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Патент USA US2412244

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Dec. 10, 1-946.
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H. J. BENNER
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23126244
SUPERHE'I‘ERODYNE RECEIVER
Filed Nov. 10, 1938
7'0 AVG
7b Osc/LM 70B Tums/a
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INVENTOR
wmqead ?av/vse
2,412,244
Patented Dec. 10, _ 1946
UNITED STATES PATENT ‘OFFICE
2,412,244
SUPERHETERODYNE RECEIVER
Howard J. Banner, Spring?eld, Mass, assignor of
one-half to Colonial Radio Corporation, Buf
falo, N. Y., and one-half to The F. W. Sickles
.Company, Spring?eld, Mass.
Application November 10, 1938, Serial No. 239,788
,
16 Claims. (01. 250-20)
1
,
tuning reactance which acts simultaneously as a
selector of desired frequencies and as an image
suppressor; that is to say, the variation'of the
variable reactance causes the circuit to select the!
desired signal, at the same time to present an ex-;
tremely high impedance to the image signal, and
I have found that circuits according to my-'invenl-'
band. Incoming radio frequency signals are het
tion produce signal to image ratios as high 'as,
erodyned or “beat” with an oscillation produced
by the local oscillator, vand this gives rise to os
2
a simple tuning circuit with only one variable
This invention relates to radio receiving ap
paratus, and more particularly to signal selecting
circuits for superheterodyne receivers,
In such receivers, as is well known, the inter
mediate frequency amplifying stage or stages are
tuned to a frequency above audibility and usu
ally below the lowest frequency of the broadcast
10 and in many cases considerably higher than, the
cillations of a frequency which may be either the
sum of or the difference between the incoming
frequency and that of the local oscillator. Only
those oscillations thereby produced which have a
frequency enabling them to pass through the in 15
termediate frequency ampli?er are then ampli
best signal to image ratios produced ‘by conven-~
tional wave trap circuits.
As an example, em
ploying the single tuned circuit of my invention,
I have been able to obtain signal to image ratios
as high as 70,000.
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Among the objects of my invention are:
H
To provide an image suppression circuit which
?ed.
does not require separate wave trap or preselec-_
For example, if the intermediate frequency am
tor circuits;
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pli?er is tuned to 400 kilocycles and a 550 kilo
cycle signal is being received, and the local oscil 20 To provide a circuit in which the image sup
pression is automatically performed by the main
lator has, when this particular signal is being re
tuning circuit,
ceived, a frequency of 950 kilocycles, then there
Still another object of my invention is to pro
will be produced a f‘beat” frequency of 400 kilo
vide a simple signal selecting circuit which will'
cycles. However, if there is also an incoming sig
nal of 1350 kilocycles at the same time, a new 25 deliver signal to image ratios as high or'higher
than those obtained from conventional wave trap
oscillation will be produced by the heterodyne ac
or preselector image suppressors.
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tion between the local oscillation and the 1350
Still other objects of my invention~ will be ap
kilocycle signal, and this new oscillation will like
parent from the speci?cation,
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wise have a frequency of 400 kilocycles and will
In this application I have particularly pointedv
accordingly pass through the intermediate fre
out and distinctly claimed the part, improvement
quency ampli?er, resulting in interference and
or combination which I claim as my invention of
cross-talk with the desired signal. The frequency
discovery and I have explained the principles
of the undesired signal is termed the “image” fre
thereof and the best mode in which I have'cons
quency, and it is equal to the frequency of the de
sired signal plus twice the intermediate fre 35 templated applying those principles so as to dis
tinguish my invention from other inventions. '
In the drawing'
It is usual to provide a signal selecting circuit
The figure is a circuit diagram of one form‘ of
in advance of the ?rst detector, and this circuit is
ordinarily arranged to be tuned to the frequency
circuit in accordance with my invention. "
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quency.
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In the practice of my invention, for some pur-.
of the desired signal. However, even when such 40
poses I prefer to employ what is known as “per-I
a circuit is used, image interference may still be
meability tuning,” although this invention is not
encountered and it has been proposed in the past
limited thereto. If such permeability tuning is
to eliminate or reduce this imagev interference by
providing preselecting circuits and the like, and
also by providing one or more wave traps asso
ciated with the antenna and variably tuned.
The employment of wave traps for image sup
pression increases the cost of the receiver, since
employed, the variation in resonant frequency is
45 obtained, not by rotation of a variable ‘condenser,
but by movement of a core of magneticmaterial
in the ?eld of an inductance. Such cores’ are sat
isfactorily formed of iron dust mixed with a suit
able insulating and binding material and pressed
it is necessary to provide an additional coil and‘
an additional condenser, one or the other of, 50 or otherwise processed to form what appears as
a solid bar.
> which is usually variable. The provision of such
Since they are easily obtainable on the marke ,
parts increases the cost of the receiver, from the
and their construction is per se, not a part of my
standpoint of material and parts employed and
invention, they are not described in detail.
also the labor of assembly,
I have discovered that it is possible to provide 554 If such a core is moved axially into and out‘
2,412,244
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of a solenoid in a resonant circuit, there is ob- ‘
3 and condenser. 5, forming a closed loop circuit,
served a variation in the inductance of the sole
noid, and a variation of the resonant frequency
of the circuit in which said solenoid is connected,
are resonant to the image-producing signal and ,
cause extreme attenuation thereof while not inter
this change of resonant frequency being due, to a .
very considerable extent, to the variation in the
value of the inductance‘of' the" solenoid with the
positionof the: core, and probably‘ also, in some. “
arrangements, to some extent at least, to the
variation of the capacity of the circuit resulting; "19
from change of position of the core,..
fering with the‘ selection by resonance of the
desired signal. ‘I have found that movement of
thecore 4 into and out of the coil 3 varies the
tuning of . the entire circuit and: also, the; tuning of
the'imagesuppressor 3+5. in a satisfactory ap
proximation to the desired manner.
"In order for the signal or mainvtuning circuit
to vary from 500 to 1500 kilocycles, i. e., 3 to 1
I represents an antenna of any suitable typew, .
ratio; the» inductance of that circuit must vary ‘
in a. 9. to 1 ratio. It will be noted, however,
which may be connected to groundz'throug‘ni
that. while the resonant circuit varies from 5037
_Referring more particularly to the ?gure; ‘
‘ coupling condenser 2. C'urrnntsprodirceidihthe 15' to. 150.0 kilocycles,_v the image frequency varies
antenna I by incoming signals will ?ow to some‘
extent through inductance 3, shunted by con
denser 5, and the voltage thereby produced‘ may
be supplied to the grid 9 of the ?rst.» tube 'l,..
whichmay be connected to ground through con 20
from. 1460. tn» 2510} kilocycles when the inter
mediate frequency is455 kilocycles. In this case
the ratio of frequencychange is 1.72 to 1 and the
changeiwofiinductance required to make the image
denser 6;
this ratio, or. 2.96-1.
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circuit track exactly should be in the square of
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From. this it iwill‘beseen that. if the main tuning:
The antenna side of coil 3, may be connected
through resistance ll, having a_high resistance,
circuit is tuned to the lowest broadcast fre
to ground or to the automatic volume control
quency, i. e., 550. kilocycles, and’the. image circuit
voltage source, if such ispresent, thereby provid
ing, a; direct. current grid return path. The.
3-.51 then tuned, by varying.v condenser 5,. to. the.
image. frequency,.then as; the. main tuning circuit.
frequency is increased by movement. of‘the core 4‘.
out of the inductance,.the. reduction of; inductance
sistance-- L2,. shunted by condenser l3;- or directly
in the image trap proceeds too fast,‘ and. the.
grounded if desired;
Sincemy invention is? not concerned with the 30 resonant? frequency of the. image circuit. rises?
cathode of=~tube 11» may be grounded through re
construction of the superheterodyne beyond this ,
above the image'frequenc'y.
point, and the same is well known in the'art, only
This. departure from. the theoretical image.
value is, in most cases, not-a serious. matter,_.be
the ?rst tube 1 is indicated.
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- cause, ordinarily, themost harmful-image. inter‘ '
The desired- signals may be selected by, move~
ment of the core 4 into and out of the ?eld of
coil 3, and at? the same time the‘ frequency of
the local oscillator is: varied. in such" 'a manner
that the signalselected in the antenna. circuit
by movement of the coil 4 is heterodyned to-pro»
f'erence is. obtained when. the. main-tuning circuit
is- tuned to thelow frequency end of. thebroadcast
band.
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'It may be noted that under certain. conditions
the value of condenser "2. may be. zero; that. is,
d-ucev oscillations of the desired intermediate fr - ‘
that physical condenser may be omitted;
quency.
In adjusting the circuit for operation, the con
denser. 5: may be omitted and the desired num
beriofqturns in. inductance 3 provided so that’
instance. of this is in automobile radio installa
tions where the. running-board's are used as. an.
aerial. In this. instance, the antenna capacity; '
whichis in parallel with condenser 2 is so large,
movement of? they core 4 causes the circuit to i ;
comparatively, that condenser 2, may be‘omitted.
Condenser 2. may be'omitted with an aerialof
tune’ over the range desired, in this instance from
small capacity also; such as av “?shpole.”
500 to 1500 kilocycles, and» the tuning. circuit
formed ‘by-inductance- 3-.and its associated‘ ele
ments, herein called the “signal tuning circuit,”
is-preferably ‘ftracked” withthe- oscillator tuner
will. now operate’ as a- conventional superhetere»
ody'neand imageinterferencemay be experienced.
In»
this-instance condenser 6- may be adjusted. to
compensate: for'the variation- in antenna capac~
ity;
bytrinnner condenser-‘6”. so that thereceiver may
be operated: by- a single control as indicated by
theconnected arrowsin the drawing. The circuit._
One.
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' ‘While I have shownand- described certain. pre-.
ferred» embodiments of my» invention, it? will. be
apparent that modi?cations.» and changes may be.
made. without departing from the spirit and scope.
~‘ of my invention, as will beelear to those skilled.
If now condenser 5 be connected across coil 3
and chosen of the proper value, a very great im
movement in signal: to image ratio is noticed. In
in the art.
I claim:
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1; In-a superheterodyne receiver, incombina-r
tion, inductance and capacity elements: associ:
choosing the value? of condenser 5, it is picked of
such magnitude as to cause the inductance 3 to 60 ated. together to form a resonant circuit, tun
resonate with condenser 5 at the image frequency
able as a whole by variation of one of- saideleej
(which, as stated, is equal to the desired signal ‘
ments to select desired. signal. frequencies, said
frequency, plus twice the intermediate frequency)
variable element forming, with another. of said. ~
whengthe- tuning circuit is tuned to a desired
signal; frequency;
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elements, a parallel tuned. resonant circuit which
.. is maintained resonant to the image ofthe SE‘:
The connection of thiscondenser, which will
' ordinarily be quite small, for instance of the 1
order of. two to twelve mmf., may slightly disturb:
1 the tracking of the main tuning circuit with the
i oscillator tuner, in which case: it may be neces-v
sary to retrim the main tuning circuit by varia- ‘
‘ tion' of. the trimmer‘ condenser 6, but it will be
found that when the operation is completed the '
entire input. circuit; as a whole, is resonant ‘fe
thedesired'signal frequency; whereas, inductance 75.
lected signal frequency.
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2. In a superheterodyne receiver, in. combina
tion, inductance and capacity elements associ»
ated togetherv to form a resonantlcircuit, tunable’
as. a whole by variation of said inductance to_ se
lect; desired signal frequencies/said inductance-v
forming with a capacity element a secondreso
nant circuit parallel tuned. to the image ofthe
selected signal frequency;
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3. In a superheterodyne. receiver, inzcombinal
tion, inductance and capacity elements associ
stantially “equal, to ‘_
ated together to form. a resonant circuit tunable
twice the intermediate frequency,
desired 5' frequency _f plus
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as a whole to select desired signal frequencies, a
9. In ajsuperheterodyne radio'lre‘ceivingi cir
core of magnetic material movable into the, ?eld
of said inductance to tune said ‘circuit, said in
ductance having a capacity connected thereto
selector circuit comprising an inductance coil, a
?rst capacitor across theends of said induct‘
and forming therewith 'a second resonant cirf
cuit maintained parallel resonant to the image of
inductance coil atone end, an impedance in
the selected signal frequency.
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cuit, an audion tube having a control grid,'-a
ance coil,,a second capacitor in series ‘with the
series with the inductance coil at the other end,
an aerial operatively connected to the inductance
coil and to the impedance, the opposite ends of
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4.‘ In a superheterodyne receiver, in combina
tion, inductance and capacity elements associ
ated tog’ether’to form a resonant circuit, tun-'
able as a whole by variationof said inductance
the impedance and capacitor being‘ grounded,
means for impressing a received signal across
the terminals of the impedance, the second‘ ca
pacitor and inductance coil being connectedto
the grid, and-means for varying theinductance
to select desired signal frequencies, and a cir“
cuit comprising a condenser in shunt with said
inductance, the circuit formed byv said induc
tance and said condenser in shunt therewith be
of theicoil to tune the circuit as a whole to a
desired frequency and to tune the image trap
composed of thejinductance coil and ‘the, first
5. In a superheterodyne receiver, a combined 20 capacitor to a frequency substantially vequaljton
the desired frequency ‘plus twice the.interrne'
signal selecting and image rejecting circuit com
, ing parallel tuned to the image of the selected
signal frequency. '
-
prising a plurality of reactance elements forming
diate frequency.
a resonant circuit, at least one of said reactances
being variable to select signals of a desired fre
quency, said variable element being shunted by
a vacuum tube with a control electrode, includ
an additional reactance of opposite sign of such
value as to constitute a second resonant circuit
parallel resonant to the image of the resonant
frequency of the ?rst resonant circuit, and means
for varying the value of said variable reactance
to simultaneously vary both resonant frequencies
while maintaining the second at the image value
of the ?rst.
6. In a superheterodyne receiver, an input
tuning circuit comprising a pair of capacity ele
ments, a connection between said capacity ele
ments, said connection including, in series, a
closed tuned circuit, the inductance and capacity
of said closed tuned circuit being so chosen that 4-0
said closed tuned circuit is resonant to the im
age frequency, and one of the reactance elements
of said closed tuned circuit being variable over a
range such as to tune the input tuning circuit as
a whole to desired signals while maintaining said
closed circuit resonant to said image frequency.
7. In a superheterodyne receiver, an input
tuning circuit comprising a pair of capacity ele
ments, 9, connection between said capacity ele
ments, said connection including, in series, a
closed tuned circuit, the inductance and capac
ity of said closed tuned circuit being so chosen
that said closed tunedcircuit is resonant to the
image frequency, and one of the reactance ele
ments of said input tuning circuit being variable
over a range such as to tune the input tuning
circuit as a whole to desired signals while main
taining said‘ closed circuit resonant to said
image frequency.
8. In a superheterodyne radio receiving cir
cuit, an audion tube having a control grid, a
selector circuit comprising an inductance coil,
a ?rst capacitor across the ends of said induc
tance coil, a second capacitor in series with the
inductance coil at one end, an impedance in
series with the inductance coil at the other end,
the opposite ends of the impedance and capac
itor being grounded, means for impressing a
received signal across the terminals of the im¢
pedance, the second capacitor and inductance
coil being connected to the grid, and means for
varying the inductance of the coil to tune the
circuit as a whole to a desired frequency and to
tune the image trap composed of the inductance
coil and the ?rst capacitor to a frequency sub
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10. An image suppression system'for a super:
heterodyne radio receiver having an antenna and
ing a ?rst resonant circuit a portion of which
is connected between said control electrode and
ground, and a second resonant circuit in series
between said antenna and said control elec
trode, said resonant circuits being tuned by in
ductance variation respectively to a signal fre
quency and to the corresponding image fre
quency.
11. An image suppression system for a super
heterodyne radio receiver having an antenna
and a vacuum tube with a control electrode, in- -
eluding a ?rst resonant circuit a portion of which
is connected between said control electrode and
ground, and a second resonant circuit in series
between said antenna and said control elec
trode, said resonant circuits including in com
mon a variable inductance device comprising an
inductance coil and a ferromagnetic core mov
able relatively thereto and being tunable simul
taneously over substantially different frequency
ranges by motion of said core.
12. An image suppression system for a super
heterodyne radio receiver having an antenna
and a vacuum tube with a control electrode, in
cluding a ?rst resonant circuit a portion of which
is connected between said control electrode and
ground, and a second resonant circuit in series
between said antenna and said control electrode,
said resonant circuits including in common a
variable inductance device comprising an induct
ance coil and a ferromagnetic core movable rel
atively thereto, said resonant circuits being
simultaneously tuned by motion of said core re-‘
spectively to a signal frequency and to the cor- ’
responding image frequency. ’
13. A preselector system for a superheterodyne
radio receiver, including a variable inductance
device comprising an inductance coil and a mov
able ferromagnetic core, ?rst and second capac
itors connected with said inductance device to
secure resonance within a ?rst range of frequen
cies by movement of said core, and a third capac
itor in shunt with said inductance device to se
cure resonance within a second range of fre
quencies by movement of said core, said capac
itors being so chosen that any frequency of said
second range is higher than the corresponding
frequency of said ?rst range by a practically
constant amount throughout said core move
75 ment.
2,412,244
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radio receiver,v including avariable inductance
able ferromagnetic ‘core, ?rst and second capac
device to securev resonance within a ?rst range of
,
said. inductance device and ‘tunable, thereby over
a second frequency. range in series between "said
device comprising an inductance coil and a mov
itors ‘in series shunted across said inductance‘
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ground, anda secondresonant circuit including,
. 14. A preselector system for a, superheterodyne
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antenna and said input electrode, said elements
being so proportioned that said resonant _cir-’
cuits are maintainedat a practically constant
frequencies by movement of said core, and a
frequency difference during movement of said
third capacitor in shunt with said inductance de
core.
vice to secure resonance within a second range .
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16. In a superheterodyne receiver, in ‘combi;
of ‘frequencies by movement of said core, said‘ 10 nation, an inductance element anda plurality of
capacitors being so chosen that any frequency
capacity elements connected together to‘ form a
of said second range is higher than the corre
single resonant signal selector circuit for con
sponding frequency of said ?rst range by a prac-'
nection at one pointto an antenna and at an-v
tically constant amount throughout said core
movement.
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n 15, In a superheterodyne radiovreceiv'ing syse
tem, an antenna, a vacuum tube having an in
putelectrode, and, elements including a variable
inductancedevice comprising an inductance coil
and a movable ferromagnetic core, a ?rst reso
other point to the control electrode'of a thermi
ionic tube, said inductance having one of said
capacity elements’ connected in shunt therewith
and forming with said inductance a resonant
circuit parallel tuned to the image of a, selec-V
table signal frequency, said parallel tuned cits
20 cuit being interposed in series between the points ~
nant circuit including said inductance device
of connection to said antenna and’ to said control
and tunable thereby over a ?rst range of. fre
electrode.
quencies connected between said antenna and
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HOWARD J. BENNER, '
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