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Патент USA US2121427

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June 21, 1938.
L. T. FOWLER
2,121,427
SENSITIVITY CONTROL SYSTEM FOR AUTOMOBILE RADIO RECEIVERS
Filed April 50, 1957
2,121,27
Patented June 21, 1938
~ UNITED STATES PATENT orrior ,
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2,121,427
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1 ‘SENSITIVITY CONTROL‘ SYSTEM FOR.
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‘AUTOMOBILEI‘RADIO
Lester
RECEIVERS
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Fdwler, Oaklyn, N. J., assignor to Radio ;
Corporation of America, a corporation of, JDela-f
ware
Application April so, 1937, SerialNo.‘ 140,064"
10 Claims. (01. 25o_20)' . .
"The present‘ invention‘ireIa'tes to a sensitivity connection with the cathode circuits of any of
control‘ system for automobile radio receivers and the ampli?er tubes, whereby interference pick-up
thelikegwhichiare normally subjected to ignition
is vreduced to a minimum.
-
tended control circuit from‘the receiving appa
stood from theT'following‘ description,»when con- 5
sidered in connection with the accompanying
drawings, and its scope ‘will be pointed out in the
ratus and which does not introduce interference
appended claims,‘
signals into the receiving apparatus.
Inthe drawing, Figure 1 is a‘ schematic circuit
diagram of a portion of a'ra‘dio receiver for auto- 10
mobiles ‘and the like provided with a sensitivityv
control system embodying‘the invention, and
‘ the character referred to‘which permits of an ex
ll) I‘Sin'ce'the sensitivity control for automobile re
ceivers and the like must be‘ ‘extended to the in
strument panelof the automobile, the control
circuit is external to the receiver and'is connected
thereto ‘by ‘a‘cable: ‘The usual method of pro
viding a sensitivity control for such receivers in
cludes ‘the use of a variable resistorlin the cathode
to ignition interference ‘and the extension of such
having a cathode ‘8, a detector diode anode 9
to prevent picking up ignition and» other inter
‘
connected with the tuned‘ secondary circuit iii of v
the transformer 6, an automatic volume ‘control
diode anode ll connected with the tuned primary
>
Cathode. resistor control» of the intermediate
25 frequency ampli?er tubes alone is unsatisfactory,
although’ less sensitive to interference. Control
of the ‘intermediate-‘frequency 'ampli?er'tube or
tubes‘ requires biasing to such a'wi'cle degree that
the‘itubeslose ‘sufficientlpower to *drive the diode
.30 recti?er-or second; detector. Also, with this meth
od of control, the distortion increases andv addi-‘ ,
tional second harmonic signals are generatedin
the plate circuitv of' the intermediate frequency am
pli?er tube ortubesa This causes the beat note
condition to be. worse than normal, so that ‘addit
tional ?ltering is necessary to suppressthe‘ beat
notes.
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It is, therefore, a further object of the‘ present
invention to provide a sensitivity control system
.40 foruautomobile radio. receivers and the like which
effectively overcomes substantially all of the above
disadvantagesrand. which'is at the‘ same tim
easily p'r‘ovidedat low cost.
‘
In 1a ‘radio. receiving "system, the automatic
‘ volume control circuit is provided with suitable
?lters comprising series- resistors and by-pass ca
pacitors for decoupling the controlled grids from
the automatic volume-controlbias source‘. It is,
therefore, a-‘furtherob'ject of-the present‘inven
‘ tion‘ to provide ‘a‘ sensitivity control‘system‘ for
automobile’radio receivers and the‘llke having a
?ltered automatic'volume, controli‘circuit which is
applied ‘to the return ‘circuit of the‘ automatic
control means to take advantage of the inherent
I‘ ?ltering and without resulting in any control
‘1
an intermediate‘ifrequency coupling transformer
'6 with a‘second detector’ and ampli?er tube 1.
The latter is of the double-diode, triode type,
. circuits involves additional ‘?lters and ‘shielding
‘
v
Referring‘ to‘ Fig. 1, 5 is an‘intermediate fre
quency ‘ampli?er tube ‘which iscoupled through
tector tube.“ Suchg tubes 'are‘essentially sensitive
ference.
‘
Figure 2 is asimilar schematic circuit diagram,
being a portion of the circuit of Fig. 1‘, showing
a modification of the sensitivity control circuit. 15
circuit»=of“0ne ormoreof the radio or‘intermediate
frequency ampli?er tubes, as wellas'the ?rst de
35
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The invention will, however, be better under
and other‘interferencaand has‘for its object to
provide an improved sensitivity control system of
circuit‘ |2 of theitra‘nsformer 6 through a coupling
capacitor I3, and having‘a control grid l4 and an
output anode 15 for the triode ampli?er portion
thereof." The cathode B is connected to chassis
or ground I 6, which isalso the automatic volume
control return circuit, through a self bias‘ or
cathode resistor comprising three sections l1, l8
and I9 providedwitha by-pass capacitor 20.
The control grid I4 is arranged to receive‘ audio
frequency signals‘ from the "detector ,diode 9,
through a diodevoutput resistor 2| and a shunt 35 ‘
Volume. control resistor 22,“conneced therewith
through a couplingl‘capacito'r 23. The grid It
receives a biasing potential‘ from a tap 24 between
the resistor sections l8 and I9, to which tap point
the volume ‘control resistor 22 is connected at its 4.0
low potential‘end‘, asshown‘.
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' The output‘L anode “l5'lo'f the‘ triode section is
coupled" through" suitable resistance coupling
means‘ 25 withv‘a ?rst audio frequency ampli?er v
tube26,‘ in the‘ output anode circuit 21 of'which 45‘
an ‘output coupling device 28 is provided for con
nection with additional ampli?er stages or other
output devices-(not shown). The ampli?er stage
26 is‘provided witha tone control means com
prising a capacitorfSU ‘connected to the output 50
circuit 21 and having‘ a control lead 3| connected
through a lead 32 ‘in an extension cable 33, with
atone control resistor 34 adapted for mounting
on the instrument panel of the automobile. A
ground lead‘35‘connected‘ with the chassis I6 is 55
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2,121,427
extended through a lead 36 in the cable 33 to a
manually adjustable tone control contact 31 in
connection with the resistor 34, whereby the tone
is controllable in a well known manner, the re
sistance in circuit with the capacitor 30 being
ireduced to reduce the high frequency response
sistance for such self bias use by an amount such
that the cathodes of the controlled tubes, such as
the cathode 50, may have a positive potential
with respect to ground or chassis su?icient to
provide the grids, such as the grid 48, with a
of the capacitor across the signal circuit.
The automatic volume control circuit is con
drop in potential through the self bias or cathode
resistor 52 is therefore greater than the‘ drop in
normal negative bias in the absence of signals,
of the ampli?er by the increased shunting action ~ whereby maximum sensitivity is obtained. The
_10 nected with the diode anode II, which receives
signals from the primary of the transformer B
and is thereby more broadly responsive than the
secondary. The diode circuit is provided by a
diode output resistor 40 connected between the
potential through the ?xed potential source in 10
the automatic volume'control return circuit at
l9, whereby the predominating bias potential on
the grid is negative by the desired amount over
provided by the drop through the resistors 11
the positive bias set up‘ in the potential source i 9.
If, now, the automatic volume control return 15
terminal 24 is connected to chassis or ground I6,
it will be seen that the grids of the controlled
tubes will become more negative with respect to
and I8. It will be noted that a lesser delay
20 potential is placed on the diode anode 9 for the
their cathodes by the amount of the potential 4
provided by the resistor I9 and the over-all sensi 20
diode anode H and the terminal 24 or other
suitable tap along the cathode resistor. This
places a delay potential on the diode anode ll
detector through the connection of the detector
output resistor 2| with a tap point 4| between
the resistor sections I1 and i8.
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for receiving local signalsrwithout' interference.
The automatic volume control potentials de
veloped across the resistor 40 are applied to an
automatic volume control lead "for the preced
ing ampli?er tubes, through a series ?lter resistor
43 and a second ?lter resistor 44, for which by
pass capacitors 45—45 are provided.
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30 ' The controlled ampli?er tubes, represented by
‘the intermediate frequency ampli?er tube 5, are
connected with the automatic volume control lead
42 through suitable leads indicated at 46, and 41.
In the present example, the control grid 48 of
the ampli?er 5 is connected through the input
circuit 49 with the lead 46, While the cathode 50
is connected to chassis or ground 5!’ through a
self bias resistor "52. Other-ampli?er tubes (not
40
shown) are'connected in a similar manner to the
chassis and automatic .yolume 'control' lead 41,
whereby the chassis provides the automatic
volume control return circuit connection.
.
Intermediate frequency signals are applied to
the second detectorand automatic Volume con
45 trolmeans included in the tube ‘land associated
,circu'its, through the ampli?er} from an inter
mediate frequency input transformer 53, the
secondary of which is included'in the input cir
, cuit 49 and the primary 54 of which may be
50 included in the anode output circuit of either the
?rst detector or apreceding intermediate fre
quency ampli?er tube (not shown), as is well
understood.
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tivity of the receiver-will be reduced accordingly,
to some desired lower value, suitable, for example,
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The automatic volume control lead 41 may be
55 connected with any of the preceding gain con
trol tubes as normallyused in 1a receiver such as
the usual’ radio frequency ampli?er, ?rst detector,
and other intermediate frequency ampli?er tubes,
This control maybe e?ected by extending a. lead
60 from the terminal 24, through a cable lead 6| 25
in the cable 33. to a switch 52 representing any
suitable control device for grounding the lead 6|.
In the present case, the switch serves to connect
the lead 6! to ground through the leads 36 and 35.
Because of the connection provided with the 30
ground return circuit of the automatic volume
' control system as shown, interference. from
ignition ,orother sources introducedinto the ex
tension leads 36 and 6! have no effect upon the
receiving circuits because of the ?ltering in the 35
automatic volume control circuit, and, the fact
that the controlled potential source is connected
adjacent to ground;
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Theextensible control circuit shown may be
connected with the receiver through terminals 40
indicated ‘at 63‘ and the control leads may in
certain, cases‘ be grounded-at R. F. and I. F.
potentials to the cable shield 33 and ground or
chassis 64 andg65 through suitable high frequency
by-pass capacitors 66 and 61 at the receiver ter
45
minals. The by-pass connections at this point
are effective in' removing ultrahigh frequency
disturbances from the internal circuits of the
receiver and in further isolating the same elec
trically' from the external-circuits connected 50
therewith:
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The circuit shown has been found to be ‘satis
factory in connection with automobile receivers
operating in the presence of heavy ignition and
other interference potentials. Furthermore, the 55
two-point sensitivity control is effective to pro
vide what may be termed local and distance re
ceiving conditions; depending upon the particular
the connections being asshownifor the tube 5. tubes used, andthe amount of potential change
60 In this circuit, the biasingpotential between grid
'required, for reducing the sensitivity for local 60
and cathode'is provided-by the automatic volume receiving conditions.
control diode output resistor 40 and thecathode
-The range vof control is determined 'by-the
resistor [9 as two potential ‘sources, together‘with potential established. across the auxiliary or
the ‘potential source provided by 'the self bias sensitivity control resistor l9 provided asthe
65 resistor 52 at the ampli?er tube. The polarity 'of
?xed potential source in the automatic volume 65
these sources is indicated adjacent thereto.
The bias circuit arrangement is such that the
automatic volume ‘control diode resistor 40, in
stead of being returned‘ directly to ground or
70 chassis I6, is returned thereto through the poten~
tial source l9 which‘is positive at ‘the terminal
’ 24 with respect to ground or chassis by an amount
determined by the degree of sensitivity control
which is desired. The self bias resistors, such as
75 the resistor 52, are of a higher than ‘normal re‘
control circuit return lead to ground or chassis.
In case, as is desirable, the ?xed potential
source for the sensitivity control is provided as'a
part of the cathode resistor of the combined
second detector and ampli?er-tube, the resistance 70
of the resistor section I 9 should be relatively'low
with respect to the resistance of the remainder of
the resistor comprising sections i7 and I8, in
order that as the sensitivity control section is
short-circuitedithe change in the bias on the 76
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2,121,427
triode section‘of‘ the detector ampli?er and'auto
‘Iqclaim as my‘ invention:
matic volume control tube‘l imay‘not be too great
for its proper operation. However,"t any suitable
?xed source of biasing potentialumay'be utilized
in place of the cathode resistor 7section‘ 19 in a
‘ LR'I'he combination with an automobile radio
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receiving systemhaving automatic volume con‘—'
trol ‘means, of» an extensible sensitivity control
circuit‘ for said system comprising a chassis
ground lead and a ground return lead for said
receiver.
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‘ If variable control of the sensitivity is desired, automatic volume control means, means provid
the automatic volume’control lead to the source ing a controllable connection between said leads
at a point remote from said receiving system to
control the sensitivity between predetermined 10
at the terminal 2'4 may be made variable, or the
I9 maybe extended externally of‘ the re
“10 section
ceiver and a‘variable return connection may be
limits, and means providing a source of poten
tial between said leads in circuit with said auto
matic volume control means and in opposition to
made therewith as shown‘in' Fig. 2, to which at
tention is now directed, and in which like circuits
'and circuitvelements as in Fig. 1 are designated
by the same reference numerals.
In‘this case, the terminal 24 and the ground
the biasingpotential provided by said automatic
volume control means in response to signals, the 15
potential of said source being of a predetermined
[6 ‘are connected through the leads GI] and 35
value determining the'range of sensitivity‘ control
with the cableleads 6| ‘and_36, respectively, as
ef‘fective- at said remote control point.~
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2.‘ The combination with an automobile radio
receiving system having automatic volume con
beiore, which‘termin‘ate in a’ potentiometer re
2o sistor 10 having a movable contact ‘H connected
through a cable lead 12 with a leadl3 in the re . trol means, of a remote control system having an
ceiver for the automatic volume ‘control ground extensible control circuit comprising a chassis
return from the automatic volume control diode
output resistor 40, whereby the said lead is vari
25 ably connected with the potential source‘ l9. It
will be seen‘that movement of the potentiometer
contact ‘H permits a varying ‘potential to‘be ap
plied to the automatic volume control circuit in
opposition to the higher‘ than normal ‘biasing po
30 tential provided in connection with- each‘ampli
?er tube by the ‘self bias‘ grounded cathode re
sistors, thereby permitting the sensitivity to be
reduced gradually from‘a maximum to a‘mini
mum determined by the range“ of' potential varial
‘ tion available across the source l9.‘ In certain
cases, where interference is less=severe,i the re
sistor l9 may be omitted and the resistor 'Hl‘may
provide the potential droprequired-‘for-the range
of sensitivity control.
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In ‘the present case, the tone control'connec
40
tion is omitted, although ‘it "mayil‘be' "applied
. through the cable connection‘ in the‘ same manner
as shown‘ in the circuit of Fig.v 1.v The present
circuit, however, reduces the number of leads re
quired in the'cable which is extended to anysuit
able‘ location for the sensitivity control ‘device.
In either of the embodiments shown in ‘Figs. 1
and 2, the‘ operation of the automatic volume
control means isi’not impaired, since'the poten
tials set up across'the diode ‘output resistor‘ 40,
to
ground lead, a tone control circuit including said
lead,'and a ground return lead for the automatic
volume control system, means for connecting said 25
leads at a point remote from said receiving sys
tem to control the sensitivity and tone between
predetermined limits, and means providing a
source of potential between said ground and
ground return leads in opposition to a normal 30
biasing potential provided by said automatic vol
ume control means and of a predetermined value
determining the range of sensitivity control effec
tive at said remote control point.
3. The combination with anvautomobile radio 35
receiving system having automatic volume, con
trol means, of an extensible sensitivity control cir
cuit for said system comprising a chassis ground
leadand a ground return lead for said auto
matic volume control means, means providing a
controllable connection between said leads at a
point remote from said receiving system to con
trol the sensitivity between predetermined limits,
means providing a sourceof potential between
said leads in circuit with said automatic volume 45
control means and in opposition to biasing po
tential provided by said automatic volume con
trol means in response to signals, the potential
of‘ said source being ‘of a predetermined value
determining the range of sensitivity control effec
in the presence of ‘signals, serve further to in
crease the negative bias oi the controlled tubes,‘
and therefore reduce the gain Whether the sen
sitivity is' set for maximum or minimum or any
tive at said remote control point,‘said automatic
volume control means including a diode signal
intermediate position by‘ either‘of the means
tem, each of said tubes having a control grid
shown in Figs. 1 and“ 2.
connected with the negativeend of said output
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In either circuit, the sensitivity control'iis ap
40
recti?er having an output resistor and a plurality
of signal ampli?er tubes in said receiving sys
resistor, a ?lter in said connection, and said
plied in the ground return connection for the ' ground return lead for the automatic volume
automatic volume control circuit, the ‘latter being control‘sys‘tem being'connected with the opposite
provided with sui?cient ?xedrnegat‘ive rbiasing po
tential on the controlled tubes to overcome a
receiving system having automatic volume con
trol means, of a sensitivity control system having
trol desired for changing ther'receiving system
- an extensible ‘control circuit comprising a chassis
from a condition of maximum ‘sensitivity to a
ground lead and a ground return lead for, the
automatic volume control system, means for con
necting said leads at a point remote from said
receiving system to'control the sensitivity 'be
tween predetermined limits, means providing a
condition of reduced sensitivity‘for‘ the reception
r of local signals.‘
‘ With this arrangement, the series automatic
volume control source" of ‘variable potential may
operate effectively to control the gain‘loc'ally‘un
der-‘any c‘onditio'n‘of ‘s‘ensitivity‘an‘d theexternal
‘ circuits from the receiver are eifectively' isolated
from the receiving circuits through the normal
?lter provided inthe automatic‘ volume control
circuit.
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‘ 4. The combination with an automobile radio
a value‘ representing‘ the ‘range 1 of ‘ biasing ‘con
series‘?xed opposing ‘positive ‘biasing potential ‘of
76
end o'fsaid output resistor.
sourceof potential between said leads in opposi
tionto biasing potential provided by‘said auto
70
matic volume control means in response to sig
nals and of a predetermined value determining
the‘range of sensitivity control e?ective at said
remote control point, ‘said automatic volume 75,
.
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2,121,427
control means including a diode signal rec
ti?er having an output‘resistor and a plurality
of signal ampli?er tubes in said receiving ‘sys
tem, each of said tubes having a self bias resistor
connected with said chassis ground providing a
potential in excess of the potential of said source
maticvolumeicontrol potentials, of an output re
sistor'for said recti?er having a negative ter
minal; an automatic volume control circuit con
nected therewith,.?lter means in said connection
including a series high resistance element and
by an amount to provide maximum sensitivity in
the absence of received signals, each of said tubes
by-pass capacitor, means providing a ?xed bias
ing potential in said last named circuit in series
having a control gridconnected with the negative
with said output resistor connected between the
opposite end thereof and ground in said system, 10
a plurality of ampli?er tubes controlled by said
automatic volume control means, each of said
control tubes having a self bias resistor means
providing a biasing potential greater than said
?rst named potential by a predetermined amount 150
and in opposition thereto, and remote control
means for reducing the elfect of said ?rst named
potential in said automatic volume control cir
cuit comprising a circuit control device and cir
cuit leads connected therewith and with said ?rst 20
10 end of said output resistor, a ?lter in said con
nection, and said ground return lead for the
automatic volume control system being connected
with the opposite end of said output resistor.
5. The combination with a radio receiver hav
ing an automatic volume control circuit provided
with a grounded chassis return connection, of
means providing a ?xed source of positive bias
ing potential for said circuit in said ground re:
turn connection of a potential value correspond
20 ing to a desired change in sensitivity between a
condition of maximum and minimum sensitivity,
means in said automatic volume control circuit
providing a negative biasing potential in excess
of and in opposition to said ?rst named potential
25 by an amount su?icient to provide a predeter
mined maximum sensitivity, and means con
nected with said ?rst named potential source for
reducing said ?rst named potential thereby to
decrease the sensitivity of the receiving system
from maximum, an extensible control circuit for
said last named means connected with the auto
matic volume control circuit, and ?lter means in
said automatic volume control circuit for isolat
ing said extensible circuit from the, receiving
35
diode'signal recti?er adapted to provide auto
system.
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6. In a radio receiving system, the combination
with automatic volume control means and a plu
rality of ampli?er tubes controllable, thereby, of
an automatic volume control‘ circuit comprising
means providing a control’ potential responsive
to variations in received signal strength, ‘means
providing a return lead to aichassis ground for
said circuit, means in said lead providing a ?xed
source of biasing potential for said tubes, means
45 providing a second ?xed source of biasing poten
tial for said tubes,-the magnitude of which po
tential is in excess of the potential provided by
said ?rst named source and in opposition thereto
by an amount to provide a condition of maximum
named potential source.
9. In a radio receiving system, the combination
of an interstage ampli?er coupling transformer
having a primary winding and a secondary Wind
ing, a signal recti?er device including a cathode 25
and an anode, means for connecting said anode
with the primary winding to receive signal energy
therefrom, an output resistor for said signal recti
?er, means providing a common chassis ground
connection for said receiving system, a cathode 30
circuit resistor connected between said cathode
and said common chassis ground and having a
connection at the cathode end thereof with the
positive terminal of said output resistor, an auto
matic volume control circuit having a negative 36
biasing supply lead connected with the negative
terminal of said output resistor, ?lter means in
said connection comprising a series resistor and
a by-pass capacitor to the chassis ground from
said lead, means for applying direct current to 40
said cathode circuit resistor to cause a pre
determined potential drop therethrough to effect
a predetermined change in sensitivity of said re
ceiving system, a pair of shielded control leads
connected with said cathode circuitresistor, and 45
remote control means connected with said leads
and operative to connect the positive end of the
signal rectifier output resistor to chassis ground
to; the exclusion of said cathode circuit resistor,
sensitivity for said‘ receiving :system, sensitivity thereby to change the sensitivity of said receiving 50
control leads extending from-said ?rst named» system through a predetermined range dependent
source of biasing potential, and means connected upon said potential.
with said leads for connecting said automatic
10. In a radio receiving system, the combina
55
volume control return lead'to said chassis ground.
'7. In a radio receiving system, the combination
with automatic volume control means and a plu
rality of ampli?er tubes controllable thereby, of
an automatic volume control circuit comprising
means providing a controlling potential responé
60 sive to variations in received signal strength, a
chassis ground connection therefor, means in said
connection providing a ?xed source of biasing
potential, means providing a second ?xed source
of biasing potential for said controlled ampli?er
65 tubes,'the magnitude of which last named poten
, tial is in excess of the potential provided bysaid
?rst named source and in opposition thereto ‘by
an. amount to provide a condition of maximum
sensitivity for said receiving system,v sensitivity
70 control leads’extendingirom said ?rst named
source of ?xed-biasing potential, and means con
nected with said leads forvariably connecting
said automatic volume control circuit to ground.
8. In a radio receiving system, the combination
with automatic volume control means including a
tion with automatic volume control means includ
ing a diode signal recti?er adapted to provide 65
automatic volume control potentials, of an out
put resistor for said recti?er having a negative
terminal, an automatic volume control circuit
connected therewith, ?lter means in'said connec
tion, an ampli?er having a cathode circuit in~ 60
eluding a resistor providing a ?xed biasing po
tential in series with said output resistor and
connected with the opposite positive terminal of
said output, resistor at a point on said cathode
circuit resistor which is positive with respect to 65
ground, said ground providing a common return
connection for said automatic volume control
circuit, a plurality of ampli?er tubes connected
with said automatic volume control circuit to re
ceive biasing potential therefrom in response to 70
signals and from said ?xed biasing potential, each
of said control tubes having a self bias resistor
means connected between cathode and ground
and providing a biasing potential greater than
said ?rst ?xed biasing potential in opposition 75
2,121,427
' thereto and by a predetermined amount sufficient
to effect substantially maximum sensitivity,
means for reducing the effect of said ?xed biasing
potential on said automatic volume control cir
cuit comprising a circuit control device and ex
tended circuit leads connected therewith and with
5
said ?rst named potential source, and means'for '
shielding said leads including by-pass paths of
low alternating current impedance at the ter
minal of said leads at said receiving system.
LESTER T. FOWLER.
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