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Патент USA US2404356

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July 23, 1946.
c. E. A'rKlNs
2,404,356 l
SECRET SIGNALING SYSTEM
Filed June 3, -1944
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July 23, 1946.
c. E. ATKlNs Y
2,404,356
SECRET SÍGNALING SYSTEM
Filled June 5, 1944
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INVENTOR
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2,404,356
Patented July 23, 1946
UNITED STATES PATENT "OFFICE
2,404,356SECRET SIGNALING SYSTEM
Carl Edward Atkins, Elgin, Ill., assignor to Tung-
.
Sol YLamp Works, Inc., Newark, N. lJ., `a corpora-
.
.
tion of Delaware
Application June 3, 1944, Serial No. '538,667
10 Claims.
(Cl. 179---1.5)
1
v2
My present invention relates to secret station
to-station communication-systems, of the general
type disclosed in my copending applications Serial
No. 443,898, ñled May 21, 1942, and Serial No.
either of two sources butY not when activated by
504,679, iiled October 2, 1943, wherein the signal
bothsources simultaneously. Thus whenkey Illa
is depressed vand if there is vnooutput fromthe
detector 4a, transmitting gate 6a will'operate- to
pass a signal, .but if the input terminals of gate
originating at one station is used to scramble the
6a are Asimultaneously activated .from the signal
signal transmitted from the other station. In the
system of application Serial No. 504,679, inter
source by lthe -key lila and from the detector 4a,
no signal is'v passed by the gate. Conversely, if
modulation -is effected by simultaneously keying
key Iûa is not depressed but a lsignal is impressed
the equipment a't the two stations. A monotone 10 upon »gate ßa'from detector 4a, the gate passes
of the same frequency Iis yinjected in such phase
the signal. The ysame is -true of transmitting gate
relationship that there is :no change in amplitude
6b and of receiving gates 2a and 2b. These gaies
when the keys at both stations are simultaneously
depressed but only a change of phase. The pres
ent system differs from the system above briefly
>described and from the system of application
Serial No. 443,898 in that when the .keys at the
are varieties of electronic switches and ywill be
more fully described hereinafter .in connection
with Fig. 2. The equipment at each stationY will
,include also, of course, the necessary radioV fre
quency apparatus for the transmission and radia
two stations are simultaneously depressed no sig
tion of the signal passed by the transmitting gate
nal is transmitted from one lstation to the other.
and for reception and demodulation of the energy
In the present system the signal »energy from one 20 radiated ¿from the other station before delivery
transmitter serves to reverse the background con
of the ysignal to the rreceiving gate. These ele
ditions for the other. Thus during a period of
ments kof the 4system Vhave been omitted from
silence a telegraphic symbol may be transmitted
Fig. 1 for simplicity .but are ‘included in the circuit
drawing of.Fig.,2.
~'
while during the subsequent period, which may
In’operation of the system of Fig. 1, if key i-Ua
be a millisecond, several seconds or even a minute, 25
the appearance of a .signal might mean that no
is depressed, transmitting gat-e -Ba is activated and
character at all was being sent but that an alter
a signal is sent to station B, where, after recep
nate type of background was being used.
tion and demodulation, receiving gate 2b is acti
For an understanding of the present invention
Vated and passes the signal on toI detector »4b.
reference may be had to theaccompanying 4draw 30 In the »output »of detector 4b the signal is Aavail
ings, 'of which
,able fas useful intelligence and is also used to
Fig. 1 is a simplified block diagram of equip
actuate ytransmitting gate 6b which causesthe ment at two communicating stations for opera
signal to be returned to station A for application
tion of the new system;
>to vone input terminal of receiving gate 2a. At
Fig. 2 is a circuit diagram of the complete 35 the same time .that the depression -o-fìkey «lilla
equipment suitable for use at 'each station and
started the signal onits wayto station B and
representing the preferred embodiment of `the
back to station A, Vit also :started a similar signal,
invention; and
,
.a pulse of exactly the same time duration, through Y l
Fig. 3 is a graph explanatory of therelati‘on
.the Ylocal ¿delay system '8a.Y Delay system 8a, yas
between charging _potential and gateY output .in -40 `.more fully described in -connection with Fig; l2,
the various networks of Fig. .2.
isconstructed to simulate @the time characteristics
'I‘he new system and its operation will 'i'lrst be
of the equipment at station B and of the inter
described by reference to the simple diagram Iof
vening space.. .'I‘hus Ythe yreturning signal-‘arrives
Fig. 1. As shown .in li‘ig. 1, the essential fequip
ment at station vA comprises a .receiving v,gate 2a,
,atione of the input terminals of receiving gate
»2a simultaneously with the --arrival at the other '
detector 4a, transmitting gate 6a, a delay system
input terminal of asimilar signal locally retained
Ba, and `a key 'lila for introduction of the signal, ' >by>an-d` delivered through the >delay system 8a and'
the output from those various instrumentalities
.hence Jboth input terminals lof the gate 2a beingy
being delivered in the directions indicated by the
activatedmo signal isjpassed‘to `detector 4a. Y Sim- 'Y
respective arrows. vStation >B .is provided with :
ilarly, when key vMib -on‘lyis depressed, the signalV '
similar equipment, namely, receiving gate 2b, a
detector 4b, a transmitting gate 6b, a delay sys
tem ’812, and a .key lûb. Each “gate” Yhas two
input terminals and one :output terminal. Its
yfunction is to .pass a signal when activated by
>is passed by transmitting :gate 6b, radiated from , ' '
station B, received at :stati-on A, 'passed by. receiv
ing gate i211, detected’ at station A, -passed by
transmitting Igate iifartransmitted back to‘s‘tation,
yB 'and L"blocked'atreceivingtgate12b :by the dupli
V
2,404,356
3
ich is depressed at the moment when the signal
the balance of the “gate” is upset and energy is
passed. When the inner grids of both tubes are
negative, both tubes are blocked and the “gate”
from key Iûa ñrst reaches the portals of trans
mitting gate 6b, that is after transmission from
three position switch which is “off” when the
cate signal retained and delayed by delay system
8b. If key Ita is depressed and subsequently key
station A, reception and detection at station B,
then transmitting gate 6b will not operate and
nothing will be transmitted to station A. How
ever the depression of key IDb will be detected at
station A because receiving gate 2a, being acti
vated only by the delayed signal through system
8a, will pass energy to operate detector 4a. If key
Ilia is still depressed, then after detection by de
tector 4m, transmitting gate 6a will cease to oper
ate. No signal will be radiated to station B but
receiving gate 2b will operate because of activa
tion through delay system 8b. Thus if both keys
passes no energy.
The gate 2 is thus a kind of
inner grids of both tubes are at ground potential,
can be turned “on” by a suitable‘negative voltage
on the inner grid of either one‘of the tubes, and
can be turned “off” again if' the corresponding
grid of the other tube is likewise made negative.
In the particular embodiment of the invention
illustrated in Fig. 2‘, receiving gate 2, as hereto
fore indicated, is excited by radio frequency en
ergy applied to the outer grids of tubes I8 and I9.
Audio frequency energy could be employed for
this purpose but radio frequency energy is pre
ferred in order that transmitting gate 6 can be
actuated by a rectiñer system containing little or
are depressed for a substantial length of time no
no time delay.
signal is sent from one station to the other but
Energy passed by the transformer 24 is rectified
the fact of the depression of the key of one sta 20
by rectiñer 26 and appears across load network
tion is made apparent by the operation of the
28. As previously indicated network 28 need in
detector at the other station. If after both keys
troduce little or no time delay and its rectified
have been depressed and no signal is being trans
potential is almost immediately applied to a grid
mitted from one station to the other, as above de
of one tube of the transmitting gate 6. The ele
scribed, one of the keys is lifted, a signal will be
ments 23, 24, 26 and 28 comprise the detector 4
sent from that station and after a suitable delay a
signal will follow from the other station. If both
keys are worked the keying at the two stations will
be superimposed and each signal will be subjected
corresponding to the units 4a and 4b of Fig. 1.
As indicated in Fig. 1, the output of the detector
may yield the useful signal, for example, the volt
to a more or less capricious scrambling. Thus if
one key is held down for a sustained period of
age across network 28 can be directly utilized as
a signal or indicator operating means. Prefer
time, periods of' depression of the other key corre
spond to periods of no signal transmission be
tween stations. Thus the holding down of one key
has the effect of reversal of background for the
operate a separate detector unit 30 as hereinafter
described.
other, so far as concerns an interceptor of the
transmitted radiation.
Specific apparatus functioning as above de
scribed in connection with the simple block dia
gram of Fig. 1 is shown in Fig. 2 to which refer
ence‘may now be had.
In Fig. 2 a suitable re
ceiving mechanism I2 is shown Within the dashed
line enclosure as including an antenna, a wave
trap tuned to the transmitting frequency of the
same station and conventional radio frequency
amplifier, demodulator and audio frequency am
plifier circuits. The output of the receiving mech
ably, however, this Voltage is used indirectly to
The transmitting gate 6 is substantially similar
to gate 2 except that it is arranged for excita
tion by audio frequency rather than radio fre
quency energy. As shown, gate 6 includes two
tubes 3I and 32 having their cathodes connected
by a resistor having a variable center tapped
ground connection, their anodes connected in par
allel to the primary of a'transformer 34 and their
outer control grids connected for excitation across
a center tapped secondary of transformer 36 con
nected to a source of audio frequency energy. The
inner control grid of tube 3l is connected to the
network 28 of detector 4 and the inner control
grid of tube 32 is connected through a network
anism I2 is fed to a rectifier I4 which differs from
40 simulating the characteristics of network 28;
the conventional half wave diode rectifier circuit
`in the inclusion of a series resistor I6. The func 50 and a resistor 4I with the key I0. The key Il),
when closed applies a negative potential to the
»tion' of resistor I6 will become apparent herin
after. rI’he output from rectifier I4 provides the
D. C. voltage needed for activation of the receiv
ing gate 2. As shown, gate 2 includes a pair of
tubes I8 and I9 such as the 6 SAlGT. The cath
odes of the tubes are connected through a resistor
2n having an adjustable center grounded tap.
grid of tube 33 suñ'icient to block operation of
the tube.
The detector unit 30 includes a high y. triode
f- 42 the grid of which is excited vby an audio fre
quency tone and the cathode of which is con
nected to the cathode of tube 3| of gate 6. Nor
mally the positive potential on the cathode of
The inner grid of tube I8 is connected to the out
tube 42, due to the space current of gate tube
put circuit of rectifier I4 and the inner grid of
tube I9 is connected to delay system 8. The outer 60 3'I so blocks the tube 42 that the audio frequency
tone is not heard in the ear phones 44 connected
grids of tubes I8 and I9 are excited by radio
to the plate of tube 42 through the' blocking con
frequency voltages from an oscillator circuit
denser 45. When gate tube 3I is blocked, how
through a tuned transformer with a center tapped
arrangement. The oscillator circuit, here shown
as of the Colpitts type, and the transformer are
indicated by the reference number 22. The plates
of tubes I8 and I9 are parallel connected to a
tuned-circuit comprising a variable capacity 23
connected across the primary of a radio frequency
transformer 24. The tap on resistorA 20 is so ad
ever, by voltages appearing across network 28 of
detector 5, tube 42 becomes ’operative and a tone
is heard in the head phones 44. This corresponds
to the keying action at the cooperative station
when the system is operating properly.
In the particular embodiment'of rthe invention
70 illustrated in Fig. 2, the output of transmitting
gate 6 is used to amplitude modulate a'trans
mitter 46. Instead of amplitude modulation,
.I9 are at ground potential, substantially no en
phase or frequency modulation could bel employed
ergy appears in the output circuit of the gate.
When a negative potential is applied to the inner
one delay
or both
system
stations.
'.8 which".
`. 21;».comprisesl
. ‘ _`
aseries
.
grid of either tube I3 or I9, that tube is blocked, 75 at'I'he
justed that when the inner gridsof tubes I8 and
2,404,356
„.6
of gates and ñlters will now be described." The
:first gate includes a. .pair of tubes 48 and 49 VAhav
ing their anodes connected in parallel through Va
load impedance 50 to a source of positive potential and their cathodes connected to ground
through adjustable resistors 5I and 452. The
networkcondensers become charged at maximum;
YIn’
3 the krelation lbetween `charging potential
andA gate output is graphically representedi If
the maximum negative charging potential for the
inner grid Vof one lof the tubes of a gate is .repre?
sented by E1 lon Fig. '3, then from the graph it
isapparent that the gate output will reach its
maximum prior to complete charging of the >gate
grid and that minor variations in the charging
outer grids of tubes 48 and -49 are connected ,for
excitation to the transformer 36. The vinner grid
of tube 48 is connected through network 40 and
resistor 4I with key lil while the inner grid of 10 potential will have no eifect upon the gate Áout
tube 49 is grounded. Thus 'when key I-ß is up,
put. On the other ihandl'with-a maximumcharg
both inner grids are at ground potential and the
ing potential represented by the lineqEe, .the gate
gate comprising tubes 48 and 49 does not pass
out-put will not reach-its maximum .value and
energy, but when key I'U is depressed, tube '48 is
variations in the charging potential result in
blocked by the application of negative voltages 15 variations in gate output; In order for the sys
to its cathode, the gate becomes unbalanced and
tem as a whole to operate ias hereinbe?ore -de'
a signal appears across impedance 5U. 'This sig
scribed, it is thus necessary to correlate` the mag.
nal is îfed through a delay filter ‘54 designed and
.nitudes of the resistors and condensers ofthe
y»adjusted to simulate the delay occasioned by
various networks and the charging potential, such
transmission of the signal through the lspace 20 as E1, E2 or Es, so as‘to insure 'equalftime delays
»from one station to the other. From the ñlter
during charging and discharging of the grids- 'of
54, the ysignal is fed through a rectiiier network
the various- gates.
' '
`
having time characteristics simulating lthose of
The invention has now beenV described in con
nection with one -speciñc embodiment thereof.
detector I4 at the other station. Output from
rectiñer 56 unbalances a second gate of the delay
system 8 comprising the tubes il and 58 causing
Obviously the invention as >diagrammatically il.
lustrated in Fig. .l -could be embodied in equip
‘the signal to appear across a load impedance ‘6B
and to be fed to a second delay ñlter 6'2. Filter
ment differing from that specifically illustrated v
in Fig. 2, andv various changes inthe circuits of
'62, like -ñlter 54, is designed to simulate the delay
Fig. 2 will -oc’cur to those skilled in the art.-` .For
occasioned by transmission of the signal through 30 example, although the blocking `of a »gatetube
space from one station to the other. LFinally, the
has been show-n and described asv being’efi'ect‘ed
output from filter 6'2 is applied to a rectifier '64
by the application of a negative voltage `to the
having time characteristics similar to rectiñer i4
inner grid of the tube, the'tube could be blocked
of the same station. The rectified potential
by other means, as for example by groundingof
across the network 66 in the output o1" rectiñer 35 the outer grid. Although the particular hal'f Y
64 is applied to the inner grid of tube I9 of re
wave rectifier `circuits with ltheir accompanying
ceiving Igate 2.
-time delay element heretofore described are `pref- '
When two stations are each equipped with the
erably employed inthe system, full wave recti
instrumentalities of Fig. 2 and when the various
iiers involving 'substantial ~reduction ‘in time delay
networks thereof are properly adjusted, the lsys 40 `could be employed if desired. îOth'er alternatives
tem will operate as previously described in con
nection with Fig. 1. In order to insure that the
concurrent depression of the keys at the two sta
tions causes an absence of signalling between the
within the -spirit >of `the invention as deñned in ’
theappended claims will 4‘occur -to ‘those skilled
in the art.
I
claim:
’
Y
'
~
'
»
c
stations, precise timing is essential, that is the 45 1.z A secret station-to-station signaling system
charge rates and also the discharge rates >of all
comprisingin combination a receiving “gate” and
important time delay networks must be identical.
ffl-'transmitting gate at each station, each of said
This is due to the fact that the depression of a
“gates” having two input terminals ‘and teach
key while the system is quiescent calls for the
vadapted to pass energywhen 'activated at'e'ither
charging of all the cascade networks and the
one of saidterminals and to block the’p'assjage
concurrent and synchronous charging rof similar
of energy when activated at neithero‘f the input
networks in the delay lsystem 8, while when the
terminals or at both simultaneously, key means
system is operative due to the depression of one
at each station connected to one of said input
key, the subsequent depression of the key at the
'terminals of each of said gatesior :activation
other station serves to discharge all the signal 55 thereof, means v interposed betweenV >‘said >key
channel networks while matching this action
means `and the 'terminal o'f said ‘receivingfgat‘e "
timewise `>with a charging procedure in the local
:for introducing a time delay between operation
delay system 8. This requirement explains the
.of the .key means Yand `activation of the terminal
‘special form of rectifier units used in the system.
ofV theV receiving gate, 'a 'detector connec'te’dfI-bei
The series resistors, such as resistor I6 in unit I 4,
>tween-said receiving. .gate andthe other' _inëput
retards the charging rate for the shunt condenser
terminal -of said transmitting gate', 'and .means
in the output network of the rectifier so that the
at each »station for transmitting energyY passed
same amount of time will .be required for charg
by :the transmitting gate to the other station Afor
ing as for discharging. It should be noted that
.actuation of the »other input .terminal of the
when the exciting input voltage of a rectiñer unit 65 `receiving gate at that station whereby 'th‘e.rle~
disappears, the rectilinear character of 'the diode
tector at each station can be made îtorespon'd
of the rectiñer serves to isolate the output net
-only to -signals initiated by the key ‘means at
work from the rest of the system so that its dis
the distant station.
.
'
_
ii .
charge rate is for the most part a function of its
Y2. A station-to-st-ation 'secret signaling system
own constants.
70 comprising interconnected receiving andfîtrans-A
Since the gates are voltage operated devices,
any consideration of the time delay involved in
operating them must also consider the magnitude
of the various negative charging potentials and
therefore the absolute value to which any of the 75
mitting means at each station, signal introduc
ing means at each station, detecting means at
each station interposed between said receiving
and transmitting means, means at each station
for creating a delayed replica of the locally in
2,404,356
8
7
6. The signaling system according to. claim 2
troduced signal, means for suppressing the trans
mission .of a signal when the signal introducing
means and the detecting means are simultane
wherein said receiving means includes a rectiñer
circuit comprising a diode, an input circuit con
nected to the cathode of said diode comprising
ously operated, and means jointly controlled by
said means for creating a delayed replica of the 5 a condenser and resistor connected in series and
a resistor having one end connected to said con
local signal and by said receiving means for
denser and to said first resistor and its other end
suppressing operation of the detecting means
connected to a source of low positive potential
when the energy passed by said receiving means
and an output circuit connectedr to the anode
results from the retransmission from the other
of said diode comprising a resistor anda con
station of the signal previously introduced at the
denser connected in parallel, the various resistors
same station whereby no signal is transmitted
and condensers being so proportioned that the
from one station to the other during simultane
time rate of charging of said output network,
ous operation of the signal lintroducing means
upon
application of energy to the condenser in
at lboth stations.
the input circuit equals the time rate of dis
3. The secret signaling system according to
charge of the output network upon cessation of
claim 2 wherein said means for suppressing the
the application of energy to the input condenser.
transmission of a signal when the signal intro
7. In a secret station-to-station signaling sys
ducing means and the detecting means are simul
tem equipment at each station comprising re
taneously operated comprises a pair of tubes each
ceiving means, an electronic switch, a detector,
having a cathode, an anode and at least two
a second electronic switch and transmitting
grids, a center grounded resistor connected be
means all connected in a chain in the given order,
tween said cathodes, an output circuit connected
key operated means connected to both of said
to said transmitting means and to which the
electronic switches, and a delay circuit interposed
anodes of said tubes are parallel connected, a
between said key operated means and the first
source of energy connected to one grid of each
mentioned switch, said ñrst mentioned switch
tube for applying alternating voltages thereto in
operating to pass energy to said detector only
opposite phase, a second grid of one tube being
when
activated either by said key means through
connected to said signal introducing means and
said delay circuit or by said receiving means and
a second grid of the other tube being connected
said second mentioned switch operating to pass
to said detecting means whereby the application
energy to said transmitting means only when
of negative voltage to the second grid of one tube
activated either by said key means or by said
only resulting either from the operation of the
signal introducing means or of the detecting
8. Station equipment in a secret signaling sys
means blocks one tube, upsets the balance of .- tem according to claim 7 wherein said delay cir
the tubes and permits passage of energy to the
cuit of one station includes networks simulating
transmitting means, whereas simultaneous ap
the time constants of the chain of the other sta
plication of negative voltage to the second grids
tion, of the intervening space between stations
of both tubes blocks both tubes and suppresses
and of the receiving means at the same station
the passage of energy to the transmitting means.
whereby energy passed by said second switch as
4. The secret signaling system according to
a result of operation of said key means, trans
claim 2 wherein each of said receiving means
mitted to the other station, passed through the
includes a rectiñer circuit and wherein each of
equipment at the other station, retransmitted
said means for creating a delayed replica of the
back to the first station and received by the re
signal includes a circuit simulating the time
ceiving means at the ñrst station Iarrives at said
detector.
constants of the rectifier circuit at the same sta- ' '
tion, a circuit simulating the time constants of
Y
..
first mentioned switch simultaneously with energy
passed by said delay circuit as a result of the
same operation of the key means.
9. The method of secret signaling between two
the rectiiier circuit at the other station, and cir
cuits simulating the time constants of the space
intervening between the stations, each of said
stations which comprises blocking the transmis
circuits having charging periods equal to their
sion of a signal between stations during such
periods as keys are simultaneously depressed at
discharging periods.
5. In a secret station-to-station signaling sys
tem, an electronic switch having two input ter
minals and one output terminal and arranged
to pass energy when a negative voltage is im
pressed on either input terminal and to be
blocked when negative voltage is impressed on
both stations and during such periods detecting
at one station the signal at the other station by
reference to the signal at the same station.
10. The method of secret signaling between
two stations which comprises passing modulating
energy to a transmitter at one station for trans
neither or both input terminals, a source of
mission to the other station upon operation of
negative Voltage, a network between said source
the key at the same station, detecting the modu
and one of said input terminals and key means `-' 6.0 lation at the other station and passing modulat
between said source and said network, said net
ing energy to the transmitter at the other station
work having equal charging and discharging
in response to such detection for retransmission
periods, a detecting circuit connected to said
to the ñrst station, blocking detection of such
other input terminal, and transmitting means
modulation at the ñrst station by energy con
connected to the output terminal of said elec fea trolled by operation of the key and delayed at the
tronic switch for transmission of a signal when
ñrst station, while blocking transmission of mod
said key is operated and the detecting circuit
ulating energy to the transmitter of a station
is not energized or when said key is in open cir
during concurrent detection and key operation of
cuit position and the detecting circuit is passing
energy.
no
the same station.
CARL EDWARD ATKINS.
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