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Патент USA US2120998

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June 21, 1938.
A. w. BARBER
2,120,998
COUPLED CIRCUITS
Filed Feb. 3, 1936
INVENTOR
gums
Patented June 21, 1938
UNITED STATES PATENT OF'FlCE "
2,120,998
COUPLED CIRCUITS
Alfred W. Barber, Flushing, N. Y.
Application February 3, 1936, Serial No. 62,074
15 Claims.
(Cl. 179-171)
This present invention of mine concerns im
provements in carrier wave receiver circuits. It
the automatic control of radio or carrier wave
receiver response by means of automatic inter
stage circuit coupling control.
with manual control.
particularly concerns methods of, and means for,
One object of my invention is to provide means
for the automatic control of radio or carrier
wave receiver or ampli?er response. Another ob
10
15
20
25
30
35
ening response when receiving conditions permit.
Since the possibility of using broadened response
usually occurs on strong stations‘, I have found
it possible to control coupling automatically as a
function of signal strength and thus do‘ away
'
In my copending application, I have shown how
automatic coupling may be provided in the con- '
trol of thermionic vacuum tube input capacity.
ject is to provide automatic control of interstage The dynamic input capacity of a thermionic
circuit coupling in carrier wave ampli?ers. A vacuum; tube depends mainly on the grid to plate
capacity and grid to plate gain of the tube.
further object is to provide automatic circuit cou
pling means easily controlled over a wide range Since the tube gain‘may be controlled by means
of its grid bias, the input capacity may also be
of responses.
In my copending application for Letters Pat- controlled by grid bias changes. If the bias is
ent dated January 2'7, 1936 and entitled “Coupled ' derived, in part, from the recti?ed signal travers
circuit systems” Serial No. 61,458, I have shown, ing the receiver or ampli?er, the couplingand
circuit coupling means consisting of the grid hence band-pass characteristics may be made to
to cathode capacity of a thermionic vacuum ‘automatically follow the received signal strength.
My present‘ invention makes use of this same
tube. I have also shown how the grid to cath
ode capacity and hence the coupling may be‘ controlled tube input capacity‘ but the sensitivity
of the control is greatly increased by using
controlled by varying the grid bias in the cou
resonant or partly resonant coupling means.
pling tube. Further, I have shown how this con
trol may be effected from‘ the recti?ed signal, The tube input capacity is used in conjunction
and hence the coupling and ampli?er response ‘with inductive coupling means and by ‘means of
made to automatically vary with the strength of series resonance, the coupling is made to vary
the, received signal. My present invention is a more rapidly as a function of tube gain than in
system devised for thesame purpose but showing the simple common impedance type of coupling.
I have found it possible to vary a 500 k. c. tuned
a more sensitive control characteristic.
pair'of circuits from a single peaked response
In radio and carrier wave ampli?ers the inter
stage selective means usually consists of pairs of to a 30 k. c. band-pass by varying the grid bias
tuned circuits. If ‘the two circuits comprising of a 1500 micromho mutual conductance vacuum
each pair are coupled together by varying tube by an amount to cause the plate current to
amounts, three general types of response are change from zero to 5 milliamperes.
The appended claims set forth, in particular,
possible. With less than a particular coupling
called “critical”, the response of two circuits the novel features to be found in this invention.
tuned to the same frequency is a single peak but The following ‘description, however, when taken
the amplitude of transmission becomes less as in connection with the drawing, will serve to
the coupling is decreased. At critical coupling set forth the theory and mode of operation of
40 the response is still a single peak but with some
broadening of the peak and a maximum ampli
tude of transmission. If the coupling is “in
creased above critical, the amplitude of response
remains the same but asecond peak appears and
45 as the coupling is increased, the frequency of
my invention.
'
-
obtainable selectivity in a radio receiver which 7
ation of my invention.
Due to receiving condi
50 requires critical coupling or less between inter
stage circuits.
However, under this condition
most systems produce serious attenuation of
speaker.
?rst detector I, intermediate frequency ampli?ers
some receivers manual means have been pro
55 vided for increasing coupling and hence broad
30
~
40
In Fig. 1, I have shown a superheterodyne re
ceiver exclusive of the audio ampli?er and loud
modulationfrequencies above 3000 cycles.
In
>
‘ Fig. 1 shows the circuit of a radio receiver,
tions, it is often necessary to use the maximum
the tuning frequency.
_
In the drawing,
up. to and including the second detector, em
bodying my invention.
Fig. 2 shows the equivalent circuit of two tuned
circuits coupled by my present system.
Fig. 3 shows a circuit equivalent to 'Fig. 2.
'Fig. 4 shows curves characteristic of the oper
the second response moves further away from
a
The tube complement consists of, a ‘
2 and 3, second detector 4, oscillator 5 and cou
pling tubes v6 and l. The ?rst detector-oscillator
2
2,120,998
circuits are conventional. +EB denotes points of
connection of plate voltage supply and +En de
notes points of connection of screen voltage sup
ply. Between plate 8 of the ?rst detector l and
the plate voltage supply is connected a tuned cir
cuit consisting of coil 9 tuned by condenser l0.
Coil 9 and condenser [0 form the tuned primary
of an interstage transformer. Coil H tuned by
condenser 12 forms the tuned secondary of the
proached and by proper choice of circuit elements
a wide range of control slopes may be obtained.
Fig. 3 shows a circuit equivalent to Fig. 2 in
terms of mutual and leakage inductance all re
duced to unity turns ratio. M12 is the mutual in
ductance between L1 and L2 and m4 is the mu
tual inductance between L3 and L4.
This circuit
shows that the series resonant coupling imped
magnetically coupled to primary coil and coil . l5
ance is not accurately L2, L3 and C23 but is
LziMiz plus L3iM34 and C23 in series. ‘Looking at 10
the system thus from the standpoint of an equiv
alent circuit, C23 is equivalent to a “high side”
coupling reactance and resonates with the leak
magnetically coupled to secondary coil H and an
age reactance of L2 and In to provide a sharp
10 interstage transformer feeding .grid l3 of the fol
lowing ampli?er tube 2. Coupling between coils
9 and II is accomplished by means of coil l4
15 external series impedance thru condenser VI 6. The
voltage induced in coil l4 from coil .9 causesa
current to ?ow in coil ill of a magnitude de
pending on the impedances of coils ‘I4 and ‘I 5 ‘and
the impedance between the lower end of coil.
20 l4 and ground. This impedance is condenser
[6 in series with the ‘input‘or grid to cathode
dynamic ‘impedance of tube *6. This input im
pedanceis essentially a capacity reactance. Con
denser i6 is shown as a'blocking- condenser having
25 -a capacitylarge compared 'to the tube input ca
pacity.
The controlled current ?owing in the
series circuit ?owsvthru 'coil I5 inducing a volt
agelinlcoil'll whichis afunction of the current.
The equivalent "circuit-of this coupling system
30 .isshown in Fig. 2 where the primary-circuit con
sists-of inductance Lrtunedby condenser 01, and
the secondary circuit consists'of inductance L4
tuned byrcondenserC-i. Coupling between L1 and
L4 is:accomplished by ‘thecoupling ‘link consist
.35 ing-of inductances L2 and L3 and condenser C‘zs
.all in series. vL2 iscmagnetically'coupled to L1 .and
Lsis .magneticallycoupled toL4. L1 induces a
.voltageinLz. and a'current ?owsin the L2, L3, C23
seriescircuit. Since-Czsis variable ‘the current
depends on .the value ofCza ‘and ‘the'voltage vin
duced in Lil-depends on thiscurrent ?owing in
L3. It should be.noted that if at the operating
frequency, C23 resonates L2 and L3 in series, a
series resonant circuit is produced in which the
45 series current increases very rapidly as C23 is
varied. C23 represents the grid to-cathode ‘ca
pacity of tube 6 or 1 in Fig. 1.
Fig. 4 shows .aplot of reactance against bias
where bias designates the variable component of
the bias'appliedto the-grids of thecoupling tubes
.6 or .1.
Thehorizontal axis may also. be con
denser capacity inorderzto explain Fig. 2. Luis
the reactance of Lz-and L3 (or'coil “and coil H3)
in series.
__1_
Co:
is the reactance of C23 (orthe input capacity of
tubes “6 or 1) as the'capacity is'varied. The re
actance of the series circuit is then shown by the
60 curve
-
1
Leo ~65
The increase in sensitivity of the tuning eiiect
over the simpleself-reactance coupling is shown
by comparingthelast two curves. Starting with
a bias or condensersetting athe bias-or capacity
alone mustbevaried to point 0 in order to halve
the series coupling reactance. However, with the
70 inductance added the reactance is halved in go
ing from a to b on the
1
Leo-a
curve. The apparent sharpening of control be
75 comes greateras the series resonant point is ap
coupling eiTect.
15
Returning to Fig. 1 the input capacity of tube
‘6 is equivalent to condenser C23 of Figs. 2, 3 and
4. This input capacity depends on the tube
characteristics, operating voltages, plate load
and grid to plate capacity. Actually it depends 20
on the-tube grid to plate gain and grid to plate
capacity. With no external applied bias the tube
gain'depends on the tube characteristics, plate
voltage ‘EB, cathode bias E0 and plate load re
sistor I1. While I .have found the simple re 25
sistor I‘! to be a satisfactory load, a complex im
pedance may be used. The‘tube is not limited to
~a triode although I prefer'one. Tube'? is shown
having a cathode 18, heated'by means not shown,
a control grid l9 and a plate .20. The grid to :30
plate capacity 2! maybe taken to represent the
internal tube capacity plus external added ca
pacity. The initial bias is provided by battery
E0 in the cathode circuit. The control bias is
supplied thru the resistor 22. Condensers 23 and 35
Marc by-pass condensers.
The circuit ‘is de
signed so that With no external applied bias thru
resistors 22 and 25, the circuit coupling is the
minimum desired which will'in general be-criti
.cal- coupling, for maximum selectivity and gain. 40
If an external positive bias is applied to grid IS,
the gain of tube 6 is increased increasing its in
put capacity. Increasing the input capacity in
creases the current ?owing in the coupling cir
cuit increasing the coupling. As the coupling is 45
increased over critical, a-double peak appears in
the response :producing a band-pass character
istic.
The same coupling system is shown between
tubes 2 and 3 that was shown and described be 50
tween tubes 1 and 2. Tube 3~feeds a tuned out
put circuit consisting. of inductance'26 tuned by
condenser 21. The double diode second detector
'4.is fedfrom coils 28 and 29 magnetically coupled
to coil 26. The voltageacross coil 28 is impressed 55
on the diode formed by plate 30 and cathode 3|
thru'the load by-pass condenser 32. The load
resistor 33 develops a recti?ed current voltage
drop which maybe used for automatic volume
control of tubes 2 and '3 by applying the drop to 60
grids l3 ‘thru‘the ?lter consisting of resistors 34
and .35 and the condensers 36 and .31.
The audio
voltage for actuating the audio ampli?er and
speaker may also be obtained from the drop across
resistor 33 or a separate recti?er may be employed. 65
The voltage across coil 29 is applied to the
diode consisting of plate 38 and cathode '39 thru
the by-pass condenser 40. The recti?ed output
is a drop thru resistor ‘4| and the direct current
component is ?ltered out by means of resistors
25 and condensers 23.
This direct current com
ponent is proportional to the signal output from
tube 3 and is a function of the signal picked up
by antenna A. Since the cathode 39 end of load
resistor-‘4| becomesmore positive thegreater the
2,120,998
signal received, the external bias supplied by
recti?cation to tubes 6 and ‘I is more positive the
greater the signal. As shown above the more
positive the externalbias, the greater the input
capacity to tubes 6 and 1 and the greater the
coupling between the interstage circuits. Thus
the system provides a response which is a func- '
tion of the received signal and the stronger the
received signal the wider the response band and
the better the ampli?er ?delity.
While not in any way. intended to limit the scope
of my invention, I have found the following con
stants to give the indicated expansion:
Tube 0 or ‘I mutual conductance at normal
15 bias 1450
Resistor-22 ______ -l ___________ __ohms__ 500,000
Bias Ec _______________________ __volts__
Plate voltage Eb _______________ __do____
25
250
Resistor ll _____________ _‘_ ____ __ohms__
400
Internal part of condenser 2|____mmf__
50
6
20 External part of condenser 2l____mmf__
Condenser l6 _____ __, ___________ __mmf__
25
2000 _
Coil 9 __________________________ __mh__
1
Coil l I ____________ _'_ ___________ __mh__
Coil I4 ___________ __-_ ___________ __mh__
0.3
.Coil l5 _________________________ __mh__
0.3
1
Condenser It to tune coil 9 to 547 k. c.
Condenser, it to tune coil H to 547 k. c.
coils ii and I5 close.
Coupling with no external grid bias very nearly
critical giving single response peak, with plate
current zero.
With external bias to give plate current 5 ma.
over coup-ling produced giving two ‘peaks sepa
rated 30 k. c.
s
1
A set of typical results is here shown as peak
frequencies for various coupling tube plate cur
40
rents.
apparent to one skilled in the art that many
modi?cations are possible without departing from '
its spirit and scope as set forth in the appended
claims.
What I‘claim is:
1.‘ In a selective carrier wave ampli?er, means
for varying the selectivity 'of said ampli?er com
prising the combination of at least two thermionic
Vacuum tube repeaters, a resonant circuit receiv
ing the output of one of said repeaters, a second 10
resonant circuit connected across the input of
another of said repeaters, a series circuit com
prising two coils, a condenser and the grid to
cathode impedance of a third thermionic vac
uum tube comprising at least a grid, cathode and 15
plate wherein one of said coils is magnetically
coupled to one of said resonant circuits and the
other of said coils is magnetically coupled to the
other of said resonant circuits whereby energy is
transferred from one of said resonant circuits to
the other wherein said impedance includes a ca
pacity reactance component of greater magni
tude than the combined inductive reactances of
said two coils at the resonant frequency of at
least one of said resonant circuits.
‘ 25
2. The combination as set forth in claim 1 and
including means for supplying a bias to the grid
of said third vacuum tube at least in part derived
by rectifying the signal traversing said ampli?er.
Coupling between coils 9 and I4 and between
35
3
‘
3. The combination as set forth in claim'l and 30
including means for applying a bias to the grid
of said third vacuum tube greater than that re
quired for plate current cut-off for all received
signals below a predetermined level.
4. In a radio receiver employing thermionic 35
vacuum tube repeaters, an interstage coupling
circuit comprising tuned input and output coils
and a link circuit, a thermionic vacuum tube
comprising at least a grid, cathode and plate, said
link circuit including in series connection two 40
coils and the grid to cathode impedance of the
0 ma.
Peak 547 k. 0.
45
last said thermionic vacuum tube all connected
20 ma.
Peck 547
Peak 497
in series, wherein said link is adapted to transfer
energy between said tuned circuits by virtue of
c.
magnetic coupling between one of said coils and 45
. 0
said output circuit, the coupling between other
An eifective delayed expansion may be pro
duced by increasing E0 beyond cut-off.
Since no
expansion will take place until the coupling tubes
50 6 and ‘i draw plate current, the delay depends on
the amount the bias E0 exceeds the cut-off bias of
tubes 6 and 1. Suppose for instance 25 volts is
the bias required for cut-off then if EC is made 40
volts it will take 15 volts of external bias to bring
55 the 40 volts to a net 25 volt bias. If 15 volts on
the recti?er corresponds to 1’ millivolt on the an
tenna, no expansion will take place until the re
ceived signal exceeds 1 millivolt. As the net
bias is reduced below 25 volts the coupling in
creases expanding the receiver response.
While I have shown my automatic coupling
system applied to intermediate frequency ampli
?er circuits, it is by no means thus limited but
may be applied to variably tuned stages such as
v65 in a tuned radio frequency receiver or in the pre
selector circuits of a superheterodyne.
Many
combinations are possible such as equal expan
sion control on two intermediate frequency
stages; a control with a different delay control
70 on a third intermediate stage and a control with
a still different delay value on the pre-selector
circuits.
-
While I have described only one system whereby
my invention may be carried into effect and have
pointed out a few possible variations, it will be
of said coils and said-input circuit and the series
connected input impedance of the last said tube
and including a condenser between gridand plate
of the last said vacuum tube and a load resistor 50
in series with said plate whereby the input-im
pedance of the last said tube exhibits a capacity
reactance‘ greater than the inductive reactance
of said two coilsin series at the resonant fre
quency of said tuned input coil.
55
5. In a selective carrier wave ampli?er, means
for varyingthe selectivity of said ampli?er com
prising the combination of at least two resonant
circuits and a coupling link between said circuits, 60
said link comprising in series at. least one coil
magnetically coupled to each of said resonant
circuits and the grid to cathode capacity of a
thermionic vacuum tube, means for causing said
grid to cathode capacity to vary as a function of 65
the amplitude of the signals traversing said am
pli?er when said signals are greater than a pre
determined amplitude.
6. The combination as set forth in claim 5
wherein at the frequency of resonance of said 70
resonant circuits the capacity reactance of said
grid to cathode impedance is greater than the
sum of the inductive reactances of said coils.
7.‘In the intermediate frequency ampli?er of
a superheterodyne radio receiver, the combina-' 75
4
12,120,998
tion of a plurality of thermionic repeaters, at
least two pairs of input and output resonant cir
cuits associated with said repeaters, energy trans
fer means linking said input and output circuits
in said pairs, in which said transfer means com
prises series circuits consisting of a coil coupled
12. The combination as set forth in claim 10
wherein the capacity reactance component of
said vacuum tube input impedance is a function i
to an input circuit and a second coil coupled to
of the amplitude of the signal traversing said am
pli?er when said signal is greater than a prede
the output circuit of a pair and the input im
termined value.
pedance of a thermionic vacuum tube and means
13. In a radio receiver embodying thermionic
vacuum repeater tubes, the combination of at
10 for causing said input impedance to exhibit a
capacity reactance component greater in magni
tude than the sum of the inductive reactances of
.15
quired ‘to produce plate current cut-off in said
vacuum tube.
least one interstage coupling system comprising
an input and an output tuned circuit and an in
said two coils at the intermediate frequency of
tercircuit coupling impedance, said coupling im
said receiver.
pedance consisting of inductive means resonated
to a frequency greater than the resonant fre 15
'
8. The combination as set forth in claim 7 and
including means for applying a control bias to
said vacuum tube which is proportional to the
di?erence between an initial ?xed bias and a
bias derived by recti?cation of the signal'travers
v20 ing said ampli?er.
9. The combination as set forth in claim 7 in
which the said vacuum tube embodies a cathode,
a grid and a plate, and is associated with an ex,
ternal circuit comprising a capacity connected
,25 between said grid and said plate and a resistor
in series with said plate and means for applying
a control bias to said grid equal to the difference
between a ?xed voltage and a voltage derived by
recti?cation of the signal traversing said ampli
30 ~?er.
10. In a carrier wave ampli?er, the combina
tion of at least two thermionic repeaters, a reso
nant circuit connected to the plate of one of said
repeaters and a second resonant circuit connected
to the grid of another of said repeaters, two coils
and the input impedance of a thermionic vacuum
tube connected in series, wherein one of said coils
is magnetically coupled to said plate connected
resonant circuit and the other of said coils is
40 magnetically coupled to said grid connected res
onant circuit, said vacuum tubeincluding a cath
ode, a grid and a plate, means associated with
said vacuum tube including a capacity connected
between said tube grid and said tube plate, a re
V45 sistance connected between said tube plate and a
source of positive potential, and external grid
bias means comprising a source of ?xed-bias and
the direct current component of recti?cation of
the signal traversing said ampli?er acting in op
50 position wherein the input impedance of said
vacuum tube exhibits a capacity reactance com
ponent of greater magnitude at ‘all times than
the inductive reactance of the two said coils in
55 series at the resonant frequency‘of one of said
resonant circuits. '
11. The combination as set forth in claim 10
wherein said ?xed bias is greater than that re
quency of either of said tuned circuits by an elec
trically controlled capacity means comprising the
dynamic grid to cathode capacity of a thermionic
Vacuum tube wherein, said combination includes
a condenser connected between grid and plate of :20
the last said vacuum tube.
14. In a selective system, the combination of
two tuned circuits and intercircuit coupling
means comprising two coils and the dynamic grid
to cathode impedance of a thermionic vacuum
tube triode connected in series, wherein one of
said coils is coupled to one of said tuned circuits
and the other of said coils is coupled to the other
of said tuned circuits and including a condenser
connected between the grid and plate of said tri 30
ode wherein said condenser has a reactance great
er than the combined inductive reactances of said
two coils.
15. In a carrier wave ampli?er, automatic
band-pass control means comprising a thermionic 35
vacuum tube feeding a tuned circuit, a second
tuned circuit feeding into a second thermionic
vacuum tube, two coils and an electronically con
trolled capacity connected in series, wherein one
of said c'oils is magnetically coupled to the ?rst
of said tuned circuits and the second of said
coils is magnetically coupled to the second of
said tuned circuits and wherein said electronically
controlled capacity comprises the effective grid
to cathode capacity of a third thermionic vacuum
tube, said third tube comprising at least acath
ode, grid and plate, and further means comprising
a condenser connected between plate and grid
of said third tube and a load resistor in series
with the plate of said third tube, means for ap~ :50
plying a bias to the grid of said third tube at
least in part derived from the recti?cation of sig
nals traversing said ampli?er wherein the ‘mini
mum Value of said electronically controlled ca
pacity resonates said two coils in series to a fre
quency greater than the resonant frequency of
either of said tuned circuits.
ALFRED W. BARBER.
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