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Патент USA US2135949

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Nov. 8_, 1938.
w. VAN B. ROBERTS
2,135,949
NOISE SUPPRESSOR vCIRCUIT
Filed June 17, 1957
A
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INVENTOR
»
WALTER VA B.ROBER7'S
ATTORNEY
Patented Nov. s, 1938
~
2,135,949
UNITED STATES PATENT OFFICE
2,135,949
NOISE SUPPRESSOR CIRCUIT
Walter van B. Roberts, Princeton, N. J., assignor
to Radio Corporation of America, a corporation
of Delaware
‘
Application June 17, 1937, Serial No. 148,627
10 Claims. (01. 250-20)
‘My present invention relates to noise silencing detector and the local oscillator networks will
“circuits, and more particularly to receivers uti- have the rotors of their variable tuning con
lizing noise suppressors.
densers mechanically arranged for uni-control.
One of the main objects of this invention is
The I. F. output of converter 2 is transmitted
;5 to provide a noise silencer circuit in which the
‘silencing action takes place when an interfering
voltage of only slightly greater amplitude than
that of the desired signal is received; the distinguishing feature of the present silencer cir~
10 cuit arrangement is the use of a multi-electrode
tube as a. diode detector which has its detecting
quality controlled by the potential on a grid of
the tube.
The novel features which I believe to be char15 acteristic of my invention are set forth in par-
ticularity in the appended claims; the invention itself, however, as to both its organization
and method of operation will best be understood
by reference to the following description taken in
a0 connection with the drawing in which I have in-
dicated diagrammatically several circuit organizations whereby my invention may be carried
into effect.
_
In the drawing:
'
25
Fig. 1 shows a superheterodyne receiver embodying one form of the invention, and
-
Fig. 2 illustrates a modi?cation of the silencer
circuit.
The invention will best be explained with ref30 erence to Fig. 1 which shows, for the sake of
illustration, a conventionalized superheterodyne
receiver including a stage of intermediate frequency ampli?cation whose gain is automatically
to one, or more, stages of I. F. ampli?cation; 5
therefore the numeral 3 is to be understood as
designating a network which may include one
or more ampli?er tubes tuned tothe operating
I. F. The last I. F. output circuit 4 is coupled to
the I. F. input circuit 5 of the second detector, 10
or audio demodulator tube D. It is to be under
stood that the coupling transformer M1 has its.
primary and secondary circuits ?xedly resonated
'to the operating I. F. Similarly the primary and
secondary circuits 4 and 5 of the coupling trans- 15
former M2 are resonated to the operating I. F.
In Fig. 1 a triode D is used as a diode detector
in combination with condenser K and resistance
Q. The anode and cathode of tube D constitute
the diode elements, while the grid 6 is used to 20
control the internal resistance of the diode. A
diode tube S is employed for the purpose of
squelching the detecting action of detector D
whenever the voltage across the transformer sec
ondary windingL exceeds a predeterminedvalue. 25
A battery B2 of low voltage may be included be
tween the grid and cathode of tube D to ‘main
tain the grid normally somewhat positive, so as
to reduce the internal resistance of the diode
circuit to a value low enough to permit linear 30
‘detection. This battery, however, is not essential
to the squelching action of the circuit.
A second battery B1 which is adjustable in
controlled in accordance with signal strength.
35 The receiver is generally of the type disclosed and
claimed in my copending application Serial No.
80,497, ?led May 19, 1936.
The receiver comprises, in general, a radio frequency ampli?er I, a converter 2, an I. F. ampli40 ?er 3 and a second detector D. A signal source
A feeds collected signals to the ampli?er l, and
the latter will include means for tuning it
through a desired signal frequency range. The
signal source A may be the usual grounded an-
value, is used to adjust the bias on diode S so
that no current flows through it unless the volt- 35
age across coil L is greater than the maximum
peak voltage of the desired signal. If, however,
an interfering disturbance, such as for example
is created by automobile ignition systems, sets‘
up a transient voltage across coil L which is sub- 40
stantially greater than the desired signal, our
rent will ?ow through diode S and set up a Volt
age across resistor R. If suf?cient in intensity,
this last voltage will make the grid 6 of detector
45 tenna circuit; radio frequency distribution line;
tube D suf?ciently negative with respect to its 45
or even the collector used on mobile vehicles such
as automobiles. The ampli?ed signals are fed
to the tunable input circuit of the converter 2.
It will be understood that the converter may be
50 of the combined local oscillator-?rst detector
type employing a pentagrid converter tube of
the 2A‘! type, or separate tunable ?rst detector
and local oscillator tubes may be used. In any
‘case, it is to be understood that the tunable cir-
55 cults of the radio frequency ampli?er, the. first
cathode to prevent any flow of current through
the detector. Condenser C, shunted across re
sistor R, is chosen as small as possible so that the
time required to build up the squelch voltage
across resistor R will be small.
Resistor R is 50
preferably large, so that the interfering voltage
will create a maximum voltage across R. The
time constant RC is chosen great enough to
maintain the squelching action for the duration
of the interfering transient voltage, but, onthe 55
2,135,949
2
erated across R by a strong interference signal.
other hand, not so great as to keep the detector
The inherent capacity X of the diode, or auxil
inoperative for an unnecessary length of time.
The best values of R and C for any particular iary capacity if desired, together with condenser
C, divides the alternating voltage across diode P
installation are best determined, however, by so that a lesser alternating voltage exists across
trial.
In
the
absence
of
interfering
voltages
the
CR
operation of the circuit is quite conventional, and diode S than the bias thereon. This reduction
both the audio output and AVC potentials may be of the alternating voltage across S under normal
circumstances prevents its drawing any current.
obtained from the detector resistorQ as shown.
The AVC bias is applied through lead 10 and This reduction of voltage should, of course, be
sufficient to prevent drawing current even when
10 ?lter resistor II to the I. F. ampli?er signal grid.
Of course the AVG bias can be applied to the net ' consideration is taken of the fact that the anode
works ! and 2 as well. The AVC action is, well of, S is maintained slightly positive by the source
B2. If the grid source B2 is omitted it will not be
known and need not be described.
In order to demonstrate the rapidity with necessary to» insure any particular amount ofre
duction in the alternating voltage across diode
15 which the detector is rendered inoperative as
S. For this reason it is preferable to use as the
the Voltage across coil L increases beyond the pre
detector, a tube whose detecting qualities are
determined value, the following calculations have ..
satisfactory without requiring any positive bias on
Let
us
suppose
that
source
B1
has
'
been made.
been so adjusted that (B1——Bz), the total 'bias thegrid.
In both Figs. 1 and 2 a certain amount of signal /
across diode S, is slightly greater than the max
imum peak voltage of the desired signal. Let E voltage may reach the detector tube grid through
represent an interfering voltage which is greater the distributed capacity of diode S, or by actual
than this total bias. Then, assuming the internal capacity as at the point a: in Fig. 2. This however,
resistance of diode S small compared to R, the merely assists in the detecting action of the de
tector, and is too small appreciably to affect the
25 recti?ed voltage across R will be very nearly
squelching action when the grid becomes strongly
E-(B1—Bz) . The total negative bias on the grid
of the detector is, therefore, E-—B1.
If, now, the tap T is located at a point on the
coil L where the voltage is a fraction F of the total
voltage across the coil, the voltage impressed upon
> the detector is FE. It is well known that no our
rent will ?ow in they detector if this voltage FE
is less than the product of the grid bias and the
ampli?cation constant a of the tube. Thus, the
35 result is obtained that the detecting action will be
squelched when the interfering voltage is appre
ciably greater than given by the equation.
[.L
40
E—-B1;_—__-T_'
From this’ equation it will be seen that if the
ampli?cation constant of the tube is considerably
greater than unity, it will make very little differ
ence where the tap T is located; so that if desired
it may be connected to the top of the coil. In any
negative. Indeed, the aforesaid distributed ca
pacity effects may be augmented by auxiliary ca
pacity for the purpose of improving the detection
action, provided that the alternating voltage thus
introduced to the grid is not suflicient to interfere
with satisfactory squelching action. It will be re
alized that whilea. triode detector is shown for
the sake of simplicity, other tubes having suitable
characteristics, such as pento-des, may be used. 35
The connections are the same in either case, ex
cept that the screen must be connected to a suit
able positive voltage if a pentode, or tetrode, is
used.
'
‘
While I have indicated and described several
systems for carrying my invention into effect, it
will be apparent to one skilled in the art that my
inventionis by no means limited to the particular
organizations shown and described, but that many
modi?cations may be made without departing
case it will be seen that the value of voltage E
from the scope of my invention, as set forth in the
which produces a complete squelch of the detec
tor circuit, is only a small percent greater than
appended claims.
the predetermined value (B1—Bz) if B2 is small
' compared to B1. This latter is the normal condi
tion as B1 will usually be set to 10 volts, or more,
in order to take care of the rather large signal
voltages developed in the modern receiver.
In case it is desired to have the adjustment of
the
voltage B1 take place automatically, and in
55
accordance with the received signal strength,
‘the circuit of Fig. 2 may be used. This circuit
may be identical with that of Fig. 1 in every way,
except in the method for obtaining the bias
60 voltage for diode S.
In my copending applica
tion Serial No. 108,427, ?led Oct. 3Q, 1936, Patent
No. 2,115,876, May 3, 1938, there is disclosed and
claimed the automatic adjustment of the bias on
the squelch diode. In Fig. 2, an auxiliary diode
65 P is employed in conjunction with a high resis
tance M and a large capacity N to provide a posi
tive potential on the cathode of diode S substan
tially equal to the modulation peaks of the desired
signal. The time constant of network MN should
not, vhowever, be so large that abnormal voltage
across M produced by interference voltages Will
What I claim is 2'
40
.
,
1. A ‘detector system comprising
a multi
electrode tube having its plate and cathode con- .
nected to a common signal input circuit as a
recti?er, said tube including a control grid in
the electron stream between the cathode and
plate, a second recti?er connected to said input
circuit to produce recti?ed current in proportion ,
to the excess of input voltage above a predeter
mined level, and a connection from the control
grid of said ?rst tube to the said second recti
?er to impress recti?ed voltage fromthe latter
on the grid.
I 2. A detecting
(PI)
system in
accordance
with
claim 1, wherein a third tube is connected to said
input circuit and second recti?er automatically
to determine the said predetermined level.
'
3. A method of operating a signal detector of 65
the type including a tube having at least a
cathode, anode and a control electrode disposed
in theelectron stream between the cathode and
anode, which includes impressing signals between
the cathode and anode for recti?cation, rectify
ing alternating current energy, representative
of interference noise, above a predetermined
persist unduly after the cessation of the interfer
amplitude, and impressing the recti?ed noise
ence,” On the other hand, N should belarge energy upon the said control electrode in a sense
enough so that the bias on S‘ will increase ap
to render the ?rst recti?cation ine?icient.
preciably only after squelch bias has been gen
3
2,135,949
4. A method of operating a signal detector of
the type including‘ a tube having at least a
cathode, anode and a control electrode, which
includes impressing signals between the cathode
and anode for recti?cation, rectifying alternat
ing current energy, representative of interference
noise, above a predetermined amplitude, impress
ing the recti?ed noise energy upon the said con
trol electrode in a sense to render the ?rst recti
?cation ine?icient, and controlling said second
recti?cation in response to signal amplitude
variation, ‘and in a sense to prevent the second
recti?cation until the said predetermined ampli
tude is exceeded.
15
5. In combination with a source of signals and
a load circuit, a detector tube including at least
a cathode, anode and control electrode, a signal
input circuit coupled to the detector anode and
cathode, means electrically connected to the
20 anode and cathode for developing a recti?ed
voltage from signal voltage in said input circuit,
a recti?er having an alternating current input
circuit in which exists alternating current energy
impressed on said detector anode and cathode,
25 means in circuit with the recti?er for developing
a unidirectional voltage from said alternating
current energy, and means for impressing the
unidirectional voltage on said control electrode
in a sense to decrease the recti?cation e?iciency
of said detector cathode and anode.
6. In combination with a source of signals and
a load circuit, a detector tube including at least
a cathode, anode and control electrode, a signal
input circuit coupled to the detector anode and
35 cathode, resistor means electrically connected to
the anode and cathode for developing a recti?ed
voltage from signal voltage in said input circuit,
a recti?er having an alternating current input
circuit in which exists alternating current energy
40 impressed on said detector anode and cathode,
resistor means in circuit with the recti?er for
developing a unidirectional voltage from said
alternating current energy, and means for im
pressing the unidirectional voltage on said con
45 trol electrode in a sense to decrease the recti?
cation e?iciency of said detector cathode and
anode.
7. In combination with a source of signals and
a load circuit, a detector tube including at least
50 a cathode, anode and control electrode, a signal
input circuit coupled to the detector anode and
cathode, means electrically connected to the
anode and cathode for developing a recti?ed
voltage from signal voltage in said input cir
cuit, a recti?er having an alternating current
input circuit in which exists alternating cur
rent energy impressed on said detector anode
and cathode, means in circuit with the recti?er
’ for developing a unidirectional voltage from said
alternating current energy, means for impress
ing the unidirectional voltage on said control
electrodein a sense to decrease the recti?cation
, e?iciency of said detector cathode and anode, a
signal ampli?er coupled to said signal input cir
cuit, and means for controlling the ampli?er
gain with said recti?ed signal voltage.
8. In combination with a source of signals and
a load circuit, a detector tube including at least
a cathode, anode and control electrode, _a signal
input circuit coupled to the detector anode and
cathode, means electrically connected to the anode
and cathode for developing a recti?ed voltage
from signal voltage in said input circuit, a recti 1O
?er having an alternating current input circuit in
which exists alternating current energy im
pressed on said detector anode and cathode,
means in circuit with the recti?er for developing
a unidirectional voltage from said alternating 15
current energy, means for impressing the uni
directional voltage on said control electrode in a
sense to decrease the recti?cation eirl'ciency of
said detector cathode and anode, said alternat
ing current input circuit being the same as said 20
signal input circuit, and means actuated by
signal amplitudes below a desired level to render
the said recti?er inoperative.
9. In combination with a source of signals and
a load circuit, a detector tube including at least
a cathode, anode and control electrode, a signal
input circuit coupled to the detector anode and
cathode, means electrically connected to the
anode and cathode for developing a recti?ed volt
age from signal voltage in said input circuit, a
recti?er having an alternating current input cir
cuit in which exists alternating current energy
impressed on said detector anode and cathode,
means in circuit with the recti?er for developing
a unidirectional voltage from said alternating 35
current energy, means for impressing the uni
directional voltage on said control electrode in a
sense to decrease the recti?cation efficiency of
said detector and anode, means for adjustably
connecting the anode of the detector tube to said
signal input circuit, and said alternating current
input circuit being said signal input circuit.
10. In combination with a source of signals
and a load circuit, a detector tube including at
least a cathode, anode and control electrode, a
signal input circuit coupled to the detector anode 45
and cathode, means electrically connected to the
anode and cathode for developing a recti?ed
Voltage from signal voltage in said input circuit,
a recti?er having an alternating current input
circuit in which exists alternating current 50
energy impressed on said detector anode and
cathode, means in circuit with the recti?er for
developing a unidirectional voltage from said
alternating current energy, and means for im
pressing the unidirectional voltage on said con
trol electrode in a sense to decrease the recti?
cation e?iciency of said detector cathode and
anode, and additional means for preventing
recti?cation of alternating current energy below
a predetermined amplitude by said recti?er.
WALTER VAN B. ROBERTS.
55
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