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Патент USA US2408684

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Oct. i, 1946.
l
-w. VAN B. ROBERTS
t ' l.
FREQUENCY-VARIABLE OSCILLATOR CIRCUIT
Filed Feb. 4, 1945’
'
2,408,684
Patented Oct. l, 1946
2,408,684
UNITED STATES PATENT OFFICE
n 2,408,684
FREQUENCY-VARIABLE OSCILLATOR
`
CIRCUIT
-
'Walter'van B. Roberts, Princeton, N. J., assignor
to Radio Corporation of America, a corporation
of Delaware
Application February 4, 1943, Serial No. 474,646
1 'ClainL (Cl. Z50-36)
.
_
1
My present invention rrelates lto frequency
variable oscillator circuits,y and more especially
to an voscillatorcircuit adapted to be shifted in
frequency without amplitude change.
v
2
electrode 5 and an anode, or plate; E. It will be
understood that other electrodes could be uti
lized between the cathode 2 and plate 6 -to ac
complish additional functions, where desired.
‘One of the main objects of my present inven
tion is to provide a single tube oscillator which
may be frequency modulated without amplitude
modulation of the oscillatory output energy.
Amore specific object ofV this invention is to
provide an oscillator circuit adapted to provide
constant-amplitude oscillations, and the fre
quencyn'o’f the oscillator circuit Vbeing determined
by a :control potential applied to a control grid
of the oscillator tube; the latter having separate
phase shifter networks in separate connections .
from the anode and screen electrodes to voltage
points on the .tank circuit which are of opposite
phase to that of a feedback grid", and the phase
shifter networks providing opposite senses of
In the present case cathode 2 is established at
an invariable alternating potential, such as
ground. The grid 3 is returned to ground through
a radio frequency choke coil ‘I in series with a
resistor 8.
'
f
'
.'I‘he Screen electrode/4 is returned to ground
through a coil '9 and the` direct current source
I0. In other Words, the Screen electrode 4 is
connected, through coil 9, to the positiveter
minal -of the direct currentsource I il, `and the
negative terminal of the latter is grounded. The
upper end of coil'9 is `connected through con
denser II Ato a desired point on the'coil `I2 of the
oscillatory tank circuit I3. The condenser I 4,
which
is arrangedin shunt with coil I2, tunes
frequency shift.
20 the coil I2 to' a desired operating oscillatory fre
. AStill other objects of my invention are to pro
quency. The circuit 'I3 is the usual oscillator
vide a single tubey oscillator capable .of frequency
tank'circuit,
'
deviation free of amplitude change, and `adapted
The plate IiV isconnected to a desired point on
for use in a frequency modulated oscillator ksys
I2, which may be at a higher or >a lower
tem or in an automatic frequency control (AFC) 25 ‘coil
alternating potential than the point. on coil I2
circuit of al superheterodyne receiver.
'
to which electrode d is connected bythe coily I5.
The plate end of coil I5 is connected to ground
through 'the‘condenser IG. The coil 9 and con
ticularity in the appended claims; the invention
denser
are shown enclosed in a dotted square
itself, however, ~as to both its organization and. 30 which isIIindicated
as “Phase shifter.” Similarly,
method of operation will best be understoodfby
coil I5 and condenser I 6 are shown enclosed in
reference to the following description, takenvin
a dotted rectangle also -labelled “Phase shifter.”
connection with the drawing,v in which I have
_The phase shifters P1 and P2 are shown ter
indicated diagrammatically several' circuit or
minating at the coil I2 in an adjustable manner
ganizations whereby my invention may be car-.
35 vto indicate thatv they may be -adjiïstably con
ried intoeifect.
'
nected to the tank coil.
`
In' the drawing:v
’I‘he control ,grid 5 is shown connected to the
Fig; 1 shows'a circuit employing the invention,
negative terminal-“of a direct Vcurrent source 20,
Figs. 2a and 2by show vector relations existing
and
the positive terminal of the latter may be
in the oscillator circuit,
` .
_
connected to av source of frequency control volt
Fig. 3 schematically illustrates.theapplication
age` 'Y This source of frequency control voltage
Äo'f. the invention to an AFC system.
may be either alternating current or direct cur
The novel features which I believe to be char
acteristic of my invention are set forth with par
Referring, now, tothe accompanying drawing,
'wherein like reference characters in the different
.figures designate Similar'circuit elements, there
is shown in Fig. 1 an oscillator circuitwhich may r
Vbe employed for any desired frequency band,
rent. In-'the case of a frequency modulation
transmitter, the sourceV of frequency control
45 voltage would be an audio frequency modulation
source. However, in the case of AFC of a super
heterodyne receivengthe source of frequency con~either in the kilocycle (kc.) or megacycle' (mc.)
trol voltage would be the direct Vcurrent voltage
ranges. The oscillator tube is of the pentode
output of the usual discriminator-rectifier net
type. Of course, the oscillator is not limited to 50
`anys'peciiic type of electron discharge tube. `It
is>> suíñcient for the purposes of the present in
vention that the tube I include a cathode or
electron emission electrode 2, a first control grid
¿3, apositive screen electrode 4, _a _third controI-
work.
_
-
f
y
y
v The plate E is maintained at a positive poten
ytial relative to ground by means of a direct cur- '
rent source
2l
whose negative terminal
is
grounded, while its positive terminal is adjust
ably connected to a desired point on coil I2. The
2,408,684
3
frequency control voltage substantially equal volt
grid 3 is connected to the low potential side of
tank circuit I3 through a direct current blocking
ages are induced in the tank circuit I3 by the
screen and plate currents I2 and I1. In this way
condenser 22, and coil 23 is illustrated as the
a frequency modulated oscillator is provided
output link to the subsequent utilizing circuit.
whose frequency is caused to deviate both above
C11
It Will be realized that Fig. 1 shows a Hartley
and below the frequency prevailing in the absence
type oscillator circuit, wherein grid 3 functions
of frequency control voltage.
»
as the oscillator grid. The oscillator tube has
Where the present invention is employed in a
two output electrodes, viz., the positive screen
electrode ¿i and the positive plate 6. The screen
transmitter of frequency modulated carrier wave
4 and plate 5 are connected to the tank circuit
at different points on the other side of the ground
tap from the grid 3. As the grid 3 varies in po
tential, both the screen current and plate current
will be produced across tank circuit I3 frequency
energy, then electrode 5 of Fig. 1 will be connected
to a source of audio modulation energy, and there
modulated oscillations having a mean frequency
of a predetermined value. The frequency devia
tion will depend/upon the relations between the
vary in the same sense. The plate current is in
dicated by the reference character I1. rt win be
Seen that the voltages introduced by the plate
and screen currents respectively in the tank cir
cuit I3 both assist in maintaining oscillation.
The screen and plate currents are introduced into
"
voltages e1 and e2, and will be dependent upon
the requirements of the system. It is to be under
stood that the present invention may also be
Y
the tank circuit preferably at such points that
the voltages induced by the two currents are
equal. However, the current I1 passes through
the phase shifter Pi.
This slightly retards its
phase. The screen current I2 passes through the
employed in connection with’phase modulated
energy, and the generic term “angle modulated”
is to be understood as applying to either of fre
quency or phase modulated carrier wave energy.
In Fig. 3, I have shown schematically a super
heterodyne receiver wherein the present inven
tion is utilized for AFC purposes.
Since those
second phase shifter P2, thereby slightly advanc 25 skilled in the art are fully acquainted with the
ing its phase. Accordingly, the voltages induced
constructional details of a superheterodyne re
in the tank circuit by these two currents may be
represented .vectorially as in Fig. 2a.
Referring to Fig. 2a, the vectors e1 and e2 cor
respond to the voltages induced in the tank cir 30
cuit I3 by the plate current and screen current
respectively. The sum of these two vectors, which
is the equivalent total voltage in the tank circuit,
is shown by the dotted arrow designated e1 plus
e2. This total voltage is preferably 180° out of
phase with the voltage on grid 3 when the fre
quency is at its mean value, i. e. in the absence
of modulating voltage.
So far, no mention has been made of the con
trol grid 5. The action of this grid is to control
the distribution of the total space current of tube
I between the screen and plate electrodes 4 and
ceiver, it is not necessary to show such details.
Generally, received modulated carrier wave en
ergy is applied to a converter, or ñrst detector,
designated by numeral 3D. The output of the lat
ter, which is at an intermediate frequency (I. F.) ,
is fed to an I. F. amplifier 3l. A second detector
32 demodulates the amplified I. F. energy. The
local oscillator, which feeds its energy to the con
verter circuit, is provided by the tube I. The
circuits of the tube I are precisely the same as
shown in Fig. 1. The difference resides in the
fact that the tank circuit I3 is tuned to a fre
q-uency which differs from the frequency of the
modulated carrier applied to the converter input
circuit by a frequency value equal to the operat
ing I. F. value.
6 respectively. If the plate voltage is chosen suffi
The grid 5 has applied to it the AFC voltage
ciently low, it is known that a negative potential
output of the discriminator-rectifier network 40.
.4.
on grid 5 will cause more and more of the total
The discriminator-rectiñer is schematically repre
space current to flow in the screen circuit and
sented, since those skilled in the art are fully ac
less and less in the plate circuit. Although the
quainted with the circuits thereof. It is fed with
total space current itself is not affected by grid 5,
I. F. energy, and the network 40 functions to pro
Fig. 2b shows the result of making grid 5 less nega 50 vide a direct current voltage whose polarity and
tive than normal. In this case the plate current
magnitude are functions respectively of the di
is increased above normal, while the screen cur
rection and extent of frequency deviation of the
rent is reduced ’below normal. Accordingly, the
I. F. energy relative to the predetermined oper
resultant of the two voltages e1 and e2 induced
ating I. F. value. The AFC voltage output of net
in the tank circuit is of a slightly different phase 55 work 4o is applied through the negative biasing
than in the normal case illustrated in Fig. 2a),
battery 20 to the control grid 5. The discrim
It will be noted that the magnitude of the re
inator-rectiñer 40 may be constructed, for ex
sultant voltage in the case of Fig. 2b is substan
ample, in the manner disclosed and claimed by
tially unaltered so that the amplitude of oscilla
S. W. Seeley in his U. S. Patent No. 2,121,103,
tions is not changed.
60 granted Jun@ 21, 1938. The AFC circuit func
However, it is well known that a phase shift
tions to change the bias of grid 5 in such a
in any part of the feedback mechanism of an
manner that the frequency of tank circuit I3 will
oscillator circuit will produce a frequency change.
be shifted to an extent such as‘to maintain the
Hence, under the conditions shown in Fig. 2b,
I. F. energy output of converter 30 close to the
the frequencies will be different from the fre
predetermined I. F. Value. It is not believed
quencies prevailing in the normal, or mean, con
necessary to describe the functioning of the in
dition depicted in Fig. 2a.. Conversely, making
vention in connection with this utilization there
the grid 5 more negative than normal will cause
of. Those skilled in the art will fully appreciate
an opposite phase shift in the resultant feedback
the advantages of an AFC system wherein the
to the tank circuit and opposite deviation of
oscillator circuit does not utilize an auxiliary re
the oscillator frequency from normal.
actance tube system across the tank circuit, and
It is further pointed out that the relative supwherein the oscillator frequency may be directly
ply voltages for the screen Il and plate 6 are pref
shifted without appreciable change in the oscilla
erably so chosen, together with the tapping points
tion amplitude.
f
of the separate connections from the screen and
While I have indicated and described several
plate on the tank circuit, that in the absence 0f 75
2,408,684
5
6
systems for carrying my invention into effect, it
will be apparent to one skilled in the art that my
invention is by no means limited to the particular
organizations shown and described, but that many
modifications may be made without departing
from the scope of my invention, as set forth in the
appended claim.
v 5
one end of said coil, a direct current connection
from the anode to a point on the coil which is lo
cated on the opposite side of said predetermined
intermediate point, a connection from the second
grid to a point on the coil on the same side of
Asaid intermediate point as the anode point, re
spective phase Shifters in said anode and second
grid connections for providing phase shifts of
What I claim is:
In an oscillator circuit comprising an electron
opposite senses in the anode and second grid cur
discharge tube having at least a cathode, an anode 10 rents ñowing through the connections, said con
and at; least three successive grids in the space
nections to said coil Ibeing chosen to produce equal
current flowing from the cathode to the anode, a
voltages inl said tank circuit from said phase
coil and condenser connected in parallel to pro~ ~
shifted currents, means for applying a negative
vide a tank circuit tuned to a predetermined os
biasing voltage to the third grid adjacent the
cillatory frequency, a source of direct current 15 anode, and means for varying the voltage of the
voltage, means connecting a predetermined in
third grid to vary the frequency of the tank cirJ
termediate point on said coil to a positive poten~
cuit but Without amplitude variation.
tial point of said source, a high frequency connec
tion from the ñrst grid adjacent said cathode to
WALTER VAN B. ROBERTS.
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