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_Dec. 3, 1946.
2,412,039
G. w. FYLER
FREQUENCY MODULATION RECEIVING APPARATUS
Filed July 16. 1945
2 Sheets-Sheet 2_
Pi 8.5.
Inventor‘:
GeoPgb’eW.P>/ler~,
bY We?)
'
His Attorney.
Patented Dec. 3, 1946
2,412,039
UNITED STATES ‘PATENT OFFICE 7
2,412,039
FREQUENCY MODULATION RECEIVING
APPARATUS
George W. Fyler, Stratford, Conn, assignor to
General Electric Company, a corporation of
New York
Application July 16, 1943, Serial No. 494,976
10 Claims. (01. 250—20)
1
2
.
My invention relates to frequency modulation
receiving apparatus and more particularly to
means suitable for automatically controlling the
tuning of a frequency discriminating circuit.
produced by temperature variation in the tunin
Demodulation ofa frequency modulated car
mediate frequency and the resonant frequency
vof the intermediate frequency channel by an
rier Wave is ordinarily carried out by applying
the waves ?rst to a frequency discriminating
circuit tuned to a resonance at the carrier mean
frequency and arranged to convert the frequency
circuits of the oscillator.
"
'
In a superheterodyne receiver coincidence is
commonly maintained between the mean inter
automatic frequency control system comprising
means for controlling the. frequency of the local
oscillator in response to changes in the unidirec
tional component of discriminator output voltage.
While such automatic frequency control is quite
satisfactory in applications where the frequency
of the signal wave supplied to. the discriminator
is subject to control, it isnot suitable for appli
modulation. For satisfactory undistorted dis
crimination, the mean frequency of the signal 145 cation to tuned radio frequency receivers and to
certain types of superheterodyne receivers in»
wave must coincide with the resonant frequency
which the frequency of the local oscillator is ?xed,
of the tuned frequency discriminating circuit.
as by crystal control.
.
Any variation between the mean frequency of
‘ modulated waves into an amplitude modulated 10
wave at the same carrier frequency. The ampli
tude modulated wave thus derived is then im
pressed upon a suitable detector circuit for de
the signal wave and the resonant frequency of
Accordingly, it is a principal object of my in
tuned discriminator circuit causes a change 20. vention to provide new and improved means for
in the unidirectional component‘ of the discrim
inator output voltage. For example, in the bal
anced diode detector type of discriminator de
scribed and claimed in Patent 2,121,103, issued
controlling automatically the resonant frequency
of a tuned circuit.
v
_
It is a further object of my invention to provide
new and improved electronic means for control
to S. W. Seeley on June 21, 1938; the discrimi 25 ling the resonant frequency of a tuned circuit.
It is a still further object of my invention to
nator load is so arranged that the net unidirec
provide new and improved means for controlling
tional component of voltage thereacross is zero
the tuning of a frequency modulation discrimi
when the mean and resonant frequencies coin
nating circuit in accordance with the mean fre
cide. In a balanced discriminator of this type
a positive or negative unidirectional‘component 30 quency of an incoming signal wave subject'to
variation.
'
'
of voltage is developed across the discriminator
It is a specific object of my invention- to pro
load upon any variation between the mean and
vide electronic means for controlling the tuning
resonant frequencies, the polarity of the unidirec
of a frequency modulation discriminator to main
tional potential being determined by the direc
tion of the variation. Such variation between 35 tain coincidence between the resonant‘ frequency
of the discriminator tuning circuit and the mean
the mean and resonant frequencies may occur in
frequency of an incoming frequency signal wave
any type of radio receiver. For example, in a
subject to variation.
receiver employing a number of stages of tuned
Brie?y, my invention comprises an electronic
radio frequency ampli?cation the resonant fre
quency of the tuned circuit, while relatively ?xed 40 reactance device, either a. small trimmer capaci
tance or inductance, connected across the termi
when tuned for the reception of a predetermined
nals of a tuned or oscillatory circuit for variation
incoming frequency, may drift slightly for a‘ va
in response to a unidirectional voltage indicative
riety of reasons, such as temperature variation
of circuit mistuning to restore the circuit sub
of the tuned circuits, and the like. Furthermore.
stantially to resonance. As applied to a fre
in a superheterodyne receiver employing a local
quency modulation discriminator, the: variable
oscillator and a plurality of amplification and
reactance is connected as a trimming condenser
limiter stages tuned to‘ a predetermined inter;
mediate frequency, the resonant frequency of
the’ intermediate frequency channel is subject
or inductance‘ across the terminals of the sec
ondary winding of the tuned discriminator input
to slight variation‘ for the same reasons as the 50 transformer and controlled in accord with the
unidirectional potential appearingacross the dis’
tuned circuits of a radio frequency receiver.
crim'inator load resistor. Suitably‘ an interelec
Additionally, the frequency of the intermediate
trode reactanceof an electron discharge device
frequency ‘carrier wave is subject to variation
‘is connected across the oscillatory circuit for
resulting from
change in the frequency of
the local oscillator as,.for example, the change 55 variation in accordance with a bias voltage: de~
2,412,039
3
4
rived from the discriminator load in response to
Speci?cally, the upper terminal of the trans
former secondary winding 22, as shown on. the
mistuning.
drawings, is connected to an anode 25 of a diode
My invention itself will be more fully under
26, the cathode 21 of which is connected through
stood and its objects and advantages further
load resistor 28 and a high frequency choke coil
appreciated by referring now to the following
1 29 to the midtap of the transformer winding 22.
detailed speci?cation taken in conjunction with
Similarly, the lower terminal‘of the winding 22
the accompanying, drawings, in which Fig. 1 is a
is connected to an anode 30 of a diode 3|, the.
schematic circuit diagram of a radio receiving
cathode 32 of which is connected through load
apparatus illustrating the principle of my inven
tion; and Figs. 2, 3, and 4 are schematic circuit 10 resistor 33 and the common high frequency choke
coil 29‘to the midtap of the transformer sec
diagrams of radio receivers embodying my inven
ondary winding. The discriminator load resistors
tion in a variety of forms.
, .
28 and 33 are bypassed for high frequencies by
Referring now to the drawings, and particu
a condenser 31 and are grounded at the negative
larly to Fig. 1, I have shown a receiving appa
ratus of the frequency modulation type employ 15 terminal of the resistor 33. The operation of a
balanced discriminator of this type is described
ing an antenna l0 and a signal channel H in
in detail in the Seeley patent mentioned above,
cluding any desired number of Stages of ampli?
and from that explanation it will be evident to
cation. The receiving apparatus may be of any
those skilled in the art that a voltage of signal
suitable type, such as one involving a number of
stages of tuned radio frequency ampli?cation, or 20 frequency appears across the electrically remote
terminals of the load resistors 28 and 33. This
one of the conventional superheterodyne type in
signal voltage has no unidirectional component
which the signal channel I I includes a local oscil~
when the mean and resonant frequencies coin
lator and a converter for supplying a signal wave
cide. However, upon variation between the mean
of predetermined intermediate frequency to an
intermediate frequency channel ?xedly tuned to 25 and resonant frequencies, the unidirectional com
ponent of current increases in one of the diodes
the intermediate frequency. Let it be assumed,
26, 3| and decreases in the other, depending upon
for the purpose of illustration, that the receiver
the direction of the frequency variation, so that
is of the superheterodyne type and that the in
termediate frequency channel terminates in a
?nal amplitude modulation limiting stage com
prising an electric discharge device I! having an
a net positive or negative unidirectional com
ponent of potential appears between the remote
terminals of the resistors 28 and 33. '
anode IS, a cathode [4, a control grid I5, a screen
The signal voltage may be impressed through
grid l6, and a suppressor grid H. The anode l3
of the discharge device I2 is connected through
a tuned primary winding l8 of a discriminator
a suitable blocking condenser 34 upon a volume
of a suitable source of unidirectional current sup~
control potentiometer 35 from which it may be
supplied to any suitable signal reproducing appa
ratus represented conventionally at 36. Pref
erably, the signal reproducing apparatus 36 in
ply such as a battery (not shown). ‘ The primary
cludes a desired number of stages of signal fre
input transformer l9 to the positive terminal B+
quency ampli?cation and a loudspeaker, head
winding l8 of the transformer 19 is tuned to
phone or the like capable of producing the voice
resonance at the predetermined intermediate fre
or musical sounds represented by signal modula
quency by a shunt capacitor 20. The cathode I4
tion of the carrier wave.
is connected to the negative terminal of the bat
If, as has been assumed, the mean frequency
tery through ground._ The screen grid I6 is con
of the incoming signal wave is not subject to con
nected to a suitable source of positive potential,
such as the B+ terminal of the battery, and is 45 trol, proper discriminator tuning may be main- .
tained by controlling the resonant frequency of
bypassed'to ground through a capacitor 2! in the
usual manner.
the discriminator transformer IS in such a man
‘
ner as to maintain coincidence between the car
The discriminator transformer l9 includes also
rier mean frequency and the resonant frequency.
a secondary winding 22 tuned to resonance at the
predetermined intermediate frequency by a‘ shunt 50 For this purpose I provide in shunt with the
tuning capacitor 23 a variable condenser 38 of
capacitor 23 and having its midpoint connected
relatively small capacity. The condenser 38 may
to the high potential terminal of the transformer
comprise a pair of ?xed plates 39 and 40 and an
primary winding through a blocking capacitor 24.
adjustable plate 4i mounted for movement upon
The tuned transformer’ I!) with the midtap con
nection through the capacitor 24 constitutes a 55 an arm attached to the moving element 42 of a
galvanometer. Since only very slight variations
frequency discriminating circuit so arranged that
of capacity are necessary in the condenser 38,
the electromotive forces at intermediate fre
the moving parts may be made of very small
quency across the two halves of the transformer
size. For example, the moving condenser plate
secondary Winding vary oppositely in intensity
with deviations of the signal wave from the mean 60 4| may be attached to the needle of a micro
ammeter. The micro-ammeter or galvanometer
carrier frequency, the direction of voltage varia
element 42 is connected for response between the
tion being dependent upon the direction of fre~
electrically remote terminals of the discriminator
quency deviation; Across each half of the sec
load resistors 28 and 33, and is sufficiently damped
ondary winding of the transformer I9 is con~
nected a series recti?er circuit for demodulating 65 by its own inertia so that it will respond only to
unidirectional components of voltage across the
the amplitude modulated signal waves appearing
terminals of the load resistors. The galvanom
across the respective halves of the transformer
eter element 42 is voltage responsive and its re
winding 22. These recti?er circuits are con
‘sistance will, of course, be high as compared to
nected in balanced opposition, or in'back-to-back
relation, in a well known manner so that the net 70 the sum of the resistances of the resistors 28
and 33.
'
i
voltage across their equal load resistors 28 and
From the foregoing explanation, it will be un
33 is zero when'the signal wave is at the desired
derstood that when the mean frequency of the
mean frequency and the resonant frequency of
signal wave coincides with the resonant frequency
the transformer coincides with the mean fre
~75 of the discriminator transformer If! no unidirec
quency.
'
’
>
2.41:2;039
eter element 42, so that~theneedle remains in a
'quency discriminating circuitiis arranged to .sup-'
‘ply, at ‘the positive terminal'of 'therdiscriminator
predetermined
load resistor 28, a potential which varies from a
tional'voltage-is impressed‘upon the 'galvanom
midposition.
‘Preferably, iof
predetermined ‘value :as, ifor example, vfrom
is of the zero center scale type so that when de O1 ground potential, either positively .or ‘negatively
depending upon variation of :the intermediate
energized ‘it assumes such-a-midposition. If now,
course, the galvanometer or micro-ammeter 42
the ‘mean frequency of the signal deviates in one
direction "or the ‘other from the resonant Jfre
carrier frequency from a desired value.
These
variations in unidirectional potential are 'im
pressed ‘upon the control grids 65 and 66 of the
quencyof thetuned transformer winding 22, 1a
net ~-positive or negative unidirectional voltage ‘is 10 discharge devices 45 ‘and 46 through the signal
impressed ‘upon-the galvanometer element 42 vin
dependence upon "the direction of the vfrequency
variation. ' The-unidirectionalvoltage moves ' the
galvanometer element ;-in {one direction or ‘the
other to change the capacity 0f~the trimming
condenser ‘36 in the'proper'sense to'bring the res
onant frequency-of the transformer secondary
frequency rejection ?lter 61, 68. The discharge
devices 45 and 46 respond to these grid poten
tial variations to effect changes in the reactance
between theanode and cathode of each device in
a manner presently to be described. ‘Since the
-anode-to-cathode circuits of the discharge de
vices45 and 46 are ‘connected in series between
the terminals of the tuned discriminator sec
winding substantially into coincidence with the
ondary transformer winding '22, changes in the
new‘mean frequency of the incoming signal wave.
‘At-Fig. 2-I have'shown'an arrangement wherein 20 apparent anode-to-cathode reactances may be
arranged to effect desired changes in the tun
a ‘pair of ‘electronic reactance devices are con
ing of the discriminator transformer secondary
nected respectively between the opposite termi
winding. It will be understood that upon a
change in carrier mean frequency the grid po
tential variation impressed upon the discharge
devices 45 and 46 is such as to change the anode
tative~or inductive-reactan'ce across the terminals
to-cathode impedances of the devices in a man
of ‘the oscillatory circuit. -In ‘the receiver illus
ner tending to make the resonant frequency of
trated at Fig. -2 the conventional portions of the
the tuned discriminator transformer follow the
apparatus are similar to those illustrated at Fig.
v1,-and like parts have been-assigned the ‘same 30 mean frequency of the received signal wave. The
direction of the retuning ‘effected by the dis
reference numerals. ‘At Fig. 2 ‘I have shown a
charge devices 45 and 46 may be controlled by
pairofelectric discharge>devices¥45 and 46 con“
the polarity of the coupling between the trans
nectedrespectively between the upper ‘and lower
former windings l8 and 22. The polarity of this
terminals of the discriminator transformer sec~
coupling should, of course, be such that mean
ondary winding 22 andground. ‘The discharge
frequency change effects a like change rather
devices-45 and i46-areconnected as reactance de-.
than an opposite change in the resonant fre
vices and include anodes-41 and 48,~respectively,
quency of the discriminator transformer.
‘connected through blocking condensers 49 and‘
nals 'of the tuned discriminator transformer-sec
ondary Winding and ground. Such reactance
tubes ‘may be arrangedto ‘act either as capaci
50*to-the respective terminals of the-transformer
winding 422. The cathodes 5| and 52 of the dis
charge devices 45and 46 are‘connected to ground
through cathode ‘resistors 53'and-54, respectively.
The cathode resistors-53 and 54-are'provided with
bypass condensers .55 and "56, respectively. The
anodes Hand ‘48 of the discharge ‘devices “and
'46 are-also‘connected ‘through'separate high fre
quency choke ‘coils "51 and 58, respectively, ‘to
‘the positive terminal B-}- of -a suitable'source of
unidirectional current supply ‘such ‘as a battery
‘(not shown). The negative ‘terminal of ‘the bat
tery is connected ‘through ground to the ‘cathodes
'51 and '52 of the devices 45 and 45. The dis
charge devices 45 and<46 also include suppressor
grids ~56 and ~66 connected, respectively, to the
cathodes 5| and 52 and screen grids 6| and \62
connected to the positive terminal -B-!- of the
battery. The screengrids 6| and 62 are bypassed
toground through suitable capacitors 63 and 64,
respectively. rThe effective impedances of the
‘discharge devices 45 and 46 are controlled, re
spectively, by control grids-65 and 66. The grids
'65 and 66 are connected to the positive terminal
of the discriminator load resistor 28 through
suitable decoupling resistors 69 and 10, respec
tively, and a, signal frequency rejection ?lter
comprising a resistor 6"! ‘anda bypass condenser
66. The control grids are also connected to ‘the
anodes 41 and 48 through resistors "H "and 12in
series with blocking capacitors v‘It! and ‘I4, re
spectively, and to ground through condensers v‘Ha
and 72a. respectively. The resistors "H and 12.
form, with the capacitors ‘(la ‘and 12a, phase
shifting circuits which will ‘be described in
greater detail hereinafter.
In operation of the device of ‘Fig. "2, the fre
The effective reactance between the anode and
40 cathode of the discharge devices 45 and 46 may
be rendered either inductive or capacitive. With
the circuit arrangement shown the anode-to
cathode impedances of the devices 45 and 46 act
effectively as serially connected inductances. It
s will be observed that in the discharge device 45,
for eXample,'the oscillations appearing across the
transformer secondary winding 22 are applied
through the blocking condensers “and ‘I3 and
the resistance ‘H to the control grid 65, and
through the blocking capacitor 49 to the anode
41. The transformer voltage is similarly applied
to the device 46. The impedance of the blocking
condenser 13 is small compared to that of the
resistor "H. Since the impedance between the
grid 65 and the cathode 5| ‘is essentially capaci
tive and'the impedance between the grid 65 and
the anode 41 is essentially resistive, the voltage
on the grid 65 lags behind the voltage of the
oscillating circuit 22, 23 by substantially 90 elec
trical degrees. Accordingly, since the current in
the anode 41 is in phase with the voltage of the
grid 65, the anode current ‘through ‘the discharge
device 45 also lags substantially 90 electrical de
grees behind the voltage of the tuned circuit 22,
23.
In other words, the anode-to-cathode im
pedance of the discharge device 45 is effectively
vinductive. The value of this effective inductance
may be varied by varying the unidirectional po
tential applied to the control grid 65 thereby to
vary the intensity of the current flowing in the
anode circuit. ‘Thus when the control grid be
comes more positive, the effective inductance is
‘reduced, and when the grid becomes more nega
tive, vthe effective inductance is .jincreased. This
effective inductance may be‘ca‘used to vary‘the
2,412,039
7
natural periods. or resonant frequency of the
tuned circuit comprising the transformer winding
22v and the condenser 23 thereby to e?ect desired
changes inthe tuning of the discriminator in
accordance with variations of the mean frequency
of the received signal wave.
'
In Fig. 3 I ‘have shown a further modification
of my invention wherein the input capacity of an
grid and the space charge is diminished thereby
to increase the input capacity of the device.
_ r .
From the foregoing explanation it is believed
that the. operation of the receiver of Fig. 3 will
be clear. As explained hereinbefore,‘ the fre
quency discriminating circuit is arranged to sup
ply at the positive terminal of the discriminator
load resistor 28 a potential which varies from a
predetermined value as, for example, from ground
electronic ampli?er is used to effect the desired
changes in oscillatory circuit capacity. The c_on~ 10 potential either positively or negatively depend
ing upon the variation of the mean carrier fre
"emional Portions of the receiving apparatus illus
quency from a desired value. These variations‘ in
trated at Fig. 3 are similar to those illustrated
unidirectional potential are ‘impressed uponthe
at Figs. land 2 and like parts have been as
control grids 88 and 89 of the discharge devices
signed the same reference numerals. At Fig. 3
I have shown a pair of electric discharge devices 15 80 and 8|, respectively, through the signal fre
quency rejection ?lter |0|, I82. The discharge
88 and 8| of the variable mu type having their
devices 80 and 8| respond to these grid potential
grid-to-‘cathode input circuits connected between
variations to effect changes in the grid to cathode
the high and low potential terminals of the
capacitances of the discharge devices. Since
transformer winding 22 and ground, respectively.
Speci?cally, the discharge devices 88 and 8| in 20 these grid tocathode capacitances are connected
inv series circuit relation between the high and
clude cathodes 82 and 83 connected, respectively,
low potential terminals of the discriminator
to ground through cathode resistors 84 and 85
transformer secondary winding 22, changes in
provided with bypass condensers 86 and 81; The
the grid to cathode capacitances may be ar
discharge devices 80 and 8| also include control
grids 88 and 89 connected, respectively, to the 25 ranged to e?ect desired changes in the tuning
of the discriminator transformer secondary
high potential and low potential terminals of the
windings. Upon a change in carrier frequenCcy,
tuned discriminator transformer secondary wind
the grid potential variation impressed upon the
ing 22 through blocking capacitors 98 and 9|.
discharge devices 88 and 8| is such as to change
By way of illustration I have shown the discharge
the input capacitances of the devices in a man
devices-88 and 8| aspentodes including screen
ner tending to make the resonant frequency of
grids 92 and 93, respectively, connected to a suit- ‘
the tuned discriminator transformer follow the
able source of positive potential such as the posi
varying mean frequency of the received signal
tive terminal B+ of a battery (not shown) and
bypassed to ground through condensers 84 and
Wave.
95, respectively. The pentodes 88 and 8! also
I wish to have it understood that my invention,
as illustrated in Figs. 2 and 3, is not limited to
include suppressor grids 96 and 97 connected
the use of a pair of electronic reactance devices
directly to the cathodes 82 and 83, respectively.
connected between each terminal of the trans
The anodes 98 and 99 of the discharge devices,
former Winding 22 and ground. The reactance
respectively, are connected to the positive ter
of the discharge devices is in the nature of a trim
minal B+ of the battery, the negative terminal
ming reactance only, and the necessary changes
of the battery being connected through ground
of reactance required for control are extremely
to the cathodes 82 and 83.
small. This necessary change may be obtained
For control of the input capacities of the dis
from only one electric discharge device, and the
charge devices 88 and 8| the control grids 88
other device may be replaced by a small ?xed bal
and 89 are connected through a signal frequency
ancing capacitance connected between one ter
rejection ?lter comprising a resistor NH and a
minal of the winding 22 and ground.
capacitor I82 to the positive terminal of the dis
At Fig. 4 I have shown a further embodiment
criminator load resistor 28. Decoupling resistors
of my invention wherein the necessary number
I 03. and I 84 are included between the audio rejec
tion ?lter and the control grids 88 and 89, respec 50 of electric discharge devices is reduced .by utiliz~
tively.
'
ing interelectrode capacity variations within the
It is known that in an electron discharge de
discriminator rectifying devices themselves to re
tune the discriminator circuit. The conventional
vice having an electron emitter or cathode, an
portions of the receiver illustrated in Fig. 4 are
electron collector or plate and a control grid for
controlling the flow of electrons between the 55 similar to those illustrated at Figs. 1 to 3, inclu
cathode and the plate there exists certain inter
sive, and similar parts have been assigned the
electrode capacity having a ?xed value when the
same reference numerals. The discriminator cir
discharge device is not in operation and having a
cuit of Fig. 4 differs from those of Figs. 1, 2 and
different ‘and variable value when the cathode is
3 in that the unidirectional conducting devices in
active and plate current is ?owing.
60 the oppositely connected series rectifying circuits
This phenomenon may be explained. by the
forming part of the discriminator are grid con
theory that the space charge or cloud of electrons
trolledelectric discharge devices H0 and ill of
surrounding the cathode in a discharge device
the variable mu type rather than the diode dis
of this type constitutes effectively a part of the
charge devices 26 and 3| of Figs. 1 to 3, inclusive.
cathode at least for the purpose of determin
So far as their demodulating function is con
ing the grid to cathode capacity. As the control
cerned, however, the grid controlled discharge de
grid becomes more negative, the cloud of elec
vices ii?rand I“ operate in the'samegmanner
trons constituting the space charge is repelled
as the diode elements 26,_andj3| by grid recti?e
from the control grid so that the spacing between
the grid and the approximate surface of the space '
cation between their control; grid ‘I I2 and | [3;
respectively, and their cathodes H4 andv H5, re-_
charge is increased. This increase in the spacing
is equivalent to separating the plates of the con
spectively. At Fig. 4 the positive terminal of
the discriminator transformersecondary winding
denser thereby to decrease the capacity there
between. Conversely, as the control grid becomes
is connected to the control grid “2 of the dis
more positive,_ thedistance between‘the control ,
charge device ||0 and the low, potential terminal
of the transformer winding 22 is connected-to the
2,412,039..
9';
accordance withsaid signal, ‘means including/uni
control. grid H3.of.the. discharge device. lll,.the_
cathodes H4and.ll.5.of.the discharge devices H0
and HI being connected to electrically remote,
directional conductingmeans connected in bal
anced relationacross saidtuned circuit for deriv
terminals of the discriminator load resistors. 28
ingfromsaidamplitudemodulated wave a signal
and 33 in the samemanner as previously de 5 wave, including a unidirectional potential» com
ponent variablein accordance with variations be
scribed in connection with. Figs. 1, 2 and 3. The
tween;saidq mean and resonant frequencies, an
discharge devices H51 and III. are provided with
electroncdischarge device including,v an anode, a
anodes I
l H, respectively, each of whichis
cathode andatleast one control electrode, means
connected through separate current. limiting: re
sistors I I8 and H9, respectively, to the positive 10 for rendering, the discharge path between said
anode and, cathode effectively reactive, said ef
terminal of the discriminator load resistor 28
fective reactance being variable in accordance
through a signal frequency rejection ?lter com
with the unidirectional potential applied to said
prising aresistor I20 and a capacitor I21.
controlele'ctrode, means including a serially con
The operation of the tuning system of Fig. 4
will be understood when it is observed that the 15 nected balancing reactor for connecting saiddis
charge path in, parallel circuit relation with said
grid to cathode capacitances of the dischargede
vices H0 and III are connected in series circuit
tuned circuit tQ control the tuning of said circuit,
relation through the load resistors 28‘ and 33
and means for applying said; unidirectional com
ponent of; signal potential to said control elec
trode to retune said tuned circuitinaccordance
with. mean frequency variations of. said carrier
across the terminals of the discriminator trans
former secondary winding 22. As previously ex
plained, the grid to cathode capacity of a dis
charge device under operating conditions, or the
input capacity, is known to be a function of the
plate current. It will be evident that by proper
selection and orientation of the tube elements the
variations in the input capacitances connected
across the tuned discriminator circuit 22, 23 may
be made to respond to changes in unidirectional
wave.
,3. In combination, a source of carrier waves
signal modulatedin frequency; about a mean fre
quency subject to variation, means comprising a
tuned circuit normally resonant at said mean fre
quency for deriving from said frequency modu
latedwave- a wave modulated in amplitude in ac
cordance with said signal, meansincluding uni
plate potential impressed through the ?lter I20,
directional, conducting means connected in bal
anced relation across. said tuned circuit for de
riving from said amplitude modulated wave a
signal wave including a unidirectional potential
component variable in accordance with variations
12! in such a manner as to retune the discrimi
nator transformer secondary winding and to
maintain resonance at the varying mean fre
quency of the incoming signal wave.
While I‘ have illustrated only certain preferred
embodiments of my invention by way of illustra
tion, many further modi?cations will occur‘ to
those skilled in the art, and I therefore wish to
have it understood that I intend in the appended
claims to cover all such modi?cations as fall with
in the true spirit and scope of my invention.
between said mean and resonant frequencies, an
electrondischarge device including an anode, a
cathode and at least one control electrode, said
electron. discharge device providing between said
cathode and said control electrode an input ca
40 pacitance variable in accordance with the unidi
rectional potential of said control electrode, means
including a serially connected balancing reactor
for connecting said input capacitance across said
tuned circuit for controlling the tuning of said
What I‘ claim as new and desire to secure by
Letters Patent of the United States is:
1. In- combination, a source of carrier waves
signal modulated in frequency about a mean fre
quency subject to variation, means cOmprising a
tuned circuit normally resonant at said mean fre
; circuit, and. means for applying said unidirec
tional component of signal potential to said con
trol electrode for maintainingresonance of said
tuned circuit at the varying mean frequency of
quency for deriving from said frequency modu
lated wave a Wave modulated in amplitude in ac
cordance with said signal, means including uni
directional conducting means connected in bal
anced relation across said tuned circuit for deriv
ing from said amplitude modulated wave a signal
wave including a unidirectional potential com
ponent variable in accordance with variation be
tween said mean and resonant frequencies, a pair
of electron discharge devices each comprising at
said-carrier wave.
50
-
4'..In; combination, a pair of recti?er. circuits
connected in opposing balanced relation, a source
of carrier waves signal modulated in frequency
about a desired mean frequency subject to vari
ation, .means including an electric circuit tuned to
resonance at‘ said mean frequency for supplying
to said recti?er circuits oscillations varying op
least three electrodes and providing a space dis
positelyl in amplitude with frequency modulation
charge path between at least two of said elec
of said carrier waves, said recti?er circuits pro
trodes, means including a third electrode of each
said devices for shifting the phase of current trav
ersing said discharge paths with respect to the
alternating potentials thereacross, means for con
necting said discharge path in series circuit re
viding an output voltage at signal frequency hav—
ing- a. unidirectional component proportional‘ to
variation between said mean and resonant fre
quencies, a pair of electron discharge devices
each having a control electrode and an internal
reactance" proportional to the voltage upon the
lation across said tuned circuit, and means in
cluding the third electrode of at least one of said 6-5 electrode, means for connecting said internal re
actances in balanced‘ tuning vrelation with said
devices for controlling the apparent reactance of
tuned: circuit, and means for applying said uni
the associated discharge path in accordance with
directional component of signal voltage to at least
said unidirectional component of signal potential
one of said control electrodes.
7
to control the tuning of said tuned circuit.
5‘. In combination, a pair of recti?er circuits
2. In combination, a source of carrier waves
signal modulated in frequency about a mean fre
quency subject to variation, means comprising a
tuned circuit normally resonant at said mean
frequency for deriving from said frequency modu
connected in opposing balanced relation, a source
of carrier waves signal modulated in frequency
about a desired mean frequency subject to vari
ation, means including an electric circuit tuned
lated wave a wave modulated in amplitude in 76 to resonance at said mean frequency for supply
2,412,039.
11“
12
ing to said recti?er circuits oscillations Varying
oppositely in amplitude with frequency modula
connected in opposing balanced relation and each
tion-of said carrier waves, said recti?er circuits
including a unilateral conducting device, each
of said devices having two electrodes connected in
providing an output voltage at signal frequency
having a, unidirectional component proportional
cluding a control electrode, a source of carrier
to variation between said mean and resonant fre
series with the associated recti?er circuit and in-,
TU!
quencies, a pair of electric discharge devices each
comprising an anode, a cathode and at least one
control electrode, said electric discharge devices
providing‘ said control electrodes and cathodes
electron stream capacitances variable in accord
11)
ance with the unidirectional voltage upon said
control electrodes, means for connecting the dis
charge paths between said grids and cathodes in
balanced series circuit relation across said tuned .,
circuit, and means for applying said unidirec
tional component of signal voltage to said con
trol electrodes to control the tuning of said cir
cuit in accordance with variations of said carrier
mean frequency.
6. In combination, a pair of recti?er circuits
connected in opposing balanced relation, a source
of carrier waves signal modulated in frequency
about a desired mean frequency subject to varia
tion, means including a parallel resonant tuned
circuit tuned to said mean frequency for sup
plying to said recti?er circuits oscillations vary
ing oppositely in amplitude with frequency modu
lation of said carrier waves, whereby said recti?er
circuits provide an output voltage at signal fre
waves signal modulated in frequency about ade
sired mean‘ frequency subject to variation, means
including a parallel resonant circuit tuned to said
mean frequency for supplying to said recti?er cir
cuits oscillations varying oppositely in ampli
tude with frequency modulation of said’ carrier.
waves, said recti?er circuits demodulating said
oscillations to supply an output voltage at signal
frequency having a unidirectional component
proportional to variations between said mean and
resonant frequencies, and means for applying
said unidirectional component of signal voltage to
the control electrode of each of said unilateral.
conducting devices to control the interelectrode
capacities of said devices in accordance with mis
tuning of said ‘parallel resonant circuit thereby to
maintain said circuit tuned to said variable mean
frequency.
'
9. In combination, a source of carrier waves
signal modulated in frequency about a mean fre
quency subject to variation, means comprising a
‘tuned circuit normally resonant at said mean
frequency for deriving from said frequency modu
lated wave a wave modulated in amplitude in ac
quency having a unidirectional component pro
portional to variation between said mean and
cordance with said signal, means including uni
directional conducting means connected in bal
anced relation across said tuned circuit for de
resonant frequencies, an electric discharge device
riving from said amplitude modulated wave sig
comprising an anode, a cathode and at least one
control electrode, means including a balancing
reactor in series circuit relation with said dis
nal wave including a unidirectional potential
component variable in accordance with variation
between said mean and‘ resonant frequencies, a
pair of electron discharge devices each including
at least three electrodes, the discharge paths be
tween two electrodes of each said device being
electrode oscillations substantially out of phase 40 connected in ‘balanced series circuit relation
across said tuned circuit, and means for apply
with the voltage between said anode and cathode
ing said unidirectional potential component tov
thereby to maintain in said discharge device a
at least one electrode of each of said devicesrto
plate current substantially out of phase with said
control the effective reactance of said discharge
anode to cathode voltage, and means for apply
ing said unidirectional component of signal volt
age to said control electrode to control the inten
10. In combination, a source of carrier waves
signal modulated in frequency about a mean
sity of said plate current in accordance with mis
frequency subject to variation, means comprising
tuning of said tuned circuit.
r
a tuned circuit normally resonant at said mean
'7. In combination, a pair of recti?er circuits
frequency for deriving from said frequency modu
connected in opposing balanced relation and each
including a unilateral conducting device having
lated wave a wave modulated in amplitude in ac
cordance with said signal, means ‘including uni
at least three electrodes, a source of carrier waves
signal modulated in frequency about. a desired
directional conducting means connected in bal
anced relation across said tuned circuit for de
mean frequency subject to variation, means in—
charge device for connecting the discharge path
between said anode and said cathode across said
tuned circuit, means for supplying to said control
devices.
a
‘
-
cluding an electric circuit tuned to resonance at ‘r ~4 riving from- said amplitude modulated wave a
said mean frequency for supplying to‘said recti
?er circuits oscillations varying oppositely in am
signal wave including a unidirectional rpotential
component variable in accordance with variation
plitude with frequency modulation of said carrier
between said mean and resonant frequencies, an
electron discharge device-including at least three
electrodes, a balancing reactor connecting the
waves, said recti?er circuits providing an out
put voltage at signal frequency having a unidirec
tional component proportional to variations be
discharge path between two of said electrodes
tween said mean and resonant frequencies, and
means for applying said unidirectional compo
nent of signal voltage to at least one electrode of
across said tuned circuit, the effective reactance
of said discharge path being variable in accord—
ance with the unidirectional potential of, one
electrode of said discharge device, and means for
each of said unidirectional conducting devices to
control the interelectrode capacities of said de
applying said unidirectional potential component
vices in accordance with mistuning of said tuned
to said one electrode to maintain said reso
circuits thereby to maintain said circuits tuned
nant frequency substantially equal to said” mean
to said variable mean frequency.
8. In combination, a pair of recti?er circuits 70
'
GEORGE W; FYLER,
frequency.
7
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