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Патент USA US2405991

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Patented Aug. 20, 1946
2,4 5,9%
UNITED STATES PATENT GFFIC
2,405,991
SECRECY SYSTEM
Harold H. Beverage, Riverhead, N. Y., and Rich
ard E. Mathes, Westfield, N. J., assignors to
Radio Corporation of America, a corporation
of Delaware
Application July 31, 1940, Serial No. 348,756
12 Claims.
(Cl. 178--22)
l
2
This invention relates to signalling systems and
especially to telegraph systems. Its object is to
insure secrecy in the transmission of messages
and, further, to provide a system in which mes
sages may be transmitted and received in char
acters of a well known code, but only the signal
ling impulses are so altered before transmission
equal length are transmitted. The machines for
transmitting the signals are labeled I, 2, 3 and
are well known automatic transmitters which re
telegraph transmitting devices, respectively.
spond to signal characters impressed on the per
forated tape 4. The perforations of the tape may
be effected by any suitable perforator (not
shown) such as the Kleinschmidt apparatus, well
known in the art. This tape is utilized to control
the transmitters I, 2, and 3 which may be of
the Wheatstone automatic tape transmitter type
for actuating a circuit in accordance with the
perforations in the tape. The individual trans
mitters are each driven by a shaft ‘í which is
connected to a motor 6. The motors S, 6 of the
transmitters I, 2 and 3 rotate at the same speed
and are synchronized as to speed and phase by
pulses received over lead 50 from a commutator
In brief, the present invention employs at each
channel or transmitting position an interrupting
5l mounted on motor 39 in a manner shown and
described in more detail in Figure l of United
over the transmitting medium that they are un
intelligible to unauthorized persons intercepting
them,
The invention is particularly applicable to a
multiplex communication system designed to
transmit a combination of signals having equal
length code characters and signals having un
equal length code characters, such as may em
anate from printer apparatus and Morse code
device such as a cam or switch for reversing the 20 States Patent 2,010,505, supra.
Of course, any
other suitable synchronization circuit may be em
sense of the signals at arbitrarily selected inter
vals; and at the central station at which the mul
tipleX distributor is located for assigning the in
ployed. The power supply apparatus which serves
to supply positive and negative potentials to the
dividual message channels to a common transmis
contacts 9.and I 0 of each transmitter is ar
sion medium, it is proposed to interlace or scram 25 ranged in circuit with a suitable double pole
ble the individual message channels as they are
switch II, which in turn responds to movement
assigned to the distributor at arbitrarily selected
of a cam follower I2 resting on the periphery of
intervals. At the receiver there is provided simi
a cam I3, in turn linked through a shaft I4 and
lar mechanisms for unscrambling the channels
gears to the shaft l. The output energy from
and similar cams and switches for restoring the
each tape transmitter I, 2, 3 is derived from an
sense of the signal characters so that they can
` armature I5 adapted to contact either 9 or I0,
be recorded correctly. For a detailed description
depending upon the perforations in the tape, and
of the type of multiplex system to which the pres
ent invention is particularly applicable, reference
is made to United States Patent No. 2,010,505, c.: Cn
granted August 6, 1935, to Callahan et al.
Apparatus for accomplishing the results of the
present invention is shown in the accompany
ing drawings, wherein:
Figure l illustrates schematically a complete
transmitting system in accordance with the pres
passes over connection I6 to a wiper arm of a
multi-bank rotary selector switch before being
passed on to the multiplex distributor. Although
tape transmitters have been shown for the indi
vidual channels, it should be understood that if
desired any tape transmitter can be replaced by
suitable printer apparatus of the well known tele
type start-stop type, in which case there will be
' associated with each printer and located between
ent invention;
the printer and the rotary switch suitable signal
Figure 2 illustrates the manner in which inter
lacing is effected at the banks of the rotary
storing mechanism in the manner described in
Callahan Patent 2,010,505, supra.
The lines I6, I6 extending to the tape trans
mitters connect to the wiper arms Il of the three
bank rotary selector switch, the individual banks
switch;
Figure 3 illustrates a receiving system in ac
cordance with the present invention; and
Figure 4 illustrates a feature which can be used.
of which are labeled I8, i9 and 20 and shown
in the receiving system of Figure 3 to overcome
separated in order to clarify the connections in
50 the drawings. In. practice, all three banks 5S, I9
possible contact transition difficulties in the re
ceiving system.
Referring to Figure 1 in more detail, there are
’ and 20 are closelj,î adjacent to one another and
have their _wiper arms I'I, l'! simultaneously con
shown three individual message channels (la
trolled and movable over correspondingly located
beled channel #1, channel #2, and channel #3)
over which regular Morse signal characters of un- f
dash line 22 extending from the stepping magnet
contacts by means of a stepping magnet 2 I. The
2,405,991
4
3
comprises a plurality of segments 26, 21 and 28,
each segment being associated with a single chan
2| to the wiper arms I?, I1 is intended to indicate
the unicontrol action of all three wiper arms.
This type of rotary selector switch is well known
in the art and is of a type commonly used in
nel at a time, and a brush assemblage 33 adapted
to sweep over the segments and to obtain there
from the signal units or pulses transmitted by
the channel equipment comprising transmitters
I, 2 and 3. The brush assemblage 33 (which is
telephone and telegraph practice.
Connected to the first contacts o_f the bank
of the rotary switch are lines 23, 24 and 25, re-`
spectively, which extend to distributor segments
26, 21 and 2B of the multiplex distributor, each
segment being individual to a channel. The con
connected to the multiplex equipment 32) is ar
ranged to make one revolution for each dot length
10
of the automatic transmitter equipment, this dot
-length comprising the basic unit (the baud)
which is equal in length to the individual unit
pulsetransmitted over each channel I3. In the
is connected at an arbitrary interVaL'depending
present instance, since a three channel circuit is
upon the position of the wiper, in turn controlled
by the stepping magnet 2l to a diiïerent segment 15 shown, the distributor is arranged to supply to
the multiplex transmitting keyer 32 at most one
' of the multiplex distributor. Only three contacts
tacts on the rotary switch are interlaced or
scrambled in such manner that each channel i6
of each bank of the rotary selector switch are
shown suitably connected and interlaced in Fig
ure 1, in order to illustrate the method of inter
lacing, although al1 ten contacts of each rotary 20
switch are shown interlaced in more detail in
third of a baud from Veach signal unit, this one
third being the length of each unit of signal taken
from each of the respective channels successively,
thus throwing away the other two-thirds of the
dot unit of each signal in each channel which is
Figure 2. More specifically, it will be noted by
referring to Figure 2 that the first contact of
the ñrst bank I8 (to which lead 23 is connected)
is connected to the second contact of the third 25
bank, and then to the third contact of the third
bank, and to the fourth contact of the second
bank, etc. The ñrst contact of the second bankV
later restored by rebuilding the signal in the ‘
rotary selector switch, that when thewiper arms
part of each one-third portion, and to discard
receiver.
The
multiplex
transmitting
keyer
equipment 32 which in turn actuates the radio
transmitting equipment 34 is assigned to each of
the channels #1, #2 and #3 and their respective
lines i6, I5 in succession, for a time equal to one
of these one-third dot or baud portions.
It will be apparent from Figure 1 that al
i9 (to which lead 24 is connected) is shown con
nected to the second contact of the `i'lrst bank 30 though three channels are shown, any number
of channels may be used. For three channel
and to the third contact of the second bank and
working, normally only one-third of each signal
to the fourth contact of the third bank, etc. The
component is actually operative for each chan
ñrst contact of the third bank 20 (to which lead
nel, and similarly for other numbers of channels.
25 is connected) is co-nnected to the second con
tact of the second bank and the third contact of 35 Although for the sake of simplicity it has been
mentioned that one-third of a dot length of each
the ñrst bank, and to the fourth contact of the
unit is assigned to .the transmitter keyer 32,
ñrst bank, etc. It will thus be seen that as the
actually it is preferred to use only a very small
wiper arms I1, l1 move over the contacts of the
are on the first contacts, the ñrst channel will 40 the remainder of the dot length of each channel
be connected through line I6 to lead 23, the sec
unit. This mode of operation has been found
ond channel will be connected through its par
to increase the tolerance of Variation permitted
ticular line It to the lead-2 4, while the third chan
a signal due to fluctuations andV bias distortion,
nel will be connected through its line I6 to lead
noise,v etc. The multiplex transmitting equip
25. However, when the wiper arms I1, l1 are 45 ment 32 functions to produce a composite sig
on the second contacts of the switch, the iirst
nal composed of successive one-third dot length
channel will now be connected to lead 24, while
portions from the three channels consecutively.
the second channel will be connected to lead 25,
This equipment with which the distributing
and the third channel will be connected to lead
brush assemblage 33 is connected comprises es
` 23. In this way there is obtained a scrambling 50 sentially a locking circuit and a shunt keyer ar
or interlacing of channels with the leads 23, 24
rangement for producing tone signals in trans
and 25 extending to the segments of the multiplex
mission line 35 which tone signals c-orrespond to
distributor, thus assuring additional secrecy, that
the composite signal received from the multiplex
is, more than that provided by the feature of the
distributor, these tone signals in turn, controlling
cams I3, i3. The stepping magnet 2|, of course, 55 the radio frequencyemanations in line 35 ex
determines when the wiper arms should advance
tending to the antenna `3l. The locking circuit
to the next contact, and the operation of this
in 32 comprises essentially two electron discharge
stepping magnet can be arbitrarily selected >to
devices (not shown), which have their anodes
provide random interlacing, and this is done by
and their control electrodes resistively intercon
60
connecting the stepping magnet to a cam fol
nected in a manner such that the performance
lower 29 whose closure with a contact 30 leading
has two >degrees of electrical stability. These
to a source of positive potential is determined
devices are unstable when both are drawing cur
by a cam 3l. This cam has'any desired number
rent but stable when one tube is passing current
of arbitrarily selected cam segments to cause the
closure of contacts 29 and 30 at certain inter 65 and the other blocked or prevented from passing
current. The change from one condition of sta
vals. By ïmeans of the cam 3l and its driving
ble equilibrium, such as when one tube is blocked
mechanism, the stepping magnet 2| `may be
and the other passing current to the other con
caused to operate the selector switch at every
dition When the last tube is passing current and
baud or at any desired integral number of bauds ,
70 the ñrst tube blocked, or the reverse, is caused by
or combinations thereof.
the presence of predetermined potential on the
The multiplex distributor consists 0f any suit
brush _assemblage 33. For a more amplified de
able means for assigning the various channels,
scription of such manner of telegraph communi
through leads 23, 24 and 25, to the multiplex
cation reference is made to United ‘States Patent
transmitting keyerV equipment 32. In the ar
rangement shown in the drawings, the distributor _'15 2,010,505, supra, and also to United States Patent
2,405,991'
5
6
1,844,950, granted February 16, 1932, to J. L.
are identical in construction, although, if desired,
the cams for the diiîerent channels may be con
structed differently to have a diiîerent number
of segments. The received message signals which
are changed in character by the cams I 3, I3 at
Finch.
Y
The multiplex distributor is driven by means of
a shaft 38 which is geared to drive motor 39,
the latter in turn .being also geared to the cam
3|. This gearing controls the speed of rotation
the receiver (that is, restored in sense to their
original form) are passed on to suitable locking
Referring now to the receiver of Figure 3, the
circuits 48. These locking circuits consist essen
tially of a pair of electron discharge devices which
composite signals are received over any suitable
type of antenna system 40, amplified and de 10 have their anodes and control electrodes resis
tively interconnected to provide two degrees of
tected in well known manner in equipment 4I,
electrical stability in the same manner as the
and~ then transmitted over transmission line 42
locking circuits in apparatus 32 oi the transmit
to a suitable central ofñce where the receiving
of the multiplex distributor and the cam 3l .
multiplex distributor -43 assigns the received in
coming signals to their respective channels, in
ter, the locking circuits at the transmitter and
receiver being substantially of the same construc
tion. Reference is here made to United States
which the received signals are rebuiltA to their
original form as in the transmitting station, the
PatentsV 2,010,505 and"1,844,950, supra; for fur
portions suppressed at the transmitting station
ther details of a well known form of locking cir
cuit which may be employed. A suitable utiliza
being restored in the receiving system.
Distributor arrangement y43 is driven by a drive 20 tion device, such as an ink recorder or other in
motor 44 which is held in synchronism with the
strument, may be connected to each locking cir
multiplex distributor driving mechanism 39 at
cuit 48 of the receiver.
In order .to avoid the production of undesirable
the transmitting station by means of a suitable
extraneous short clicks in the locking circuit 4S
correction unit (not shown) which may be con
of Figure 3, due to the fact that the closure of
trolled by the incoming signals. This correction
unit for synchronizing the motor ¿M with the mo
the contacts of relay 65 and those of cam I3
tor 39 of the transmitter may be of a type de
might not be exactly simultaneous, it is proposed
scribed in United States Patent 2,010,505, supra,
to employ »a circuit as shown in Figure 4 which
includes a kicker commutator 52 to be inserted
between each locking circuit 48 and its associated
cam i3 in each channel. The knicker commu
tator 52 includes a pair of brushes 53 designed to
or of a type shown in Mathes United States Pat
ent No. 2,062,009, granted November 24, 1936.
Associated with the individual segments of the
multiplex distributor d3 are the banks IS', I9’
and 20’ of a rotary selector switch of a type iden
tical with that described in connection with the
transmitter. The contacts of this rotary selec
tor switch at the receiver are interlaced in the
same way as the contacts of the rotary switch
be connected together at predetermined intervals
by a short-circuiting copper bar 54 mounted on
the insulated surface of 4a rotating drum-like ele
ment driven by `a shaft 55. The rotation of the
drive shaft 55 is of course synchronized as to
at the transmitter, and the stepping magnet 2i’
speed with the other driving units to produce clo
for the rotary switch at the receiver is arranged
to operate by means of cam 3i’ in synchronism
sure of the controls 53 only at the central por
tion of each band of received signal. Thus the
kicker 52 selects the central portion of each band
as it is passed to the locking circuit 48 and uses
the kicks produced thereby for the operation of
the locking circuit 43. In this way the kicker
commutator permits a certain degree of transi
tion time at the contacts of relay ¿l5 and cam I3
with the operation of the cam 3i at the trans
mitter. Cam 3i' at the receiver is, of course, of
identical construction as the cam di at the trans
mitter, and both of these cams rotate in syn
chronism, whereby the rotary selector switch at
the receiver unscrambles the signals caused by
the scrambling arrangement of the rotary switch
at the transmitter, thus producing on leads 23',
24’ and 25’ signals substantially identical in form
to the signals on leads i5, i5 and It respectively,
at the transmitter.
Associated with each ci the leads 23', 2li’ and
25' there is provided a suitable relay 45 of the
vacuum or electromagnetic type which is operm
ated by the rectined signal assigned to its asso
without affecting the signal produced by the lock
ing circuit.
For a more detailed description of
this form of ' kicker commutator reference is
made to Mathes Patent 2,038,375, April 2l, 1936
(Figure 2 thereof).
In the operation of the transmitter of Figure l,
the rotation of cam I3 in each channel will move
the cam follower i2 up and down in accordance
' with depressions on >the cam.
Movement of the
In
cam follower I2 will accordingly cause movement
the output of relay ¿i5 there is provided a double
pole switch II' which is moved in response to the,
receiver are of identical construction as the cams
of the double pole switch II, thus changing the
polarities applied to contacts 9 and I0 by the
power supply. The circuit path from the power
supply through the switch il to the contacts S
and i0 of the automatic transmitter of each
I3, I3 at the transmitter, and are driven simulta
neously at the same speeds as the cams at the
channel will be obvious from a mere inspection
of the drawings. The change in sense of the
ciated lead extending te the rotary switch.
movement of a cam follower i..
periphery of cam i3.
resting on a
The cams i3, i3 at the
polarities applied to contacts 9 and I0 by the
transmitter. For this purpose there is provided at
the receiver a drive motor At which drives the cams 65 cam I3 is arranged to occur in synchronism with
the mechanism in its associated transmitter I, 2
through a suitable shaft and gearing arrange
or 3, whenever it tends to move armature I5.
ment indicated by the dotted line 4l. The Ino
Putting it another way, the polarity reversals
tor 46 is, of course, synchronized to operate at
produced by the cam I3 in each transmitter mair
exactly the same speed as the motor Ei, which
is at the transmitter and is controlled as to speed 70 occur where a dot or baud of unit length is to
be transmitted only at the end of the baud;
and phase from commutator 52 mounted on mo
where a dash having a length equal to a plural
ity of bauds is to be transmitted, the polarity re
connection with motor E in the transmitter. At
versal may occur at the end of any of the com
this time it should be noted that the transmitting
and receiving cams i3, I3 for the same channel 75 ponent bauds constituting the dash, The oc
tor #3Q in the same manner as is described in
2,405,991
7
currence of lthese reversals is determined bythe
arrangement of the cam and Ymay occur at the
end of every baud or at multiple sequences there
of. For example, the cam may be constructed to
produce reversals at the end of every four bauds,
or to produce reversals at non-uniform periods
to further insure secrecy. Further, the cams may
be replaced by tape transmitters serving thev
same purpose. Any suitable type of synchroniz
ing system may be employed for insuring proper
phasing and synchronization of the various ele
ments of the entire system.
What is claimed is:
so long as these periods include an integral num
l. In a multiplex telegraph system, the meth
ber of bauds, although the cams for different
od of signal communication which comprises
transmitters may have different constructions to
produce reversals at the end of a different num 10 transmitting over individual lines a plurality of
message signals corresponding to the number of
ber of bauds.
channels in the system and whose elements‘are
of unit length and multiples o-f unit length,
changing a characteristic of certain elements of
and 25 depending upon the interlacing at .the 15 said signals at predetermined intervals, and as
signing said lines in a predetermined irregular
banks I8, I9 and 20 of the rotary selector switch.
'I'he stepping magnet 2l under control of the cam
sequence to a transmission medium.
2. In a-multiplex telegraph system, the method
3| will determine the intervals at which the
interlacing occurs. The multiplex equipment
of signal communication which comprises trans
per se illustrated by .the multiplex distributor 20 mitting over individual lines a plurality of mes
assigns only a very small portion of the sign-a1 on
sage signals corresponding to the number of
each channel to the keyer and locking circuit 32
channels in the system and whose elements are
of unit length and multiples of unit length, as
for transmission over the antenna 31.
The signals sent out by the transmitters of
the three channels over lines I6, I6 are assigned
at random to different ones of the leads 23, 24
Thus, it will be seen that there are four c0
signing said lines in irregular order to a trans
operative features which contribute to assure 25 mission medium, dividing the successive basic
secrecy in the transmission of the signals. The
time units of the message characters of each
iirst feature comprises cam I3, which produces
channel into substantially equal portions of like
reversals in sense of the signals at arbitrarily se
number not less than the total number of chan
lected intervals. The second feature is the rotary
nels used, and transmitting over said medium a
selector switch which by its interlacing causes 30 composite signal formed by combining equal por
the signals to go to the multiplex distributor over
tions from thesuccessive channels consecutively.
different leads at different times. The third fea
3. In a multiplex telegraph system, the method .
ture resides in the cam 3| at the transmitter
of signal communication which comprises trans
which controls the random or arbitarry stepping
mitting over individual lines a plurality of mes
or operation of the magnet 2I which causes the
sage signals corresponding to the number of
wiper arms I'I to change position at arbitrary
channels in the system and whose elements are
intervals determined by cam 3l and its speed of
of unit length and multiples of unit length,
rotation. The fourth feature lies in the multi
changing the sense of some of the signals prior
plex equipment per se which selects only a small
to transmission over said lines and at predeter
portion of each signal unit and discards the re 40 mined discrete intervals, assigning said lines in
maining portion of the signal.
irregular order and at arbitrarily selected inter
At the receiver there are employed means
vals to a transmission medium, dividing the suc
which correspond to the foregoing means at the
cessive basic time units of the message characters
transmitter for unscrambling and restoring the
into equal portions of like number as the total
signals to their original form. For example, the L. number of channels used, and transmitting over
cams I3 at the receiver function to restore the
said medium a composite signal formed by com
signals back to their true sense or true polarity,
bining equal portions from the successive chan
which they had before they were affected at the
nels consecutively.
transmitter by the polarity reversal cams.-V The
4. In a multiplex telegraph system, the method
three bank rotary selector switch at the receiver
of signal communication which comprises trans
is interlaced in identical manner as the rotary
mitting over individual lines a plurality of mes
selector switch at the transmitter for unscram
sage signals corresponding to the number of chan
bling signals produced by the interlacing at the
nels in the system and whose elements are of unit
transmitter; and the cam 3l’ at the receiver of
length and multiples of unit length, changing the
like construction as cam 3i at the transmitter ' » sense of some of the signals prior to transmission
and operating at the same speed, causes the wiper
over said lines and at predetermined discrete in
arms of the receiving rotary switch to move in
tervals, and assigning said lines in irregular order
synchronism with the movement of the wiper
at arbitrarily selected intervals to a transmission
arms on the rotary switch at the transmitter.
medium.
Finally, the locking circuits 48 at the receiver 60
5. In a multiplex telegraph system, the method
associated with the channels function to restore
of signal communication which comprises trans
or rebuild the individual signal units to their
mitting over individual lines a plurality of mes
original full length, whereby the portions of the
sage signals corresponding to the number oi'
signal units discarded at the transmitter are
channels in the system and whosel elements are
filled in at the receiver.
of unit length and multiples of unit length,
It should be understood that the present in
changing the sense of some of the signals prior
vention is not limited to the precise arrangements
to transmission over said lines and at predeter
of parts illustrated in the drawings, since various
mined discrete intervals, which terminate only
modifications may be made without departing
at the end of a unit length, and assigning said
from the spirit and scope of the invention. The 70 lines in irregular order at arbitrarily selected in
rotary switches may be of any suitable form and
tervals to a transmission medium.
'
may comprise any desired number of contacts.
6. In a multiplex telegraph system, a transmit- ,
The cams may be of any suitable construction
ter employing for each channel a code having
and are not limited in form to those illustrated
characters composed of one or more signal units
in the drawings and may be changed frequently
of fundamental time duration, leads extending
Y n
2,405,991
10
from a transmitting multiplex distributor to said
transmitters, switching means associated with
constituting a component element of a character,
rotating mechanisms for said transmitters, means
said leads and located between said transmitters
and said distributor for assigning said transmit
>ters at different .predetermined irregularly spaced
for synchronizing the speed of said mechanisms,
times to diiîerent ones of said leads, a transmis
leads extending from a transmitting multiplex
distributor to said transmitters, switching means
associated with said leads and located between
sion medium, said distributor serving to assign
said transmitters and said distributor for assign
said medium to said leads in succession and to
each for a period of time equal at most to the
ing said transmitters at different times to differ
ent ones of said leads, a transmission medium,
longest period of which the duration of the funda 10 said distributor serving to assign said medium to
mental time unit is an exact multiple of the num
said lines in succession and to each for a period
ber of channels.
of time equal at most to the longest period of
7. ~A multiplex -telegraph system in accordance
which the duration of the fundamental time unit
with claim 6, characterized in this that said means
is an exact multiple of the number of channels.
l1. In a multiplex telegraph system, a trans
for assigning said transmitters at different times 15
to different ones of said leads comprises a multi
mitter for each channel employing a code hav
ing characters composed of one or more signal
bank rotary selector switch, the contacts of said
banks being interlaced to provide connections
units of fundamental time duration, means at
each transmitter for reversing at predetermined
between said leads and said transmitters which
change in accordance with a predetermined 20 intervals the sense of the signals to be transmit
schedule as said switch advances.
ted, said reversals in sense being arranged to occur
8. In a multiplex telegraph system, a transmit
only at -the end of a unit length of signal con
Iter employing for each channel a code having
stituting a component element of a character,
characters composed of one or more signal units
rotating mechanisms for said transmitters, means
of fundamental time duration, leads extending 25 for synchronizing the speed of said mechanisms,from a transmitting multiplex distributor to said
leads extending from a transmitting multiplex
transmitters, switching means associated with
distributor to said transmitters, switching means
said leads and located between said transmitters
associated with said leads and located between
and said distributor for assigning said transmit
said transmitters and said distributor for assign
ters at different times to diiïerent ones of said
ing said transmitters at different times to diiîer
leads, a transmission medium, said distributor
ent ones of said leads, a transmission medium,
serving to assign said medium ,to said lines in
said distributor serving to assign said medium to
succession and to each for a period or” time equal
at most to the longest period of which the dura
tion of the fundamental time unit is an exact
multiple of the number of channels, a receiver for
receiving the signals sent out over said trans
mission medium, a plurality of receiving circuits
associated with the different channels of said
system, a receiving multiplex distributor for suc
cessively assigning the output of said receiver to
different ones of said receiving circuits for a
period of time to each receiving circuit equal to
a fraction of the period during which each trans
mittei- is assigned to the transmission medium,
switching means located between said last dis
tributor and said receiving circuits for changing
the connections of said receiving circuits to said
distributor at such times and in predetermined
manner to conform with the changing assign
ment of the transmitters to their associated leads,
whereby the receiving circuit of each channel is
associated only with the transmitter for the same
channel.
9. A multiplex telegraph system in accordance
with claim 8, characterized in this that the
switching means associated with both the trans
mitting and receiving multiplex distributors are
said lines in succession and to each for a period
of time equal at most to the longest period of
35 which the duration of the fundamental time unit
is an exact multiple of the number of channels,
a receiver for receiving the signals sent out over
said transmission medium, a plurality of receiv
ing circuits associated with the diiîerent chan
40 nels of said system, a receiving multiplex dis
tributor for successively assigning the output of
said receiver to different ones of said receiving
circuits for a period of time to each receiving
circuit equal to a fraction of the period during
45 which each transmitter is assigned to the trans
mission medium, switching means located be
tween said last distributor and said receiving cir
cuits for changing the connections of said receiv
ing circuits to said distributor at such times and
50 in predetermined manner to conform with the
changing assignment of the transmitters to their
associated leads, whereby the receiving circuit of
each channel is associated only with the trans
mitter for the same channel, and means at each
55 receiver operative in synchronism with the sense
reversal means at the transmitter for the same
channel for restoring the sense of the signals.
l2. In a multiplex telegraph system wherein
signals are composed of marking and spacing ele
similarly arranged multi-bank rotary selector
switches, the banks of each switch having its con 60 ments of unit length and multiples of unit length,
the method of rendering communication secret
tacts interlaced in predetermined manner, said
selector switches operating in synchronism, there
being motor operated means provided for driving
the distributors synchronously.
which comprises periodically reversing the polar
ity of the impulses corresponding to said mark
ing and spacing elements, assigning signal im
10. In a multiplex telegraph system, a trans
pulses of one message at irregular intervals to
different ones of a plurality of multiplex channels
in the system, and assigning signal impulses of
other messages at the same irregular intervals
to the remaining ones of said channels.
mitter for each channel employing a code hav
ing characters Composed of one or more signal
units of fundamental time duration, means at
each transmitter for reversing at `predetermined
intervals the sense of the signals to be transmit 70
ted, said reversals in sense being arranged to oc
cur only at the end of a unit length of signal
HAROLD H. BEVERAGE.
RICHARD E. MATHES.
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