmission and remain
closed as long as at least one character
is sent every five seconds.
Release of the mark-hold circuit
during a receiving condition causes
Light weight and small size make equipment
suitable for airborne and mobile use
a green-capped "rec" lamp to light.
At the same time that the marking
hold is released, the sending
control circuit is disabled to prevent
accidental operation of the
keyboard from interfering with the
incoming signals. During the transmitting
condition, a red-capped
"send" lamp is lighted and the
circuit for lighting the "rec" lamp
is disabled.

When signals are being received,
the 1,615-cycIe marking and 1,275-
cycle spacing tones, together with
the important side band components
resulting from signaling, are
passed by the input band pass filter
to a fast-acting amplitude-limiting
circuit and applied to frequency-
discrimination circuit.

Operating System
The output of the discriminator
circuit is a positive voltage for
marking and a negative voltage for
spacing signals which result in a
current of 20 milliamperes in the
selector magnet for a marking condition
and zero current for a spacing
condition.

The output of the amplitude limiter
is also applied to the "markhold"
circuit. The marking elements
of the first teletype character
to be received cause the marking
hold on the output circuit to
be released so that subsequent signals
may pass through the output
circuit to the printer selector
magnet.

The Model 31 teletype printer is
10y2 in. high, 10 in. wide and 13y2
in. deep, and weighs only 24 lb.
The converter-control unit is 5 in.
high, 7 in. wide and 9 in. deep, and
weighs 8 lb. This makes it possible
to provide teletype service
over existing press-to-talk radiotelephone
circuits by adding less
than 35 lb. to the weight of the
communications equipment. No
modification of the radiotelephone
equipment is necessary.

New lightweight teleprinter equipment extends
the usefulness of the system to include mobile 
service in airplanes, trucks, for marine
service and in military operation where a printed
record of instructions, orders, etc., may be 
received without continuous attention from an 
operator and without the need for skilled operators.

Two Articles From Bell Laboratories
 RECORD November 1946

 

 

HIGH FLYING TELETYPE  (p 396-399)

:::::::::::::::::::::::::::
R. A. VANDERLIPPE 
Telegraph 
Development 
:::::::::::::::::::::::::::
 

Another milestone in the history of radio communications has been reached, for it is now practicable to send teletype messages to and from airplanes in flight. The equipment which makes this possible is the new lightweight Model 31 teletype printer, developed by the Teletype Corporation, and an associated converter-control unit, developed by the Laboratories. 

Smaller and lighter than a standard typewriter, this printer uses the regular teletype keyboard and signaling code. The converter-control unit at a station which is sending changes this code into frequency­signals in the audio-frequency range for transmission over existing radio-telephone equipment. At a station which is receiving, the converter-control unit changes these frequency shift signals into electrical impulses for operating the receiving-typing part of the printer. 

An interesting feature in connection with the use of this new instrument is that it will work with any existing radio-telephone installation capable of carrying on satisfactory two-way voice communication. This, of course, means that by the simple addition of the radio teletype equipment, weighing less than thirty-five pounds, and without any modification of the radio-telephone equipment, two-way, typed communication, with all its advantages, may be achieved. The normal use of the radio-tele­phone equipment is in no way affected by the installation of the radio teletype. 

A radio teletype network installed in aircraft and ground stations operates very much like a press-to-talk radio-telephone network, except that instead of spoken words it handles typed messages. No manual operation of a "press-to-talk" control is required since the radio transmitter is turned on automatically when the first teletype character is sent. As in standard land wire teletype equipment, two signaling conditions, commonly referred to as "marking" and "spacing," are used for transmission of teletype signals. The unit of time during which a character is transmitted is broken into seven intervals. Each character begins with a spacing "start" interval and ends with a marking "stop" interval. During these intervals all printers which are receiving are synchronized with the printer which is sending. During each of the five time intervals between the start and stop intervals, the signaling condition may be either marking or spacing, depending on the teletype character being transmitted, so that thirty­two different signaling combinations are possible. By assigning one combination for "upper case" and one for "lower case," any or all of the remaining thirty combinations may be used for the transmission of either of two characters or symbols so that there are enough combinations for all characters and symbols on the keyboard of the teletypewriter. 

Circuits in the converter unit provide an automatic closure to condition the radio­telephone equipment for transmission when the first teletype character is sent. This function is disabled when a message is being received; Other control circuits provide for holding the selector magnet circuit of the teletype printer in a marking condition during idle periods of the circuit, so that radio noise will not cause false characters to be printed, and to light lamps to indicate whether the terminal is in a transmitting or a receiving condition. 


Openings and closures of the printer transmitting contacts which occur as the keyboard is operated are applied to the sending circuit and shift the frequency of an oscillator between 1,615 and 1,275 cycles as required by the marking and spacing elements of the character to be transmitted. 

The output of the sending circuit modulates the radio transmitter in the same manner as a voice signal. A small amount of energy from the sending circuit is applied to the receiving circuit in which it functions in the same manner as a signal received from a distant station. In this way, a local copy of the teletype characters being transmitted is obtained. During transmission, the auxiliary contacts of the teletypewriter close during each character and, operating through the control circuit, cause the press­to-talk control circuit of the radio transmitter to close at the beginning of transmission and remain closed as long as at least one character is sent every five seconds. 

Release of the mark-hold circuit during a receiving condition causes a green-capped REC lamp to light. At the same time that the marking hold is released, the sending control circuit is disabled to prevent accidental operation of the keyboard from interfering with the incoming signals. During the transmitting condition, a red-capped SEND lamp is lighted and the circuit for lighting the BEC lamp is disabled. 

When signals are being received, the 1,615-cycle marking and 1,275-cycle spacing tones, together with the important side band components resulting from signaling, are passed by the input band pass filter to a fast-acting amplitude-limiting circuit and applied to frequency-discrimination circuit. The output of the discriminator circuit is a positive voltage for marking and a negative voltage for spacing signals which result in a current of 20 milliamperes in the selector magnet for a marking condition and zero current for a spacing condition. The output of the amplitude limiter is also applied to the "mark-hold" circuit. The marking elements of the first teletype character to be received cause the marking hold on the output circuit to be released so that subsequent signals may pass through the output circuit to the printer selector magnet. 

The primary source of power for the converter-control unit and the Model 31 teletype is the 26.5-volt battery commonly used in airplanes. Plate voltage supply of +250 volts for the converter-control unit is normally obtained from a generator winding on the teletype driving motor. This high­voltage supply is also used for an electronic speed regulating circuit that is incorporated in the printer. 

Tubes having 6.3-volt heaters are used in the converter-control so that this unit could be adapted for vehicles having a 6-volt battery by reconnecting the filament circuits. A vibrator type high-voltage supply circuit operating from 6-volt battery has been constructed for supplying plate voltage to the converter-control unit. 

The Model 31 teletype printer is only 10 1/2 inches high, 10 inches wide and 13 1/2 inches deep, and weighs only 24 pounds. The converter-control unit is 5 inches high, 7 inches wide and 9 inches deep, and weighs 8 pounds. This makes it possible to provide teletype service over existing press­to-talk radio-telephone circuits by adding less than 35 pounds to the weight of the communications equipment. No modification of the radio-telephone equipment is necessary. An additional feature of importance to aircraft operation is the fact that this equipment will operate in any position, even upside down. 

With teletype operation, a printed record of all communications is available at all stations in the network. Messages may be handled easily and accurately by inexperienced personnel, and are received without attention from the operator. Since a standard teletype code is used, messages may be sent from any other teletype station such as a land-wire "weather" network. In international service code groups of teletype characters could be standardized to cover all routine phases of weather reporting, takeoff, landing and other instructions to be-given to the plane. 

The new lightweight terminal equipment has special application to other fields in which the large size and weight of standard equipment· has prevented the use of teletype methods of operation. These fields include mobile service to trucks, cars and harbor craft and military applications to landing operations and forward command posts of advanced echelons of a battle force. Of particular importance in these uses is the advantage of making a record of instructions or other data without continuous attention from an operator. Also of importance is the fact that messages may be handled easily and accurately by inexperienced operators. 

"Picao" at Indianapolis (p-420)

CAPTION- Al Wilson in plane equipped for teletypewriter
and telephone service 

Teletype Model 31 used as a portable Telecommunications Terminal
for the Deaf and Hard of Hearing  - Clipping from the  Paul and Sally Taylor Collection at  SMECC

WESTERN UNION PORTABLE VERSION OF THE MODEL 31 TELETYPE

Teletype Model 31  from the Paul and Sally Taylor Collection at  SMECC  prior to  cleaning it.

Photo  to the right shows Sally Taylor, Ed Sharpe Archivist  and Paul Taylor playing with the  Model 31 portable.

We need  parts to support  this  unit! Please let us know of you have any model 31  spares, books drawings or stories!

Military Version Teletype  Model 31

2275 cps Space, 2475 cps Mark Audio FSK adapter - 
"used in conjunction with any voice-modulated
transmitter and receiver"
Includes 

TT-30/AGA-1 Teletypewriter
(Teletype Model 31)
TT-31/AGA-1 Terminal Unit 

TT-30/AGA-1 manual is here 

AN/AGA-1 specification. do you have more info on this?  Email info@smecc.org 

Photo Courtesy  AWA 

Enclosed is a scan of the Truman plane photo (AWA has an original print). The date is "10-8-47" The operator is typing on a SIGNIN. Which as far as I can tell is a M31 and a SIGCUM (or something similar) in one package. Note that the TTY is an "ASR" with tape perf & reader. (never seen any mention of that option on the M31 !).

The lower AN/ART-13 has a switch on the side labeled "Nornal < > TTY" and a large vent probably for forced-air cooling.

Photo Courtesy  AWA 

A submitted  group of Model 31 photos... sure would like to buy this one ( or one like it!)

CLICK TO SEE  THE 14 PAGE PATENT!