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Патент USA US2404712

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July 23, 1946.
Filed Dec. 30, 1943
Patented July 23,1946
' 2,404,712
R. Lee Hollingsworth, Riverhead, N. Y., assignor
to Radio Corporation of America, a corporation
of Delaware
Application December 30, 1943, Serial No. 516,148
7 Claims.
(01. 250-20)
This invention relates to automatic gain con
trol systems and is particularly adapted for use
with a radio receiver which is intended to receive
interrupted carrier wave telegraph signals.
winding III, the space path through triode tube
l6 and resistance [1. A bias battery furnishes
a potential gradient in a potentiometer 26, and
adjustable taps 20 and 2| on this potentiometer
may be set to maintain suitable threshold biases
on the grids of tubes l6 and 22‘ respectively. The
It is an object of my invention to ‘provide an
automatic gain control system whereby the gain
'of the receiver is adjusted to an optimum value
tap 2i. biases the grid in tube 22 more. negatively
during each signal impulse, that gain value be
than the bias which is applied to the grid of tube
ing retained during a space interval until the
next succeeding impulse.
It is another object of my invention to pro
vide an automatic gain control system which
I 6 through tap 20. Resistor 23 and capacitor‘
l0 24 constitute the time constant device for this
AVC system.
Output potentials derived from the recti?er
tube 1 I may be taken either from the cathode of
produces almost instantaneous adjustment of
the gain to a new level in response to a change
tube l6 or from a suitable point on the poten
in the incoming signal level.
It is another object of my invention to con
15 tiometer I‘! in the anode circuit of tube [6. ‘The
trol the gain in an interrupted carrier wave re
ceiver in such a manner that the tube noise cur
the setting of a double pole switch I8. ‘By means
of the circuit arrangement shown and described
it is, therefore, possible to control any desired
20 translating device such as a_ keyer tube, a bal
rents in the receiving circuitswill be substan
tially eliminated.
It is another object of my invention to provide
a system comprising a plurality of discharge
polarity ofthe output potential depends, upon
anced modulator, or a recorder.
‘ '
In operation the signal wave energy is ampli
tubes operative to so influence an automatic gain
control circuit that incoming static impulses are
?ed by vacuum tube ‘5_ and heterodyned with the
local oscillations to produce an intermedate‘fre
quency, which is further ampli?ed by interme
diate frequency ampli?er tube 8, output from
which is recti?ed by the recti?er tube H; The
prevented from paralyzing the receiver circuit.
The invention will now be fully described, ref
erence being made to the accompanying drawing,
the sole ?gure of which shows a circuit diagram
triode tube l6 has applied thereto a low bias .
of a preferred embodiment.
potential sufficient to render this tube non-con
Referring to the drawing, I show an antenna 30 ductive to very. low strength signals and, tube
l for collecting electromagnetic wave energy.
noise currents. When signal energy passes
This antenna is connected through coupling coil
through tube l6 and resistance. I l the full
2 and thence to ground. Electromagnetic wave
~voltage across tube 16 and resistance I] is ap-_
energy ?owing through coupling coil 2 induces
plied to the AVG circuit. The application of
signal currents in the tuned circuit comprising 35 this AVC voltage reduces the gain of the receiver
the transformer secondary 3 and the adjustable
during a single impulse and the gain remains at
capacitor 4 in shunt therewith. Applied to the
that particular gain value since the control , grids
suppressor grid g3 of converter tube 5 is the
of vacuum tubes 5 and 8 are isolated until recti
energy from a local oscillator 25. The ‘local
?er tube [6 is again conductive. If the next
oscillations beat with the incoming signal to pro
succeeding signal impulse be stronger than the
duce an intermediate frequency of a desired
value. This intermediate frequency energy is
preceding impulse, the gain of the receiver will
be lowered still further, whereasfif the follow
transferred to the control grid of an amplifying
ing signal impulse be less in value than the pre
tube 8 by way of an intermediate frequency
ceding impulse, ‘the gain of the receiver will be
transformer which is included in tuned circuits 45 increased and will retain this gain value as here
5 and ‘I. The intermediate frequency energy be
tofore mentioned until another impulse causes
ing ampli?ed by ampli?er tube 8 is coupled by
tube IE to again be conductive to reset the gain
tuned transformer windings 9 and Ill to a diode
level of the receiver at a new level depending
recti?er tube ll. Parts 12 and I3 represent a
upon the strength of the incoming signal.
bias resistance and a radio frequency bypass 50
The action of the tube 22 in this AVC circuit
condenser respectively, as do parts l4 and I5.
is as follows: If very strong signal currents, or
A triode tube 16 is connected in series with
heavy atmospheric impulses are received, tube 22'
the output of a recti?er tube II and a resistor
becomes conductive since a slightly more negative
IT. ‘The output terminating resistance of recti
bias is applied thereto, than is applied to the grid
?er tube ll includes the transformer secondary 55 of recti?er tube l6, creating ‘a bypass’ circuit
to the input circuits of said stages, a load resistor
which prevents the grids of ampli?er tubes 5 and
8 from [becoming blocked. Another e?ect present
and electronic switching means in series with said '
rectifying means whereby said gain control circuit
is rendered effective to adjust the gain in said
is that the AVG‘ circuit is momentarily drained
of electrons when tube 22 suddenly becomes con
receiver to a desired value in the presence of
marking signals and to hold thatgain adjustment ’
during carrier wave interruptions of normal spac
ductive, causing the gain of the receiver to slight
ly increaseas a result of a strong static impulse,
whereas, in normal AVC practice the gain of the
receiver would be greatly reduced and the time
constant circuit would'be overloaded with voltage
ing signal duration, an electronic limiter device
connected in shunt with said load resistor and
switching means, said limiter device being opera
possibly producing dropouts of one or more sub
able in the presence of peak impulses due to static
sequent signal impulses.
and other excessive wave energy, and threshold
The time constant circuit 23, 24 is preferably
biasing means for so controlling the conductivity
small in value in order to provide substantially
of said switching means and of said limiter device
instantaneous gain compensation. This arrange
ment has proven very practical when receiving 15 respectively, that said gain control circuit is ren
telegraph signals under conditions such that the
, dered relatively insensitive to noise energy of low
amplitude and also to static crashes of, relatively
strength of the incoming signals varies over a
high amplitude.
very wide amplitude range. Since the 'rate of
3. Apparatus for automatically controlling the
gain compensation canibe extremely fast it nat
yurally follows that the recti?ed signal energy 20 gain in the ampli?er stages of an interrupted car
rier wave receiver comprising a gain control ,cir
' available at switch laremains relatively constant
though theinput signal may befadingover a very
cuit having time constant elements ins‘nunt with
with adiversity receiving system which is at pres
?er stages to said gain control circuit, means
operative in response to the reception of model"?
a unilateral impedance of the tri'ode discharge
wide range.
tube type, means including a recti?er for sup
,It will belappreciated that thismethod of auto
.matic gain ‘control may ‘be used in conjunction 25 plying recti?ed output energy‘ from said, ampliw
ent in wide ‘usage for short wave, long-distance
ate strength static crashes and ‘other interfer
ence waves of moderate amplitude for causing
.Furthenthis method of automatic volume lcon~
trol may be utilized in a conventional all-wave 30 said recti?ed output energy to automatically con
trol the gain of the receiver, and means opera
vbroadcast receiver and will be found particularly
tive to increase the gain of the receiver when
useful in establishing a maximum volume at
receiving strong static'or other interfering po
which positive llimiting results, there-by prevent
tentials, this means comprising an auxiliary dis
ing heavy atmospheric noises from exceeding the
maximum level of modulated waves as received. 35 charge tube rendered conductive by said strong
,radio telegraph-telephone reception.
interfering ‘potentials, thereby to shunt ‘to ground
This is-accomplishedbyadjusting recti?er tube 22
a portion .of said recti?ed output energy ,along
with ya portion of the charge previously, stored
‘to be ,conductiveat approximately 6 to .10 deci
:bels below the . maximum modulation level.
in said time constant circuit.
, ~
Various modi?cations and applications will be
suggested by this disclosure .to those skilled in 40 4. An automatic gain control circuit for use
in airadio telegraph receiver, said circuit having
the art. The scope oftheinventio-n is to be under
.a recti?er coupled to .a certainstage of the re
stood, therefore, as comprehending embodiments
ceiver, a load in series with the vrecti?er, said
other than that which is herein ‘iliustratively
load including two discharge tubes which are
. ‘
mutually vin parallel, a negative biasing means
so connected between the cathode and control
grid of each one of said'tubes that one tube
-1. In an interrupted .carrier wave receiver ,an
automatic gain control-circuit comprising means
for rectifying the output from said receiver, .a
?rst electron discharge tube the space path of
which is inseries withlsaid rectifying ,means, said
conducts recti?ed signal .energy‘within a normal
range of amplitudes and the other tube conducts
only in the presence of peak wave impulses ‘and
strong atmospherics, and a time constant device
tube ‘having a cathode, an anode .and a control
grid,=a load resistor connected between said an
ode and ground, a-second electron discharge tube
the .space vpath-oi? which is connected in shunt
between the cathode of .the ?rst .said tube and 55
ground, 'said‘second tubelhaving a cathode, an
composed of resistance and capacity forming part
[of said gain control circuit andarranged for co
operation with .saidload .to control the gain in
.said receiver.
5. Apparatus for-automatically controlling the
gain .in the ampli?er stages of an interrupted
anode and a ‘control grid, means for maintaining
vcarrier wave receiver, said apparatus comprising
different threshold biases on the grids ‘of said
a recti?er circuit coupled to a particular stage
tubes whereby the ?rstsaid tube is rendered non
of said receiver, said circuit including the space
:conductive ‘)in the presence of signal and noise
path of an electron discharge tube having a
energy below- a predetermined level, and .the sec
cathode, an anode and a control grid, negative
ond tubeis :held non-conductive in the presence
‘biasing means connected between the cathode
of recti?ed.signalenergywithin a normal volume
and control grid of said tube, means including
range, and-a time ,constantcircuit comprisingse
ries resistance and shunt capacity so connected 65 a time constant circuit in shunt with the ‘space
path of said tube, said means havingresistance
‘as tosupplygain control potentials to the ampli
and capacitance for prolonging the gain control
?er stages .of said receiver, said potentials being
effects through space intervals between the mark
subject “to ‘the :limiting action of said discharge
ing signal elements, and means responsive to
' 2. interrupted carrier wave receiver hav
70 static impulses and high amplitudesignals which
circuit “comprising series resistanceand shunt ca
tend to paralyze the receiver for reducing the
bias that would otherwise be derived from said
;pacityin circuit with rectifying means coupled
\toaparticular stage of said receiver, said circuit
caused to compensate for excessive gainvcontrol
ing ampli?er stages, an automatic gain control
being operative to apply gain control potentials 75
negative biasing means, whereby said vtube is ,
6. Apparatus in accordance with claim 5
wherein said bias reducing means includes a sec
charge tube type, said circuit being operative to
reduce the gain in said ampli?er stages in re
ond electron discharge tube the space path of
sponse to the reception of moderate strength
which is in series with a resistor, this tube and
resistor being in shunt with the space path of 5 static crashes and other interference waves of
moderate amplitude, means occasionally opera
the ?rst said tube and the second tube being
tive to increase the gain in said ampli?er stages,
operatively biased to supply substantially in
this means comprising an electron discharge
stantaneous adjustment of the gain control po
device the space path of which is connected in
tential to a new level in response to a change in
shunt with said time constant elements, and
the incoming signal level.
10 means operative upon reception of strong static
7. Apparatus for automatically controlling the
or other noise energy for reducing the impedance
gain in the ampli?er stages of an interrupted
said space path, thereby to effect said gain
carrier wave receiver, comprising a gain control
circuit having time constant elements ‘in shunt
with a unilateral impedance of the triode dis- 16
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