Document text
June 24, 1952
B. S. VILKOMERSON
FREQUENCY CONVERTER FOR AM-FM RECEIVERS
Filed Au£. 28, 1948
2,601,475
INVENTOR
ATTORNEY
Patented June 24, 1952 2,601,475
UNITED STATES PATENT OFFICE
2,601,475
FIEQUENCY CONVEITEI FOI AM-FVI
RECEIVEIS
]enamin S. Vilkomerson, Camden, N. J., assignor
to Radio Corporation of America, a corporation
of Delaware
Application August 28, 1948, Serial No. 46,594
8 Claims. (CI. 250--20)
1
This invention relates generally te frequency
converters and particularly te an oscillator and
mixer circuit for a combined frequency-modu-
lated (FIVD and amplitude-modulated (AiVI)
carrier wave receiver of the superheterodyne type. 5
If is convenional practice te provide a fre-
quency converter for a superheterodyne receiver
which bas an oscillator section electronically
coupled te the mixer section. Usually, a fre-
quency converter of this type includes a pentagrid 10
tube. It is well known, however, that a penta-
grid converter tube has a high noise level, partic-
ularly when operated at the high frequencies
encountered in the reception of waves.
is also well known that the signal-te-noise ratio 15
of a receiver can be considerably improved either
by utilizing a separate radio-frequency ampli-
fier aheadof the mixer or by providing a triode
mixer tube, since a triode inherently has a low
noise level at high frequencies. Accordingly, 20
ïrequency converters have been designed which
consist of a triode oscillator and a triode mixer
tube.
In order te inject the oscillatory energy into
the mixer tube and for other reasons it is con- 25
ventional practice te provide an impedance ele-
ment between the mixer cathode and ground se
that the cathode is operated at a radio fre-
quency potential above ground. Such a circuit
design, however, introduces certain other dis-
advantages. Thus, due te the inherent and un- 0
avoidable capacitive coupling between the two
triodes, body capacitance on the antenna of the
receiver will detune the oscillator te such an
extent that the receiver will no receive a given
station without retuning. The cathode of the 35
oscillator is also conventionally operated at a
radio frequency potential above ground. Hence,
the .capacitance existing between the cathode
heateï and the cathode oï the oscillator may
vary and this in turn may cause the frequency 0
oî the oscillator te drift. Also, the cathode
heater may vibrate mechanically which will cause
an undesired hum modulation of the oscillator
frequency. In accordance with the present in-
vention these and other disadvantages of previ- 5
ously known oscillator and mixer circuits can be
overcome by grounding the cathodes oï both
the triode oscillator and the triode mixer. Such
an arrangement will eliminate the frequency
drift which would otherwise be caused by the 50
varying capacity between the heater and the
cathode of the oscillator because the cathode
and the heater wi!l be at the saine potential.
Furthermore, the choke coils conventionally ïe-
quired in the cathode heater supply are ruade 55
2
superfiuous. P-rthermore, by grounding the
cathodes of both the mixer and the oscillat0r
tube, it is feasib!e te utilize a twin triode of the
6J6 type having a single cathode in common te
the two triode sections. Such a tube is cheaper
than a twin triode hving two separate cath-
0des. Furthermore, the common cathode acts
as an electrostatic shield between the two grids
of the twin triode.
An efficient frequency converter circuit for a
combined AIV!_-IVf receiver should also meet some
further requirements. Thus, high frequency
(F1Vf) carrier waves should be suppressed belote
they can reach the mixer grid when the con-
verter is used for ïeceiving low frequency (AM)
waves. Such high frequency waves may beat
with a harmonic of the low frequency oscillator
te, produce an undesired intermediate-frequency
wave. Furthermore, radiation of the oscillatory
energy should be minimized. Finally, the oscil-
latory energy developed by the oscillatov should
be of uniform amplitude over the desired fre-
quency ranges, and this energy should be in-
jected efficiently into the mixer tube se that the
escillatory energy required is a minimum. This
is, oî course, in line with the requirement that
the oscillatory energy should net be radiated
into space by the antenna.
It is the pïinicpal object of the present inven-
tion, therefore, to provide novel oscillator and
mixer circuit for a superheterodyne receiver
which utflizes a twin triode tube having a com-
mon cathode or cathode circuit for the two triode
sections thereby to improve the signal-to-noise
ratio anc to simplify the design of a super-
heterodyne receiver.
A further object of the invention is to provide
a local oscillator for a superheterodyne receiver
which will develop oscillatory energy of substan-
tially uniform magnitude over two widely sepa-
ïated frequency ranges.
Another object of the invention is to provide
an oscillator and mixer circuit for an AM-F1VI
receiver where radiation of the oscillatory energy
is minimized without the use of a radio-frequen-
cy amplifier stage and where a low pass filter is
effectively provided between the antenna and
the mixer input circuit for A1VI operation with-
out the necessity of utilizing additiona! circuit
elements.
Still a further object of the invention is fo
provide a simplified oscillator and mixer circuit
for an AM-FIOE superheterodyne receiver which
will have an improved performance and which
minimizes frequency drift of the oscillator due
2,601,475
3
to variations of the capacitance between the
cathode heater and the cathode.
A frequency converter in accordance with the
present invention includes a triode oscillator and
u triode mixer each having a grounded cathode.
Preferably a twin triode is used with a colnmon
grounded cathode. The oscillator section com-
prises for /kM operation a tuned-grid tank cir-
cuit with an anode ïeed-back coil. The oscil-
latory energy is injected into the mixer grid
by an inductance element inductively coupled fo
the tank circuit and serially connected between
the AM antenna and the mixer grid.
For F1VI operation, the oscillator consists of a
modilied Colpitts circuit which includes a portion
of the oscillator coil between the tank circuit
and the oscillator grid. A circuit of this type
will bave substantially uniform output energy
over the required frequency range. The FM
oscillator tank circuit is inductively coupled fo
a tuned input circuit provided between the FlVI
dipole antenna and the mixer grid. ]During FlVI
operation the anode feed-back coil in the
oscillator plate circuit functions as a choke coil
for the anode voltage supply.
The novel ïeatures that are considered char-
acteristic of this invention are set ïorth with par-
ticularity in the appended claires. The inven-
tion itself, however, both as fo ifs organization
and method of operation, as well as additional
objects and advantages thereof, will best be un-
derstood from the ïollowing description when
read in connection with the accompanying draw-
ing, in which:
Figure 1 is a circuit diagram of an oscillator
and mixer circuit in accordance with the present
invention illustrated in connection with an
AM-FtVI superheterodyne receiver; and
Figure la is a modification of a portion of Fig-
ure 1 showing seRarate cathodes for the mixer
triode and oscillator triode.
Referring now fo Figure 1, the converter com-
prises a twin triode which may have a common
cathode 2 as illustrated. Twin triode prefer-
ably is of the 6J6 type. Twin triode ïurther
comprises control grid 3 and anode 4 which, fo-
gerber with cathode 2, form the triode mixer.
Control grid 5, anode 5 and cathode 2 form the
triode oscillator of the converter circuit. Coin-
mon cathode 2 is grounded as illustrated and ifs
cathode heater 7 bas one terminal grounded
while ifs other terminal 8 is connected to a suit-
able source of heater supply voltage. R. F. by-
pass capacitor J5 shunts the two cathode heater
terminals.
Thus, heater chokes are ruade unnecessary in
the leads of cathode heater 7 and accordingly
there is no hum modulation of the oscillation ïre-
quency due to variations of the capacitance be-
tween cathode heater 7 and cathode
A suitable antenna for the interception of AM
waves, such as loop antenna 2, is coupled to
mixer grid . Loop antenna f2 has one terminal
grounded and may be tuned by tuning capacitor
3 connected across the terminals of antenna
Tuning capacitor 3 may be shunted by trimmer
capacitor 4. The high alternating potential
terminal of loop antenna 2 is coupled fo mixer
grid 3 through series coil 5, the movable arm of
single-pole double-throw switch 5 and coupling
capacitor . Mixer grid 3 is also connected fo
a source of automatic volume control voltage
(AVC) through grid leak resistor B. The AVC
voltage may be derived in any conventional man-
ner hot shown.
By moving the arm of switch ! G from the posi-
4
tion marked "AM" fo the position marked "FM"
a suitable antenna for the interception of FM
waves such as dipole antelma 25 may be coupled
fo mixer grid . Dipole 25 has one terminal
5 grounded through a suitable transmission line
while ifs other terminal is connected fo an in-
termediate point on coil 2 . Tuning capacitor 22
is connected in parallel with coil 2 fo provide
a variable resonant circuit. Trimmer capacitor
10 23 may be connected in parallel with tuning ca-
pacitor 22. The connection of dipole antenna 25
fo coil 2 will provide impedance matching be-
tween the radiation impedance of the dipole and
the characteristic impedance of its transmission
15 line on the one hand, and the impedance of the
input circuit of the mixer triode on the other
hand.
The triode oscillator circuit comprises a low
frequency tank circuit 25 which may be selective-
20 ly coupled to oscillator grid 5 and which is used
during reception of AM waves. Tank circuit 25
consists of coil 2G and tuning capacitor 27 con-
nected in parallel fo form a parallel resonant cir-
cuit. Tuning capacitor 27 may be shunted by
65 trimmer capacitor 2B. One terminal of tank cir-
cuit 25 is grounded and ifs other terminal is
coupled to oscillator grid 5 through coupling ca-
pacitor 3 , single-pole single-throw switch 3 and
resistor 3-. Resistor 2 has a low resistance of
30 the order of 10 fo 100 ohms and serves the purpose
of suppressing spurious oscillations. Oscillator
grid 5 is returned to ground through grid leak
resistor 3.
For the purposes oï impressing a feedback
35 voltage on oscillator plate 5 there is provided coil
5 having one terminal connected fo a suitable
anode voltage supply ÷B through dropping re-
sistor 3 while ifs other terminal is COlmected
fo oscillator plate5. The junction point of drop-
40 Ring resistOr 36 and coil 35 is by-passed to ground
for radio-frequency currents by capacitor .
Coils 26 and 5 are inductively coupled as in-
dicated by arrow 8. Accordingly, the AM os-
cillator has a tuned-grid circuit with a feedback
coupling provided by coil 35 between tank circuit
45 25 and the oscillator anode 6. The oscillator
functions in a conventional manner, and its op-
eration requires no explanation. The oscilla-
tory energy developed in tank circuit 25 is im-
pressed upon mixer grid through series coil 5
5o inductively coupled fo coils 26 and 85 as indi-
cated by arrow 8.
For FM operation the oscillator comprises a
high frequency tank circuit 8 which includes
coil 4 having one terminal coupled fo oscillator
55 grid 5 through coupling capacitor 42 while its
other terminal is coupled to oscillator plate 6
through coupling capacitor 3. Coils 4 and 2
are inductively coupled as indicated by arrow .
60 An intermediate point of coil 4 is grounded
through capacitor 44. The lower portion 45 of
coil 4 , that is, the portion effectively between
capacitor 4 and oscillator anode 8 is shunted by
tuning capacitor 47 across which trimmer ca-
65 pacitor 49 may be connected.
Mixer a.node is serial]y connected fo the pri-
mary windings oï F'M intermediate-frequency
transformer 5}, shown in block form, and fo AM
intermediate-frequency transformer 5. Both
70 the ÷B voltage and the AVC voltage are applied
fo transformers 58 and 5. The transformers may
be selectively oçeÆated by a single-pole double-
throw switch 52 which is connected fo short-
circuit the primary winding of the transformer
7. ot n use.
2,601,475
The oscillator and mixer circuit of the inven-
tion operate as follows. Let it be assumed that
switches , 3t and 52 are in the position illus-
trated in the drawing, that is, in their "AM" po-
sition. Preferab!y, switches , 3 and 52 are
connected together for unicontrol. The receiver
is new arranged te receive AM waves which aïe
intercepted by loop antenna 2 and impressed
upon mixer grid 3. Preferably, tuning capaci-
tors 3, 22, 27 and 47 are connected together for
mficontrol as indicatd at 5& Accordingly, an-
tenna input circuit , 3, 4 may be tuned te a
desred AM station. Low-frequency tank circuit
25 is aise tuned te deve]op oscillatory energy of
predetermined frequency which is impressed
through fl]ductive coupling upon series coil 5
se that both the local oscillations and the M
wave are impressed upon mixer grid 3. The AM
wave ai the intermediate frequency may be ob-
tained frein output terminal .
Series coil performs a numbr of functions.
Thus, most of the oscil]atory energy is impresed
upon mixer grid 3 and very litte appears acïoss
the antenna. This is due te the îact that the
grid terminal of series coil 5 is effectively iso-
lated frein ground, since the ground path in-
cludes only the comparatively sma]l interetec-
trode capacitance between mixer grid 3 and catl]-
ode 2. The antenna terminal of serie coil 15
is effectively bypassed te ground through tuning
capacitor 13 and trimmer capacitor 4 which are
both large compared te the interelectrode ca-
pacitance. Thus, the major portion of the oscil-
latory energy appears on mixer grid 3 and on]y
a negligible portion is radiated into space through
loop antenna 12. Accordingly, less escil!otory
output energy is required because a!most no en-
ergy is lest. In view of the more efficient cou-
pling between the oscillator and the mixer, the
oscillator output energy which is impressed on
mixer grid 3 is more uniform over the entfl-e AIOE
range.
Furthermm.e, series coil I effectively functions
as a low pass P.-F. filtre'. Thus, for high ïre-
quency waves, the reactive inïpedance of coil $,
is re!atively high while the ïeactive impedance
of the interelectrode capacitance between mixer
grid 3 and cathode 2 is relatively small. Conee-
quently, the high fre]uency voltage applied te
the grid is effectively reduced. If this were net
done, the high-frequency waves might boat with
a harmonic of the fundamental oscillatory en-
ergy te provide an undesired output wave of in-
termediate-frequency.
Let it new be assumed that switches , 3 $ and
52 are rotated into their "F'M" positions. In
that case, dipole antenna 29 and its tuned input
circuit 21, 22, 3 is conp]ed te mixer grid te
impress an intercepted FM wave on the mixer.
Tuning capacitor 22 is moved in unison with ca
pacitor 47 te select the desired FM wave. Ai the
saine rime, low-frequency tank circuit 25 is dis-
connected frein osciilator grid se that only
high-frequency tank circuit g'3 remains con-
nected thereto. In this case, coil 3 no longer
fuuctions as the feedback coi! for low-frequency
tank circuit 25 but it is new used as a choke coil
for the parallel-feed ÷B supply. This change
of function is accomplished without switching.
The oscillator may be considered a modi-
fied Colpitts oscfllator. Thus, the junction point
(ground) of capacitors and 47 is connected
te cathode 2. The portion 8 of coil l which is
between the tap and mixer grid 5 functions as a
feedback coil te the oscfilatm: grid 5 since cofi.
6
@ is an autotransformer. A circuit of this type
wfll have a substantially uniform output energy
over its range. The value of capacitor is se-
lected se that for low frequencies it has a cern-
5 paratively high reactive impedance se that the
oscillator functions essentially in the manner of
a Colpitts oscfllator. However, for high frequen-
cies the reactive impedance of capacitor de-
creases whfle that of feedback coil portion
10 increases. Consequently, the oscfllator functions
a high frequencies as a tuned-plate circuit with
a grid feedback. The FM output wave at the
intermediate frequency may also be derived frein
output terminal 55.
15 leferring new te Figure I, which is a modifi-
cation of that portion of Figure 1 enclosed by a
dotted rectangle, separate cathodes 2' and 2 are
provided in the oscil]ator circuit and mïxer cir-
cuit respectively. The cathodes are directly con-
20 nected te ground. The cathode heaters 7 and
7 » are connected in parallel, each having one
terminal grounded while the other terminal $ is
connected te a suitable source of heater supply
voltage. Tube ' may be of the 63N7 type.
25 Whfle it wi!l be understood that the circuit
specifications of the frequency converter of the
invention may vary according te the design for
any particular application, the following circuit
specifications are included by way of example
30 only:
Twin triode $ ......... Type 6J6
Tuning capacitor 3__. 12.5 te 498 micromicro-
Trimmer capacitor 14_
35 Tuning capacitor 22__.
Trirnmer capacitor 23_
Coupling capacitor 7_
Tuning capacitor 2L__
Trimmer capacitor 28_
40 Coupling capacitor 30_
Tuning capacitor 47__.
farads
2 te 17 micromicrofarads
7 te 28 micromicrofarads
2 te 17 micromicrofarads.
1,500 micromicrofarads
9 te 150 micromicrofarads
2 te 17 micromicrofarads
150 micromicrofarads
7.5 te 22.5 micromicro-
farads
Capacitor 4 .......... 56 micromicrofarads
Coupling capacitor 4_ 22 micromicrofarads
43 Capacitor 43 .......... 68 micromicrofarads
Capacitor 4 .......... 2 micromicrofarads
Capacitor ............ 01 microfarad
lesistor I 8 ........... 3,900,000 ohms
lesistor 33 ............ 22,000 ohms
50 Resistor 3¢ ........... 2,000 ohms
Resistor 32 ........... 100 oluns
It is te be understood that the frequency con-
verter circuit of the invention need net be used
55 for an £1VI-F1VI receiver, but may be used for any
multirange superheterodyne receiver.
There has thus been described an oscillator
and mixer circuit which may be used, ïor ex,
ample, in an AIOE-F1Vi receiver. The oscillator
and mixer circuit utilizes two triodes with
grounded cathedes. Accordingly, the inherently
low signal-te-noise ratio of a triode mixer is
utflized. The oscillator is arranged in such a
manner that its output energy is substantially
uniform over both its frequency ranges. Fur-
65
thermore, radiation of the oscfllatory energy is
minimized, and a ]ow pass filter
tween the Ali antenna and the mixer te prevent
the cccurrence of undesired intermediate-fre
quency waves. The oscillator and mixer circuit
70 of the pîesent invention has a simplified design,
it is cheaper in manufacture and it has an im-
provd performance.
What is claimed is:
1. In a multiband superheterodyne receiver, a
75 twin triode having a single cathode, a first and
2,601475
second anode, a first and a second control grid,
said single cathode being connected fo a point
of common reference potential, a low-fïequency
resonant tank circuit, switching means for selec-
tively connecting said low-frequency tank cir-
cuit between said first anode and said first con-
trol grid, a high-frequency resonant tank circuit
permanently coupled between said first anode
and said first control grid, a first rneans includ-
îng a capacitor having a large value relative fo
the grid-to-cathode capacitance of said second
grid and said cathode and an inductance element
comprising a circuit resonant af a frequency
below the resonant frequency of said low-fre-
quency resonant tank cri'cuit selectively connect-
ed in series arrangement between said point of
common reference potential and said second con-
trol grid, ïor impressing a modulated carrier wave
within a low-frequency range on said second grid,
second means adapted fo be connected fo said
second grid for impressing a modulated carrier
wave within a high-frequency range on said sec-
ond control grid, said inductance element bein2
inductively coupled to said low-frequency tardç
circuit and ProvidLug in conjunction with the
relatively small grid-to-cathode capacitance of
said second control grid and said cathode a high-
ly effective coupling between said low-frequency
resonant tank circuit and said second control
grid and in conjunction with said capacitor to
minimize the coupling between said lowmfre-
quency resonant tank circuit and said first means,
and an output circuit coupled to said second
anode.
2. In a superheterodyne receiver, a triode
mixer having an anode and a contro! grid, a
triode oscfllator having an anode and a control
grid, cathode means for said mixer and said os-
cillator, a common cathode circuit for said triode
mixer and said triode oscfllator dri'ect]y con-
nected between said cathode means and one tel'-
minal of a source of potential, a hi2h-frequency
tank circuit connected between said oscillator
anode and control grid, a low-frequency tank
circuit adapted fo be selectively connected to said
oscfllator control grid, a tuned input circuit con-
nected between said one terminal and said mixer
grid for impressing a modulated carrier wave on
said mixer grid, an inductance elernent serially
connected between said input circuit and said
mixer grid and inductively coupled fo said low-
frequency tank circuit, said inductance elernent
having a reactive irnpedance which, for frequen-
cies higher than that of said carrier wave, is large
compared fo the reactive Lmpedance of the grid-
fo-cathode capacitance of said mixer, thereby
providing a low pass filter between said input
circuit and said mixer grid, and an output cir-
cuit connected between the other terminal of said
source and said mixer anode.
3. In a superheterodyne receiver, a twin triode
having a single cathode, a first and a second
anode, a first and a second control grid, said sin-
gle cathode being directly connected to one ter-
minal of a source of potential, a high-frequency
tank circuit connected between said first anode
and said first control grid fo provide a high-fre-
quency oscillator, a low-frequency tank circuit,
switch means for selectively connecting said low-
frequency tank circuit fo said first control grid
fo provide a low-frequency oscillator, a tuned
input circuit including a capacitor having a large
value relative to the grid-to-cathode capacitance
of said second grid and said cathode coupled
from said_ one terminal fo said second grid îor
impressing a modulated carrier wave thereon, an
inductance element having a reactive hnpedance
which, for frequencies higher than that of said
carrier wave, is large compared fo the reactive
5 impedance of the grid-to-cathode capacitance
of said second grid and said cathode, said in-
ductance element being serially connected
tween said input circuit and said second grid
and inductively coupled fo said low-frequency
10 tank circuit, said inductance element providing
a low pass filter between said input circuit and
said second grid and also functioning in conjunc-
tion with ther relatively small grid-to-cathode
capacitance of said second grid and said cath-
15 ode to maximize the coupling between said low-
frequency tank circuit and said second grid and
in conjunction with said capacitor fo minimize
the coupling between said low-frequency tank
circuit and said input circuit, and an output cir-
20 cuit connected between the other terminal of saîd
source and said second anode for deriving a fre-
quency-converted carrier wave.
4. In a multiband superheterodyne receiver, a
triode mixer having a cathode, an anode and a
25 control grid, a triode oscillator having a cathode,
an anode and a control grid, said cathodes being
dri'ect!y connected to one terminal of a source of
potential, a low-frequency tank circuit, a switch
for selectively connecting said low-frequency
0 tank circuit to the control grid of said oscflla-
for, a first inductance element connected between
the other terminal of said source and the anode
of said oscillator and inductively coupled fo said
low-frequency tank circuit, a high-frequency tank
ô5 circuit permanently connected fo said oscillator,
a grid circuit including a switch connected to said
mixer grid for selectively connecting circuit means
to said rnixer grid for irnpressing a moduiated
carrier wave within a low-frequency range or
40 within a high-frequency range on the control
grid of said mixer, and a second inductance ele-
ment selectively connected in series with the grid
circuit of said mixer and inductive!y coupled fo
said low-frequency tank circuit.
5. In a multiband superheterodyne receiver, a
45
triode ]nixer having a cathode, an anode and a
control grid, a triode oscillator having a cathode,
an anode and a control grid, said cathodes being
directly connected fo one terminal of a source of
50 potential, a low-frequency tank circuit, a switch
for selectively connecting said low-frequency
tank cri'cuit fo the control grid of said oscillator,
a first inductance elernent connected between the
other terminal of said source and the anode of
55 said oscillator and inductively coupled fo said
low-frequency tank circuit, a high-frequency
tank circuit permanently connected between the
control grid and the anode of said oscfllator, a
first mixer grid input circuit, a second mixer
60 grid input circuit and a further switch for se-
lectively irnpre'ssing a modulated carrier wave
within a low-irequency range or within a high-
frequency range on the control grid of said mixer
through said input circuits selectively, a second
65 inductance element serially connected in said
first mixer grid input circuit and inductively
coupled fo said low-frequency tank circuit, and
an output circuit coupled to the anode of said
mixer.
70 ô. In a multiband superheterodyne receiver, a
triode mixer having a cathode, an anode and a
control grid, a triode oscillator having a cathode,
an anode and a contïol grid, said cathodes being
directly connected fo one terminal of a source of
fixed potential, a low-frequency tank circuit, a
2,601,475
9
first swich for selectively cormecting said low-
frequency tank circuit fo the control grid of
said oscillator, a first inductance element con-
nected between the other terminal of said source
and the anode of said oscillator and inductively
coupled fo said low-frequency tank circuit, a
high-frequency tank circuit permanent!y con-
nected fo the anode of said oscillator, a feedback
winding inductively coupled to said high-fre-
quency tank circuit and connected fo the control
grid of said oscillator, a first tuned input circuit,
a second tuned input circuit and a second switch
for selectively connecting one of said input cir-
cuits to the control grid of said mixer to impress
a modulated carrier wave within a low-frequency
range or within a high-frequency range thereon,
a second inductance element seria]ly connected
in said flrst input circuit and inductive]y coupled
fo said low-frequency tank circuit, and an out-
put circuit connected between said other termi-
nal of said source and said mixer anode.
7. In a two-band superheterodyne receiver, a
triode mixer having a cathode, a control grid,
and an anode, a triode oscillator having a cath-
ode, a control grid and an anode, a low-frequency
tank circuit, a lïrst switch means for selectively
coupling said low-frequency tank circuit fo said
oscillator grid, a source of potential having one
terminal directly connected fo said cathodes, a
first inductance element connected between the
other terminal of said source and said oscillator
anode, said first inductance element being induc-
tively coupled to said low-frequency tank circuit,
a low frequency antenna, a high frequency an-
tenna, a connection incinding a second switch
means for selectively connecting one of said an-
termas to said mixer grid, a second inductance
element seria]ly connected between said low-
frequency antenna and said second switch means
and inductively coup]ed fo said low-frequency
tank circuit for impressing osci]latory energy de-
veloped in said low-frequency tank circuit on
said mixer grid, a high-frequency tank circuit
comprising a further inductance e]ement having
one terminal couiled fo said oscillator grid and
having ifs other terminal coupled to said oscilla-
for anode, a fixed capacitor coupling said cath-
odes fo an intermediate point on said further
inductance element, a variable capacitor con-
nected between said other terminal of said fur-
ther inductance element and said oscillator cath-
ode for tuning said high-frequency tank circuit,
said high frequency antenna connection includ-
ing a third inductance element inductively cou-
pled fo said further inductance element for im-
pressing oscillatory energy developed in said
high-frequency tank circuit on said mixer grid,
50 Number
2,011,941
2,038,918
2,289,147
2,295,383
55 2,355,47O
2,443,935
10
and an output circuit connected between said
other terminal of said source and said mixer
anode.
8. In a two-band superheterodyne receiver, a
5 triode mixer having a cathode, a control grid,
and an anode, a triode oscillator having a cath-
ode, a control grid and an anode, a low-frequency
tank circuit, a first switch ïneans for selectively
coupling said low-frequency tank circuit to said
10 oscillator grid, a source of potential having one
terminal directly connected to said cathodes, a
first inductance element connected between the
other terminal of said source and said oscillator
anode, said first inductance element being in-
15 ductively coupled to said low frequency tank cir-
cuit, a low frequency antenna, a high frequency
antenna, a first tuned input circuit, a second
tuned input circuit, a second switch means for
selectively connecting one of said antennas fo
20 said mixer grid, a second inductance element
serially connected between said first input cir-
cuit and said second switch means and inductive-
ly coupled to said low-frequency tank circuit for
impressing oscillatory energy developed in said
25 low frequency tank circuit on said mixer grid, a
high-frequency tank circuit comprising a fur-
ther inductance element having one terminal
coupled to said oscillator grid and having ifs
other terminal coupled to said oscfllator anode,
30 a fixed capacitor coupling an intermediate point
of said further inductance element to said cath-
odes, a variable capacitor connected between said
other terminal of said further inductance ele-
ment and said oscil]ator cathode for tuning said
35 high-frequency tank circuit, said second input
circuit including a third inductance element in-
ductively coupled fo said further inductance ele-
ment for impressing oscillatory energy developed
in said high-frequency tank circuit on said mixer
40 grid, and an output circuit connected between
said other terminal of said soin-ce and said mixer
anode.
BENJAIVIIN S. VILKOIOERSON.
45 EEFERENCES CITED
The following references are of record in the
file of this patent:
UNITED STATES PATENTS
Naine Date
Snider ............. Aug. 20, 1935
Bafley ............ Apr. 28, 1936
Shea .............. July 7, 1942
Carlson ............ Sepç. 8, 1942
Root .............. Aug. 8, 1944
Shea .............. June 22, 1948