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Dec. 23, 1947.
D_ $_ BOND
Filed Oct. 1, 1942
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Patented Dec. 23, 1947
Donald S. Bond, Philadelphia, Pa., assignor to
Radio Corporation of America, a corporation
of Delaware
Application October 1, 1942, Serial No. 460,339
7 Claims. (Cl. 318-28)
This invention relates to remote control sys
tems, and more particularly to an improved sys
tem requiring but a single telephone circuit or
radio link between the control member and the
controlled device.
It is an object of the invention to provide an
improved method of and means for transmitting
the signals required to establish control of the' ~‘
position of a movable object in response to the
position of a control member.
Another object is to provide an improved
method of and means for deriving a control sig
nal including a modulated carrier, in which the
phase relationship between certain components
Y 2
detector 23 is connected through a low pass filter
21 to a balanced modulator 29. Voltage from an
alternating current power line 3| is applied to
the modulator 29 through a phase adjuster 33.
The output of the modulator 29 is connected to
an ampli?er 35. A two phase motor" 31 is pro
vided with one phase connected to the output of
the ampli?er 35 and the other phase connected
to the power line 3|. The motor 31 is mechan
ically connected to the phase shifter 2| and to
of the signal corresponds to the intelligence to be 15 the load device 39.
The operation of the system is as follows: The
A further object is to provide an improved
output of the oscillator 5 is shifted in phase by
method of and means for converting a signal
the device 3 to an extent depending on the posi
comprising two voltages of equal frequency and
tion of the control member I. The 60 cycle out
varying phase relationship into a signal which 20 put of the phase shifter 3 is combined in the
may be transmitted through a single channel,
‘balanced modulator ‘I with the 1000 cycle output
and reconverting said signal after transmission.
of the oscillator 9. The 60 cycle component is
These and other objects will become apparent ; suppressed by the action of the balanced modu
to those skilled in the art upon consideration of . lator, thus providing an output comprising the
the following description of the invention, with 25 1000 cycle sidebands of a 60 cycle carrier, namely,
reference to the'accompanying drawing, of which
940 cycles and 1060 cycles, as well‘ as the 1000
‘ Fig. 1 is a schematic block diagram of an embodi
cycle modulation. The phase of the sideband
ment of the invention, Fig. 2 is a circuit diagram
frequencies with respect to a ?xed reference is
of a balanced modulator, Fig. 3 is a circuit dia
similar to that of the output of the phase shifter
gram of a bridge type mixer, and Fig. 4 is a 30 3 with respect to that of the oscillator 5. Phase
circuit diagram of a phase discriminator.
reference voltage is provided by the oscillator 5,
Referring to Fig. 1, a control device, of which
and is added to the products of the modulator
the angular position is to be reproduced at av
Tin the mixer circuit I I. The function of the
remote point, is mechanically connected to a
mixer II is merely that of superposition, not
phase shifter 3. An oscillator 5, operating at a 35 modulation. The mixer I I is arranged to isolate
frequency of, for example, 60 cycles per second,
the oscillator 5 from the modulator 'I to prevent
is connected to the input of the phase shifter .3.
interaction between their outputs, as more fully
The device 3 is constructed like a goniometer or
described hereinafter. The output of the mixer
in any suitable manner so that it provides a con
II thus comprises components at 940 cycles, 1000
tinuous change of phase upon rotation of its 40 cycles, 1060 cycles, and a ?xed-phase component
control shaft. ‘The output of the phase shifter
at 60 cycles.
is applied to a balanced modulator ‘I.
A second ‘
phase shifter 3. The output of the phase shifter
2|" is applied toa phase detector 23. The output
of the ?lter I5 is applied through an ampli?er
25 to the phase detector 23. The output of the
The higher frequency components aresepa
oscillator 19- operating at a frequency of, for exam
rated at the receiver station by the ?lter I3. The
ple, 1000 cycles per second is also connected to
demodulator I'I regards these components as a
the balanced modulator. The output of the bal 45 1000 cycle carrier with 60 cycle sidebands at 940
anced modulator ‘I is applied to a mixer circuit
and 1060 cycles, and accordinglyprovides a 60
II, which is also connected to the oscillator 5.
cycle output. This 60 cycle output varies in
The output of the mixer I I is transmitted over
phase with the variations in phase of the output
a telephone circuit or radio link to the receiver
of the phase shifter 3 at the transmitter]
station, where the motion of the device I is to 50 The 60 cycle constant phase component of the
be duplicated by a load device 39. The trans
‘transmitted signal is separated by the ?lter I5,
mitted signal is applied to ?lters I3 and I5. The
ampli?ed by the ampli?er 25. and applied to the
filter I3 is connected to a demodulator I‘! which
phase detector 23. The variable phase 60 ‘cycle,
is connected in turn through an ampli?er I9 to
output of the demodulatpr n is ampli?ed by the’
a phase shifter 2| similar in construction to the 55 ampli?er I9 and applied/through the phase shift
er 2| to the phase detector 23. The output of
the phase detector 23 is i_a D.-C. voltage, having
a magnitude related to the magnitude of the
phase displacement between the output of the
phase shifter and the reference phase voltage,
and a polarity depending upon the direction of
said displacement. This voltage is conducted
through the ?lter 21 to remove any remaining
ripple from the 60 cycle inputs, and controls the
former 59 produces no output at the terminals
69 and ‘H, and a voltage applied to these termi
nals produces no effect at the primary of the
transformer 59. The voltage across the primary
65 of the transformer 61 is proportional to the
_ sum of the two input voltages.
This circuit or
some equivalent thereof is necessary in the sys
tem of Fig. l to prevent plate circuit modulation
in the modulator ‘l by voltage from the oscilla
balanced modulator 29, varying the magnitude 10 tor 5.
Fig. 4 shows the circuit of the phase detector
and polarity of the voltage derived from the power
23 of Fig. 1. Two diodes l3 and 15 are connected
line 3| through the phase adjustor 33. It should
as shown between center tapped input and out
be noted that the power line frequency may be
put circuits ‘l1 and ‘I9. The variable phase signal
entirely independent of the frequency of the local
oscillator 5. In any event the power line frequency 15 voltage is applied to the diodes in push pull
through a transformer 9|, and the constant phase
output of the balanced modulator 29 is amplified
reference voltage is-applied to the two diodes
by the ampli?er 35 and used to energize the wind
in phase between the center taps of the input
ing 4| of the motor 31. The motor winding 43 is
and output circuits. When the two inputs are
energized directly from the power line. The
phase at one diode, they are out of phase at
phase adjustor 33 is adjusted to provide quadra 20
the other, thus causing current to flow through
ture phase relationship between the voltages ap
the corresponding section of the output circuit,
' plied to the two motor windings. The motor 31
toward the center tap. When the two inputs are
runs in the proper direction to drive the phase
in quadrature, no output voltage is produced.
shifter 2| toward a position such that its output
is 90° out of phase with the reference phase volt 25 Thus the device provides a unidirectional output
voltage, of magnitude and polarity depending on
age. At this point the output of the phase de
the phase relationship between the two input
tector becomes zero, the power line frequency
output of the modulator 29 likewise drops to zero,
and the motor winding 42 is de-energized, stop
It is usually necessary, in a control system of
ping the motor. Upon further displacement of 30 the follow-up type, in which the driving motor
the control device I, the same action occurs and
the phase shifter 2| is again rotated to stop the
operates to reduce the control signal to zero
value, to incorporate some means to prevent
motor. Consequently, the controlled device 39,
being mechanically connected to the phase shifter
hunting, Although such anti-hunting system has
been omitted from the above description for the
43, and two resistors 5| and 53 are connected in
pressed, and replaced by the original constant
phase low frequency voltage. This signal is: '
sake of clarity, one suitable system is described
2| and the motor 31, is maintained in positional
in U. S. Patent, No. 2,208,623 to D. S. Bond.
agreement with the control device I.
Thus the invention has been described as an
Fig. 2 shows a circuit which may be used for
remote control system. A low fre
the balanced modulators T and 29. A pair of
quency voltage is generated and shifted in phase
tubes 4| and 43 are connected in push-pull to a
load circuit such as the primary 45 of an output 40 to correspond to the control information to be
transmitted. The shifted voltage is then modu
transformer. A pair of input terminals 41 and
lated, the shifted low frequency carrier is sup
49 is connected to the grids of the tubes 4| and
series between the two grids. A second pair of
input terminals 55 and 51 is connected between
the junction of the resistors 5| and 53 and the
common grid return circuit of the tubes 4|
and 43.
When no input is applied to the terminals 41
and 49, no voltage appears in the output circuit,
regardless of the input to the terminals 55 and
57, because the individual outputs of the two
tubes are applied to the load in phase opposition.
However if a voltage is applied to the terminals
41 and 49, it is ampli?ed and applied to the load,
and at the same time modulates any input to the
terminals 55 and 51. This action occurs because
the circuit is periodically unbalanced, first in one
direction and then in the other by the/input
to the terminals 41 and 49. In the circuit of
Fig. 1, the output of the oscillator 9 is connected
to the terminals 4'1 and 49 of the modulator ‘l,
and the output of the phase shifter 3 is connected
to the terminals 55 and 51. The modulator 29
has its terminals 55 and 51 connected to the
phase adjuster 33 and the terminals 41 and 49
to the ?lter 27.
Fig. 3 shows a suitable circuit for the mixer
||. The center tapped secondary 5|,of a trans
former 59 is connected to the primaries 83 and
65 of a pair ‘of transformers El and 68 to form
a balanced‘ bridge circuit. A network 52 is con
nected to the transformer 68 to balance the im
pedance of the load on the transformer 51. A
voltage applied to/the primary of the trans
transmitted to the control station, when the con
stant phase voltage is separated from the variable
phase modulation. The modulation is detected,
providing variable phase low frequency voltage.
This voltage is compared with the constant phase
low frequency component of the signal, providing
a control voltage which is used to control an
electric motor, A. single signal channel suffices
to carry all of the necessary information, and in
fact may be used simultaneously for a plurality
55 of systems of the type described, operating with
different modulation frequencies.
I claim as my invention:
1. The method of transmitting control infor
mation including the steps of generating an al~
60 ternating voltage, shifting the phase of said volt
age in response to the information to be trans
mitted, generating a second alternating voltage
of substantially higher frequency than said ?rst -
alternating voltage, modulating said phase shift
65 ed voltage in opposite phases by said second alter
nating voltage to provide two modulated signals
whose carriers are 180 degrees out of phase with
each other and whose respective side bands are
in phase with each other, combining said modu
70 lated signals to cancel said carriers and provide
a suppressed carrier signal comprising only said
side band signals, adding to said suppressed car
rier signal a constant phase alternating voltage
of the same frequency as said phase shifted volt
75 age, transmitting the resultant combined signal,
‘ 2,438,195
receiving said transmitted signal, separating the
constant phase component of said signal from
the variable phase sideband components thereof,
demodulating said variable phase components to
provide a variable phase alternating voltage, com
bining said variable phase voltage with said con
stant phase signal component to produce a direct
current related in magnitude and polarity to the
mitting and receiving through a single channel
the combined output signal of said mixer, ?lter
means for separating the modulated component
of said signal from the remainder thereof, and
demodulator means arranged to derive from said
component a modulation voltage corresponding
to one of said original voltages.
5. A remote control system including means
for deriving a variable phase control signal and
difference in phase of said variable phase voltage ,
and said constant phase signal component, shift 10 a constant phase reference signal, an auxiliary
source of alternating current, av balanced modu
lator arranged. to‘modulate one of said signals
.with the output of said auxiliary source, means
said phase difference to zero, and deriving con
for transmitting and receiving the output of said
trol information in response to the extent of said
phase shift of said variable phase component.
15 balanced modulator and said other signal, a de
modulator'arranged to derive from said modu
2. The method of transmitting a variable phase
lator output a voltage similar to the signal input
control voltage and a constant phase reference
ing the phase of said variable phase component
in response to said direct current so as to reduce
voltage through a single channel including the
to said modulator, and motor control means re
sponsive to the phase relationship between said
steps of generating a modulating voltage of sub
stantially different frequency from said ?rst 20 voltage and said unmodulated signal.
6. A control system including a source of A.-C.
mentioned voltages, modulating one of said ?rst
vvoltage, means connected to said source for de
mentioned voltages in opposite phases by said
riving, in response to control information to be
_'modulating voltage to provide two modulated
transmitted, a second A.-C. voltage variable in
signals whose carriers are in phase opposition to
each other and whose corresponding side bands 25 phase with respect ‘to said ?rst A.-C. voltage; a
second source of A.-C. voltage of different fre
are in phase with each other, combining said
quency from said ?rst and second A.-C. voltages,
modulated signals to cancel said carriers and
provide a suppressed carrier signal comprising
a balanced modulator, means for applying said
variable phase A.-C. voltage and said voltage from
only said side-band signals, adding the other of
said two ?rst-mentioned voltages to said sup 30 said secondsource to said balanced modulator
to provide a signal comprising a carrier of the
pressed carrier signal, to provide a combined sig
frequency of said second source and sidebands
nal transmitting said combined signal, receiving
corresponding to said variable phase A.-C. volt
said combined signal, separating said suppressed
age, means for combining said signal with'said
carrier signal component from said added voltage
component, demodulating said suppressed car 35 ?rst A.-C. voltage to provide a composite signal;
means responsive to said composite signal to pro
rier signal component to produce a voltage sim
duce voltages having the same phase relationship
ilar to the carrier component which was sup-‘
to each other as said ?rst and second A.-C.
pressed, combining said last mentioned voltage
voltages, said last mentioned means comprising
with said added voltage component, and deriving
a control signal from the product of said com
3. A control system including a source of rel
a ?lter connected to separate said ?rst A.-C.
voltage from said composite signal, and a de
modulator connected to said ?lter to derive from
the remainder of said composite signal an A.-C.
voltage corresponding to said second A.-C. volt
atively low frequency. alternating current, a con-,
trol member arranged toshift the phase of said
alternating current, a source of relatively higher 45 age.
7. In a remote control system in which control
frequency alternating current, a balanced modu
information is derived in the form of two A.-C.
lator arranged to modulate said lower frequency
voltages of the same frequency but of variable
current withsaid higher frequency current, a
phase with respect to each other, a system for
mixer connected to combine the output of said
balanced modulator with that of said source of 50 transmitting said information over a single chan
nel including a source of carrier voltage, balanced
low frequency current, means for transmitting
and means for receiving the combined signal
output of said mixer, ?lter means arranged to
modulator means for modulating said carrier
voltage with one of said A.~C. voltages to provide
a suppressed carrier signal including sidebands _
separate the low frequency component from'the
higher frequency components of said combined 55 corresponding to said modulating voltage, means
for combining said suppressed carrier signal with
signal, a demodulator arranged to derive from
the other of said A.-C. voltages to provide a com
said higher frequency components a variable
posite signal, and means including a demodulator
phase low frequency voltage, a phase detector
for deriving from said composite signal two A.-C.
connected to respond to said variable phase volt
voltages having the same phase relationship to
age and said low frequency signal component,
means responsive to the output of said phase 60 each other as said ?rst mentioned two .AJ-C.
detector to shift the phase of said variable phase
component soas to produce zero output from
said phase detector, and means for operating a
controlled member as a function of said phase 65
The following references are of record in the "
4. A system for reproducing at a remote point
?le of this patent:
the phase relationship between a variable phase
control voltage and a constant phase reference
voltage, including an auxiliary source of alter 70 Number
Name '
nating current, balanced modulator means for
Seeley ___________ __ Dec. 19, 1939
modulating one of said voltages with the output
Marrison _______ .... Mar. 25, 1941
of said auxiliary source, a mixer arranged to
Isbister et a1 ______ __ Sept, 23, 1941
Moseley et al. ____ __ Sept, 23, 1941
combine the other of said voltages with the out
Moseley _________ .. June 16, 1942
put of said modulating means, means for trans 75 2,287,002
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