In reponse to many inquiries, RTTY, with permission from the TELETYPE CORPORATION, presents this material to assist the newer RTTYers to know what some of the others are talking about.
There are as many reasons for wanting tape gear as there are
amateurs. It provides the most rapid means of handling traffic on
amateur frequencies. It is accurate, reliable, and fast. It also
provides a means of preparing an answer while receiving another
station. This makes even the slowest typist sound like an
"old-timer". Also it can be used for bulletins of
general interest, such as the ARRL broadcast from W1AW's copy.
Equipment lists of your station (BRAG TAPES), Hi. For MARS net
and RACES net operations it can be used very effectively. Net
rosters, net call ups and so on. Its limitations are those of the
operator. Many circuits to enable cutting type from "local
loops" and from the TU have been printed in RTTY.
Tape equipment, like many other items, comes in many forms. Fig. 1 shows the popular Model 14 Transmitter-Distributor (L4TD). Teletype's description is given below.
General
The transmitter distributor is a motor driven device
which translates code combinations, perforated in a paper tape,
into electrical impulses and transmits these impulses to one or
more receiving stations. The tape may he perforated by any one of
several models of Teletype perforating or reperforating machines.
There are two kinds of transmitter distributors; one for transmitting five unit code, and the other for transmitting six unit code. These two kinds are identical except that the six unit code machine accommodates a wider tape and provides for the transmission of an additional impulse. The following description pertains specifically to the five unit transmitter distributor.
NOTE: In all the figures of this bulletin, end views of fixed pivot points are designated by solid black circles.
Theoretical Transmitting Circuits
The portion of the unit through which the perforated
tape feeds is known as the transmitter The transmitter prepares
electrical paths from the signal line battery to the commutator
segments of the distributor. These paths are controlled by tape
pins which sense the perforations in the tape and thereby
determine the positions of the contact tongues with relation to
their upper and lower contact screws.
The distributor completes the connections to the signal line. Connections are made in sequence at a constant rate of speed by brushes which traverse the segments and the collector ring.
The Tape Sensing Mechanism
The contact levers are positioned vertically in the
transmitter. They pivot on a shaft S and have extensions to the
right C, left A, and downward B. The right-hand extensions
project upward at the ends and have tape pins embedded in them.
An opening is provided in a tape guide, located above the
right-hand extensions of the contact levers, to permit the tape
pins to enter the code holes in the tape. The left-hand extension
of each contact lever carries a contact tongue which is attached
to the contact lever by a pivotal mounting. Each contact tongue
is positioned to move between two contact screws, a spacing
contact screw above, and a marking contact screw below. A contact
lever spring is attached to the mounting end of each contact and
tends to hold it against the lower contact screw. A contact lever
bail, pivotally mounted just below contact lever lower
extensions, has an arm extending downward engaging a transmitter
operating lever. This transmitter operating lever has a central
pivot screw and moves in a horizontal plane. A roller on the rear
end of the lever rides a transmitter operating cam mounted on the
lower end of the distributor shaft. The motion imparted to the
transmitter operating lever by the operating cam causes the
contact lever bail to rotate the contact levers on their shafts
sufficiently to move the contact tongues up and down between the
marking and spacing contact screws. After the tongues strike the
upper screws, any additional clockwise rotation of the contact
levers is absorbed by the contact lever springs. When the
distributor brush comes to rest on the stop segment the
transmitter operating lever roller is on the peak of its cam,
thereby holding the tongues against the spacing contacts and also
holding the tape pins, located in the right-band extensions of
the contact levers, below the holes in the tape. As the
transmitter operating lever roller rides to the low part of its
cam, the tape pins rise. If tape perforated with code
combinations is in the tape guide at this time, the contact lever
pins will project through the tape wherever the tape is
perforated and permit the associated contact tongues to rest on
the marking contacts, while the pins will he blocked at the
unperforated portions and the associated contact tongues will he
held against the spacing contacts. The tape will be held
stationary and the contact tongues will maintain their positions
as determined by the code perforations while the distributor
brush is traversing segments one to five inclusive. The inner
distributor brush will transmit marking impulses to the line from
segments associated with tongues that rest on the lower contacts,
and spacing impulses (for polar signal transmission) from
segments associated with tongues that are on the upper contacts.
When "make-break" signal transmission is used (battery
applied only to the lower contacts), a no-current interval occurs
when the contact tongues are against the spacing contacts.
The Distributor Mechanism
The distributor is made up of two concentric conducting
rings mounted on a fiber disc. The outer ring is divided into
seven segments. Segments Nos. 1 to 5, inclusive, correspond to
the five intelligence intervals of the five unit code and are
connected to the five contact tongues
Immediately preceding No. 1 segment is the start segment. The segment following No. 5 segment is the stop segment. The stop segment and the lower contact screws are permanently connected to marking line battery. The start segment and the upper contact screws are connected to spacing line battery only when it is desired to transmit polar signals; otherwise, the upper contact screws and the start segment have no battery connections. When the distributor brush passes over the start segment, a spacing impulse is always transmitted, whereas a marking impulse always results when the brush traverses the stop segment. These two invariable impulses cause the receiving mechanism to operate in unison with the distributor brush arm.
Tape Feeding Mechanism
Positioned to the rear of the contact levers and pivoted
on the contact lever shaft is a feed lever which is similar in
shape to a contact lever. The feed lever has a spring attached to
its left-hand extension and a feed pawl mounted on its right-hand
extension C. A feed pawl spring holds the feed pawl in contact
with a feed wheel ratchet. Pins on the circumference of the feed
wheel project through an opening in the tape guide and mesh with
the feed holes in the tape. A retaining lid, under which the tape
passes, holds the tape in contact with the feed wheel pins. When
the action of the contact lever bail on the contact lever moves
the tape pins downward, the feed lever responds in a similar
manner, causing the feed pawl to engage a tooth on the feed wheel
ratchet and rotate the feed wheel. With each downward motion of
the feed pawl, the tape will be advanced from right to left, the
distance required to bring the succeeding code combination over
the tape pins. The setting of the feed pawl is such that it does
not start to rotate the feed wheel until the tape pins have moved
clear of the tape. A feed wheel detent is provided to insure
alignment of the code perforations with the tape pins. The
position of the operating cam with relation to the distributor
brush is such that the contact tongues are not moved from the
lower contacts until after the brush has reached the stop
segment. While the brush is passing over the stop segment, the
tape is advanced.
Starting and Stepping Transmission
The main shaft is driven by a motor through the medium
of gears and a friction clutch. When the motor is running,
transmission is stopped by blocking the rotation of the main
shaft and started by unblocking it. This is done through the
medium of a stop arm which is under the control of a tape stop
magnet and a sprint. The magnet, when energized, holds the stop
arm clear of the lug. The spring holds the stop arm in the path
of the lug when the magnet is de-energized. The circuit to the
magnet may be opened or closed by means of the tight-tape stop
contacts, tape stop switch, or the end-of-tape stop mechanism
contacts which are described in the three paragraphs that follow.
Tight-Tape Stop Mechanism (Auto-Stop Mechanism)
When the slack in the tape between the tape perforator
and the transmitter is taken up, the tape raises the tight-tape
stop lever which opens the circuit to the tape stop magnet
allowing the stop arm to engage the lug on the stop cam. A tape
guide wire may also be employed to guide slack tape within close
proximity of the tight-tape stop lever so as to raise the lever
and stop transmission if the tape feeding into the transmitter
becomes tangled, thus preventing mutilation of the tape feed
wheel perforations.
Tape Stop Switch
Transmission can also be stopped by manually operating
the tape stop switch. This switch controls the release magnet in
a manner similar to that of the mechanism described in the
preceding paragraph.
NOTE: On some types of distributors, this switch is connected in the motor circuit and is then used to start or stop the motor.
End-of-Tape Stop Mechanism
Another means may be provided for automatically stopping
transmission when a length of tape has passed through the
transmitter. This is accomplished by another pair of contacts
located beneath the tape guide which are operated by a pin that
projects through the tape guide When the tape retaining lid is
closed, the end-of-tape stop pin is depressed and the contacts
are held closed so long as there is tape between the pin and the
lid. When the end of the tape passes the pin, the tension of the
contact spring raises the pin and opens the contacts, stopping
transmission.
Synchronous and Governed Motors
Where regulated A.C. power is available, a synchronous
motor maybe used, otherwise governed motors must be used.
Governed motors are available for operation on either A.C. or
D.C. The speed is controlled by a centrifugal contact mechanism
having commutator rings or discs. In general, motors are mounted
directly to the base casting and the resistors and condenser used
with governed motors are mounted on the base and in the base
cavity. However, some governed motors are mounted to a base plate
having governor resistors and a condenser mounted on it so as to
form a complete motor unit assembly.
When an A.C. governed motor is used, a contact assembly is provided which is operated by the tape stop magnet stop arm (figure 9). The purpose of the contact assembly is to provide better speed control by introducing a resistor in series with the motor when the distributor shaft is rotating, and by shunting the resistor when the load of the friction clutch is added to the motor.
In addition to the 14TD, many versions of the MXD
have been issued through MARS channels. Also some have been found
on the surplus market. Figure 2 shows one such unit. A
description of the MXD is given below.
Multiplex Transmitter Distributor (MXD)
The multiple transmitter distributor set is a mechanism
which, when used in combination with reperforators, provides
combined sending and receiving facilities for tape message
relaying. A complete set consists of three multiple transmitter
distributor units and a motor unit mounted on a base which is
equipped with cross shaft, gears and terminal strips. Two of
these units are message transmitters and the third is a number
transmitter. The function of the number transmitter is to insert
automatically into the signal line successive numbers, from a
number tape, which will identify each message before it is
transmitted. The number transmitter is like the message
transmitter except that it is equipped with a letter sensing
mechanism which makes it responsive to the letters combination in
the number tape causing stoppage of the number transmitter and
starting of a message transmitter through external electrical
control circuits.
The multiple transmitter distributors (message or number
transmitters) are arranged to handle either perforated or
chadless tape received from other stations on reperforators, or
prepared locally on keyboard perforators.
The message transmitter consists essentially of the following mechanisms: a 7.42 unit code transmitting cam cylinder with associated transmitting contacts, a tape feed and tape sensing mechanism, a hinged tape lid, an automatic tape out control feature, a manual control mechanism, a magnet operated clutch, a driven gear, and a transmitting contacts filter. (See figures 3 and 4.) This unit is geared for transmission at the speed of 368.1 o.p.m.
The transmitting cam cylinder is normally held stationary because the clutch members on the transmitting shaft are held disengaged by the clutch throwout lever. When the clutch magnets are energized, the clutch members engage and the rotation of the transmitting cam cylinder begins the cycle of operation.
The transfer of the code combination in the perforated tape to the contact levers which control the transmitting contacts is accomplished by means of the selector lever bail, its cam, selector pins and selector levers.
The selector lever bail extension roller rises from
the indent on its cam and causes the selector lever bail to move
away from the selector levers. The selector lever springs pull
the selector levers up toward the tape. The selector p ins which
encounter perforated holes in their path advance through the
perforations, but the pins which do not encounter perforations as
they come in contact with the tape, are blocked by the tape and
are prevented from advancing farther.
Each selector lever is positioned through the medium of the perforations in the tape, to correspond with each signal impulse to be transmitted. Each selector lever controls the motion of a contact lever either by allowing the contact lever to close its contact when the cams revolve, or by restricting the motion of the contact lever. If the selector pin does not enter a perforation in the tape, corresponding to a spacing impulse, the lower end of the selector lever engages the associated contact lever and prevents it from rising into an indent of the cam, as the cam rotates, thus holding the circuit open for that impulse. If the selector pin enters a perforation in the tape, corresponding to a marking impulse, it does not interfere with the movement of the contact lever. Then, as the cam revolves, the contact lever rides on the cam periphery and drops into an indent, thereby allowing its contact to close and send out a marking impulse. As the cams rotate, the impulses, either marking or spacing, are transmitted in succession.
The start-stop cam controls a contact lever which, in turn, actuates the start-stop contacts. These contacts are opened at the beginning of each revolution of the cam cylinder to transmit the start impulse (spacing) and remain open during the transmission of the five impulses. After the fifth impulse has been transmitted, the start-stop contacts again close, sending the stop impulse (marking) to the line.
After the fifth impulse has been transmitted, the selector lever bail extension drops into the indent in its cam causing the selector lever bail to retract all the selector levers from their sensing position. At this moment the feed pawl arm roller drops into the indent in its cam and the feed pawl engages the feed wheel ratchet, stepping it forward, thereby advancing the tape one character space over the selector p ins. A feed wheel detent establishes the relative setting of the feed wheel.
The transmitting cam-cylinder rotates continuously as long as
the clutch magnets are energized. An interruption of the clutch
magnet circuit causes the clutch throwout lever to engage the
cammed surface of the driven member of the clutch due to the
action of the clutch throwout lever spring and, as the
transmitting shaft rotates, the driven clutch member is cammed
out of mesh with the driving member.
Within the unit there are two provisions for interrupting the
clutch magnet circuit. The clutch magnets are connected in series
with a set of automatically operated contacts and a set of
manually operated contacts. The opening of either set of contacts
stops the unit.
The functions of the number and message transmitters are identical with the exception of the letters sensing mechanism which is a feature of the number transmitter.
Letters Sensing Mechanism
The letters sensing mechanism is used to stop the number
transmitter and to start one of the message transmitters when the
letters combination is sensed in the tape.
During every operating cycle, when the selector lever pins are sensing the code combination in the tape, a letters operating lever senses the ends of the five selector levers. If one or more selector levers are in the spacing position, the letters operating lever is prevented from continuing its travel. If the code combination is letters (all marking impulses), the letters operating lever is not blocked by any of the selector levers and therefore is rotated through a larger angle. The letters operating lever has two extensions, one of which rides on a cam and permits the letters operating lever to sense the selector levers, while the other engages the tape-out contact lever when a letters combination is sensed in the tape and consequently opens the tape-out contacts. These contacts are opened momentarily since the tape-out contact lever is disabled in the number transmitter. The momentary opening of these contacts causes the number transmitter to stop and starts one of the message transmitters by means of an external electrical control circuit.
The multiple transmitter distributor base has facilities for
mounting a motor unit and three transmitter units. The number
transmitter is mounted on the left side and the two message
transmitters are in the middle and right sides. A series governed
motor is used for operation on 115 volts D.C. or AC., 50 or 60
cycles. The motor is demountable as a complete unit and is
equipped with a governor filter.
The motor power is transmitted to the individual units through a
cross shaft. Each transmitter unit has an individual terminal
strip to facilitate disconnecting the transmitter cable to remove
the units. Underneath the base are the governor circuit elements,
a terminal block for external power connections and three sets of
spark protectors for the automatic and manual contacts on the
three transmitter units. A two-conductor power cord and an
eight-conductor cable, which terminates in plugs, provide
facilities for external connections.
A complement of covers provides dust protection. Although the
various sections of the covers are removable, a lid is provided
in the motor cover which may readily be opened to provide a view
of the speed target and access to the speed adjusting members. A
guard is provide on e cover in front of the number transmitter
through which the number tape will pass and be protected from
damage from external sources. A tape chute is provided to direct
the used tape from the unit on the right.
The front of the base is equipped with a card holder.
Another version, which incorporates a typing reperforator, is the
FRXD series. Several versions of these units have shown up
recently. A brief description is given. See Figure 3.
General
Typing and Reperforating Mechanism General
Later models of the TD series used with Model 28 equipments are shown in Figs. 4 and 5. Single and dual versions are available for such operations.
Several manual tape perforators are available, one
such unit is the Model 14. Fig 6. A DC supply is required to
operate the punch magnets, and "end of line" indicator
lamp.
The Five-Unit Tape Perforator is a unit of apparatus that is
used to prepare perforated tape for automatic telegraph
transmission. Combinations of holes are perforated in the tape,
which correspond to the key lever depressed. The perforator tape
with the code combinations thus recorded may be fed automatically
through a tape transmitting device, operating a printer unit at a
distant point.
The Five-Unit Tape Perforator is a self contained magnet
(solenoid type) operated, portable unit. It consists essentially
of a set of keys and key levers; perforating, tape feeding, and
end-of-line indicating mechanisms. The unit is equipped with a
power cord and attachment plug for making connections to a source
of direct current power supply.
Signaling Code
The signaling code used to transmit characters is the
"Five-Unit Code," which consists of five selecting
impulses used in various combinations of spacing and marking
intervals. The large holes in the tape represent marking
impulses, whereas the impulse positions on the tape that are not
perforated represent spacing impulses. The small holes are feed
holes, which are used to feed the tape through the perforator and
the transmitting device.
Perforating Mechanism
The perforating mechanism consists essentially of a set
of punches for perforating the tape; a pair of punch magnets and
a punch hammer for operating the punches; a set of punch bars and
bell cranks; and loops and combs attached to each key lever used
in selecting the punches. The five punch bars are fitted in guide
slots in the punch hammer, just behind the punches and in line
with them. The right end of each punch bar is attached to a bell
crank and the opposite end of each bell crank engages a notch in
a loop extension. Each character or function key lever has a comb
with notches arranged so that its particular code combination
will be selected and perforated. The combs are cut out in such a
manner that the depression of a key will cause the comb to strike
the top edge of one or several of the loops, moving them
downward.
In addition to the five loops controlling the five punch bars,
there is a sixth or power loop which is operated by the
depression of any key. The downward movement of this loop closes
the punch contacts, energizing the punch magnet, and thus
operating the punch hammer.
The depression of a loop causes the punch bar connected to it to
be moved away from a punch so that when the punch hammer is
operated by the magnet, the tape will not be perforated at this
position; hut when a loop is not depressed, the punch bar
connected to it will be allowed to remain in the path of a punch
and a hole will be perforated. A feed hole is perforated with
each forward movement of the punch hammer.
For instance, if the "K" key lever is depressed, only the #5 punch bar will be moved away from its punch. All the other punch bars, however, will be driven against their punches, causing the first four impulses to be perforated in the tape.
Tape Feeding Mechanism
The tape feed roll is located to the left of the
punches. Spaced at equal intervals around the tape feed roll is a
series of projecting feed pins which mesh with the feed holes
punched in the tape. A tape tension lever holds the tape against
the tape feed roll, keeping the feed holes in the tape in
constant mesh with the tape feed roll pins.
During the forward movement of the punch hammer, the tape feed
pawl, which is attached to the punch hammer, engages a tooth on
the tape feed roll. When the punch hammer moves back, the tape
feed roll will revolve, advancing the tape one character space. A
star wheel affixed to the lower end of the feed roll and a detent
insure equal spacing of the tape.
End-of-Line Indicating Mechanism (Nonadjustable)
The end-of-line indicating mechanism is intended for use
in connection with page printer reception. When sixty-four or
sixty-five combinations have been perforated in the tape, a red
lamp, under the keyboard, is lighted by the closing of contacts.
These contacts are closed by the action of the indicator gear.
This gear meshes, through an idler gear mounted on a lever, with
the tape feed roll pinion on the tape feed roll. Whenever the
tape feed roll moves the tape forward one space, the indicator
gear is advanced one tooth.
Mounted on the indicator gear is a pin "A". When the indicator gear is advanced sixty-four or sixty-five teeth from its starting position, pin "A" will move the lamp contact ever so that its contact spring will touch the lamp contact screw, lighting the lamp.
The advancing of the indicator gear winds up an indicator return spring, one end of which is attached to the indicator gear. When the operator depresses the "Carriage Return" key, the key lever strikes a bell crank which moves the release rod to the left. This throws the indicator idler gear out of mesh with the tape feed roll pinion and the indicator gear is returned to its starting position by the indicator return spring.
Since the "Carriage Return" key may not be held depressed long enough to allow the indicator gear to completely return to its starting position, a release rod holding pawl is provided to insure that the gears stay out of mesh while the indicator gear is returning. This holding p awl moves into a notch in the release rod when the release rod is in its left-hand position. When the indicator gear is almost returned to its starting position, pin "B" (on the indicator gear) moves the holding pawl out of the notch in the release rod and permits the gears to again mesh.
End-of-Line Indicating Mechanism (Adjustable)
The adjustable end-of-line indicating mechanism is
similar to the non-adjustable end-of-line indicating mechanism
described in the foregoing.
The adjustable end-of-line indicating mechanism has an adjustable stop plate mounted on the indicator gear. A projection, extending downward from this stop plate, is used instead of pin "B" to move the release rod holding pawl out of the notch in the release rod.
The adjustable stop plate moves the release rod holding pawl against an adjustable stop screw which determines the stop position of the indicator gear. The adjustable stop plate may be positioned so that the lamp contacts close on any operation from the sixty-fourth to the seventieth.
Backspace Lever
A backspace lever is provided for moving the tape
backwards for the correction of errors. When the backspace lever
is being moved from left to right, it engages a pin projecting
from the tape feed pawl and cams the tape feed pawl out of
engagement with the tape feed roll ratchet. Toward the end of the
travel of the backspace lever, the backspace pawl (which is
mounted on the backspace lever) engages a tooth of the star
wheel, rotating it backwards one space. The "Letters"
key may then be depressed, causing five holes to be perforated
over the previous perforation. This combination may be passed
through the tape transmitting device without causing any
character or letter to be printed on the receiving printer.
However, if a character in the upper case is corrected, it will
be necessary to strike the shift key (Figures) again, because the
"Letters" combination will unshift the receiving
printer.
Repeat Mechanism
The repeat mechanism provides a means of continually
perforating a desired code combination in the tape. With any key
lever and the repeat push button simultaneously held depressed,
the code combination corresponding to the key lever depressed
will continue to be perforated until the repeat push button is
released.
When any key lever is held depressed, the punch magnet circuit is completed through the punch magnet contacts. The operation of the punch magnet permits the magnet yoke contacts to close, completing a circuit through the winding of the repeat relay if the repeat push button is depressed. The operation of the repeat relay breaks the punch magnet circuit. The punch magnet yoke is released, opening its contacts, which open the repeat relay circuit. The repeat relay releases its armature, closing the punch magnet circuit, thus setting up a repeated cycle of operation. Repeat action will continue as long as any key lever and the repeat push button are simultaneously held depressed.
Another manual tape perforator is the Model 15 perforator transmitter, keyboard, which is used on the Model 19 set. Fig. 7. It also requires an external DC supply to operate the punch magnets.
General
The Model 15 perforator transmitter is a combination
transmitter and perforator with an electrically operated
character counter. It is inserted in the base of a Model 15
printer when the Model 15 printer is used in conjunction with a
Model 19 table and a Model 14 transmitter distributor. When this
combination of units is used together, it is known as a Model 19
printer set.
The perforator transmitter is furnished with the character counter mounted either to the left or to the right of the unit. When the counter is mounted to the right of the unit, a separate cover is provided for it. When mounted to the left of the unit, the counter is covered by an extension of the printer cover.
A manually operated, three position keyboard control operating lever is mounted at the right-hand end of the unit. The selection of any one of the four methods of operation may be made by placing this operating lever and the line test key in one of the following positions:
Signaling Code
The signaling code used to transmit characters is the
"Start-stop" five-unit code, which consists of five
selecting impulses used in various combinations of current and
nocurrent intervals. Each group of five selecting impulses is
preceded by a start impulse and followed by a stop impulse, which
are used to maintain synchronism between stations on the circuit.
Impulses which energize the selector magnets on the printer are
known as marking, and those which do not are known as spacing. 
The Model 14 Typing reperforator is shown in Fig. 8. This is by far the typing reperf to be found in most amateur RTTY stations who have tape equipment. Several of the typing reperf units only, less base and cover, have been listed in the Horse Trades section of RTTY in the past. Both type of selectors magnet assemblies are found on these units. Hence, provision for either 20 or 60 mils can be had on the units with the holding type of selectors, and some have the series or parallel switch which is found mounted behind the selector unit. Some also have an "end of line indicator" assembly which operates a lamp after 72 or what ever number of characters it has been set for, has been perforated. The unit shown has a keyboard, but many 14 typing reperfs have been issued by MARS which are receiving only, in other words, no keyboard.
Another version of the 14 reperforator is shown in Fig. 9 which is called "Single Magnet Reperforator". It also is made in a six level tape version, which has been used on the TELETYPESETTER, in news service.
There are two types of Teletype single magnet reperforators;
the 20 type, which operates on the six-unit code and the 14 type
which operates on the five-unit code. This bulletin mainly covers
the 20 type six unit reperforator. However, the mechanical parts
of the 14 type reperforator are the same as the 20 type except
the parts associated with the zero pulse are not used, such as
the zero selector lever, sword, "T" lever, transfer
lever, and punch lever. Also, different range scales, punch
blocks, selector cams, feed rolls and guides are used on the five
unit reperforators. 
The Teletype reperforators are motor driven tape reperforating machines which receive electrically transmitted signals and translate these signals, through the medium of selecting and perforating mechanism into code combinations of holes in a paper tape. This tape may then be used for retransmitting these code combinations on other similar printing telegraph circuits; thus eliminating manual preparation of tape with a perforator at the relaying station.
Signaling Code
The signaling code used for the 20 type single magnet
reperforator is a six unit start-stop code which consists of six
selecting impulses used in various combinations of current and
no-current intervals. Each group of six selecting impulses is
preceded by a start impulse and followed by a stop impulse to
maintain unison between the sending and receiving apparatus.
Impulses which operate the selector magnets are known as marking
and those which do not operate the selector magnets are known as
spacing. Figure 1 shows graphically the six unit code.
The signaling code used for the 14 type single magnet reperforator is the same as the six unit code except that the zero impulse is omitted.
RTTY is indebted to the TELETYPE CORPORATION for permission to reprint portions of this material. Their current equipment is being widely used for TWX service (MTWX) and also in association with many computers. An example of such advanced equipment is the Model 33 ASR which was shown on the cover of the July 1963 RTTY. If your non-hobby needs are for such equipments, write to them at:
TELETYPE CORPORATION
5555 Touhy Avenue
Skokie, Illinois
