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Патент USA US2129021

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sept. 6, 1938.
2,129,021
M. G. NICHOLSON, JR
AUTOMATIC VOLUME CONTROL
Filed NOV. 25, 1931
2 Sheets-»Sheet l
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INVENTOR
BY
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ATTORNEY
Sept. 6, 1938.
l
M. G. NICHOLSON, JR
Y
2,129?021
AUTOMATIC VOLUME CONTROL
/80
#50
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ATTORN EY
Patented Sept. 6, 1938
2,129,021
UNITED STATES PATENT OFFICE
2,129,021
AUTOMATIC VOLUME CONTROL
Madison G. Nicholson, Jr., East Orange, N. J., as
signor, by mesne assignments, to Radio Corpo
ration of America, New York, N. Y., a corpora
tion of Delaware
Application November 25, 1931, Serial No.577,235
15 Claims. (Cl. 250-20)
'I‘his invention relates to automatic volume con
trol in radio receiving sets, and more particularly
is directed to the elimination of noise encoun
tered in tuning from one station to another.
In present day receiving sets it is common prac
tice to obtain automatic volume control through
automatic control of the radio frequency ampli
ñer. This form of control has two serious disad
vantages, namely, noise is encountered in tuning
from one station to another and exact tuning is
difficult unless a tuning meter is used.
It is an object of my invention to provide an
automatic volume control circuit arrangement
which eliminates noise when tuning between sta
15 tions.
It is another object to provide a circuit or
ganization in which automatic volume control
may be successfully applied Without using a tun
ing meter.
Another object of the invention is the provi
sion of a circuit organization in which certain
instrumentalitìes thereof are so connected as to
block signals below a certain level, which level
might be adjusted to pass only signals `strong
enough to be relatively free from noise disturb
ances.
«
the various circuit arrangements, reference may
be had to Fig. l. I have shown therein, by the
block diagram method, the incoming signal being
received by the radio frequency ampliñer. The
output of the radio frequency amplifier divides
into two circuits, one of which actuates the radio
frequency automatic volume control and the other
the detector. From the detector the output feeds
the audio frequency amplifier and thence to the
loud speaker. By this circuit arrangement noises 10
occurring between stations and the like would
be heard in the loud speaker when tuning from
one station to another.
.
By the introduction of a special automatic con
trolling circuit I largely overcome or eliminate 15
these noises entirely, depending upon the selec
tivity or non-selectivity of such controlling cir
cuit. This controlling circuit is actuated by the
output of the radio frequency ampliñer and con
trols the audio frequency amplifier output.
Asl
20
shown in Fig. l the controlling circuit may have
inserted therein any satisfactory form of selec
tive circuit such as a loosely coupled highly se
lective resonant circuit.
.
Referring to Fig. 2, which is intended to illus 25
trate my invention reduced to its simplest form,
To avoid the above mentioned difficulties and it will be seen `my controlling circuit may com
prise using the detector tube as both the detector
accomplish the objects of the invention I pro
pose to exercise control over the output of the , and the audio frequency automaticl volume con- '
A o
audio frequency ampliñer through a controlling
circuit actuated by the output of the radio fre
quency amplifier.
In the accompanying drawings:
Fig. 1 represents very schematicallythe gen
eral circuit arrangement of present _day automatic
volume control having associated therewith my
auxiliary circuit for effecting automatic volume
control of the audio frequency amplifier.
_ Fig. 2 represents schematically my invention
40 reduced to its simplest form.
' Y
Fig. 3 is a modification of the circuit arrange
ment shown in Fig. 2, this modification making
the control contemplated more positive.
Fig. 4 illustrates schematically the invention
45 embodied in a commercial form ofsuperhetero
dyne.
Fig. 5 represents another application of my in
vention of a circuit employing diode type detec
tion; and
50
a
Fig. 6 is a circuit arrangement whereby com
pensation is obtained in cases of inadequatecon
trol of the radio frequency automatic .volume con
trol.
To obtain a general understanding of the in
vention before proceeding to describe inndetail
trol.
Only such part of the apparatus is shown 30
in this and other circuits as is necessary to appre
ciate the working of the circuit. In this instance
the incoming signal comes from the plate of the
last radio frequency amplifying tube (which may
be in any conventional circuit) and is received 35
by the detector. The received signal in the de
tector causes an increase in the cathode current,
thereby raising its potential in the positive direc
tion. This potential is applied through an ap
propriate circuit (either resistive or inductive), 40
as grid bias to the ñrst audio frequency amplifier
which has been biased negatively to or beyond
the cut-off. It is seen that if the potential of the
cathode of the detector is raised sufliciently in
the positive direction the audio frequency ampli 45
ñer becomes operative. By suitable adjustment
and a selection of suitable resistances and poten
tials the circuit will be inoperative except for
signals above a certain value. The desired value
is one just above the existing noise level for a 50
given location. As indicative of what might be
satisfactory voltages for the 227 type tubes I have
given certain voltages but it is understood that
the same will vary with choice of resistances,
tubes, etc.
55
2,129,021
Referring to Fig. 3 there is shown a modifica
tion of the circuit arrangement of Fig. 2 Which
gives a controlling action of larger magnitude
by the insertion of a Vacuum tube (V. T. l) used
Ul as a constant current amplifier. This changing
cathode potential actuates the constant current
matic volume control tube. The diode detector
action occurs between the cathode and the control
grid of this tube (tetrode) While the screen grid
amplifier which in turn supplies the controlling
grid bias for the audio frequency amplifier. As
in Fig. 2 I have merely indicated potentials which
dition to supplying large voltages this circuit also
has the advantage of additional automatic con
and. plate serve as amplifier for the radio fre
quency voltage to be applied to the audio fre
quency automatic volume control tube. In ad
trol of the magnitude of the voltage applied to
vthe audio frequency automatic volume control
tube. This is true because for an increase of the
heterodyne circuit which is required to illustrate radio frequency voltage to the detector grid, the
output voltage to the audio frequency automatic
my auxiliary controlling circuit as applied there
may be used with the 227 type tube.
Fig. 4 is only that part of a standard super
to. In this circuit organization a highly selective
circuit is inserted between the source of radio
volume control tube will not be increased propor
tionately, since the diode action of the detector 15
frequency voltage and the audio frequency auto
causes ,an increase in the effective negative grid
matic volume control tube. 'I‘he selective circuit
may comprise the usual parallel resonant circuit
bias of the tetrode relative to its use as a radio
loosely coupled to the radio frequency voltage
In each of the circuit arrangements shown in
Figs. 4 and 5 I have indicated certain voltages 20
which, as intimated above, Will depend upon the
electrical characteristics `of the tubes used in the
circuit and the values of the resistances' used.
source.
It is to be appreciated that the radio
frequency voltage is theincoming signal Whether
it be a broadcasting'station or noise.` The ñrst
audio frequency amplifier tube is biased beyond
the cut-off, thereby making it inoperative until
a signal of sufficient magnitude is applied to the
audio frequency automatic volume control tube
which makes it operative by virtue of reducing its
grid bias to normal. In this circuit a constant
current amplifier is used to aid and stabilize this
With the notations or legends used in the draw
ings it is believed that these circuits are suf 25
flciently clear to those skilled in the art as not
to require reference characters to designate the
controlling action.
It is appreciated that the signal reaching the
audio frequency automatic volume control Will
various electrical devices which are employed in
asmuch as they are conventionally represented
30
and their functions Well understood.
Referring to the circuit arrangement illustrated
very schematically in Fig. 6, it will be noted that
only be one which can pass through the highly
the same is a modification of the circuits repre
selective circuit. Therefore, the audio f_re
quency amplifier is operative only when the signal
of the radio frequency is supplied to the highly
sented particularly by Figs. 4 and 5. A special
feature of this circuit is the compensation system 35
selective circuit from the radio frequency (in this
Which the radio frequency automatic volume con
trol does not adequately control or keep down to
a certain level arbitrarily established. The opera
tion of the compensation circuit is to increase the 40
bias voltage on the audio frequency automatic
volume control tube as the applied signal to the
audio frequency automatic volume control tube
increases by virtue of the fact that the radio fre
quency automatic Volume control tube does not
precisely hold the radio frequency level to a con
stant or established value.
The compensating circuit in short may be re
garded as a refinement of the audio automatic
volume control circuit shown in Figs. 4 and 5 and 50
has for its principal function to bring about
smoother action or control of extremely strong
instance intermediate frequency) amplifier.
If
a broad band of frequencies (noise) is applied to
40 the highly selective circuit only a small percent
age of said frequencies will be passed through to
the audio frequency automatic volume control
tube. The audio frequency volume control tube
is so adjusted that this small amount of radio
frequency voltage does not actuate it but a signal
of suiiicient magnitude and of the right fre
quency will actuate said control tube.
That is to say, if the receiving set to which the
above is applied has a radio frequencyautomatic
volume control that holds the radio frequency
50
level reaching the added selective circuit reason
ably constant, and this circuit is selective enough,
the set Will be silent except when a station is
properly tuned in. The set is insensitive to noise,
m
~ Ul since the added selective circuit is not sensitive to
for compensating when receiving strong signals
signals.
so-called diode detector method. The same tube
is also used to feed a highly selective circuit
Various modifications of the invention Will sug
gest themselves to those skilled in the art. As 55
for example the highly selective coupling cir
cuit for supplying the voltage to the audio fre
quency automatic Volume control tube may be
modified to give greater or less selectivity de
pending upon the type of set to which the in 60
vention is applied. `The method of coupling the
output of the radio frequency ampliñer to the
highly selective circuit may also be varied.
Another modification which suggests itself
Would be to control the output of the audio fre (i5
quency amplifier by means of a relay, rather
than to control the input or gain of the audio fre
quency amplifier by biasing one of the audio
frequency amplifier tubes to cut-off, as described
above.
Such modifications are obvious from a proper
appreciation of my invention, which in its broad
est aspects contemplates automatic volume con
trol through a circuit arrangement Which is
which in turn supplies the audio frequency auto
adapted to effectively interrupt the audio cir- 75
a band of frequencies (noise), but only to a con
stant frequency of the right frequency, i. e., the
carrier wave of a properly tuned in station. If
the signal being received fades to such a point
60 Where the ratio of noise to a signal is greater
than a certain amount (depending upon selectiv
ity of added tuned circuit, etc), the receiving
set automatically becomes silent until the strength
of the signal increases to the necessary amount
above that of the noise. The above holds true
when tuning in Weak stations. Only the ones
Which are sufficiently stron‘g above the existing
noise Will be received, the receiving set being silent
at all other times.
70
frequency amplifier.
~
The circuit shown in Fig. 5 is a modification of
the one shown in Fig. 4, the essential difference
being that the detection is accomplished by the
2,129,021;
3
cuits of aV receiving system at any point between
gain of said ñrst amplifier in such a manner that
the> detector and therloud speaker. It is my in
tention to cover all such modifications as come
within the scope of the appended claims.
What is claimed is:
1. In a radio receiving set, a radio frequency-
the signal input level to the demodulator is sub
stantially constant, a second control arrange
ment, responsive to variations in the gain of said
first amplifier, for rendering the said second am
plifier inefncient when the gain of the first am
amplifying system, a detector tube, an audio fre
plifier increases above a predetermined level, and
quency amplifying system, means for automati
said second control arrangement including a
highly selective network resonant to an operating
cally controlling the volume of the signal output
10 of the radio frequency amplifier, means for au
tomatically controlling the volume of the signal
output of the audio frequency amplifier in such
a manner that its sensitivity is a minimum when
signals below a predetermined intensity level are
15 received, said last mentioned means including a
highly selective controlling circuit energized by
the radio frequencyoutput taken from the plate
circuit of the audio detector tube.
.
2. In combination with an amplifier having an
20 output circuit resonant Vto an operating super
audible frequency, a detector having an input
circuit coupled to said circuit resonant to said
frequency, an amplifier for the audible frequency
output of the detector, an automatic volume con
25 trol circuit for said super-audible amplifier, said
audio amplifier being normally maintained biased
to cut-off whereby it is inefficient to amplify, a
control network having a highly selective input
circuit, resonant to said super-audible frequency,
30 coupled to said first output circuit and being in
dependent of said volume control circuit, the out
put of said network being connected to the aud
ible frequency amplifier for reducing said bias
and rendering the latter efficient to amplify
35 Whenever energy of said super-audible frequency
is impressed upon said super-audible frequency
amplifier.
3. The combination, in a superheterodyne re
ceiver, with a radio frequency amplifier resonant
40 to an operating intermediate frequency, a de
tector, an audio frequency amplifier and an au
tomatic volume control means for said radio fre
quency amplifier, of a control tube having a
highly selective input circuit loosely coupled to
45 the radio frequency amplifier, said input circuit
being resonant to said frequency, an amplifier
coupled to the output of the control tube, for
normally maintaining an input electrode of the
audio amplifier biased to cut-off, and a direct
5,0 current connection between an output electrode
of the amplifier for the control tube- output and
said input electrode such that said cut-off bias
is reduced when energy o-f said frequency is im
pressed on the radio amplifier.
v
.
4. In 'a radio receiver, the combination of an
Aaudio frequency amplifier, a network resonant to
a desired operating frequency preceding the am
plifier input, and coupled thereto, for providing
an audio frequency signal to be amplified, said
60 network including an automatic volume control
circuit means for normally maintaining an in
put electrode of the amplifier biased to cut-off,
and a control circuit connected between said
electrode and a desired point in said network for
5 5 sufficiently reducing the bias to render the am
plifier conductive only when said signal is pro
vided, said -control circuit including a highly se
lective input resonant to the said frequency but
which is independent of said volume control cir
70 cuit.
5. In a radio receiver provided with at least a
high frequency signal amplifier, a demodulator
of the diode type, a demodulated signal amplifier
and a control arrangement, responsive to vari
ations in signal intensity level, for adjusting the
signal frequency and which is independent of
said first control arrangement.
6. In a radio receiver provided with at least
a high frequency signal ampliñer, a demodulator,
a demodulated signal amplifier and a control ar
rangement, responsive to variations in signal in
tensity level, for adjusting the gain of said first
amplifier in such a manner that the signal input
level to the demodulator is substantially con
stant, a second control arrangement, including a
rectifier coupled to said first amplifier for devel
oping a control bias potential, for rendering the
said second amplifier inefñcient when the gain of
the first amplifier increases above a predeter
mined level, and said second control arrange
ment including a. highly selective network reso
nant to an operating signal frequency and which
is independent of said first control arrangement.
7. In an automatic volume control system for
a radio receiver, said receiver including at least
two> successive high frequency amplifier stages,
a detector, and at least one audio frequency am
plifier stage, an automatic gain control network,
responsive to variation in high frequency signal
carrier intensity level, forl adjusting the sensi
tivity of the high frequency amplifier stages in
such a manner as to maintain the signal input
to the detector substantially constant, a second
gain control arrangement having a resonant in
put network tuned to the frequency of the sig
nal energy delivered to said detector, said reso 40'
nant network being coupled to receive signal car
rier energy from the output of said cascaded
high frequency amplifiers, a means for connect
ing the second gain control arrangement to said
audio stage in such a manner that the sensi- .
tivity of the audio stage is a minimum when the
sensitivity of the high frequency amplifiers is
substantially a maximum, and a conductive con
nection between both of said gain control ar
rangements.
8. In a superheterodyne receiver provided with
an intermediate frequency amplifier, a second de
tector and at least one stage of audio amplifica
tion means, a transformer coupled between said
intermediate frequency amplifier and the input ..
electrodes of the detector, an arrangement for
automatically,regulating the sensitivity of said
audio ampliñer, `said arrangement including an
electron discharge device having a resonant net
work connected between its input electrodes, said 60
network being tuned to the operating interme
diate frequency and including a connection to
the primary of said transformer, and means in
cluding an electron discharge tube, for connect
ing an output electrode of said discharge device
to an input electrode of said audio amplifier.
9. In a modulated carrier wave receiver, the
combination with a carrier wave amplifier, a de
modulator tube including at least a control grid,
cathode and anode, and an audio frequency am 70
plifier tube, an audio frequency signal coupling
path connected between the demodulator tube
and the said audio tube, means automaticallyto
regulate the gain of said amplifier in response
to received carrier Wave variations, a resistor 75
4
2,129,021'
operatively associated with the demodulator tube
coupling said last resonant network to said tuned
for developing a direct current voltage variable
with said variations, an electron discharge tube
having an input electrode connected to a point
on said resistor, a resistor in the grid circuit of
circuit, a control ampliñer tube having its input
circuit connected to the output circuit of the
put circuit of the last vampliñer tube and the
the audio amplifier tube and the anode circuit
of said last tube, said point being so Vchosen that
the gain of said audio tube is substantially de
input circuit of the second of said two tubes. I
13. In a radio receiver of the type including a
creased when received carrier waves decrease in
amplitude below a predetermined level.
10. In a radio receiver of the type including
a plurality of cascaded tubes, a network coupling
at least two of the tubes, said network including
a circuit tuned to a desired signal frequency, the
first of said two tubes being a radio frequency
signal amplifier, a noise suppressor system for
the receiver comprising a control electron dis
charge tube provided with a resonant input net
work between its input electrodes, the last net
20 work being tuned to said desired frequency,
means for coupling said last resonant network
to said tuned circuit, a control amplifier tube
having its input circuit connected to the output
circuit of the control tube, and a resistor com
mon to the output circuit of the last amplifier
tube and the input circuit of the second of said
two tubes.
11. In a radio receiver of the type including
a plurality of cascaded tubes, a network cou
30 pling at least two of the tubes, said network in
cluding a circuit tuned to a desired signal fre
quency, the first of said two tubes being a radio
frequency signal amplifier, a noise suppressor
system for the receiver comprising a control elec
tron discharge tube provided with a resonant in
control tube, and a resistor common to the out
tuned high frequency amplifier, a demodulator,
an audio ampliñer network, automatic volume
control means for regulating the gain of the
tuned amplifier in a sense to maintain the sig
nal'carrier amplitude at the demodulator input
substantially constant over a range of signal
carrier amplitude variations at the tuned ampli
fier input, a second control means, responsive to 15
a decrease in the signal carrier amplitude below
a desired intensity level, for impairing the de
modulated signal transmission efficiency through
said audio network, a third control means con
nected between the Volume control means and
said second control means for rendering the lat
ter operative to impair said demodulated signal
transmission eñiciency when the signal carrier
amplitude increases above a desired intensity
level.
25
14. In a radio receiving circuit, a selecting cir
cuit, and an auxiliary circuit for rendering the
set operative at frequencies immediately adja
cent to and including the carrier frequency and
at the same time rendering the set inoperative 30
and silent when tuned over a substantial part of
a given broadcasting channel, said auxiliary cir
cuit comprising loosely coupled tuned circuits in
cluding audions, one of said audions having its
control grid connected to said auxiliary circuit 35
put network between its input electrodes, the >and its plate and an audio tube including a re'
sistor, connected through said audions to one of
last network being tuned to said desired fre
quency, means for coupling said last resonant said tuned circuits through the medium of a coil
and a detector tube, the plate of said second
network to said tuned circuit, a control ampli
named audion being connected to the resistor of 40
40 fier tube having its input circuit connected to
said audio tube.
»
the output circuit of the control tube, and a re
15. Radio receiving apparatus of the type in
sistor common to the output circuit of the last
cluding a radio frequency automatic volume con
amplifier tube and the input circuit of the sec
trol arrangement, means for biasing a tube of
ond of said two tubes, and means operatively as
sociated with at least one of said control and the receiver to a. point where it is inoperative 45
and apparatus for automatically removing such
control amplifier tubes for adjusting the sup
bias in the presence of a transmitted modulated
pressor action.
12. In a radio receiver of the type including carrier signal, which apparatus consists of means
for diverting a part of a modulated carrier sig
a plurality of cascaded tubes, a network cou
nal voltage to a highly selective tuned circuit 50
50 pling at least two of the tubes, said network in
for selectively relaying the modulated signal car
cluding a circuit tuned to a desired signal fre
quency, the first of said two tubes being a radio rier tota vacuum tube operated as a rectifier, said
frequency signal amplifier, a noise suppressor tuned circuit being independent of said volume
control arrangement, and means for applying the
syst-em for the receiver comprising a control elec
rectified voltage to modify the bias of the first 55
tron
discharge
tube
provided
with
a
resonant
55
input network between its input electrodes, the mentioned tube to render it operative.
last network being tuned to said desired fre
MADISON G. NICHOLSON, JR.
quency, means including a signal amplifier, for
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