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Патент USA US2501330

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March 21‘, 1950
J. H. HAMMOND, JR
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2,501,330
AMPLITUDE MODULATION SIGNAL CORRECTION SYSTEM
Filed July 13, 1948
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INVENTOR
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AT ORNEY
March 21, 1950
J. H. HAMMOND, JR
2,501,330
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AMPLITUDE MODULATION SIGNAL CORRECTION SYSTEM
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INVENTOR
JOHN HAYS HAMMONDfJRl
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2,501,330
Patented Mar. 21, 1950
UNITED
STATES
’‘
AMPLirooa MonULAEnoN SIGNAL
oonnaorion SYSTEM
John‘ Hays i-l‘ammond, J12, Gloucester, Mesa, as,
signor to Radio Corporation of America, New
York, N. Y.,' a corporation of Delaware
Application .l’uly 13, 1948, Serial No. 38,463
6 Claims. (01. 25044;)"
2
1
store the ‘carrier and the signal ‘side bands to the
proper amplitude modulation relationship. This
This invention relates to improvements in the
quality of received signals which have been sub
jected to selective fading.“ It is especially useful
results in an improved quality of transmission.
rThe nature ‘of the invention‘, will be better
for Converting and demo‘dulating signals which
understood from the following description, taken
are to be rebroadcast in accordance with my
in connection with the accompanying drawings,
in‘which ‘certain speci?cernbodiments have been
U. S. Patent #1313360, and for making record~
ings which may be made available subsequently
to the listening public by radio or by pressings.
set forth for purposes of illustration.
‘ It is Well known that systems of radio tele
In the drawings:
,
_
,
_
,
‘
Fig“ 1 is a schematic block diagram illustrating
by labeled rectangles and‘ connections a system
arranged in accordance with my invention for
receiving; amplifying and demodulating signals
phonicgcommunication of the type using carrier
and a. single ‘side band, or single side band alone,
have improved properties as to selective fading.
However, a large number‘ of transmission channels in use are not of this type, ‘and the present
transmitted as a carrier and associated low and
invention relates" especially‘ to ‘radio telephonic
channels employing a‘ carrier and both side bands,
In this type of transmission, the carrier and
side bands start out related as‘ in amplitude modu~
high side bands,
,
,
‘ ‘
Fig.‘ 2 illustrates the details of portions of the
system of Fig. 1 relating to the use of the pilot
frequency for making amplitude corrections,
Fig. 3 illustrates the details of portions of the
lation. But in transmission, very often the me
system of Fig. 1 relating to the use of the pilot
frequency for making phase corrections, and
Figs. 4a to 4h illustrate the relationships be
tween electrical voltages of various wave com
ponents, at different parts of the diagram of
dium operates differently on the loW side band.
the carrier, and the high side band,‘ so that as
received, the wave ‘represents one with amplitude
modulation in combination ‘with phase or fre—
quency modulation. That is, the two signals pro-t
Fig. 1‘ and Fig. 3.
duped by demodulating the ‘carrier and a‘ low side
,
‘Fig. 1, illustrates by schematic representation‘
frequency, and by demodulating the carrier and
a high side frequency‘ are not in general equal
in magnitude and equal in‘ ‘phase, as they would
be if the wave which is demodulated represents
pure amplitude modulation.
It is the object of this invention to restore the
wave form to the amplitude modulated condition
prior to demodulation, so that the two outputs
will properly cooperate inproducing a ?nal sig
3 til ‘
nal in the utilization circuit.
In this invention, I employ a‘ pilot transmission
which may consist of one or a plurality of modu
lating frequencies which are mixed in with the
transmitter signal frequencies. For some pur
poses, the pilot transmission may be of the order
of 800 cycles per second, or perhaps the geometric
mean of the lowest and highest modulating fre
quencies normally to be transmitted and utilized
in the receiver. In‘other cases, the pilot trans
the essentialf‘eatures‘ of a receiving system ar
ranged for operation‘ in ‘accordance with my in
vention. In rectangle Ill is located‘ the initial
circuits of the receiver system, such as the tuner,
hetero‘dyne, ‘?rst detector, the major parts of the
intermediate frequency circuits,‘ and the auto
matic volume control system of a superheterodyne
system for receiving amplitude modulated signals.
To the input of this‘ rectangle is connected an
antenna H and ground !2, upon which are im
pressed the transmitted ‘wave shown spectrally
by it“ at the left of the‘antenna. This wave com
prises a carrierC, ‘lower side signal band LS,
higher side signal band HS, lower side pilot fre
quency P1, and higher side pilot frequency P2.
Of these, C, P1 and P2 are transmitted‘ continu
ously, while LSand HS are variably on" and on,
mission may contain frequencies at the lower or ‘L.
withv various distributions ‘in accordance with the
signal modulation. It ‘will be understood that
higher end, or bothpof the useful transmitted
due to‘ the nature or" the transmission medium P1
modulation band. For simplicity, however, I dis
and P2 are not necessarily of equal magnitude,
close a system‘ in which only one pilot frequency
is used‘. This pilot frequency is mixed with the
sentations of C and ‘Pi is not necessarily the same
signal frequencies prior ‘to modulation of the
radio carrier, and is subjected to the same selece
tive fading‘ and distortion’ effects as the signal in
and, that the angle between’, the vector ‘repre
50
as the angle between the Vector representations
of P2‘ and C, Furthermore, similar ‘differences
willexist between‘ the various components LS‘,
C’, and HS. The output of rectangle ld‘is of simi
transmission.‘ ‘At the receiver,‘ the relation‘ be
lar nature spectrally to the input |‘3‘,except that
tween the carrier and the two pilot side fre
quencies is in' effect examined and utilized to reé 5'5 the frequencies of all components have been 1ow~
2,501,330
4
ered from radio to intermediate frequency by the
C, low band pilot frequency P}. and high band
pilot frequency P2, both as they exist compositely
heterodyne process. The rectangle I8 is con
nected through output leads l4 and IE to an inter
in the input to circuit l0, and as they exist in
dividually in the circuits 22, 24 and 26. It will
be further understood that the pilot side fre
quencies P1 and P2 of spectrum i3 receive the
mediate frequency delay circuit [6, the output of
which is connected by leads l‘! to a band splitting
circuit E8. The delay circuit has the purpose of
allowing the control circuits associated with the
pilot frequencies su?icient time to operate, and
same general treatment in transmission as the
may take the form of an arti?cial transmission
line. The rectangle :Hl is also connected through 10
leads l4 and 19 to a band splitting circuit 2!].
The energies in the inputs to the two band split
ting circuits I8 and 20 are of similar nature, ex
cept that the wave form of the input to circuit
I8 occurs after a like wave form has just previ
15
ously occurred in the input to circuit 2!]. Al
though these wave forms both include repre
sentatives of the entire received wave form, only
the carrier and signal side bands are of impor
tance for circuit 51, and only the carrier and pilot 20
side frequencies are of importance for circuit 28.
Therefore, the rectangles l6 and I8, and all below
them will be referred to as the signal channel, and
rectangle 20 and all below will be referred to as
the pilot channel. Certain connections to be de 25
scribed later provide for control of the opera
tion of the signal channel from the pilot chan
nel, so that the pilot channel may also be con
sidered to be a control channel.
The band splitting circuit it of the signal chan~ 30
nel operates to separate the carrier, lower side
band, and upper side band into three individual
channels by which these components of the sig
nal may be separately treated. Thus, output
leads 2! provide carrier energy to rectangle 22;
output leads 23 provide lower side band energy
to rectangle 24; output leads 25 provide high side
band energy to rectangle 26. The circuits of
rectangles 22, 24, 26 may provide for further
purification of the three-selected energies, by cir
cuits which eliminate more completely the un
wanted components. The circuits are so adjusted
that if the outputs of the circuts 22, 2t, 26 were
again recombined, the resulting wave form would
be substantially the same as in the input to the 45
low and high side signal bands LS and HS, and
that corrections applied from circuits 3? and 38
to the pilot elements in the signal channel will
serve also to correct the signal elements.
The output of low side band circuit 24 is con
nected through leads 39 to amplitude adjuster
circuit All, the output of which is connected by
leads ill to detector 42. Similarly, the output
of high side band circuit ‘26 is connected through
leads 43 to amplitude adjusted circuit till, the
output of which is connected by leads ‘it to de~
tector 46. Carrier energy for demodulating the
low and high side bands applied to these de
tectors t2 and 1Z5 is supplied from carrier cir
cuit 22, which is connected through leads 4? to
a phase adjuster t8, the output of which is ap
plied through leads 49 and lie to the detector
42, and also through leads I59 and 5! to the de
tector 46. In general, the amplitude adjusters
‘ill and to may be variable gain ampli?ers, to be
controlled from the pilot ?lter circuits 3'? and 38
such that the side ban'd energies in leads 4H and
45 are equal. Under these conditions, with de
tectors of like characteristics, and equal carrier
signals applied to both, the pilot and therefore
the signal output of detector 132 will be the same
as the pilot and therefore the signal output of
detector 46, as far as magnitudes are concerned.
Also, the phase adjuster 48 may be a variable
phase shifting device, to be controlled from the
pilot ?lter circuits 3'! and 38 such that the nu
merical angle between the carrier and side band
vectors for detector 42 is the same as the nu
merical angle between the carrier and side band
vectors for detector 136. In other words, the am
plitude and phase adjusters 40, 4d, 138 are to op
erate such that the carrier and side bands are
related as in amplitude modulation, as regards
circuit l8.
the operation of the detectors "i2 and 46, so that
In the pilot or control channel, the band split
their individual outputs of the pilot and therefore
ting circuit 20 separates out energy representa
of the signal frequencies will be of the same mag
tive of the carrier and lower side band, and en
nitude and the same phase.
ergy representative of the carrier and high side
The outputs of the two detectors 42 and £36 are
band, and feeds these energies through leads 2'!
connected individually by leads 52 and 53 to a
and 29 respectively to circuits 28 and 3!}, Here
mixer and pilot eliminator 54, wherein the out
the arrangements are such that if the outputs of
puts are combined additively, and the pilot fre
circuits 28 and 3!] were recombined, the result
ing wave form would be substantially the same 55 quency component eliminated, as by a sharply
selective ?lter. The signal output is then ap
as in the input to band splitting circuit 20. The
plied by leads 55 to a further ampli?er and uti
output of circuit 28 is connected by leads 3! to
lization circuit 55, which may be a loudspeaker,
a detector 32, and the output of circuit 30 is con
nected by leads 33 to a detector 34. The outputs
or recorder, or input to a repeater radio trans
of these detectors, which contain currents of fre 60 mitter. In this manner the tonal quality pro
quencies corresponding to the signal and pilot
duced in utilization circuit 56 may be made to
frequencies introduced into the transmitter prior
approach that which would have been possible
to modulation, are connected by leads 35 and 33
if the transmitted signals of spectrum it had
to pilot ?lter and ampli?er circuits 3'! and 38,
been related as in amplitude modulation.
which discard the unrequired signal components 65
To provide for the control of the amplitude ad
and retain the pilot components for future use
justers 4G and Ill?- and the phase adjuster 63, the
in controlling the operation of the signal chan
outputs of pilot ?lters 3i and 38 are connected
nel.
through leads 5? and 58, and 59 and 6!! to the
The circuits employed so far are conventional
two inputs of an amplitude comparator ti ; and
and can be readily provided by those skilled in the 70 the outputs of these pilot ?lters are also con
art, and need not be described in detail. It will
nected through leads 5'! and 62, and 59 and 63
be understood that the system is accurately lined
to the two inputs of a phase comparator 64. The
up so that the relation of the outputs of pilot
amplitude comparator is connected by leads 65
?lters 3'! and 38 as to magnitude and phase will
and by leads lit‘ to the control inputs of ampli-»
correspond to the relations between the carrier 75 tude adjusters GB and all respectively, while the‘
Monaco
5
phase‘ comparator MI is; connected: by leads . 61- to
ground... The anode'plateof. tube l3.is.lconnected
the control inputof phase. adjuster 48.
through capacitors 831' and, 85 to the anode of;
recti?er 81 and the. cathode of. recti?er 89, and:v
the anode plate. of tube 14 is‘connected through
capacitors 84 and 85 to the cathode of recti?er‘ 88‘
In‘ operation, the amplitude. comparator BI‘
compares the outputs of’ the‘ pilot ?lter circuits
31. and 38 as to magnitudaandmodi?es the gains
of. the amplitude adjusters 40- and 44 in, correc
tive senses; such that thesignals in the. leads 52
and the anode of recti?er‘ 90. These‘ recti?ersl
may be‘ of the crystal or copper oxide type, or a
thermionic diode may be‘ used it desired. The
terminals of these recti?ers are connected to!
and 53 become of. equal value. Similarly, the
phasecomparator. circuit 64‘ compares the out
puts of the pilot ?lter. circuits. 3'! and 38 as:- to
' ground through resistors .9I to 94 and resistors
phase, and modi?es thephasechange- of the car
95- to. 9B, the latter set. of which are shunted by
rier in passing through the. phase adjuster 48 in
?ltering capacitors 99' to I02. One side of line
acorrective sense suchthat the detected‘ signals
66: is. connected to ground, and the other side is
inthe leads 52 and 53 become of the same phase.
connected. through resistor. I03Ito the cathode of
The delay circuit It provides.‘ suitable delay so 15 recti?er 81, and through resistor Hill to the anode
that. the. controls start to be. operative somewhat
of recti?er 88.; one'side" of line 65- is connected to
prior to the arrival of the signalswhich are to be
ground and the‘ other side is connected through
controlled, to reduce the e?ects of the time con
resistor I05 to the anode. of. recti?er 891 and
stants of the control circuits. In this manner,
through resistor lll?lto the cathode of recti?er 90.
the combined signal in utilization circuit. 56 is.‘ k
of much higher quality than if the pilot trans
mission had not been used to correct for the de
?ciencies of transmission.
Since the devices which may be used for ampli
tude. comparison and adjustment by circuits ‘El,
40,. 44. and for phase comparison and adjustment
It is thus evidentthat a recti?er‘ system is pro‘
vided to develop D.-C. voltages across resistors
95 and 91' due to the impressed A.~C. voltage E1,
¢1; and to develop D.-C. voltages across resistors
96 and 98 due to the impressed A.-C. voltage Em
¢2. The D.-C. currents ?owing in these‘resistors
are indicated by arrows, the senses being de
by circuits 64 and 48 are not well known in the
termined by the recti?er connections, and‘ the
art, it is desirable to show illustrative circuits,
magnitudes‘ by the A.-C. voltages. The elements‘
and therefore, I haveshown in Fig. 2 the. details
of the circuits are balanced such that, for ex.
of a typical amplitude comparison and adjust 30 ample, the currents in the four resistors 95'to 98
ment circuit, and in Fig. 3 the detailsof a typical
will be all numerically equal if E1 and E2‘ are
phase comparison and adjustment. circuit. For
equal. It will be notedthatthe values of ca and
clarity, I show these connected between terminal
¢2 are‘ irrelevant as. far as the magnitudes and
senses‘ of the recti?ed currents areconcerned.
circuits and by leads corresponding to the cir
cuits and connections depicted in Fig. ‘1.
For
>
With equal resistors I03? and I04, itis apparent
that the D.-C. potential of the non-ground wire‘.
illustrative, purposes, conditions are shown when
the transmission conditions. are such. that the
output voltage. from pilot ?lter 31- is greater than
that from pilot ?lter 38, and leads in phase‘. by
about 90 electrical degrees.
In Fig. 2 is shown the amplitude comparator BI,
driven from pilot ?lter circuits 3'! and. 38, con
trolling through leads 65 the. passage of low. side
of line 5% will be the mean of the D.~C. potentials,
assuming the far end is not loaded. Thus, in
the present: instance. with‘ the current in resistor
95 exceeding that in resistor 96‘ making the cath
odeof recti?er 8'1 numerically more positive: than
the anode of recti?er 88 is numerically negative,
a positive voltage is developed for the line 56.
frequency energy from» low side band circuit 24
through amplitude adjuster 40. to the detector. 42,
I, a negative voltage for the line 55. since the anode
and controlling through leads 66 the. passage. of.
of recti?er 89 is more negative. than the cathode
high side frequency energy fromhighside band
circuit 25‘ through amplitude adjuster 44- to the
detector 46. These. circuits together with the
of" recti?er 90 is positive. Thus, in general, no
voltage is developed on‘ lines 56 and 65. if
E1=Eu; the voltage on line 66 is positive and that
connecting leads. are numbered identically with
correspondingcircuits and lines of Fig.1.
In this present ?gure, voltage from circuit 31
on line 65 is negativeif as in the illustrated con
is impressed through leads 51-, 58 and by coupling
capacitor 69. and input resistor 'II upon the grid
of a recti?er driver tube: ‘I3, voltage from circuit
38. is impressed throughleads 59’, Bllandby, cou
pling. capacitor ‘I0. and. input resistor 12 upon
thegrid of a recti?er tube 14. For clarity, ele
ments associated with or driven by tube ‘I3 are
assigned odd numbers, andthose associated with
or driven by tube ‘I4 are assigned even numbers,
correspondingly, the: recti?er system develops
dition E'1>E'2; the voltage on line 66 would be‘
negative and thaton line. 65- would be positive if
conditions were'such that E1<E2. While the load“
on the far‘end of the lines 66‘ and 85 determines
the amount of the voltage on the line, it does not
determine the» sense of the voltage as long as‘
the load does not of itself. contain a voltage.
source.
The amplitude adjusters 40 and 44 may be
of identical construction, but since they operate
referencethe markings E1,.¢1, andEz, ¢z.at. the
in opposite senses, both adjusters are shown.
The adjuster 40 will: be described in detail, and
parts of adjuster 44 corresponding to those of‘ 40‘
grid leads of tubes '13. and ‘I4 indicatethe magni
will be-indicated by. primed numbers.
for theentire amplitude. comparator circuit. For
tudes and. phase angles. of . the voltages impressed 65
The" low side band circuit 24 is connected by
upon the grids, and the. illustrations. refer. to a
line. 39 to the primary side. of an intermediate
condition. where E1 is greater. than. E2. in a. ratio
frequency transformer I‘ll'l. One terminal of the
of about. two to one, and¢1 is ¢2 plus ninety elec
secondary of transformer Ill‘! is connected to. the
tribal. degrees.
?rst or control grid of a pentode ampli?er tube
The cathodes of tubes ‘I3 and ‘Mare connected ‘I I08, and‘ the other terminal is connected through
to ground throughcathode bias resistors 15‘ and
76,,bypassed. by capacitors ‘I1 and.'I8.- The anode
plates of tube". andlllrare connectedlby. resistors
resistor I09 to ground, paralleled by capacitor
III]. The ground side of line 65 is connected to
the grounded end of resistor I09; and the active
side, in the present case at negative potential,
19». and‘ B0. to the. positive. ends of. batteries .8 I ‘ and
82., the negative endsor which: are. connectedrto. 75. I is: connected to thejunction or": resistor I59.‘ and;v
7
2,5013%
the secondary of transformer IN. The. anode
plate of tube I08 is connected through the pri
~mary of an intermediate frequency transformer
8
two cases. Thus,’ if the voltages across resistors
III and H8 to ground are E1, gin, and E2, e2, re
spectively, then the voltages from grid to ground
III to the positive end of battery IIZ, the nega
for tubes I23 and I24 will be .707 E1, (¢1+¢l5), tive end of which is connected to the positive
and .707 E2, (¢2—4=5) respectively. The net re
end of battery M3, the negative end of which is
sult, therefore, is a 90 degree phase advance of
connected to ground. The positive end of bat~
the voltages for tubes I23 and I24 with respect
tery H3 is connected to the second or screen grid‘
to the advance of the phase of the output of 31
of tube I08, and is connected through the bleeder
with respect to that of 38, with no relative change
resistor I III to the cathode and the third grid 10 in the ratio of signal strengths. For the illus
of tube I08, which Iin turn are connected to
tration example, with the voltage across resistor
ground through resistor H5 ‘shunted by capaci
II'I’ leading that across resistor M8 by ninety
tor H5. The constants are so chosen that when
electrical degrees, it is seen that the additional
the voltage from line IE5 is zero, the tube‘ W8 op
phase shift causes the tubes I23 and I24 to be
erates with somewhat higher grid bias than cor
driven with 180 degrees diderence of phase, so
responding class A ampli?er operation, produc
that the grid voltage of one has a peak maximum
ing a moderate ampli?er gain. The gain of the
when the grid voltage of the other has a peak
system is ‘increased whenever a positive voltage
minimum. While under other conditions the
is impressed upon the grid circuit across resistor
phase relations may be numerically vdiliferent,
I09, and is decreased whenever as in the instance
there will be a net advance of 90 degrees of the
shown, the voltage impressed into the grid cir
relative phases of the signals due to the circuits
cuit from line 65 is negative. The circuit for ad
I I9 to I22.
‘
juster M operates in a similar fashion, but it will
The cathodes of tubes I23; and 52d are con
be noted that whenever the gain of one of cir
nected to ground by bias resistors I25 and I26,
cuits t0 and MI is higher than normal, the gain
shunted by capacitors I2‘! and I28. The anode
of the other is less than normal. In this man
plates of these tubes are connected through in
ner, the ampli?er can be adapted to compensate
ductors I25.I and I39 to the positive ends of bat
for a very high or very lowlratio of voltages E1
teries I ti and I32, the negative ends of which are‘
and E2. It will be noted from Fig. 1 that the
connected to ground. The inductors I29 and I30
ratio of side band outputs of circuits 2t and 26 is 30 may be shunted by capacitors I33 and I35, to
also the ratio of E1 to E2. Therefore, the ampli
provide resonant circuits tuned to the pilot fre
?er with the weaker input signal has the greater
quency, due care being taken that the entire sys- gain, and the one with the stronger input signal
tem is balanced so that the currents in the in
has the lesser gain. The constants are so chosen
that the ratio of side band inputs to detectors
42 and 46 will be close to unity, over a wide value
of ratios of outputs of circuits 24 and 26. The
signal level at the inputs of the ampli?ers I08 and
I08’ will be adjusted to be sufhciently low so that
little or no wave form distortion results, although 0
the ampli?er with the lowest gain is receiving
the greater signal. Thus, provision is made to
provide about the same amount of low side band
energy for detector 1:12 as high side band energy
ductors I29 and IIIEI will have the same ratio as
the input voltages E1 and E2 but with the proper
ninety degree phase advance relation. In the
present instance, the current in inductor I29 is
indicated as being twice that in inductor I30,
with a total phase difference of 180 degrees, cor-'
responding to the ninety-degree difference in
the inputs to the system plus the ninety-degree
shift created by elements I III to I22.
.
The two inductors I2t and I30 are the pri
maries of transformers each with two secondaries,
for detector I6, so that with equal carrier values, ~15 which are cross coupled to a rectifier‘ system.
the detected outputs will be closely equal.
Thus, the anode of a recti?er I35 is connected
In Fig. 3is shown the phase comparator 64,
to ground through secondary I3? coupled to in—
driven from pilot ?lter circuits 3“! and 38, and
ductor I 29, and through secondary I38 coupled
controlling through leads 6'! the amount and
to inductor I39, while the cathode of recti?er
sense of phase shift of the intermediate frequency I
I36 is connected to ground through secondary
carrier in passing from carrier circuit 22 through
I39 coupled to inductor I39 and through second
phase adjuster I8 to the detectors I32 and iii.
ary let coupled to inductor I29. It will be noted
In this circuit, the output of pilot ?lter 31 is con
nected by lines 57! and 62 to the terminals of a
resistor III, and the output of pilot ?lter 38 is >
connected by lines 59 and 63 to the terminals
of a resistor H8, with one end of each of these
resistors II? and H8 connected to ground. The
other end of resistor III is connected to ground
through a phase advancer circuit comprising ca
pacitor H9 and resistor I2I in series, with the
junction between these elements connected to
that one of the windings, such as MEI, is wound
in a reverse sense, so that in effect one recti?er
is driven in accordance with the vector difference
between the primary currents, while the other
recti?er is driven in accordance with the vector
sum of the two primary currents. Thus, for the
illustrative example, the magnitudes and senses
of the voltages induced into the secondaries may
be as indicated by the arrows associated with
the individual secondaries, whereby in a ba‘l
the grid of an ampli?er tube I 23. The other end
anced system with 180 degrees difference of pri
of resistor H8 is connected to ground through a
mary'currents, the net A-C'. voltage impressed
phase lagging circuit comprising resistor I29 and 65 upon recti?er I35 is seen to be three times the
capacitor I22 in series, with the junction between
voltage impressed upon recti?er I36. Or if, for
these elements connected to the grid of an ampli
example, there were zero phase difference be
?er tube I213. The impedances of all elements
tween the primary currents, resulting, for ex
H9 to I22 are made numerically equal for the
ample, in a reversal of the arrows for couplings
pilot frequency, and of sufficiently low value so 70 I38 and I 39, then the recti?er I35 would be driven
that the input impedances of the tubes I23 and
by only one third of the voltage by ‘which recti
I24 produce negligible e?ect. In this case, the
?er I36 is driven. Finally, if the primary cur
circuit H9, I2I produces a phase advance of 45°,
rents Were quadrature related, as for example,
and the circuit I20, I22 produces a phase lag of
with the input from 3'! and 38 either in phase,
45°, with equal drops in the signal strength in the 75 or-"180 degrees diiferent in phase, then the recti- A
2,601,330
‘Id
?ers I35 and ‘I36 ‘would‘be equally driven, since
then the grid will be at ground potential.
the numerical value ‘of the vector sum of two
vectors is equal to the numerical value of the
however, the voltage of the arm is positive or
not su?iciently negative,. then the grid of tube
vector difference of those vectors, provided the
two vectors are at right angles. Accordingly,
the relative difference of drives of recti?ers I35
potentiometer arm is in the process of becoming
If,
I58 will be positive. In the condition shown, the
sufliciently negative to reduce the contact I55
and I35 may be taken as a measure of the phase
to zero potential. The servo-mechanism is of
difference of the inputs to the comparator system.
a type which tends to make the grid of tube I58
The cathode of recti?er 435 is connected to
approach a de?nite value, which in the present
ground through resistor IIII shunted by ?lter 10 case is zero. For this purpose, a transformer IE3
capacitor I43, and the anode of recti?er I36 is
is provided, the primary of which is connected
connected to ground through resistor M2 shunted
to a power source such as a 60 cycle line, ‘with the
by ?lter capacitor I44. One side of line ‘61 is
outer terminals of the secondary connected to
connected to ground, and the other side is con~
the anode of tube 158 and to the cathode of a
nected through resistors I45 and Hit to the cath— 15 recti?er I54. The center tap of the transformer
ode of recti?er I35 and the anode of recti?er
secondary is connected to ground through the
I36, respectively. Thus the voltage of the un—
armature of motor I48 which has a ?eld of ?xed
grounded side of line .51, under no load at the far
polarity as produced, for example, by use of a
end, is the mean of ‘the voltages across the rec—
permanent magnet, so that the sense and speed
ti?er output resistors MI and I42, and in the
of rotation of said motor are determined by the
present illustrated instance it “will be a positive
sense and amount of the D.-C‘. current through
voltage. In general, the open circuit output
voltage Em ‘will be given very closely by
the armature. Capacitor I55 paralleled by a'D.-C.
center zero voltmeter I65 is connected ‘across the
armature of motor MB to remove A..-C. compo
nents of the recti?ed current to the motor, and
where k is a constant of the system, E1, E2, ¢1 and 25 to indicate the D.-C'. voltage value. The recti?er
422 refer to the magnitudes and phase angles of
circuit is completed by use of a battery I61 the ‘
the input voltages to the system. This formula
positive end of which is connected to the cathode
is analogous to that for the output torque of a
of triode I58, and the negative end of which is
two-phase induction motor. The "voltage devel~
connected to, ground, and by use of a variable
oped by the phase comparator may, therefore, be
resistor I58 which is connected from the anode
a measure of the ‘phase ‘difference ‘between the
of recti?er I54 to ground. Thus, it is seen a bal
input signals from sources 31 and 35.
anced ‘arrangement results, in which the sense
The phase adjuster circuit is or an electro
of the output current of the system to the motor
mechanical type utilizing a continuously variable , I58 depends upon the relative amounts recti
phase shifter I41 driven from a D.-C. motor III;
?ed by devices I58 and I64. By throwing ‘the
with a. permanent magnet ?eld, through a gear
switch I56 so that the grid of tube I58 is con
reducer I49, which also drives a potentiometer
nected to ground, and by setting the variable re
I50 with the sense of rotation and the speed of
sistor I58 at a suitable value, the two recti?er
rotation of motor I48 determined by the} opera
. currents may be equalized 'for zero grid voltage
tion of a D.-C. ampli?er system I5I in accord
of triode I58, as indicated by zero reading of in
ance with the D.-C. voltage impressed upon the
dicator I56. When the switch is restored to the
[line 5'! and the position of the potentiometer and
position indicated, the tube I58 will rectify more
phase shifter. This constitutes a type of electro
than device I64 if the grid of tube I58 is posi
mechanical servo mechanism, with D.-C. input
tive, and less if it is negative, with a correspond
and mechanical output.
ing condition of rotation of the motor armature.
More speci?cally, resistor I52 shunted .by ca
Therefore, in a sense the circuit comprising tube
pacitor I53 is connected across the control line
I58 and recti?er I64 is a D.-C. ampli?er where
57 across which the control voltage is impressed
by the amount of D.-C. output to motor I43 is
upon the system. In the case illustrated, the
by the amount of 11-0. voltage on
voltage impressed is positive. The ungrounded 50 controlled
the grid of triode I58.
end of resistor I52 is. connected through resistor
The motor I43 operates through the gear box
I54 to a contact I55 of a single pole double throw
MI! with a shaft I 69 operativelv connected to
switch I55, the moving blade I5'I of which is con
drive the arm of'potentiometer I50. In the case
nected to the grid of a triode tube I58, and the
depicted. the motor is driving ‘the potentiometer
55
other contact I59 of which is connected to ground.
to make the arm more negative, thereby reducing
Normally the blade‘is closed on contact I55 as
the potential on'the grid of tube I58. The speed
depicted. The terminals of potentiometer I55
of rotation will ‘be reduced as the grid of tube
are connected to the positive and negative ends
I55 approaches zero, and the motor will stop
respectively of equal voltage batteries Hill and
I5I, the other ends of which are connected to 60 when this condition is reached. Thus, a system
is provided whereby a one-‘to-one relationship is
ground, ‘whereby the moving arm of the poten
maintained between the angular setting of the
tiometer may have a positive or negative poten~
potentiometer I50 and the 11-0. voltage im
tial depending upon its position. The connec
pressed across line 51.
tions are such that counter clockwise motion of
The servo~mechanism described above is uti
the arm makes the arm move negative in poten 65
lized to operate the phase shifter ‘I 51, shown sche
tial. The moving arm is connected through re~
maticaily. Here, inductors III and IIZ represent
sistor I52 to the contact 155. It is thus seen
two vwindings about the same region of space
that a network exists making the potential of the
with the magnetic axes of the two coils at right
contact I55 and therefore of the grid of tube
angles, and inductor I13 represents a coil rotat
I55 a function both or the operation of the
abiy mounted so that it may be variably cou
recti?ers I35 and ‘I35, and of the position of
the arm of potentiometer I50. Thus, if resistors
pled magnetically to the two windings III and
I 55 and IE2 are of equal value, with the volt
Illa in varying proportions and senses. The ar
age across the resistor I52 positive, and the
rangement is analogous to the mounting of a
voltage from the armto ground equally negative,
coil in ‘the armature space of a two-phase in
2,501,330
12
duction motor, except that here the operation is
both decreasing the angle 01 between C and P1 of
at intermediate frequency. One end of each of
Fig. 41: by 45 degrees, and increasing the angle 02
the three coils is connected to ground and to one
between C and P2 by 45 degrees, thereby equaliz
side, termed the ground side, of each of the leads
ing the angles 01 and 02, which were previously
lil from carrier circuit 22 and the leads fit, 50,
different by ninety degrees. The equalization of
SE to detectors t2 and 4B. The other end of
magnitudes is by the circuits depicted in Fig. 2,
rotor coil H3 is connected to the other ungrounded
the equalization of angles is by the circuits de
sides of leads (i9, 59, and iii. The other ends of
picted in Fig. 3, and the net result is an equal
stator windings Hi and I12 are connected through
ization of the output currents of detectors 42 and
capacitor EM and resistor W5, and through in 10 lit, both for the pilot frequencies and for the
ductor lit and resistor I'll to the ungrounded
signal frequencies that accompany the pilot
side of line 4?. Constants are so chosen that
frequencies. A delay is put in the signal channel
the current in winding HI leads that in wind
by circuit It so that the devices in the control
ing E72 by ninety electrical degrees, with equal
ling circuits 453, Ml, 48, iii, 64 may have advance
current values for a symmetrical system. The
notice of the changes in transmission in progress,
rotor H3 should be sui?ciently loosely coupled
and may initiate corrective changes which will
to the stator windings so that the currents in
be accomplished at the proper time.
duced into the rotor do not appreciably alter the
For illustrating the operation of the phase
amount or phase of the current in either stator
comparator by which the phase equalization is
winding.
In this manner, a, phase shifter may
controlled, Figs. 4c and ‘if show the manner in
which the rectifier I35 of Fig. 3 receives a greater
be constructed such that the amount of elec
trical phase shift in passing from circuit 22 to
detectors I22 and (it may be equal to the angular
setting of an index attached to the rotor shaft.
Since the rotor shaft is geared to the shaft for
driving voltage than recti?er I36, when the pilots
are as indicated in Fig. 411. Thus, the voltages
E137 and E138 of Fig. 46 due to ‘windings i3? and I 38
are in phase due to the phase shifting effects of
elements lid to I22, and add up to a large volt
age E135 for recti?er I35. On the other hand, the
voltages E139 and E140 of Fig. 1i)‘ due to windings
the potentiometer M8, it follows that the rotor
> setting will follow up the changes in D.-C. volt
ages impressed upon the ‘line ii'l. Connections
are such that the phase shifter, which is ap
plied to the carrier, causes phase changes of half
the value and in the opposite sense to the change
S39 and Mil are opposing and produce a rela»
tively small voltage E126 for recti?er I36. If E2
leads E1 by 90‘ degrees, instead of as in Fig. 4d,
then recti?er l36 would receive a greater voltage
than recti?er i357. If, on the other hand, the
pilots were in phase with ¢1=¢2, then conditions
in the difference between pilot phases 451 and ¢2.
Because phase relations are not as generally
understood as amplitude relations, it appears de
sirable to describe the overall operation in con‘
nection with vector diagrams shown in Fig. ll,
which includes various lettered sub designations.
would be depicted as in Figs. 4g and 4b, with the
plitude modulated signal due to modulation by
voltages in the two sets of windings quadrature
related because of the shifting effect of circuits
i W to 522. In Fig. 4g, the voltages E137 and E138
due to windings I 37 and I 38 add up to a vector
a pilot wave, with C the carrier vector, P1 the
.= E135 which is of the same numerical magnitude
Fig. 4a is the normal representation of an am
low side pilot frequency and P2 the high side
pilot frequency. P1 and P2 are equal and less
as voltage E136 of Fig. 4h which is compounded
from the voltages E139 and E140 due to windings
its and Mt. As a result, the outputs of the two
recti?ers would be equal in magnitude, and be»
than 1/2 C‘. The angles 01 and 02 are at all times
equal but in the example shown are about 45°,
and increasing since P1 rotates slower than C, '
and P2 faster than C. This 'represents'conditions
at 45° of the modulation cycle, and if C and P1
were being demodulated by one device and C and
P2 by a like device, the two outputs would be
equal and of the same phase, momentarily 45° in ’
the case shown, as illustrated in Fig. (lb. But if.
voltage would be impressed on the control line 5",’.
The invention shown and described may be im~
due to the transmitting medium, the phases and
dividual corrective arrangements and detectors,
cause of the balanced arrangement, no D.-C.
proved upon readily by those skilled in the art,
in various fashions. Thus, the entire signal band
may be broken up into a plurality of bands for
which individual pilots are provided, with in
magnitudes of C, P1 and P2 are differently dis
thereby increasing the accuracy with which a
turbed, the relation at the receiver input might
pilot can represent the band with which it is
be, for example, as in Fig. 40 with P1=2P2, and
associated. Further, the pilots P1 and P2 may be
01=62+99°. As a result, the two detected cur~
transmitted by reversal of phase of one, say P2, so
rents would not be equal and equally phased but
that C, P1 and P2 are related as the carrier and
would be as depicted in Fig. 4d. The wave form
?rst order side frequencies of a phase modulated
represented by Fig. 40 can be restored to that
signal. These pilots may be eifectively used for
of amplitude modulation by reducing P1 and in 60 control of the signals transmitted by amplitude
creasing P2 until they are equal, and retarding
modulation, for example, by reversing the leads
C in phase by 45 degrees until 01 and 62 are equal.
59 at the output of the pilot ?lter 38. The ad
Fig. 4_~c depicts the nature of the carrier and
vantage of such a transmission is that in the out
pilots as they exist in combination in rectangles
put of detectors 42 and 46, the signals would add
28 and 30 of Fig. 1, and as they exist individually C: Or correctly, but the pilots would cancel, reducing or
in rectangles 2'2, 24, 2E neglecting the effect of
eliminating the need for a pilot eliminator in cir
delay circuit l6. Fig. 4d depicts the pilot signals
cuit 54.1. , Still further, limiters may be inserted in
after demodulation as they appear at the inputs
the leads 62 and 63 to the phase comparator 64
of rectangles 6i and fill. The amplitude conn
to equalize the signal strengths E1 and E2 im
parator ‘6i operates differentially upon the rec 76 pressed upon the system of Fig. 3, thereby making
tangles lit! and M to equalize the pilot intermedi“
the output of the phase comparator more cor
ate frequencies P1 and P2 impressed upon the
rectly a measure of the phase relation between
detectors t2 and db. The phase comparator (it
¢1 and ¢2, which relation is not influenced by the
operates differentially on the carrier C by re
limiting process. Still further, a super-effective
tarding the carrier phase by 45 degrees, thereby 75 automatic volume control system may be con
14
structed making use of the fact'that C, P1 and ‘P2
are transmitted all of the time. Thus, suitably
weighted samplings of C, P1 and P2 as they exist
in the intermediate frequency part of circuit l0
could be taken and the automatic volume control
voltage determined by the totalized energy repre
sented by the three components instead of only
the carrier component, due allowance being made
for the carrier value being normally greater than
the pilot values. Still further, it may be pos 10
energy to each-thereof, ‘upper side band ‘energy
to one thereof and lower side band energy to
the other thereof, ‘apparatus coupled to said de
tectors for combining the detected signal side
bands to recover the original signals, a detector
for each side tone frequency and the carrier,
apparatus coupled to said last named detectors
for comparing the amplitudes of the detected
tone frequenciesto derive energy representative
of differences in amplitude of the detected tone
sible to improve the phase comparison system by
driving the phase adjuster circuit 48 from pilot
frequencies in the outputs of detectors 452 and 46,
frequencies, and apparatus associated with the
the value and quadrant location of the phase dif
ferences of the two pilots with precision.
resulting from modulation of the carrier by sig
frequency and the carrier, apparatus coupled to
said last named detectors for comparing the
phases and amplitudes of the detected tone fre
quencies to derive energy representative of dis
placements in the relative phases of the detected
tone frequencies and energy representative of dif
ferences in amplitude of the detected tone fre
quencies, and apparatus controlled by said de
rived energies respectively for adjusting the rela
tive phases and relative amplitudes of the de
tected signals in accordance with said derived
detectors.
respective side band selecting circuits and con
trolled by said derived energy for adjusting the
making the adjustment by servo feedback so that
relative amplitudes of ‘the side bands as detected
these pilots do not differ appreciably in phase. 15 to correspondingly control the amplitudes of the
Still further, it is possible to design. an improved
detected signals as combined.
phase comparator circuit using two devices pro
4. In apparatus for receiving wave energy com
ducing two D.~C. outputs, which will identify
prising a carrier and upper and lower side bands
20 nals and a substantially single tone frequency, a
Although only a few of the various forms in
detector for each signal side band and the carrier,
which this invention may be embodied have been
apparatus coupled to said detectors for combining
shown herein, it is to be understood that the in
the detected signal side bands to recover the
vention is not limited to any speci?c construction
original signals, a detector for each side tone
but might be embodied in various forms without 25 frequency and the carrier, apparatus coupled to
departing from the spirit of the invention or the
said last named detectors for comparing the
scope of the appended claims.
phases and amplitudes of the detected tone fre
What is claimed is:
quencies to derive energy representative of dis
1. In apparatus for receiving wave energy com
placements in the relative phases of the detected
prising a carrier and upper and lower side bands 30 tone frequencies and energy representative of
resulting from modulation of the carrier by sig
differences in amplitude of the detected tone
nals and a substantially single tone frequency, a
frequencies, and apparatus controlled by said
derived energies for controlling the phase of the
detector for each signal side band and the car
rier, apparatus coupled to said detectors for com
carrier used in each of the ?rst named detectors
bining the detected signal side bands to recover 35 and for controlling the amplitudes of the upper
the original signals, a detector for each side tone
and lower side bands used in said ?rst named
5. In apparatus for receiving wave energy com
prising a carrier and upper and lower side bands
resulting from modulation of the carrier by sig
nals and a substantially single tone frequency,
a detector for each signal side band and the
carrier, apparatus including carrier and side band
selecting circuits coupled to said detectors for
4.7 feeding carrier energy to each thereof, upper
side band energy to one thereof and lower side
band energy to the other thereof, apparatus cou
pled to said detectors for combining the detected
energies.
2. In apparatus for receiving wave energy com
signal side bands to recover the original signals,
prising a carrier and upper and lower side bands 50 a detector for each side tone frequency and the
resulting from modulation of the carrier by sig
carrier, apparatus coupled to said last named
nals and a substantially single tone frequency, a
detectors for comparing the phases of the de
tected tone frequencies to derive energy repre
detector for each signal side band and the car
rier, apparatus including a carrier selecting cir
sentative of displacements in the relative phases
cuit coupled to said detectors for feeding car 65 of the detected tone frequencies, apparatus as
rier and side band energy thereto, apparatus cou
sociated with the carrier selecting circuit and
pled to
detectors for combining the detected
signal side bands to recover the original signals,
said phase comparing apparatus for controlling
the phase of the carrier fed to said ?rst named
detectors in accordance with said representative
carrier, apparatus coupled to said last named de 60 energy, apparatus coupled to said second named
tectors for comparing the phases of the detected
detectors for comparing the amplitudes of the
tone frequencies to derive energy representative
detected tone frequencies to derive energy repre
sentative of differences in amplitude of the de
of displacements in the relative phases of the
detected tone frequencies, and apparatus con
tected tone frequencies, and apparatus associated
with the side band selecting circuits and con
trolled by said derived energy and associated with
the carrier selecting circuit for controlling the
trolled by said last named representative energy
for controlling the amplitudes of the respective
phase of the carrier used in said detectors in ac
cordance with the derived energy.
side bands selected and fed to said ?rst named
3. In apparatus for receiving wave energy comdetectors.
prising a carrier and upper and lower side bands
6. In apparatus for reducing the effects of
resulting from modulation of the carrier by sig
fading on modulated energy comprising a carrier
nals and a substantially single tone frequency,
and side bands resulting from modulation of car
a detector for each signal side band and the car
rier energy by signals and by oscillations of sub
rier, apparatus including side band selecting cir
stantially single frequency, a time delay circuit
cuits coupled to said detectors for feeding carrier
excited by said modulated energy, selective cir
a detector for each side tone frequency and the
2,501,380
15
16
cuits coupled to said delay circuit for separating
of the side bands in accordance with the output
of said amplitude comparing circuit.
JOHN HAYS HAMMOND, JR.
the upper side band, carrier and lower side band
each from the other, other selective circuits for
isolating the carrier and one side band and the
carrier and the other side band, a detector coupled
to each of said other selective circuits, a circuit
coupled to each detector for selecting and ampli
REFERENCES CITED
The following references are of record in the
?le of this patent:
fying said oscillations of substantially single fre
UNITED STATES PATENTS
quency, a phase comparing circuit coupled to
Name
Date
each of said selecting and amplifying circuits '10 Number
for deriving an output depending upon the rela
tive phases of the oscillations of single frequency
selected thereby, means for adjusting the phase
of the carrier derived from said ?rst-mentioned ' ‘
selective circuits in accordance with the output 15
of said phase comparing circuit, an amplitude
comparing circuit coupled to each of said detec
tors, and means for controlling the ampli?cation
1,743,132
1,777,355
1,882,653
Green ____________ __ Jan. '14, 1930
Fetter ____________ __ Oct. '7, 1930
Sedlmager ________ __ Oct. 11, 1932
1,999,902
Hansell __________ __ Apr. 30, 1935
2,375,126
Mathes ____________ __ May 1, 1945
'
Number
543,602
FOREIGN PATENTS
Country
Date
Great Britain ______ __ Mar. 5, 1942
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