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Патент USA US2406790

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Sept. 3, 1946-
Filed Jan. 16, 1941
2 Sheets-Sheet 1
Fig. 1.
Tl wvml
Sept. 3, ‘1946. V
Filed Jan. 16, 1941
Fig. 5.
2 Sheets-Sheet 2
Patented Sept. 3, 1946
William Arnold Beatty
and Leslie Wilfred
Houghton, London, England, assignors to In
ternational Standard Electric Corporation, New
York, N. Y.
Application January 16, 1941, Serial No. 374,660
In Great Britain January 16, 1940
10 Claims.
(Cl. 179-15)
This invention relates to a transmission sys
trailing and leading edge being ?utter modulated
in phase by similar amounts) pulses as described
tem which for the purpose of conveying intelli
gence utilises pulses which are time modulated
in such a manner that their durations or times
of occurrence are characteristic of the ampli
tudes of sound or like waves. The system has
particular application to secret or camou?aged
communication methods, and although the de
scription which follows relates to such methods
of communication, the system is not limited to
secret transmission but can with advantage be
employed in other manners.
In United States Patent 2,256,336, September
in the above mentioned patent application Ser.
No. 375,814, transmitting said duplex time
modulated pulses by wire or wireless, and at a
receiver reconstituting in any known manner, if
desired, the intelligence characteristic of the
main time modulation, while for the purpose of
reconstituting the intelligence due to said modi
fying time modulation, pulses of constant dura
tion are derived from said modi?ed ?xed edges,
said derived pulses of constant duration occur
ring at cyclically varying intervals of time giving
16, 1941, and U. (S. application Ser. No. 375,814,
the intelligence characteristic of the modifying
?led January 24, 1941, reference is made to time 15 time modulation.
modulated pulses of various types, and these dif
In a, practical example adapted for the pur
ferent types of pulses for the purpose of conven
pose of transmitting a camou?aged communica“
ience Were given identi?cation code letters, and
tion, the system Works as follows, referring to
some of the same code letters for similar types
accompanying drawings serving to illustrate the
of pulses will also be used in the description 20 description in which, Fig. l is a diagram of the
which follows.
modulating circuit; Figs. 2, 3 and 4 are curves
The objects of the invention are achieved by
illustrating operation of the system, and Fig. 5
modifying the time modulation of a train of
is a discriminating circuit arrangement.
pulses which in the normal unmodi?ed condition
RT-l-F pulses are generated according to the
are time modulated so that their durations are 25 method disclosed in the above mentioned patent
characteristic of the amplitude of a sound or like
application Ser. No. 375,814, the main modulation
wave, said train of pulses being characterised in
of the RT pulses being much greater than the
that in the unmodi?ed condition one series of
modifying modulation (1. e. ?utter modulation) of
edges, referred to as the “?xed edges,” either the
said pulses. Referring to Fig. 1 of the drawings
leading edges or the trailing edges in every case,
a signal wave characteristic of speech is taken
of the pulses in the train, occurs at equal inter
from source II to speech scrambling apparatus
vals of time (i. e. the pulses in the unmodi?ed
I2 referred to as “unintelligible scrambling ap
condition are rectangular trailing edge RT or
paratus,” and also to speech scrambling appara—
rectangular leading edge RL pulses), said modi
tus l3 referred to as “intelligible scrambling ap
?cation of said time modulation being the cyclic 35 paratus.” The apparatus l2 scrambles the in
changing of the times of occurrence of said nor
coming speech in such a random fashion that
mally ?xed edges, or the cyclic changing of the
intelligible speech cannot be reconstituted, while
times of occurrence of both the normally ?xed
the apparatus l3 scrambles the speech in such a
manner that with suitable apparatus intelligible
speech can be reconstituted. The scrambled
speech outputs from apparatus l2 and is are
edges and the other edges of the pulse train, said
cyclic time changes being characteristic of the
amplitude of a sound or like wave (the ?rst of
the above stated time modulations being for the
fed to the above mentioned>RT+F pulse gener
ating and time modulating apparatus it, said
time modulation,” while the second is referred
apparatus producing a train of RT-l-F pulses 15,
to as the “modifying time modulation,” the com 45 part of such pulse train being shown in Fig. 2.
bined systems being referred to as “duplex time
The durations of the pulses l5 vary cyclically in
modulation,” i. e. the pulses are RFL (rectangu
accordance With the variations in amplitude of
lar with ?uttering leading edge the trailing edge
the unintelligible scrambled speech from appa
being variable) or RFT (rectangular with ?ut
ratus I2, while the time of occurrence of the
tering trailing edge the leading edge being vari 50 trailing edges iii of said pulses varies cyclically
purpose of convenience referred to as the “main
able) or are RL-i-F (rectangular pulse with‘ lead
ing edge normally ?xed and trailing edge vari
able the trailing and leading edges being ?utter
in accordance with the amplitude of the scram
‘ bled speech from apparatus l3, said cyclic tone
variations being shown relative to the equal time
intervals indicated by the dotted lines IT.
RT-l-F (rectangular pulses with trailing edge 55 The RT-l-F pulse train time modulated in the
normally ?xed and leading edge variable, the
manner described above, now has two types of
modulated in phase by similar amounts) or
time modulation, and when such a, train is re
ceived by ‘known amplitude modulated apparatus
the intelligible and unintelligible scrambled
works are employed for the establishment of the
pulses 18, some of the intelligence due to the main
time modulation also appears inrthe circuits giv
ing the ‘pulses E8. The . effect of such break
speech can be made audible. Owingto‘ the fact
through of the main time modulation is obviated
that the unintelligible scrambled speech has a
by feeding some of the pulse train shown in Fig. 2
time modulation much greater than that of the
in reversed phase to the break through modula
intelligible scrambled speech, the presence of the
tion thus cancelling out the break through inter
latter would not be suspected by persons unfa
fering signal. The method described is capable of
miliar with the system. Suchpersons desiring
to reconstitute the speech intelligence would con 10 giving signal discrimination such that when with
normal receivers the intelligence due to the mod
centrate on the main modulation, and since this
ifying modulation is entirely masked by the in
is due to speech which has been scrambled in a
random fashion it would be impossible to recon
telligence due to the main modulation, with spe
stitute the resulting signal into‘ intelligible
cial reception methods as described the intelli
speech. The modifying modulation due to the
gence due to the modifying modulation can be
intelligible scrambling would with ordinary‘ separated out with practically no remaining trace
methods of reception be entirely masked by the
of the intelligence due to the main modulation.
A circuit arrangement which gives good dis
much stronger main modulation, and unless per
sons were familiar with a method of separating
crimination between the intelligence due to the
the modifying time modulation from the main
modifying time modulation, and the intelligence
time modulation ‘the intelligence conveyed by the
due to the main modulation Will now be described.
former time modulation would always be unin
Referring to Fig. 5 there is shown a three valve
circuit arrangement.
telligible and its existence would not even be sus
The duplex time modulated pulse train is fed
A method of separating the F type of modula 25 into the circuit at the two terminals 3|, earth,
tion from an RT-i-F time modulation has been
and 32 across which is connected a short time
described in the above mentioned patent applica
constant circuit consisting of condenser 33 and
tion Ser. No. 375,814, this method consisting of
7 variable resistance 34 in series, capable of differ
setting up at the end of pulse signals, damped
' entiating the leading edges of the pulse train con
trains of varying amplitudes and separating the 30 stituting the signal, these edges in the, case under
resulting damped. trains from the main signal.
consideration being normally ?xed edges and are
The above mentioned method employing damped
slightly time modulated by the modifying time
trains requires very careful adjustments at the
modulation, the resulting differentiated pulses
, transmitter and receiver, and one object of this
are pulses of constant Width occurring at vary
invention is to disclose simpler methods of sepa 35 ing time intervals. These pulses are now fed
rating a modifying time modulation from a main
through resistance 35 to the control grid 41 of
time modulation.
valve 31, which also has an anode 38, suppressor
The improved method of separating the modi
grid 39, screen grid Ml, cathode 42 to which is
fying time modulation from the main time de
connected the suppressor grid 39, and a heater 43.
pends upon deriving from the pulse edges which
As the incoming signal consists of a positive
pulse, the diiferentiated pulse will be negative so
in the unmodi?ed condition would occur at equal
that this will appear as a positive ampli?ed pulse,
time intervals, short marking pulses of constant
duration but occurring at time intervals charac
across the anode resistance 41 of valve 37. To
prevent a differentiated pulse from the trailing
teristic of the modifying time modulation. Such
a derived pulse train is shown in Fig. 3 the pulses 45 edge of incoming signal pulse appearing here also
the grid 4| is kept at a positive potential by
18 of constant duration occurring at time inter
means of resistance 36 connected from H. T.+.
vals characteristic of the times of occurrence of
to the junction of condenser 33 and resistance
the trailing edges I6 of the pulses It. The effect
34. The unwanted signal which this edge pro-_
of such pulses occurring at unequal intervals of
time is to time modulate the interval periods of 50 vides is also further reduced by resistance 44
connected from input terminal 32 to cathode 42,
time between successive pulses, and on an analysis
it can be shown that such time modulation is
characteristic of the changes in amplitude of a
sound or like wave, this novel time modulation
from which is also connected cathode resistance
45, and cathode condenser 46.
Adjustment of
variable resistance 34 gives a position at which
characteristic being diiferent to that usually ob.-v 55 the ratio of wanted signal to unwanted signal
(1. e. modifying intelligence to main intelligence)
tained when the time modulation is characteristicv
is a maximum. The circuit for valve 31 is further
of the amplitude of a sound or like wave. It has
completed by screen resistance 48 and associated
now been found that time modulation character
condenser 49.
istic of the changes in amplitude of a sound or like
The required signal, in the form of short dura
wave is as effective for the purpose of conveying. 60
tion pulses occurring at varying time intervals
intelligence as the previously known time modula
are now detected and converted into an audio fre
tion which is characteristic of the amplitudeof
quency signal by passing them from the anode
' 3B of ‘valve 31. to the grid 54 of valve 52 via con
One method of obtaining a pulse train as shown
in Fig. 3 is to feed the pulses 15 to a simple con 65 denser 50 and grid leak resistance 5|. This audio
frequencyvwhich thenappears across anode re
denser and resistor differentiating circuitof short
sistance 51 is passed to valve 63 through con
time constant, giving in any known mannerthe
denser 59,’ and resistance 60 to the grid 61 for
type of train it shown in Fig. 4 the leading edges
of the pulses 20 corresponding to the vtrailing ‘ further ampli?cation.
In addition to grid 54, valve 512 has an anode
edges R6 of the pulses l5, while the pulses 2| .cor 70
53, cathode 5s and heater 5s, and its circuit is
respond to the leading edges 22 of the pulses |5.,
completed by connnecting cathode 515 to earth,
The pulses 2| can be removed from the train l9
also in- addition, there is a condenser 58 from
by means of an amplitude ?lter, giving the train
of pulses I8 shown in Fig. 3. ' q
anode 53ito earth to bypass the higher unwanted
Owing to the fact that resistance capacity ‘net
be reconstructed therefrom.
5. The method according to claim 1, further
comprising deriving said one kind of intelligence
from a first source of original intelligence by
random scrambling of said original intelligence
so that said original intelligence cannot be recon
stituted therefrom, and deriving said other kind
‘l3, and an inductance ‘5:’! as an anode load from
anode 64 to H. T.
The required signal which
is developed across this is then fed to the out
put terminal 14 via condenser ‘H and is there
fore obtained between terminals ‘iii and 15, the
latter being at earth potential.
Another method of obtaining from the train
of pulses I5 shown in Fig. 2 of the drawings a
train of pulses substantially similar to those
shown in Fig. 3, is to feed the pulses [5 over two
channels one of which has a time delay greater
than the other by a time period equal to the
duration of the pulses [8. ‘The pulses l5 fed
intelligence so that said original intelligence can
The circuit for valve 63 which also consists of
an anode 64, suppressor grid 65 connected to
cathode t8, screened grid 66 and heater 69, is
completed by grid leak 6i, across which is con
denser (52, cathode resistance 72 and condenser
of intelligence by intelligible scrambling of origi
nal intelligence from a second source of original
intelligence so that said second original intelli
gence ‘can be reconstructed therefrom.
ii. The method of signalling with two kinds of
a single train of pulses of constant
amplitude, comprising giving to said pulses a
time modulation of one magnitude by a ?rst of
said two kinds of intelligence, giving to said pulses
a time modulation of a lower magnitude by the
second of said two kinds of intelligence, receiving
in phase and combined with the pulses [5 fed 20 said pulses after both modulations, and discrimi
nating between said two modulations to produce
over the other channel, giving a pulse train sub
a signal by said second kind of intelligence.
stantially similar to that shown in Fig. 4. Using
7. A receiver for receiving energy from a sys
an amplitude ?lter as already described the posi
tem in which a main intelligence and a modifying
tive pulses are separated from the train having
intelligence are transmitted by different time
positive and negative pulses, resulting in a pulse
modulations of a single train of main pulses of
train similar to that shown in Fig. 3 except that
constant amplitude and adapted to separate said
the trailing instead of the leading edge of the
modifying intelligence from said main intelli
pulses coincide with the trailing edges it of the
gence, including intelligence separation means
pulses i5.
If desired the camou?aging of the intelligence 30 comprising apparatus to establish a train of
marking pulses having constant durations which
can be made more certain by arranging at the
are short compared to the main pulses, said mark
transmitter that the circuit between the appara
ing pulses serving to indicate the times of occur
tus l3 and M is closed only when an output is
rence of the normally ?xed edges of said main
being obtained from the apparatus I2. This can
be achieved in any known manner for instance 35 pulses, combined with output apparatus ar
ranged to give an output due to the time modula
by means of mechanical or thermionic relays.
tion of the time intervals between said marking
Although the duplex time modulation system
pulses, said time modulation being due to the
has been described having reference to camou
cyclic variations in the times of occurrence of
?aged communication methods, it should be obvi
ous that it can be applied in other manners. For 40 said normally ?xed edges, and means coupled to
said output apparatus for suppressing any output
instance, the duplex time modulation could re
due to said main time modulation.
late to the stereophonic transmission of a. sound
8. A receiver according to claim 7 further com
wave, or the modifying time modulation could
prising apparatus serving .to establish said train
relate to the degree of volume expansion or com
of marking pulses, said apparatus comprising
pression of the signal conveyed by the main time
means adapted to differentiate said main pulses,
modulation, by continuously transmitting by
and to given an output due to the normally ?xed
means of said modifying time modulation a sub
edge differential pulses and to simultaneously
audible signal the mean amplitude of which is
suppress the other edge differential pulses.
characteristic of said volume expansion or com
9. A receiver according to claim 7 further com—
prising apparatus serving to establish said train
What is claimed is:
of marking pulses, said apparatus comprising
1. The method of transmitting two kinds of in
means for feeding said main pulses in reversed
telligence simultaneously by means of a single
phase over a channel having a delay equal to the
train of pulses of constant amplitude, comprising
time modulating said pulses in one sense to trans 55 duration of said marking pulses, and being fur
ther adapted to give an output due to the commit one of said kinds of intelligence, and time
bination of said reversed phase and delayed pulses
modulating said impulses in a different sense to
with said main pulses, said output comprising two
transmit the other of said two kinds of intelli
trains of marking pulses one positive and the
2. The method according to claim 1, wherein 60 other negative, and apparatus arranged to give
an output due to whichever of said positive or
said one of said kinds of intelligence permits one
negative marking pulses serve to mark the nor
corresponding edge of each of the impulses to
mally ?xed edges of said main pulses, and to
occur at equal time intervals.
simultaneously suppress the other marking pulses
3. The method according to claim 1, wherein
‘marking the other edges of said main pulses.
the time modulation of said one kind of intelli
10. A receiver according to claim '7 wherein
gence is greater than the time modulation of said
said means serving to suppress an output due to
other kind of intelligence.
said main time modulation, comprises means for
4. The method according to claim 1, further
reversing the phase of said main pulses and for
comprising deriving said one kind of intelligence
from a source of original intelligence by random 70 combining said reversed phase pulses having any
desired amplitude with said main pulses which
scrambling of said original intelligence so that
may appear in said ?nal output circuit.
said original intelligence cannot be reconstituted
therefrom, and deriving said other kind of intelli
gence by intelligible scrambling of said original
over the channel with the more delay are reversed
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