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Патент USA US2111764

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March 22, 1938.
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D. E. FOSTER
SIGNAL
CONVERTER
' 2,111,764
CIRCUIT
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Filed April 13, 1956
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March 22, 1938. ,
D. E. FOSTER
2,111,764
SIGNAL CONVERTER CIRCUIT
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Filed April‘l3, 1936
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LOCAL OJ'C/LLA 70R
INVENTOR
' DUDLEY E. FOSTER
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ATTORNEY
March 22, 1938.
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SIGNAL CONVERTER CIRCUIT
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Patented Mar. 22, 1938
NlTD ‘STATES PATENT OFFICE
2,111,764
‘SIGNAL CONVERTER CIRCUIT
Foster, Orange, ‘N. ‘7.1., assignorf to
Radio Corporation of America, a corporation
‘Dudley
‘ ‘of Delaware
. Application 'April' v13, 1936, Serial no. 73,998
9 Claims.'- (01.‘ 250-20)‘
'
c., thenthe oscillator frequency will be 1500
My present invention relates to radiov frequency k.
0. when the receiveris tuned for reception of a
signal converter circuits, and more particularly k.
1000 k. 0. signal. .2 If nowv the oscillator frequency
to converters of the electron coupled type. ‘
, Asis well known, the-frequency converter tube,
be slightlychanged to 1501 k. c., then the result»
ant I. F. from'the'i?rst order term will be 501 k. c. 5
.5' or first detector, of a superheterodyne receiver. The ‘secondaorder-Itermlwill give a frequency equal
p-roducesin its output circuit the sum and differ
signal frequency, i. e., the difference
ence frequencies of the signal and locally pro, to'twicethe'
between ‘2000 k. c. and 1501 k. c.-, or 499 k. c. It
duced loscillation‘frequencies. In‘ ‘addition to
these sum and'differencei frequencieathere are
=10 also produced-frequencies equal to‘ the sum and
difference of integral multiples of the signal and
oscillator frequencies. These latter frequencies
are usually referred to as higher order effects,
since they are due ,to terms .inthel expression
'1‘5 ‘representing the tube characteristic higher. in
order than the term which‘results in. the desired
will,.thus, be seen’ that there will be applied to
the second detector. two frequencies of 501 k. c'. 10
andl499- kc c.,‘:withi the,‘ result that a beat note
equal-totheir difference, 2 ‘k. 0., will be heard.
‘ At signal frequencies other than twice the I. F.,
multiple response will be‘evidenced instead of
audible whistles. Consider again a superhetero- 15
operating intermediate ‘frequency. For example,
in the simple type of converter tube, wherein the
signal and oscillator voltages are simultaneously
30 applied to a common‘control grid, if. the charac
teristic of the .plate current be expressed as a
‘power series, i. e., a series whose, successive terms
are ascending powers of the grid voltage, then
the‘ second order (voltage squared) term results
05 in the desired conversion frequency‘andhigher
orders in undesired frequency terms.
.
The electron coupled type of frequency con
verter, and its many circuit forms, is well known
at the present time.
In such a converter the os
39 cillator voltage is applied to one control grid
whilethe signal voltage is applied-to another grid,
dyne receiver using a 500 k. c. I. F. with an input
signal of 10201:. c. If the oscillator frequency
is'1'520 k. 0.," then the 1.1“. of 500 k. 0. will be ob
tained; Furthermore, if the oscillator frequency
is 1540 k. .c., the second order term of the signal 20
grid characteristic will give an output of twice
signal frequency minus oscillator frequency, or
2040 k. 0., minus 1540 k. c., resulting in 500 k. c.
It is seen, therefore, that for any applied signal
frequency, there-are at least two oscillator fre- 25
quencies which willresult in the correct I. F.
Accordingly, it may be stated that it is one of
the main. objects of my present invention sub
stantially to reduce undesired responses in a con
verter of the electron coupled type, which re— 30 v
sponses correspond to terms higher than the ?rst
order term in the expression representing the
tube characteristic; the reduction in
and both grids being disposed in theiel'ectron ‘converter
stream flowing between the cathode and out-put undesired responses being accomplished by ap
3;, electrode of the tube. In this typerof- converter plying the local oscillator voltage simultaneously 35
the higher order terms give undesired frequencies, to-the signalrand. oscillator grids, but the oscil
just as inythe simple type of converter tube. Only lator voltage being impressed on the two grids in
those frequencies falling within the response band out-of-phase relation, and the magnitude of the
the latter being usually spaced fromthe former,
of the‘intermediate frequency network'will be
4') transmitted to the second detector, or demodu
lator. However, any undesired term falling with
in the intermediate frequency network response
band will likewise reach the demodulator, and
thus give an undesired response. This di?iculty
3 is most commonly encountered when twice the
intermediate frequency falls within the signal
frequency range it is desired to receive. In this
case, ‘the intermediate frequency can result not
only from the difference between the signal and
50 oscillator frequencies, but, also, from the differ-,
ence between twice the signal frequency and ‘the
oscillator frequency.
The latter problem can be more clearly under
stood when viewed in the light of an actual ex
ample. Assuming that the operating'I. F. is 500
out-of-phase oscillator voltage being chosen to
secure the‘ substantialreduction of the higher 40
orderterms referred to.
}
Anotherimportant object of the present inven
tion is to cancel from the output circuit of an
electron coupledtype of frequency converter, un 45
desired responses produced by the second order
effect; and this-cancellation being accomplished
by applying the- local oscillator voltage simulta
neously to the oscillator grid and the signal grid,
the oscillator ‘voltage being applied in reversed 50
phase to the respective grids; it being pointed
, out that since ‘the second order effect is less than
the ?rst order‘ effect, the amount of local oscil
lator voltage on the signal grid which causes
cancellation of the second order effect will result 55
2
2,111,704
in only a slight decrease in the desired ?rst order
frequency conversion.
In existing electron discharge tubes of the type
employed in electron coupled converters, the
amount of local oscillator voltage to be applied to
the signal grid for cancellation of undesired re
sponses, is a function of the bias on the signal
grid since the tube characteristic with respect to
the signal grid is not purely exponential. Hence,
10 it may be stated that it is another object of the
present invention to apply local oscillator voltage
of an electron coupled converter to the signal‘
and oscillator grids in phase and magnitude re
ent invention. The numeral l designates a pen
tagrid converter tube which is well known to those
skilled in the art, and is usually designated as
a 2A7. The input electrodes of the tube are con
nected across a tuned signal input circuit 2, the
latter circuit being coupled to a source of signal
energy. The local oscillator is schematically rep
resented by the numeral 3, and is connected
between the ?rst grid and the grounded side of
the cathode bias resistor 4, the latter being
shunted by the usual by-pass condenser 5. The
fourth grid 6 is connected to the high alternat
ing potential side of the input circuit 2, and the
lations substantially to reduce the higher order
effects resulting in undesired responses in thefre , signal grid 6 and oscillator grid 1 have disposed
quency range it is desired to receive, and yet between them a pair of positively biased grids.
employ automatic volume control action on the A positively biased grid is also disposed between
the output plate electrode 8 and the signal grid 6.
converter; this dual result being secured by uti
The numeral 9 denotes the usual variable tun
lizing a phase inverter tube to impress local os
20 cillator voltage on’ the signal grid, and the bias :ing condenser disposed in the input circuit 2,
of the inverter tube being varied concurrently and the condenser 9 is to be understood as being
adjustable over a relatively wide frequency range,
with that of the signal grid of the signal con
verter tube with the result that the'proper amount as for example the broadcast range of 500 to
of local oscillator voltage is :applied to the signal 1500 k. 0. Of course, the tuning range of cir
cuit 2 may be in the higher frequencies, and it
grid for any value of signal grid bias.
'
Another object of the invention may be stated is vto be clearly understood that the local oscil
lator circuit 3 is simultaneously tunable, by
to reside in the provision of an electron coupled
converter tube which not only has applied-to its means of its own tuning element, over a fre
signal grid a local oscillator voltage in phase and quency range which differs from the signal fre
quency range by the operating I. F. The I. F.
magnitude substantially to eliminate the-unde
sired responses due to the higher orderi e?ects, network is disposed in the circuit connected to
but wherein the direct current voltageof the the plate 8.
It is not believed necessary to go into the de
oscillator and signal grids are varied in depend
tails of the functioning of the converter tube I.
ence upon received signal amplitude variation.
Still other objects of the present invention are Those skilled in the art are fully aware of the
to improve generally the e?iciency and operating fact that there is produced in the circuit con
nected to the outputelectrode 8, the sum and
reliability of frequency converters of the elec
tron coupled type, and more especially to provide difference frequencies between the applied signal
frequency and the local oscillator frequency, as
such’ converters which are not only durable, re
well as frequencies equal to the sum and dif
~10 liable and simple in operation, but economically
manufactured and assembled in radio receivers ference of integral multiples of the signal and
of the superheterodyne type.
oscillator frequencies. The electron stream ?ow
ing between the cathode and plate 8 is modu
The novel features which I believeto be char
lated at the frequencies of the signal and oscil
acteristic of my invention are set forth in par
lator voltages, and the various modulation fre
45 ticularity in the appended claims; thev inven
tion itself, however, as to both its organization quencies, as explained above, are produced in
and method of operation will best be understood the circuit connected to the plate 8. The I. F.
by reference to the following description taken network being resonated to the desired operat
in connection with the drawings, in which I ing I. F., only those frequencies falling within
have indicated diagrammatically several circuit the response band of the I. F. network will be
transmitted to the demodulator.
organizations whereby my invention may be car
ried into effect.
'
However, undesired responses produced by the
In the drawings:
second, third or higher order effects will like
Fig. 1 is a schematic circuit diagram showing wise reach the demodulator, and give undesired
responses if any undesired term falls within the
the basic circuit employed in this invention,
Fig. 2 shows a converter network embodying I. F. network response band. To reduce substan
one form of the invention,
tially these undesired responses there is im
Fig. 3 shows an alternative arrangement of the pressed upon the signal grid 6 a portion of the
invention,
'
1
locally produced oscillator voltage, and this im
60
Fig. 4 illustrates another embodiment/of the pression is made through the impedance Z. The
invention,
impedance Z is designed to provide the proper
Fig. 5 illustrates another converter arrange
phase so as to produce reduction of the higher
ment,
1
order effects.
Fig. 6 shows a converter network embodying
The impedance Z may be inductive or capaci
still another form of the invention,
‘
tative; the various following ?gures illustrate the
Fig. 7 shows a converter network employing the impedance in these two aspects. The impedance
invention, and utilizing automatic volume con
Z must be chosen of such phase and magnitude
trol,
>
Fig. 8 shows a modi?cation of the arrange
ment of Fig. 7.
. .
Referring now to the accompanying drawings,
wherein like reference charactersin the. di?erent
figures designate similar circuit elements, there
is shown in Fig. 1 a purely schematicrepresen
tation of the basic principle involved in the pres
15
20
25
30
35
as to cancel out the response due to the second
order term. If the third, or higher, order effect
results in undesired responses in the desired fre
quency-range, then the amount of out-of-phase 70
oscillator voltage applied to the signal grid 6,
through impedance Z, isadjusted to cancel higher
order responses.
In Fig. 2, there is shown a converter network 75
3
2,111,764
In the circuit arrangement of Fig. 6, the con
wherein the out-of-phase oscillator voltage is ap
plied to the signal grid 6 of the converter tube ' verter tube I is of the type shown in Fig. 2.
l (of the 2A7 type) ‘through condenser ID. "The Otherwise, the arrangement is a‘variation of that
latter is made adjustable so that it can be varied
shown in Fig. 4. - Here the local oscillator has its
in magnitude to the point where the undesired
normal coupling to oscillator grid 1 through con
denser C1; the latter being connected to the high
alternating side of oscillator circuit 2'. The har
monic cancellation coupling in this case com
responses in I. F. network I I can be cancelled.
The condenser I0 is connected between the grid
6 and the high alternating potential side of the
tunable oscillation circuit 2' of the local oscil'-'
10 lator. The dotted line l2 denotes the usual me
prises the mutual inductance M1’ provided be
tween cathode coil I1 and the coil of the tunable 10
oscillator circuit 2’. In a practical embodiment
of this arrangement it was necessary to decrease
the magnitude of condenser C1 to cut down the
chanical coupling between the rotors of the vari
able tuner condensers 9 and 9'. It is to be clearly
understood that the coupling between the oscil
normal oscillator injection. With this adjust
lator grid 7 and the oscillator is conventional.
15
15 Further, the tuner circuits may be of the multi - menta decrease of approximately 20 db. in the
second ‘order effect was obtained upon proper
range type, if desired.
proportioning of M1.
The circuit arrangement shown in Fig. 3 em
When AVC action is applied‘to the converter
bodies a form of the invention wherein the signal
tube the second harmonic cancellation is a?ected.
grid 6, disposed adjacent the cathode of the con
This arises by virtue of the fact that the signal 20.
20 verter tube l, is connected to the plate of the os
grid characteristicris not purely exponential in‘
cillator tube 3’ through condenser In. The oscil
lator is of a conventional form, and needs no existing tubes. The amount of oscillator voltage
detailed description. The oscillator grid 1, dis—_ to be applied to the signal grid for harmonic can
posed in the positive shielding ?eld, is connected
25 to the grid of the oscillator tube. The condenser
It] may be‘adjusted to balance out the second
harmonic effects in the I. F. output network II.
The circuit arrangement of Fig. 4 diifers from
the preceding arrangement in the harmonic can
30 cellation coupling between the local oscillator and
the signal grid 6. This coupling comprises the
mutual inductance M provided between coil l3
and tunable circuit ‘coil 14. The magnitude of
M may be varied until the undesired second har
35 monic response in network II is cancelled out.
With the oscillator higher in frequency than
the signal, the signal circuit appears capacitive
to the oscillator frequency. If the signal circuit
were a pure capacity, then the feedback coupling
40 and signal tank circuit would act as a simple
capacitive voltage divider.
However, the tank.
circuit appears as capacity and resistance, so for
phase as well as magnitude balance the feedback
circuit should comprise resistance, which may be
45 in series or parallel with the feedback‘ capacity.
In practice, appreciable reduction is secured
without phase balance, but better reduction of
spurious components will result from phase as
well as magnitude adjustment. Similarly a
resistance in conjunction with M would produce
better balance by adjustment of phase as well as
magnitude. Capacitive and inductive couplings
are shown to indicate alternative arrangements.
The modi?cation shown in Fig. 5 involves the
55 connection of the signal gridB to the high alter
nating potential side of ‘signal input circuit 2.
The local oscillations are impressed'on the signal
grid 6 by connecting the low alternating potential
side of oscillation circuit coil l5 to the low alter
nating potential side of signal circuit coil [4
through adjustable condenser ill. The junction
of condenser H) and coil I4 is grounded through
condenser U5. The oscillator grid 1 is connected
to the high alternating potential side of oscil
65 lator circuit 2’. Coil l5 of Fig. 5, padding cone
60
densers iii and iii and the variable condensers
connected to coil l5 represent the tank circuit
of a separate oscillator tube.
70
The common cou
pling to the signal circuit is condenser l5. Con
denser l6 is the cancellation coupling condenser;
condenser It is added in series therewith, the
series combination of condensers Hi and Ill act~
ing as an oscillator padding condenser. Adjust
ment of It affects padding, but does not affect
the coupling magnitude to signal network.
cellation is a function of the bias on the signal
grid. Since the signal grid bias varies in magni 25
tude when AVC is used, it follows that the'har
monic cancellation voltage will also vary. It,
therefore, becomes necessary to employ a‘ device
for insuring the application of the proper amount
of oscillator voltage for any signal grid bias.
Fig. '7 shows one arrangement for automatically
correlating the harmonic cancellation voltage
with the converter signal bias value. The local os
cillator applies the oscillations to the oscillator
grid 1 through condenser C2. The AVC network 35
20, of conventional type‘, automatically regulates
the conversion gain of tube l. The AVC network,
in general, may embody a signal recti?er supplied
with I. F. energy, and which recti?er furnishes
the direct current voltage component for auto 40
matically regulating the signal grid bias of the
converter tube I.
Of course, the AVG network
may also regulate any of the high frequency sig
nal transmission tubes in gain. Furthermore, the
AVG‘ recti?er maybe an independent recti?er, or
may be part of the demodulator of the system,
and in the latter case the direct current voltage
component of detected I. F. voltage would be used
for the AVG action.
The harmonic cancellation oscillator voltage is ‘
applied to the signal grid .5 through a phase
inverter tube 2!. The electron discharge tube 2|
has its plate connected to the high alternating
potential side of signal circuit 2 through a con
denser C3, the plate being supplied with proper
positive voltage through the choke 22. The con
trol grid of the inverter tube 2! is connected to
the high alternating potential side of the local
oscillator circuit 2' through condenser C4, and the
cathode of the inverter tube is grounded through
bias network 24.
When bias increases on tube l, the bias decreases
on tube 2|. By taking screen voltage for tube i
through resistors 25 and 26, as tube l is biased
negatively the screen potential increases in a
positive direction, and with it, to a lesser degree,
the potential of point 2? of resistor 26. By con
necting the control grid of tube 2|, through
resistor 23, to point 27, the grid potential of tube
2! becomes less negative'when that of tube I be
comes more negative. Resistor 24’ in the cathode
of 2! is required so that the cathode of tube 2|
is at greater positive potential, relative to ground,
than point 21; the grid of tube 2| thus being
4
2,111,764
maintained negative with respect to its own
cathode.
In this way a change in gain control bias on
the signal grid 6 will automatically vary the bias
LT on the grid of the inverter tube 2!, and the gain
of the latter will be varied. The function of the
tube 2| is to invert the phase of the applied
tude such ‘that undesired responses due to the
second order, or higher, term of the detection
characteristic are substantially reduced.
3. In a superheterodyne receiver, a ?rst detec
local oscillator voltage so as to secure the proper
tor system comprising a tube having a cathode 5
and an oscillation electrode, means electrically
connected with said oscillation electrode for vary
ing the alternating current voltage thereof at a
harmonic cancellation phase.
The variation in
predetermined locally produced oscillation fre—
10 gain of tube 2| is chosen so that the proper
quency, said tube including a control grid and
an anode, said control grid being located in the
amount of oscillation voltage is applied for every
change in converter signal grid bias. In this
way the departure of the converter signal grid
characteristic from the pure exponential type
is compensated for; the compensation involves
the automatic correlation of the magnitude of the
applied harmonic cancellation oscillator voltage
with the value of the converter signal grid bias.
At the expense of some conversion sensitivity
the phase inverter tube 2! may be dispensed with.
The local oscillator, conventionally represented
in Fig. 8, is shown coupled, through condensers,
to the local oscillator grid T and the signal grid
6. The AVC connections, from the usual AVC
network, are made to the signal and oscillator
grids. The bias of the oscillator grid is automatically varied with that of the signal grid in
this modi?cation. This requires that the oscil
lator grid ‘I draw little current for practical AVC
action, and it must, therefore, be run negative.
Both grids vary in the same polarity sense, but
at different rates. In general, grid 6 varies less
than grid 1.
While I have indicated and described several
Li 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 par
ticular organizations shown and described, but
that many modi?cations may be made without
40 departing from the scope of my invention, as
set forth in the appended claims.
What I claim is:
1. In an electron discharge tube which is pro
vided with at least a cathode, an output elec
trode and an electron path therebetween, the
method which includes drawing electrons to an
intermediate point in said path, retarding said
electrons to form a virtual cathode which is be
yond said point, modulating the density of the
virtual cathode by varying the attraction of said
electrons through attracting the part of said
electrons from said virtual cathode to said output
electrode, causing a received signal to vary the
further attraction of said part of the electrons,
- the modulation of the density of the virtual
cathode thereby causing modulation of the signal
in said tube, and simultaneously modulating said
part of the electrons in out-of-phase relation
with said ?rst modulation and to an extent such
60 as to reduce substantially the appearance of sec
ond order, or higher, term effects.
2. In a superheterodyne receiver, a ?rst detec
tor system comprising a tube having a cathode
and an oscillation electrode near said cathode,
means electrically connected with said oscillation
electrode for varying the alternating current volt
age thereof at a predetermined locally produced
oscillation frequency, said tube including a con
trol grid and an anode located in the space path
beyond said oscillation electrode, a source of sig
nal voltage coupled between said control grid and
said cathode, and additional means connected
between said control grid and said ?rst means
for impressing upon said control grid said 10
75 cally produced oscillations in phase and magni
space path between the cathode and said oscilla
tion electrode, a source of signal voltage coupled
between said control grid and said cathode, and
additional means connected between said control
grid and said ?rst means for impressing upon said
control grid said locally produced oscillations in
phase and magnitude such that undesired re
sponses due to the second order, or higher, term
of the detection characteristic are substantially 20
reduced, means for developing a bias control volt
age which automatically varies with the intensity
of said signal source, means for applying said
bias voltage to said control grid, and additional
means, responsive to the variation in .said bias
control voltage, for automatically correlating the
local oscillation voltage impressed on said con
trol grid with the change in said bias control
voltage.
4. In combination in a ?rst detector network of
a superheterodyne receiver, an electron discharge
tube provided with at least a cathode, an output
electrode, a pair of control electrodes disposed be
tween the cathode and output electrode, and
means electrostatically shielding said pair of con
trol electrodes, a tuned signal input circuit con
nected between the cathode and one of the control
electrodes, means coupled to the cathode and the
other control electrode for varying the alternating
current voltage of said other control electrode at
40'
a frequency rate which di?ers from the signal
frequency by a predetermined intermediate fre
quency, and means coupling said input circuit
and said varying means for impressing on said
?rst control electrode alternating current voltage 45
varying in frequency at said oscillation frequency
rate, the phase of the alternating current voltage
impressed on said ?rst control electrode being
related to the phase of the voltage on said other
control electrode substantially to reduce the e?ect
of the second order term of the detection char
acteristic on the electron stream ?owing between
the cathode and said output electrode.
5. In a ?rst detector network of a superhetero
dyne receiver, an electron discharge tube which 55
includes a cathode, an anode and at least two
control grids disposed in the electron stream be
tween the cathode and anode, a resonant net
work in the anode circuit which is tuned to an
operating intermediate frequency, a tunable sig 60
nal input circuit connected between the cathode
and one of the control grids, a source of local os
cillations, variable over a predetermined local
oscillator frequency range, coupled between the
cathode and the other control grid, and means, 65
electrically connected with said local oscillation
source and the said signal input circuit, for im
pressing upon said ?rst control grid local 0s
cillator voltage which is out-of-phaserwith the
oscillator voltage impressed on the other control 70
grid.
6. In a ?rst detector network of a super
heterodyne receiver, an electron discharge tube
which includes a cathode, an anode and at least
two control grids disposed in the electron stream 75
2,111,764
between the cathode and anode, a resonant net
work in the anode circuit which is tunedto an
operating intennediate‘frequency, a tunable sig
nal input circuit connected between the cathode
and one of the control grids, a source of local
oscillations, variable over a predetermined local
oscillator frequency range, coupled between the
cathode and the other control grid, and means,
electrically connected with said local oscillation
10 source and the said signal input circuit, for im
pressing upon said ?rst control grid local oscillator
voltage which is out-of-phase with the oscillator
voltage impressed on the other control grid,
means, responsive to variations in signal ampli
tude, for automatically regulating the ?rst con
trol grid bias, and additional means responsive to
said last named means for varying the magni
tude of the oscillator voltage impressed on said
?rst control grid.
.
'7. A frequency converter tube comprising a
cathode, an anode and at least two additional
electrodes disposed in succession in the electron
5
stream between the cathode and anode, a source
of oscillations connected to one of the said elec
trodes to vary the potential thereof at a prede
termined frequency, a source of signals connected
to the other electrode to vary the voltage thereof
at a frequency different from the oscillation fre
quency, a circuit connected to the anode to utilize
the frequency component of anode current equal
to the difference between said signal and oscilla
tion frequencies, a high frequency coupling path, 10
independent of said electron stream‘, between said
electrodes, said path including a reactive im
pedance whose magnitude and phase are chosen so
that said oscillations are impressed on said sig
nal electrode in out-of-phase relation with the 15
oscillations impressed on said one electrode there
by to prevent the production of harmonic re
sponses in said anode circuit, and means, re
sponsive to signal amplitude changes, to vary the
gain of said converter tube.
20
9. In a ?rst detector network of a super
heterodyne receiver, anelectron discharge tube
stream between the cathode and anode, a source of
oscillations connected to one of the said electrodes
to vary the potential thereof at a predetermined
frequency, a source of signals connected to the
other electrode to vary the voltage thereof at a
which includes a cathode, an anode and at least
frequency different from the oscillation frequency,
a circuit connected to the anode to utilize the
frequency component of anode current equal to
the difference between said signal and oscilla
tion frequencies, and a high frequency coupling
path, independent of said electron stream, be
nal input circuit connected between the cathode
and one of the control grids, a source of local
oscillations, variable over a predetermined local 30
tween said electrodes, said path including a re
active impedance whose magnitude and phase are
chosen so that said oscillations are impressed on
said signal electrode in out-of-phase relation with
the oscillations impressed on said one electrode
thereby to prevent the production of harmonic
40 responses in said anode circuit.
8. A frequency converter tube comprising a
cathode, an anode and at least two additional
electrodes disposed in succession in the electron
two control grids disposed in the electron stream
between the cathode and anode, a resonant net 25
work in the anode circuit which is tuned to an
operating intermediate frequency, a tunable sig
oscillator frequency range, coupled between the
cathode and the other control grid, and means
electrically connected with said local oscillation
source- and the said signal input circuit, for im
pressing upon said first control grid local os 35
cillator voltage which is out-of-phase withthe
oscillator voltage impressed on the other control
grid, means responsive to signal amplitude varia
tion for controlling the potential of said one grid,
and additional means responsive to said signal
amplitude variation for controlling the magnitude
of said out-of-phase voltage.
DUDLEY E. FOSTER.
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