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Патент USA US2405876

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Aug. 13, 1946.
M. G. cRos’BY
'
2,405,876
VARIABLE DOT KEYER
Filed June 50, 1943
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Patented Aug. 13, 1946
2,405,876;
UNITED STATES PATENT'oFFICE
2,405,876
VARIABLE DOT KEYER
Murray G. Crosby, Riverhead,- N. Y., assignor to
Radio Corporation of America, a corporation of
Delaware
Application June 30, 1943, Serial No. 492,854
14 Claims.
(Cl. 250--17)
l
2
This invention relates to vairable dot keyers for
radio transmission of modulated waves. More
particularly, the invention relates to a system for
converting phase or frequency modulated Waves
square wave having the characteristic of variable
frequency and variable dot Width;
patents systems were shown for producing a
square wave output. The means employed and
3.
Figs. 3 and 4 show wave representations illus
trative of the input and output energies applicable
into square waves having a variable percent mark. E to Fig. 1; and
The art of dot keying is quite extensive. Cer
Figs.- 5 to 8 inclusive are similar wave represen
tain typical patents which disclose systems of one
tations> applicable to the circuit arrangement of'
kind or another for use in on-and-off keying of
Fig. 2.
modulated waves are as follows: Heising Pat
Referring first to Fig. 1, I show therein a con
ent No. 1,655,543; Finch Patent No. 1,887,236;
ventional representation of a carrier source I,
and Kell Patent No. 2,061,734. In all of these
the output from which is fed to a phase modulator
The modulations are derived from a modula
tion source 2 which' is connected to the phase
the methods disclosed were, however, quite dif
modulator 3'. Either a pair of discharge tubes
ferent from what is Shown in the instant appli 15 or a single tube having independent electron dis
cation. Th'e technique which I prefer is one
charge structures may be employed for control
which is more comparable with the practice of
ling a subsequent stage from which the desired
limiting in an amplifier or detector. Such tech
square wave output may be derived. The tube
nique is disclosed for other purposes in my Pat
envelope 6 contains two triode structures and
ent No. 2,263,615, dated November 25, 1941, and 20 may, therefore, be considered the equivalent of
also in my Patent No. 2,276,565, dated March 17,
two triode tubes. One of the triode combinations
1942.
includes cathode l, one of the anodes 9, and a
It is an object of my invention to provide a
grid IB. The other triode combination includes
system of dot keying, or square wave generation,
the cathode l, the other anode 9 and a grid I2.
as a result of converting a phase modulated wave
Grid I0 is controlled by variations in potential
so as to produce a square wave of variable percent
across the grid leak resistor I I when influenced by
mark. Such a wave is generally termed a con
output from the phase modulator 3, the energy
stant frequency variable dot wave.
`Another object of my invention is to provide
a system for converting a frequency modulated
wave into a square wave having variable fre
quency and variable dot width.
Still another object of my invention is-to pro
vide a method of wave limiting similar to the
aforesaid method, but having a characteristic of
variability both of frequency and of dot width.
-Still another object of my invention is to pro
vide a modulation system wherein the dot width
from which is impressed across coupling con
denser 5. Grid I2 is controlled by carrier fre
quency energy derived directly from the source
I and applied across coupling condenser 4. The
input circuit on the right hand side of the tube
6 includes grid I2 and grid leak resistor I3 which
is grounded.
Since the two triode structures in tube 6 have
substantially a common cathode l, it is a feature
of my invention to provide a cathode resistor 8,
connecting the cathode ‘I with ground. The
variation in a square wave output is accom
cathode 'I is connected to the cathode I 5 in a tri
panied by an inverse frequency variation, such 40 ode tube I4 which' is disposed in a subsequent
that th'e energy in the modulation wave remains
stage. Tube I4 also possesses an anode I6 and a
substantially constant.
control grid I'I, the latter being directly grounded.
Further objects and advantages of my inven
The anodes 9 in tube 6 are interconnected and
are supplied with positive direct current potential
tion will be brought out in the detailed descrip
tion to follow. This description is accompanied 45 indicated as +B through a resistor I8. A capac
itor I9 is connected between the anodes 9 and
by a drawing, in which:
ground in order to by-pass unwanted frequencies.
Fig. 1 shows a circuit diagram of a preferred
The output from tube I4 may be utilized by means
embodiment, in which a phase modulated wave
of a coupling condenser 22 which feeds energy to
is converted by means of electronic devices into
50 a load resistor 2 I, the lower end of which is con
a square wave output having a characteristic of
nected to ground and to the minus terminal of
constant frequency and variable dot keying;
the direct current source indicated as _B. The
Fig. 2 sh'ows a somewhat similar circuit ar
output energy may. if desired, be rectified as by
rangement, but modified so as to utilize a fre
means of the diode tube'- 20. This method of
quency modulated wave and to convert it into a 55
rectification and detection'isconventional. ' Such
2,405,876
3
output may, if desired, convey facsimile or voice
signals or other types ofmodulated waves, as is
well understood by those skilled in the art.
4
across capacitor 21. The other terminal of the
tank circuit is coupled across condenser 4 to the
grid I2 in the right hand triode section of tube
In the operation of the circuit arrangement. _ 6. The grid I0 in the left hand section of tube
shown in Fig. 1, it should be noted that the output 5 0 derives control potentials from the tuned sec
ondary winding of transformer 24. Tuning is ob
from the phase modulator 3 is variably phase
tained by means of the variable condenser 26.
related to the constant frequency output from the
The circuit arrangement of Fig. 2 is arranged
carrier source I. This relationship determines
to
produce variable-frequency-variable-dot key
the timing and duration of conductive states in
ing. The frequency-modulated wave is separated
the cathode resistor 8. The potential drop
into two components one of which is converted to
through this resistor 8 also controls the tube I4,
a frequency-and-phase modulated wave by means
since the grid I‘I is grounded and the potential
of the transformer 24. The primary of trans
on cathode I5 must follow that of the cathode l.
former 24 is tuned by condenser 25, and the sec
If, therefore, the output from the phase modu
lator 3 is in phase agreement with the output from is ondary by condenser 26. The phase modulation
component is imparted by the transformer to
the carrier source I, then both sides of the twin
grid I0. The other component, which is only fre
triode tube become simultaneously conductive and
quency-modulated, traverses capacitor 4 and is
are simultaneously cut-ofi. The result is to pro
applied across the grounded resistor I3 for con
duce unidirectional pulses in the cathode resistor
20 trolling grid I2. The potentials on the two grids
8 which persist for 50% of the time.
I0 and I2, therefore, have a phase relation to
When, however, the phase angle between the
one another which is varied in dependence upon
input potentials applied to grids I0 and I2 ap
frequency departures from the fixed frequency to
proaches 180°, the conductive periods in the cath
which the tank circuits on the two sides of the
ode' resistor 8 are proportionately shortened and
are completely cancelled out at 180°V phase dis 25 transformer 24 are tuned.
In the system according to Fig. 2 the circuit
placement. But the alternating voltage applied
parameters may be so chosen as to provide any
to 4grid I2 is at the fixed frequency of the carrier
one of three different modes of operation as fol
source I. Hence, the cathode resistor 8 has non
lows:
conductive periods which vary between 50% and
ModeV #l is best understood. by reference to
100% of the total time; one non-conductive pe 30
Fig. 5. Here the undistorted frequency modu
riodl and an immediately following conductive
lation component applied to grid I2 is represented
period always representing a full cycle of the
by the solid line. The frequency-and-phase mod
carrier frequency.
The value of the anode potential applied to
ulation component is represented by the broken
tube I4 is so chosen in relation to the potential 35 line. Fig. 6, which is drawn to the same time
scale as Fig. 5 shows a square Wave the mark
drop across resistor 8 that when either side alone
ing peaks of which are co-extensive with the
or both sides of the tube 6 are conductive then
complete cut-off periods in tube 6, during which
tube I 4 will be substantially biased to cut-0E.
periods tube I4 is conductive and capacitor 22
Tube I4 is, therefore, conductive only when both
discharges. At the frequency to which the tank
sides of tube 6 are simultaneously blocked. Dur
circuits on the two sides of transformer 24 are
ing the cut-olf periods of tube I4 capacitor 22
tuned a phase displacement of 90° exists in the
takes a charge through resistors IB and 2I. The
output from this transformer. The square wave
diode tube 20 is also conductive during the charg
peaks then occupy 25% of the total time. As the
ing periods. Capacitor 22 discharges through
frequency is increased the phase displacement
tube I4 during conductive periods of the latter.
of the transformer output component approaches
The discharging circuit includes the space path
180° and the percentage of marking time of the
of Ítube I4 and the impedances of resistors 2I and
square Wave peaks approaches zero as a limit.
8, but no Vcurrent flows through tube 2i) during the
When the frequency swings below the resonant
discharging periods. _
frequency of the tank circuits, then the phase
The utilization circuit may include a modula
displacement of the transformer output compo
tor in a radio transmitter, or any other appa
nent approaches 0° and hence the percentage of
ratus which it is desired to control by means ofv
marking time approaches 50% as a limit.
the square wave output from capacitor 22. The
Operating mode #2 with respect to the sys
capacitor 32 may or may not be needed, depend
ing upon the working potentials at which the 55 tem of Fig. 2 is also illustrated by Figs. 5 and 6,
but it is a specific adjustment falling within the
utilization device is driven.
The curves drawn in Figs. 3 and 4 have the
same time scale. In Fig. 3 the two sine waves,
one represented by a solid line curve and the
other by a broken line curve, represent input 60
voltages applied to the respective grids I2 and
general range of adjustments covered by mode
#1. Here the frequency variation and the phase
rotation are so related that the average energy
in the square wave peaks, or dots, remains con
stapt.
One object to be attained in this mode
ID in tube 6. The resultant square-wave shown
in Fig. 4 is drawn so that its peaks represent con
ductive periods in tube I4. These are the pe
of operation is to provide a measure of secrecy in
the transmission of signals. Any decrease in the
from which is fed to the two terminals of a tank
#1. This mode is illustrated in Figs. 7 and 8.
At the frequency of the tank circuits on the two
dot length is exactly compensated for by an in
65 crease in the number of dots per second.
riods during which capacitor 22 discharges.
Special detecting means not commonly used
Referring now to Fig. 2, I show certain ele
would, therefore, be required in the receiving sys
ments in the circuit arrangement thereof which
tem in order to translate the signals into intel
correspond with those of Fig. 1. They, there
ligence. Such means might not be available at
fore, bear similar reference numerals. In Fig. 2,
an unauthorized receiving station.
however, the modulation source 2 is arranged to
Operating mode #3 is just the reverse of mode
feed into a frequency modulator 23, >the output
circuit consisting of the primary winding in a
transformer 24 and a variable capacitor 25. One
sides of transformer 24, the output from this
terminal of the tank circuit is coupled to ground 75 transformer bears a 270° phase Yrelation to the
2,465,876'
. .
sÁ
Iu'ndistorted frequency modulation component~`
Asl the frequency increases Athe phase displace
ment also increases up ’ac3-60°, and contrarywise,
6.
trolling each of two space discharge paths" by’
a respective one» of said sinek waves, means for
combining' the currents which flow in the twov
as the frequency decreases the phase displacement '
said paths, and means vfor so controlling the cur'-I
approaches 180° as a limit'. Hence the dot length ’ rent in a third discharge path as to 'render the
varies between 50%> and 0%, but vanishes at the
peak-s of said square wave coextensive with peri
low frequency end of the spectrum andV is a max
iinum at the high frequency end.
One advantage of operating the system accord
ing to mode #3 is that the composite modulation:
produces extremes of vari-ation in the energy con
tent of theA signals which have wider limits than
when the phase alone is varied.
In other words, .
the lower the frequency', the more the' marking
ods of current cessation in both of the two discharge paths first-mentioned. '
e. Apparatus for producing a square wave the
marking elements of which vary in duration be
tween 5'0'% and 0% in accord-ance with the de
gree of overlap of two sine waves, comprising
means for frequency-modulating one' of said sine
waves, means for deriving the second of said sine
dots will be reduced inv width, and the higher the 15 waves from the first by phase modulation thereof,
frequency, the' more closely will the marking
the phase displacement being an inverse function
dots approach 50 %.
of thel frequency variation, means for separately
In order to render theV circuit of Fig. 2 selec
controlling'each of two space discharge paths by
tively operative according to either mode #l or
by a respective one of said sine waves, 'means for
kmode #3 it is only necessary to choose the proper 20 combining the currents which flow in the two
terminal of the secondary winding in transformer i
24to be coupled across capacitor 5to grid Ill.
Reversal of this connection with respect to' the
ground connection of the remaining secondary
terminal obviously rev'erses the phase of the in
put potentials applied to grid I0.
'
said paths, and means for so controlling the cur
rent in- a third discharge path as to render the
peaks of said square wave coextensive with peri-YV
ods of current cessation in both of the two dis-r
charge paths first mentioned.
l
’
5. A signaling system comprising a carrier wave
source', a source of signals, means controlled by
In the circuit of Fig. 2 there is no need for the
rectifier tube 20 of Fig, l. A bias is applied to
said signals for phase-modulating an output com
the grid I1 as by means of a potentiometer 28,
ponent from said carrier source, amplifier means
one end of which is grounded and the other end
comprising two discharge paths and a common
connected to a source of negative bias potential
`cathode resistor, means for separately control
indicated as -C. This source has its positive
ling the two said discharge paths, one'by poten
terminal connected to ground, as indicated by
Ítials derived from the unmodulated carrier source,
the reference +C. In the operation of tube |14,
and the other by ypotentials derived from the
as shown in Fig. 2, one half of the output wave 35 phase-modulated carrier wave, and electronic
is cut-off. The square-wave output is, therefore,
means having a square wave output whose wave
unidirectional and the positive peaks represent
crests are coextensive in time with periods of
marks of variable width. This output appears
zero potential drop in said cathode resistor.
across the resistor I8 to which the utilization de
6. A system in accordance with claim v5 and
vice is coupled across capacitor 22.
40 including means for rectifying a component of
While I have described and shown two em
the output from said electronic means.
bodiments of my invention, it is to be clearly un
7. A signaling system comprising a frequency
derstood that these embodiments are only illus
modulated Wave source, means for phase-modu
trative and that other modifications within the
lating an output component from said source,
scope of the invention may be made.
ampliñer means comprising two discharge pathsY
What I claim is:
and a common cathode resistor, means for sep
1. The method of signaling which includes com
arately controlling the two said discharge paths,
paring the phase of half-cycles of a phase mod
one by potentials derived from the frequency
ulated wave with half-cycles of an umnodulated
modulated wave source itself and the other by
component of said wave, producing a square wave
potentials derived from the phase-modulated
the positive components of which vary in dura
Ícomponent thereof, and electronic means having
tion between 50% for the condition of phase
a square wave output whose wave crests are co
agreement between said half-cycles and 0% for
extensive in time with periods of zero potential
the condition of phase opposition, and transmit
drop in said cathode resistor.
ting a carrier wave which is interrupted by half
8. A system according to claim '7 and includ
cycle components of said square wave.
ing tuned coupling elements in said phase-modu
2. The method of signaling which includes com
lating means, and an input circuit for said “other”
paring the phase of half-cycles of a frequency
discharge path so arranged as to cause the gen
modulated wave with half-cycles of a phase
eration of a square wave the crests of which vary
modulated derivative of said wave, producing a 60 _in duration as a direct function of the phase dis
square wave the positive components of which
'placement between the currents in the two said
vary in duration between 50% for the condition
discharge paths.
of phase agreement between said half-cycles and
9. A system according to claim 7 and includ
0% for the condition of phase opposition, and
ing tuned coupling elements in said phase-modu
transmitting a carrier wave which is interrupted 65 lating means, and an input circuit for said “other”
by half-cycle components of said square wave.
discharge path so arranged as to cause the gen
.-3. Apparatus for producing a square wave the
eration of a square wave the crests of which
marking elements of which Vary in duration be..
vary in duration as an inverse function of the
tween 50% and 0% in accordance with the degree
phase displacement between the currents in the
of overlap of two sine waves, comprising means 70 two said discharge paths.
for frequency-modulating one of said sine waves,
10. A square wave keying system comprising a
means for deriving the second of said sine waves
pair of electron discharge devices having a com
from the first by phase modulation thereof, the
mon cathode resistor connected to ground, each
phase displacement being a direct function of
said device having at least the usual electrodes
the frequency variation, means for separately con 75 of a triode, means for controlling the respective
2,405,876
7
grids of said devices by signal potentials which
8
responsive to a square Wave output from said>
third device, and means for so coupling the cath
odes of the three said devices together that the
are variably phase-related to each other, a thirdy
discharge device having cathode, anode and con
crests of said square wave are commensurate with
trol grid electrodes, the cathodes of al1 three de
vices being interconnected, a ground connection 5 periodsV of simultaneous cut-off of current flow
in the iirst and second of said devices.
for the grid in said third device, a load imped
13. A circuit arrangement comprising a sourceA
'of frequency modulated waves, a trìode discharge
device for amplifying an energy component de
for causing said third device to function as a
limiter tube the output from which has a square 10 rived from said source, a transformer havingv
ance connected between the anode of said third
device and a source of anode potential, and means
wave characteristic the Wave crests whereof are
Ituned primary and secondary windings, the pri
commensurate with periods of zero potential drop
in said cathode resistor.
11. A system according to claim 10 and includ
4second triode discharge device arranged to am
plify phase rotated energy fed thereto by said.
the grid of said third device.
12. A circuit arrangement comprising a carrier
two said triode discharge devices and means in
eluding a third triode discharge device having itscathode connected to the cathodes of the ñrst
mary winding being coupled to said source a
ing threshold bias adjusting means applicable to 15 transformer, a common cathode resistor for the
source, a modulation source, an electronic device
for amplifying a component of output energy from
and second discharge devices for producing square
said carrier source, a second electronic device ar 20 `.waves the crests of which are commensurate in>
time with periods of Zero potential drop in said
-ranged to amplify a component of energy from
common cathode resistor.
14. lA circuit arrangement according to claim
13 and including threshold biasing means for the
device connected through a load resistor to an 25 grid in said third discharge device.
anode potential source. a ground connection for
MURRAY G. CROSBY.V
the grid in said third device, a utilization circuit
,said carrier source after phase modulation there
.of by said modulation source, a third electronic
device of the triode type, an anode for the third
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