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Патент USA US2390768

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Deco-1,1, 1945.
2,390,768
‘K. B.‘ AUSTlN ETAL
VARIABLE SELECTIVITI AMPLIFIER
Filed Oct; '7, 1944
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Kirby 15. Austin,
' George G.Young.,
by
Their" Attorney.
V
‘2,390,768
Patented Dec. 11, 1945
umrsp STATES PATENT
'
OFFICE
ascents
VARIABLE SELECTIVITY
Kirby B. Austin and George G. Young, Bridge- *
' port, Conn, assignors to General Electric Com5
pany, a. corporation of New York
1
Application October 7, 1944, Serial No. 557,.tt9 '
8 Claims. writs-171)
This invention relates to" high frequency am
pll?ers and particularly to such ampli?ers which
are provided with. switching devices for selec
tively changing the resonance bandwidth.
It is an object of this invention to provide a
variable selectivity high frequency amplifier in
cluding an improved arrangement for changing
the resonance bandwidth of the ampli?er.
v
.
Referring now to the drawing. the ampli?er
shown in Fig. 1 includes ?rst and second stage
. electron discharge devices I and 2, respectively.
The device I is coupled to the output of a radio
frequency ampli?er and converter 3 through a
pair of tuned circuits 4 and 5. The circuit a is
the primary circuit and includes a main induct
ance 8 and a main capacitance ‘l. The second
ary circuit 5 includes a main inductance 8 and
It is another object of this invention to provide
a variable selectivity high frequency ampli?er 10 a main capacitance 9. and the two circuits are
directly coupled through an inductive reactance
including an improved bandwidth selection ar
rangement of simpli?ed construction.
v
element “I which is connected in series with the
main inductance it of the circuit s. In the posi
The novel features which are believed to be
‘tion shown the direct coupling is effected through
characteristic’ of this invention are set forth with
particularity in the appended claims. The in 15 the left-hand contact of a double-throw switch
vention itself, however, both as to its organiza
tion and method of operation, together with fur
ther objects and advantages thereof, may best be
it so that only a portion‘ of the reactance III is .
common to both circuits. The main inductance
elements 8 and t are provided with movable
cores l2 and M respectively‘ for tuning purposes,
tion taken in connection with the accompanying 20 and these circuits are tuned to resonance at a
predetermined frequency when switch It is in its
drawing in which Fig. 1 represents an embodi
left-hand position as shown. The circuit 571s
ment of the invention, and Figs. 2, 3, 4, and 5
represent certain operating characteristics of the _' connected across-a resistor ll to a control grid it
apparatus of Fig. 1.
of the device 9, which also includes an anode it
and a cathode it. The devices I and 2 are cou
Brie?y the apparatus illustrated in the draw~
pled by a pair of tuned circuits l8 and it. The
ing comprises a two-stage intermediate fre
circuit It includes a main capacitor 29 and a
quency electronic ampli?er provided with tuned
main inductance M which may be tuned by
circuits directly coupled through suitable react-v
movement of a core 22. The circuit 19 includes
ance elements, one pair of tuned circuits being
arranged in the input of the ?rst stage of the 30 a main capacitance 23 and a main inductance 24
ampli?er and a second pair of tuned circuits in
which may be tuned by movement of a core 25.
understood by reference to the following descrip
the output thereof. The coupling reactances are
associated with the primary tuned circuits of
A capacitive reactance element comprising ca:
'pacitors 26 and 2? connected in series with the
main capacitor it is provided for coupling the
each pair and are of opposite sign; that is, one
is inductive and the other is capacitive. " A 35 circuits l8 and I8, and the circuit i9 is connected
switching arrangement is provided for simul
in common with the capacitor 21 through the
taneously changing the coupling of the ‘second
left-hand contacts of the gouble-throw switch 28.
ary circuits from, the position including only a
A suitable source ofano' e voltage indicated as
portion of the reactance elements to the position
a battery 28 is provided and is connected to .
including all of the reactance elements, together 40 the plate It through the inductance 2| and a »
resistor 30. The battery 20, is also connected
with an additional resistance element included
only in the secondary circuits. The values of
through the inductances 6 and ill to supply the
the reactances are selected so that when the
anode voltage for the last tube in the ampli?er
and converter 3.
'
units are tuned to resonance with only portions
of the elements common to the two circuits, the 45 _ The pair of circuits l! and i9 is similar to the
changing of the control to include the entire ele
pair 4 and 5 except that the direct coupling is
ments provides a wide resonance bandwidth, one
capacitive rather than inductive, and the circuits
of the secondary circuits being detuned below the
Ill and II are tuned to resonance at the same
resonance frequency and the other above the res
predetermined frequency when the switch 20 is
onance frequency so that the combined or over 50 in its left-hand position. The output of the cir
all characteristic is symmetrical about the res
cuit I0 is connected'to a control electrode it of
the device 2 which ampli?es the output and sup
onance frequency. The voltage gain for the two
positions of the control is made substantially
plies it to a. suitable utilization device 32 con
cqual so that no adjustment of the gain is nec
nected between the anode 33 and the cathode 84
cssary.
of device 2.
'
2
I
.
'
2,890,768
The ampli?er of Fig. 1 when operated with the
being plotted against attenuation. In each of
switches H and 28 in their left-hand position
these ?gures, the sharp resonance characteristic
is sharply tuned and highly selective. Under
curve is indicated at 42, this being the desired
certain conditions, however, it is desirableto con-v
sharp resonance curve with the switches in their
nect the ampli?er to operate with ‘a broad res
left-handjposition and at a frequency indicated
onance bandwidth. This may be accomplished
by the dotted line 43. Fig. 3 represents at 44 the
by moving the switches II and 28 to their right
selectivity curve of the pair of circuits 4 and 5 .
hand positions. To facilitate the simultaneous
when the switch II is in its right-hand position,
movement of the switches, they may be con
_ the secondary circuit 5 producing detuning in
nected by a suitable mechanical coupling indi 10 the range'of frequencies below the frequency 43.
cated by a dotted line 35. When the switches are
Fig. 4 represents at 45 the selectivity curve of
in their right-hand positions, the entire react
the circuits l8 and I9 when-the switch 28 is in‘
ance elements I!) and 23, 21 are connected in
common with their respective primary and sec
its rightehand position, this curve showing that .
the circuit 5, and a resistance 31 is connected
inductive reactance I'll and the capacitive re
actance 26, 21, a symmetrical over-all curve may
be obtained as indicated at 46 in Fig. 5. The
the secondary circuit is detuned for.frequencies
ondary circuits. Furthermore a‘ resistance 35 15 above the frequency 43 due to the capacitive cou
pling. .By proper selection of the values of the
is connected in_ series with the reactance ill in
in series with the condensers 26 and 21 in the
circuit l9. _These resistors reduce the eifective
ratio of the energy stored in the resonance cir 20 curve 46 is a broad over-all resonance curve re
sulting from the combined operating character
cuits to the energy dissipated therein, and thus Y
reduce the - sharpness of resonance. Further
istics of the two pairs of tuned circuits 4, 5 and
more when the entire coupling reactance ele
l8, l9.
»
ments are included in common in both circuits,
After selecting the desired values of _the cou
the pairs of circuits are overcoupled. The tun 25 plingreactances ‘I0 and 26, 21, the circuit of Fig.
ingof the primary circuits is not appreciably dis
1 is prepared for operation by placing the
turbed. However the secondary circuits 5 and
I9 are detuned to some extent, the circuit 5 be
switches II and 28 in their left-hand positions
as ‘shown in the drawing and. then tuning the
circuits 4, 5, l8, and 19 to resonance at the de
ing detuned oppositely from the circuit l8 since
the reactance added to the circuit 5 is inductive 30 sired predetermined frequency 43. This simple
tuning operation is the only tuning required, it
whereas that added to the circuit' 19 is capaci
tive. The values of the portions of the coupling.
being unnecessary to make anyfurtheradjust
ments of the tuning when the coupling 35 is
reactances connected in the secondary circuits
may be selected so that the voltage gain, that is
changed to place the switches I l and 28 in ,their
ratio of the input voltage to the output voltage, 35 right-hand positions.
It is readily apparent from the foregoing that
of each pair of circuits remains the same for both
a simple and e?’ective circuit has been provided
positions of the double-throw switches. That
this may be accomplished is illustrated in Fig. 2
for securing either a broad or a sharp resonance
where the mutual coupling curve for the pair of
bandwidth in a high frequency ampli?er and that
circuits 4 and 5 is illustrated. It will be noted 40' a minimum number of circuit components areyre
that the curve has a hump 31 which has a maxi
_quired. Furthermore only a single tuning opera
mum value of gain at the point of critical cou
tion is necessary for bothpositions of the band
pling where the transfer of energy is maximum. " width selecting‘ device. Furthermore all the
By selecting two points 38 and 39 respectively
switching may be effected on the low voltage end
below and above the critical couplingvalue, it is ' 45 of the tuned circuits and it is unnecessary to I
possible to provide two points of equal gain with
different values of coupling and ‘the values of
shield the switching mechanism. Furthermore
this circuit makes it possible to provide constant
the two portions of the reactance l0 are selected
gain for both positions of the selectivity chang
accordingly, the value of the portion of the re
ing device. By way of illustration only and not ,
actance connected when the switch II is in its 50 by way of limitation, there are listedbelow values
left-hand position being that at 38 and the value
of circuit constants which have been found to be
when the entire reactance is included in the cir
suitable for the circuit of Fig. 1 when employed _
cuit and the switch II is in its right-hand posi-_
in a particular intermediate frequency ampli?er.
tion being that at 39. A similar curve may be
The electronic discharge devices I and 2 were
drawn to illustrate the variation of gain with 55 12sG7 pentodes, and the circuits 4, a. la, and I3
mutual coupling for the pair of circuits l8 and
were tuned to an intermediate frequency of 1225
I8, the values of the condensers 26 and'21 being
kilocycles when the switches I l and 28 were in
- selected‘ to provide equal gain in a manner simi
- their left-hand positions. The other values were
lar to the selection of the two portions of the in
I
ductance l0.
as follows:
'
‘
"
-
'Inductances 8, 8, 2|, 24____'__'_- 85 microhenries
Capacitors 1, 9, 20, 23_-___ 200 micromicrofarads
The coupling between the primary and second
ary circuits of each pair may be made entirely
dependent upon the impedance of the coupling
' element by electromagneticallyand electrostati
Inductance l0 ____ __ 1.8 microhenries, tapped at
'
'
I
_
0.7 or 07.8 microhenrles
cally isolating the _circuits of each pair from each c5 Capacitor 26____.._____-___.._____ .01 microfarad
Capacitor 21_..___'_______ _'_ ____ .._ .05 microfarad
other and from the ‘other circuits by suitable
Resistor 38, 31 _____ _'. _______ __'_'_'_____ 3.3 ohms
shielding indicated by dotted lines 40 and 41, the
switches [I and 28 and the coupling reactances
While the invention has been illustrated in con
i0 and 26, 21 being located outside the shielding.
nection with an intermediate frequency ampli?er
The manner in which the circuit shown in Fig. 70 for a superheterodyne receiver, ‘other applica
1 operates toprovide a broad resonance band
tions will readily be apparent to those skilled in
width when the switches, II and 2,8 are in their
the art. Therefore, it is not desired that the in
right-hand positions is illustrated in Figs. 3, 4
vention be limited to the specific vcircuit arrange- and 5 which are selectivity curves, the frequency . - ment described and illustrated, and it is intend
above and below the mean resonant frequency, 75, ed by the appended claims to cover all modiacas;
2,390,768‘ f
' '
‘\
3
means
movable
into
one
position
for
connecting
tions within the spirit and scope of the invention.
the other circuit of each of said pairs across a
What we claim as new and desire to secure by
predetermined portion of the corresponding one
-of said elements in the pair and movable into a
second position for connecting said other circuits
to include a greater portion of each of therespec
tive ones of said elements, said circuits being
tuned to resonance when said selectively operable
Letters Patent of the United States is:
1. A variable selectivity high frequency amplié
?er comprising in combination, ?rst and second
pairs of tunable circuits, means for interconnect
ing said pairs of circuits, a reactance of one sign
connected in ‘one circuit of said ?rst pair and
having a portion common to the other circuit of
said ?rst pair for coupling said circuits of said
?rst pair, a reacta'nce of the opposite sign con
‘ means is in said ?rst position whereby in said
10
nected in one circuit of said second pair and hav
ing a portion common to the other circuit of said
second pair for coupling said circuits-of said sec
, (and pair, said circuits being tuned to a predeter
second position said other circuits are detuned
oppositely to provide a broad over-all resonance
bandwidth.
'
-
5. A variable selectivity high frequency ampli
?er comprising in combination, ?rst and second
15 pairs of tuned circuits, each comprising a primary
’ mined resonance frequency, and selectively oper
tuned circuit and a secondary tuned circuit,
means for interconnecting the secondary circuit
= actances common to said other circuits whereby
of said first pair and the primary circuit of said
said other circuits are detuned in opposite direc
second pair, each of said pairs of circuits includ
tions and the resonance bandwidth of said am 20, ing a reactance element connected in the primary
pli?er is broadened,
‘
'
‘
circuit and having a portion thereof common to
2. A variable selectivity high frequency ampli- ' both the primary and secondary circuits for di
?er comprising in combination, ?rst and second
‘rectly coupling the primary and secondary cir
pairs of tunable circuits, means for interconnect
cuits of each pair, one of said reactance elements
ing said pairs of circuits, one of the circuits of 25 being an inductance and the other a capacitance,
each of said pairs including a reactance element,
and selectively operable means for varying said
the one of said reactance elements in one pair - common portions of said reactance elements
being inductive and that in the other‘ pair being.
solelyby changing the portions of said elements
capacitive, each of said elements having a por
included in said secondary circuits whereby the
tion connected in the other circuit of its respec 30 resonance bandwidth of said ‘amplifier .may'be
able means for increasing the portions of said rc
tive pair for directly~ coupling the circuits in each -
pair, said circuits being tuned to resonance at a
varied.
‘
,
'
6. A variable-selectivity high frequency ampli
predetermined frequency, and selectively operable
?er comprising in combination, ?rst and second
means for increasing the portions of said elements
pairs of tunable circuits, means for interconnect
common to said other circuits whereby both. said 35 ing said pairs of circuitsfone of the circuits of
pairs of-circuits are overcoupled and said other
each of said pairs including a reactance element,
circuits are detuned in opposite directions to DI'O-r
the one of said reactance elements in one pair
vide an over-all broad resonance bandwidth.
3. A variable selectivity high frequency'ampli
?er comprising in combination, ?rst and second
pairs of tunable‘ circuits, means for interconnect
ing said pairs of circuits, one of the circuits of .
each of said pairs including a reactance element,
the one of said reactance elements in one pair be
ing inductive and that in the other pair being ca
pacitive, each of said elements having a portion
connected in the other circuit of its respective
pair for directly coupling the circuits in each '
pair, said circuits being tuned to resonance at a
being inductive and that in the other pair being
‘capacitive, each of said elements, having a por
tion connected in common with the other circuit
of its respective pair for directly coupling the
circuits in each pair, said circuits being tuned to
resonance at a predetermined frequencyya re->
sistance element associated with each of said pairs
of circuits, and selectively operable means for
increasing the portions of said reactance elements
common to said other circuits and for inserting
the respective ones of- said resistance elements
in said other circuits whereby both said pairs of
predetermined'frequency, and selectively operable 50 circuits are overcoupled and. their resonance
means for increasing the portions of said elements
common to said other circuits to provide a broad
er over-all resonance bandwidth for said ampli
.
bandwidths are broadened and said other circuits
are detuned in opposite directions to provide an
over-all bro'ad resonance bandwidth.
"
7. A variable selectivity high frequency ampli
?er, the valuesof the common portions of said
reactance elements being selected to provide over 55 ?er comprising in combination, ?rst and second
coupling in one position of said selectively oper
pairs of tunable circuits, each comprising a pri
mary circuit and a secondary circuit, means for
able means and less than critical coupling in the
interconnecting the secondary circuit of said ?rst
other position thereof and to provide a substan
pair and the primary circuit of said second pair,
tially constant ratio of input voltage to output
voltage for both pairs of circuits in both posi 60 each of said primary circuits including a reac
tions of said selectively operable means.
‘
tance element, the reactance element in one of
4. A variable ‘selectivity high frequency ampli
said primaries being inductive and that in the
other capacitive, and selectively operable cou
?er comprising in combination, ?rst and second
pling means movable into one position for con
pairs of tunable circuits, means for interconnect
ing said pairs of circuits, each of said circuits in-, 66 necting a predetermined portion of each of said
cluding a main, inductance and‘a main capaci
elements in common. with the secondary circuit
of its respective one of said pairs and movable into
tance, means for electromagnetically and electro
a second position for connecting a greater portion
Istatically shielding the main inductance and ,main
capacitance of each of said circuits, an inductive
of each of said elements in common with the
reactance element and a capacitive reactance ele 70 respective secondary circuit, said circuits being
tuned to ‘a predetermined frequency when said
ment arranged outside said shielding means,
selectively operable means is in said one posi
means for connecting one of said elements in one
tion whereby said one- position provides a sharp
circuit of said ?rst pair, means for connecting the
other of said elements in the corresponding cir
resonance bandwidth and said second position .
cuit of said second pair, and selectively operable 75 provides a broad resonance bandwidth, the values
2,390,?”
of the common portions of said reactance ele- '
ments being selected to provide substantiallyv
equal ratios of output to input voltage for both
pairs of circuits in both positions or said selectively
operable means.
8. A variable selectivity high i’requency ampli
fler comprising in combination, ?rst and second
I pairs of tunable _gircuits, each of said pairs in
cluding a primer‘? circuit and a secondary cir
.
,
series with the main capacitance of the other of '
said primary circuits, both or said elements being
arranged outside said smeldin's‘means. and selec
tively operable switching means arranged outside
5 said shielding means and movable into a first
position for connecting a predetermined portion
01.’ each 0! said elements in common with the _
‘secondarycircuit 01' the respective pair and mov
able into a second [position for connecting a
cuit, means for interconnecting the secondary 10 greater portion of each of said elements in com
mon with‘the respective secondary-circuit. said
circuit of said ?rst pair and the primary circuit
of said second pair, each of said circuits including
a main inductance and a main capacitance,
circuits‘ being tuned to resonance when said
capacitance of each‘ of said circuits, an inductive ,
resonance bandwidth.
switching means is in said ?rst position whereby
means for electromagnetically and electro- '
in said ‘second position said secondary circuits are
statically shielding the main inductance and main‘ 15 detuned oppositely to'provide a broad over-all
reactance element connected in series with the
main inductance of one of said primary circuits,
a capacitive reactance element connected in
Y 3. sperm.
GEORGE o. YOUNG.
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