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Патент USA US2404626

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‘my 23,1946.
Y
a w, FYLER
'
‘
2,404,626
NOISE LIMITING CIRCUIT
_
Filed 001;. 5, 1942
Fig I.
Fig.2. “ .
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Fig.3.
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VOLMGE
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Ihven'Eor:
_> Georg?
v
. F‘ ler‘,
.3
M
Hus Attorney.
'
Patented July 23, _1946
2,404,626
UNITED STATES PATENT OFFICE
George W. Fyler. Stratford, Conn, assignor to
General Electric Company, a corporation of
' N ew York
1
Application October 5, 1942, Serial No. 460,781
14v Claims. (Cl. 250-20)
,2
-My invention relates‘to‘ signal translating sys
tems and has for its'object. to provide‘ an im
proved control circuit for such systems.
'
.
- High frequency carrier waves, modulated by d.e-'
’ sired audio signals, arev supplied’ from any. suit
_
More speci?cally, my’ invention relates to a
noise limiting circuit particularly adapted for use
in radio or television receiving apparatus.
ablesignal receiving apparatus,not shown, to the
detector input. through theinput‘ transformer I i
having a ‘tuned primarylwinding l2 anda plural
,
ity' of secondary windings l3 and I4, said second
‘It is an object of my.v invention to provide an
ary' windings being connected to separate sig
improved noise limiting circuit which effectively
discriminates‘ between undesired noise impulses
nal translating channel's; ~The'secon'dary winding
i3‘suppliesithelhigh frequency oscillations to the
and desired signals impressed on the input’oi‘ a 10 signal detector‘ ‘HI which is‘ shown to‘ be‘ of the
- radio or television receivin'g'apparatus and which
diode type having‘ an‘ anode" 1'5‘ and‘v a; cathode
prevents such impulses from appearing in. the
it. The signal detector circuitextendsrirom the
output circuits of the apparatus.
anode. f5? through a diode. load resistor 11' and
'
a
.
In my copending application S. N. 364,160, ?led
high frequency by-pass capacitor [8
parallel
November‘ 4, 1940, entitled Control circuits, now 15 andv the‘ secondary winding 13 to the'cathode IS.
matured as U. S. Patent 2,298,083, and assigned to
The operation of this portion of the‘ circuit is
the same assignee as the. present invention, I
well known‘ to‘ those skilled‘ in theart and will
have disclosed a noise limiting circuit in which
a noise limiting’ diode is-connected in shunt to a
not~be detailed: here. The detector is effective
to démod'ulate the‘ carrier waves impressed- upon
signal-rectifying diode, the noise limiting. diode 20 the‘ transformer II‘. In" av superheter'odyne- re
providing its ownthreshold bias for variations in
ceiver these carrier waves will: generally be of an ‘
both‘ carrier and modulation levels by peak recti
?cation-of the voltages appearing across the sig
inter-mediate high‘ frequency lower‘ than the car
rier frequency ofv the" received signal: The‘ de
modulation products. developed across the diode
25 load’ resistor l1 include" audio frequency .compo
nents and a direct current component. ‘The audio
nal‘ diode. The threshold is maintained by a re
sistance-capacitance network which has a rela
tively long time constant.
-
It is an object of my invention to provide an
frequency components are coupled through the '
improved‘noise limiting circuit of’ the shunt diode
coupling‘ capacitor I9 to a succeeding stage of the
type in‘ which the‘ threshold bias for the noise
receiver which may be,.for example, a ?rst audio
limiting diode is obtained from a separate low im 30. frequency ampli?er, not shown. Subsequent
ped'ance source and'is adjusted in accordance with
stageslof the‘, receiver may‘ include further audio
the magnitude ofiinward or negative peaks of the
ampli?cation'stagesl and a sound‘ translating de- ..
modulating wave.
vice.
~
‘
»
’
Another object of" my invention is to provide
As is‘ well; known, interfering electrical dis
an improved noise limiting circuit in which the 35 turbances of shortduration and'considerable mag
threshold level‘, is maintained above the peaks
nitude are often received‘ on thesignal channel
of the modulatinglwave', isadjusted in accordance
along with the desired? signal. These may form
with the carrier level" and the‘ per cent modula
an undesirable‘ noise background‘. with the" desired
tion, and is substantially unaffected by‘ repeated
signal or even mask it completely. Such disturb
impulse noise.
'
ances are generally grouped'under the term “im
The features of my invention which I believe to
pulse noise” as- distinguished from “shot noise”
be novel are set/forth with particularity in the
or “thermal agitation noise.” These disturbances
appended claims. My‘ invention» itself, however,
may arise from‘ various causes; For example,
together ‘with further objects and advantages
within this category‘ are" natural atmospheric
thereof; may best be understood by‘ reference to 45 static surges‘; man-made electrical‘disturbances,
the following description taken in connectionwith
as from“ high’. ‘frequency apparatus; ignition sys
the accompanying drawing, in which Fig. 1 dia
tems', and similar apparatus; and other sharp im
grammatically represents a portion of’ the cir
pulses. The characteristics of these undesired
cuits of a radio receiving apparatusembodying
my invention, and Figs. 2 andv 3v aregraphs to 50 noise impulses may vary widely depending‘ upon
their source. 'They may be of short duration
which reference is made for a better understand‘
occurring at irregular intervals or’. they may ap
ing of the operationof my invention.
pear as-repeated' impulse noise. In all cases they
The radio receiver circuitsofr Fig. 1‘ include a
detector‘ l0 which may be, for example, the second
have'a de1eterlous'e?‘ect upon the fidelity ofsig
detector of a superheterodyne radio: receiver.‘ ,5; nal reproductioneitherbydirect interference with
2,404,626
'
. ing on the network l1,
the signals or through shock excitation effect in
the receiving system.
l8 reproduce the modula
tion envelope. On the peaks of alternate half
cycles, the maximum voltage impressed across
the diode 20 from the detector I ll is approximate
.
Undesired noise pulses of the type under con
sideration are random in nature and, as such,
their occurrence follows no regular pattern.
They may be considered, therefore, as compris
ing a very large number of frequencies, having
ly equal to the sum of the maximum diode load 7
voltage on the network ll, 18 and the peak volt
age of the applied carrier wave. These two volt
ages areapproxi'rnately equal and;,hence,lthe peak
irregular ‘phase’ and amplitude components. Be-.
‘
4
'3
voltages applied across the diode~20and ‘the net
cause they are‘ random in nature, 'it is character- .
1.0 work 2l, 23, 24, 21, from the secondary winding
high frequency carrier wave, these noise pulses» 13 and the detector circuit .are approximately
,istic that when they are superimposed on a given
io'vequaloto twice the peak amplitude'of the carrier
ordinarily, in the absence of cross modulation in .7
wave developed across the winding l3
the preceding stages of the receiving apparatus,
reason for this phenomenon becomes apparent-v
Impulse noise- of the type discussedyabove ap
pears as'outward peaks of modulation on the
when it is realized that in order to occur as an
inward or negative peak of modulation Of alligh ,_ _
iter; for these, high outward peaks, the threshold '
occur’ only as outward modulation~ peaks}? The
I <
carrier wave and the diode 20 functions as a lini
frequency carrier wave, an impulse must have. . levelfor the limiter'being established by the volt- .,
age-across capacitor 2 I. When'an undesired noise
de?nite frequency, phase and amplitude ‘chara'c-W
teristics, as well as an observable period of du
20 impulse of greater magnitude than the threshold ‘
level'gand'ofshort duration is impressed .onithe
ration, so that an=.appreciab1e interval or. the high
frequency wave iscanceledbythe impulse. Noise
secondary l3 of .the transformer .H, a lowgim-v
pedance'path for voltages of; either polarity. is
pulses such as described above; being random in
, provided through one. or the other of the two 'di-,
nature, do not have these ‘requisites of. de?nite, '
ness.. Hence, such pulses ordinarily. do ,not occur, V25 odes since the ,diodes are reversely connected to
pass current. through the output load resistor I].
with such regularity as to cancel aportion of the ,
in both directions andv capacitor 2| is of low im-'
carrier wave and dcnotoccur as inward modula
pedance ,for impulses which arevconducteduby
tion peaks, but only as outward or additive peaks
diode 20. Therefore, sinceno netrecti?cati'onof
This characteristic :of, :noise'
of . modulation.
pulses is used toadvantage in my. noise limiting‘ 30 the intermediate frequency. noise transient takes
circuit inthe manner described later, -- _
place, it ise?ectively suppressed producing sub- .
In order:to limit. the, eiiectof suchnoise
pulses. on the modulationvoltagesappearing on
suppliedthrough thefc'oupling capacitor. l9.
stantially no effect'on, the audio output circuit
.
Patent. ‘2,298,083,. this . network includes
In the operation of .thelimiter thus :Iar de
scribed, it is observed that, while effective limit:
ing is obtained for a' sharp impulse-noise, in the
to the signal diode l0 through a capacitor ,2 L- A‘ '
2| tendsto be charged to a'higher threshold level '
the network I'l,.-|8,a noise. suppression network:
is provided. .As is‘ disclosedin my aforesaid U. S.‘ 35
second‘
diode detector 20 reversely connected inparallel ' presence of repeated impulse noise-the capacitor
by a?rst impulse so that a greater. portion of a
discharge circuit comprising resistor. 23 and the
rapidly succeeding impulseis developed across
the output resistor l'l before. the diodeZU bee
upperportionof resistor 24 in. series is also con:
nected across ithecapacitor 2!. In order to_ con
trol the potential across capacitor 2| an electronv '
discharge device 21. is provided having its anode
connected to'the common point, of resistor 23 and
comes conductive to limit‘ the passage of further
noise. This action is cumulative so that on ,re_-_
peated, impulse noise, the limiting circuit, tends "
capacitor 2 Land its .cathodeconn'ected to a point 4.5 to “open up”v to permit the passagegof noise; to
of ?xedpotential at the lower, end .Qfresistor 24..
Operating‘ potential. for the. anodeof device 21
may. be provided from any suitablesource, such
'as the battery 28;,theresistor .23 serving, as; ‘a;
subsequent stages of the receiver.
~
The above-mentioned limitation voperates also
with certaintypes of ‘signal to: introduce‘ distor, j
values of the elements of this‘pqr?ion of,_the cir-j
cuit,ycapacitor. 2| is made quite, large, for exam-1
ple of the order ofl mfd., and resistors 23 andzll‘
tion.. vWhen the limiter, biasing capacitor is
charged by narrow, widely,separated-modulating
peaks, suchfas occur, for example, in speech cur-V
rents, thecharge on thecapacitorzl itendseto‘
leak off between peaks. If thelimiter-pperates
have as low 'a value as is. permittedby the type
of amplifying tube selected as'thedevice 21. , The
belowv the modulation level, , such decrease of
charge on the biasing capacitorjtends to limit a '
internal resistance of the diode 2]] inv the current
conducting direction should also be approximatee
1y equal to the internal resistance of the signal
troduce distortion in the output signal.
'
Ideal noiselimiting is more closely approached '
loadresistor for the device 21. In selecting ‘the
diode
H! for bestresults;
,
,
,
.
.
.
.
- ,z
,.
succeeding wave of modulating voltage and in
if. the, threshold level ,is maintained a small
amount above the signal level andheld at this
_Considering for the moment only those ele-v
desired level in the presence of repeated impulse
ments oi the noise limiting network thus far de-,
noise. In accordancewith my invention, this is
scribed, it will be observed that‘ the diode ‘29 is in‘
accomplished by utilizing a separate low imped
circuit, with the secondary winding 13 and the
ance source to obtain the thresholdcapacitor
network i7’, 18 and that it is poled to pass current.
through these elements when conductive inthe '. biasing potential, by varying the threshold level
in accordance with the, strength of the _;?car_rier
opposite direction from current flowing inthe
wave and theper cent modulation, and byv derive
signal diode l6. Thiscircuit fex’tendsifrmn the
ing this level from inward peaks of modulation
anode 25 of the diode ZOthr-‘oiigh the‘, secondary
winding E3 of thetransformer'lLthe network l1,
l8 and‘ the network 2|, 23,124, 21‘ to the cathode
of the carrier wave.
a ,
-
-
.
"
low; impedancersource‘ comprises
retheThef's'eparate
secondary winding l4 supplying themodw
lated high frequency wave to the, auxiliary de-,
The signal diode IE1 passes current on the ‘peaks
of those half-cycles of the ~applied carrier wave ' tector.3ll, shown as a diode havingthe diode load
which make. its anode‘positivei with vrespect‘ to , resistors 3| and 32 connected in series. .The corn-,1~ '
its cathode ‘and the modulation voltages appear; ‘Id mon point? 341. of load,resistors;3l,.1321 is heldat, .
$404,626
5
6
The potential appearingacrossgthe resistor 46‘
ground potential‘ and the resistors are by-passed‘
respectively by the high frequency by-pass ca
is" adjustably supplied by means of the variable
pacitors 35 and 36, Resistors 3| and 32 prefer
contact. armv 50' tothe- controLelectrode 5| of the
ably have aboutequal resistance values, forex-i
voltage divider comprises resistor 31 and resistor
controlidischarge device, 21. The‘cathode 53 of
the discharge device 211' is directly connected. to
ground and the anode is connected through the.
loadresistor 23170 the: source of-operatin-g' poten
tial shown as the,‘ battery 28. The anode 54 is
likewise directly, connected-to the upper’ plate of j
38, having a ‘variable contact arm 39. Anaudio 10.
the threshold bias capacitor 2 I.
ample 50,000 ohms. In order to obtain a- control,
potential, which varies in accordance with the
strength of the: carrier, wave, avoltage divider'is
connected across the diode loadresistor 3!. This
r
.
frequency by-pass capacitor 40 is connected be
, .Theoperationandadjustment; of the noise ‘m. . I
tween the variable contact arm 39 ‘and the point,
iting circuitis better understood from a‘ consid
34 at ground'potential..Kv Both resistorsl?'land 38'
eration-of the curves of Fig. 2 in conjunction
are of large ohmic value andthe capacitor 48
with; the following description. First, assume
also is of a. large capacitance,- for example 1 1.5 thatzjthecontrol electrode 5| is at ground poten
tial, that‘no signals are being received and that
microfarad. As a result the carrier control volt
age network comprising the- portion of the re
anode; potential is applied to the control device '
21, The device 2'! draws anode current through
sistor 38 between the. contact arm 391 and the
point 34 and thelcapacitor» 4il~hasa relativelylong
the. resistor;23‘ producing a certain potential on
time constant.’ Hence, the unidirectional poten 20 the upperplate of the capacitor 2| and thecath
tial appearing across the portion of the resistor
ode 26,‘ The potential of the lower plate of the
capacitor 2] j is now. adjusted by variation of the
38 betweenrthe contact arm'3i3 and the point 36
varies directly with ‘the strength ofv the carrier,
contact arm 55.:on the voltage divider-.24 to ob
tain a small biasingpotential on the capacitor 2!
Wave and is una?ected- by modulation voltages
appearing on resistor 3|.
) .l
. ~§
= 5 ~ _ ;
25 such that the cathode 26 is slightly positive with
respect to the anode 25. In Fig. 2, this slight bias
The direct current component of the demodu
potential: is shown by the portion?e of the curve
lated signals appearing on resistor.- Sll may be uti
lized for automatic gain control. , Unidirectional
at the left of the ?gure.
potentials, negative with respect tolground, are
developed at- the left-hand end of ‘resistor 3| and
~
7
across the diode, Ill and the load resistor H, the
by-pas‘s capacitor. 22 maintaining the anode i5
7 at ground-potential for alternating current. The
capacitor El-I'tends to be charged through the
control connections willreadily be understood by
those skilled in the art withoutgelaboration.1’.{The
noise diodelil duetothe peak recti?cation action _
oithelnoise ilimitin'g circuit as previously de
potentials are applied to control electrodesof one
or more-ofthe tubes preceding.‘ the, detector to’
vary the ‘receiver gain in accordance with the
strength of the received signals, as is wellunder
stood in the ‘art.
'
quency carrier ‘waveis impressed upon the re-"
ceiver apparatus' A voltage is now developed
applied'through a low pass ?lter comprising: re
sistor 4! and capacitor 42 to the gain control con
nections of preceding stages. of the receiver, not
shown, Arrangement and. operation ,of'thegain
>
Assume. ‘now: that‘ any unmodulated high fre
scribed. If the ‘carrier wave is represented by the. ,
curve 6| in Fig. 2, the line 62 represents the bias
potential of the cathode 25 due to the action of
devices 39 and 21 in conjunction with the sepa
rate low impedancehsource comprising the sec--.
'
In,controliing the thresholdbias of‘the noise
limiter diode v52,6 in accordance with the per cent
ondary winding I4 and its associated circuit. > As
pointed out previously, the negative unidirec
impressed across the detector l0,jit.-,is desirable to 4-5, tional potential, developed across the portion of
the resistor 33 betweenthe contact arm 39 and
take ‘.advantage' of the fact- that-impulse, noise
peaks occur ordinarily only as'outward module-' a. the point 34, varies in accordance with the
modulation of the highfrequencycarrier waves
tion-ipeaksqfor the reasonsdiscussed above and‘
to obtain a control potential from the inward
peaks of modulation. -In accordance with my in
vention, a modulation controlv potential is ob
tained from the unidirectionalpotentials appear
strength of the carrierwave impressed upon the»
receiver, audio and sylla'bie modulating. waves
50 being removed therefrom by the long time con
stant circuit comprising. the resistor 38 and the
‘ ing across the diode load resistor 32;. The poten
capacitor 450/ This carrier‘control potential is'
supplied by means of the contactarm 39 and
tial at the upper end ,of the loadresistor 32, that ' resistor '66. to control electrode 5!. and is'e?ecti've v
is at the point 43, is always positive with respect 55 to reduce the anode current drawn by the device
to ground.
Since it is desired; to obtain a nega
21.
The reduction of, the anode current of the
tive potential varying in proportionto the nega
device 251 results in a decrease in the potential
tive peak value of modulation, the unidirectional
drop. across resistor 23 and an. equal increase in.
component of the potential atfthe point 43 is
the potential across the capacitor 21, the poten
eliminated by the capacitor Mi: Then, by use of 60 tial of the lower plate of the capacitor 2|, of
the diode 45 as the peak recti?er; a'negative po-'
course, being determined by the position of the
tential is produced on the resistor?‘i5 which varies
contactarm 55. . It is apparent that the potential
in accordance with the 7 negative‘ modulation‘
of thecathode 26, shown by thecurve '62, is main
amplitudes. The capacitor 4? vbye-passes the re
tained above the maximum ,valueof the wave 6|
sistor 45 to prevent‘ audio’ frequency voltages 65
‘from appearing on this resistor; However, syl
appearing across the diode 20.- ‘
labic voltage variations do occur on resistor d6"
limit very weak signalsgit is desirable that the
in accordance with the negative modulation peak
,
In order that the diode .20 will not operate to
_ potential across the threshold bias capacitor 2|
The values of the resistor 45 and the. capacitor‘
be raised to a value indicated by the curve 63.,
Glare sufficiently high that this network has a 70 This is accomplished by adjustment of the con
relatively long time constant with respect toaudio
frequency voltage variations and is responsive
only to syllabic voltage variations; fI'he‘loadree
tact arm 39 until the desired value of threshold’,-;;;
bias potentialis obtained. If the strength'ofthe;
carrier wave 5| is subsequently increased, ‘the.
sistor 48 completes thecircuitofgjthe.diodepeaki' bias onrthecontrol electrode 51 is correspondingly
7.5 ideefsessfls?thatsiheeb'tsntialiii?ereece between
recti?er 45.
'
2,404,626
7
'
‘ the curves mud a3 is maintained.- By proper
in a manner slmilar'to the adjustment of arm 39.
It is realized,‘of course, that the differences be-
selection of the elementsof the voltage divider
circuit supplying control potentials to the elec-.
trode' 5|, the biasing potential may be‘mad'e-to
vary substantially linearly with “the carrier
strength.
‘
r
8
.
"
‘
'
' tween'curves ‘I0 and ‘H and curves ‘l2 and .13 may
represent a" desirable safety factor which pro
vides acomplete absence of distortion for sudden
transients inv the 'receivedhsignals; ‘Since the
'
threshold bias potential is obtained from a sourcev
which isinde‘pendentrof the signal detector l0
lated by a signal ?ltwhich includes’ a plurality of 1
and does not rely upon the self-recti?cation ac
impulse noise peaks, such as the peaks 65. AS .
' tion of the diode 20, it-is possible to obtain a com-_
is pointed out above; the noise‘peaks 65 ordinar
Assume now that‘the carrier wave 6| is modué '
plete absence of distortion in the. received-"sig
ilyloccur only‘as outward or additive peaks-of
modulation; vAccordingly, in my'noise limiting
circuitt'he'inward or negative modulation; peaks
nals and there is no necessity for compromising
between distortion and limiting. Furthermore,
of thee'signal 64 are recti?ed and the threshold
' bias B3. is adjusted in accordance with the recti
when inward'negative peaks of modulation are
Y ?cation voltages thus produced. As the result
of such a system, the threshold bias 63 is substan
the limiter to open up on large or repeated noise
usedpto provide a threshold bias,ethe tendency of
interference is eliminated.
tially: unaffected by the presence of the noise
'
t
>_
It may be noted at this'point thatthe effective-v
peaks 65. Instead of being reproduced in the out
put circuits of the receiver,'the noise voltages are reduced toa low value by the short-circuiting ac-,
1y increased by employing wide band interme-.
tion of the' two 'reversely connected'diodes i0 and
and limiter and relatively narrow band audio cir
ness of the noise suppression circuit is material- 2
diate frequency circuits preceding the detector
cuits following" them.’ This fact becomes ap
parent froma study of impulse excitation char
20, which action appears as a load of large mag- "
nitude in circuit of the primary winding l2. In
order to obtain desirable operating characteris 25 acteristics of tuned circuits. 7 ‘In' a wide band cir
cuit the train of oscillations, set up bysingle
tics for the noise limiter circuit, the secondary
short sharp impulse, has a very high decrement
windings are closely coupled to each other and are
' critically coupled to the primary’ winding I72, so
‘that the 'short-circuiting action ofthe diodes - l0
whereas in a narrow band circuit, the'converse
is true. In otherywords, the length‘of the-decay
‘and'20 on the winding 13 appears also in circuit 30 train is inversely proportional to'the acceptance
of the winding
l4.
1
I band width of the system.- On the other'handit
7 _
has been found that. the ‘peak amplitude of thev
The potential variations of the point 43 are
similar to, those represented by :the curve 64 of » '
Fig. 2,‘the potential comprising a unidirectional:
age value of’ a given impulse train is practically
component'due to the recti?cation of the carrier
‘ -wave plus a modulating Wave component.
train is almost directly proportional'tothe band
width; Therefore, it can be shown that the aver
independent of bandwidth.
The
capacitor; 44 removes the unidirectional compo- ‘ V,
‘ - nentjleavingonl'y the'modulation wave, such as '
' T -
l
1
From the above principles, it follows that sharp
noise impulses impressed on the wide band iri
' termediate frequency ampli?ers preceding 'the
the wave '54’. The negative peaks of the wave 64' j
detector l0 remain sharp and of short duration»
in transmission to those circuits. If these im
pulses are now limited substantially to: the peak _
V are recti?ed by the diode 65, audio frequency
' components are removed by'the by-pass capaci-'1
tor 41' and the syllabic voltage variations are re;
produced on the resistor 46 by the negative modu~ v ' ' carrier level in the manner previously’ described, ,
lation peaks, A portion of this negative voltagej t_ very little energy remains‘ and; if they are fur
is‘supplied by means of contact arm 5ilyto, the‘ is ‘ ther ?ltered at thediode load I6, 18 and further '
' reduced in ~ peak‘ amplitude by restriction in. rela;-
control electrode 5| of the device 21 and is effec- ‘
'1 .‘tive torreduce still further the anode currentv ' tively narrow band audio circuits following- the".
' ?owing throughythe device 21 and the ‘potential j , detection stage,‘they ‘are actually reduced in ame
plitude far below the signal level.
drop across the resistor 23. _ This reduction in‘
anode current is effective to increase the poten
tial lacrossrthe capacitor 2] and. to maintain this
threshold bias slightly above the peaks ofithe
50
V
r -
,
Merely for purposes of illustration, the follow
ing-datais given for a particular radio receiving
- apparatus embodying my invention. These val-V
signals appearing across the diode 20 in a man- I ‘ 'ues were found to give satisfactory results in a
her-illustrated by the right-hand portion of the
curve 63 of Fig. 2.
V
V
,The curves of Fig. 3 assist still further in ex
plaining the operation of my noise limiting cir- ‘
cuit. 'Curve ‘[0 gives values of'the bias voltages
particular case, although they are not to be re
garded as necessarily applicable to allembodi
ments of my invention. '
'
Frequency of IF ampli?er‘
megacycles__
8.25
across the limiter 20 which are required to pre
vent limiting of a carrier wave.
, Band width of IF amplifier‘
This value is a 60 Band with of IF ampli?er
minimum value for the threshold bias that cor
responds to the unmodulated conditions as dis- 1
Ycussed in connection with curves 51; 62, 63 of‘
Fig, 2.’ Curve ‘H illustrates the manner in which
the potential supplied by the contact arm 39 to
‘
‘
,
"
‘
t
kilocycles__
.About 300
micromicrofarads__
50
Capacitors 18, 35,736
_
'
Capacitors 21, 22____microfaradx__
- 1
Capacitor’ V 44 ______ _; ____ __do___ _
.25
the control: electrode 51 is effective to raise the ‘ Y Capacitors 40, 4'7 ________ .._do___._
-1
threshold bias ‘for di?’erent carrier levels. By ad- ‘
Resistor 23 ‘_ ____________ __ohms__
‘ 10,000
justment of the position of contact arm'39 on the 7 1 Resistors 17,31, 32 _______ __do;___’ About 50,000
150,000
resistor :38, the curve, ‘H may beomade to occur , ‘Resistor, 48 __________ _;_'___do____
' .
1
. aboveor below curve 70. Curves ‘I2 and 13illus- I 70 Resistors 37, 38__.;___o_megohms__
“traterespectively the increased robiasjvalues and .
thefoperating bias values for/a 30% modulation ‘
Resistor 46_'_.'_'___'_ _____ __'_'_do____
.
' I’
Resistor. 24 _~_ ______ _a_____ohms___
'
Owens-get were The. position .ofwrve 13 l 7 Control ampli?er 52 _______ __-_,_>__
37 with respect tothe optimum-curve 1.2 jcanjbead- ';
justed by, varyingthe'position of‘ contact arm 50 i
VAnode voltage on ampli?er 52
'
volts».
5':
10,000
Type 6J5
‘
I
'
150
,
' 2,404,626
I10
' Many ‘modi?cations ‘within the scopeof my
invention will‘ doubtless iioccur ‘to those skilled'in
the (art. ‘Hence, while I have ‘shown a particular
carrier waves, a ?rst'signal channel normally
operative for the translation of signal voltages,
a shunt circuit including a capacitor connected
embodiment of my invention, ‘it'will be under
stood that I do vnot wish to ‘be limited thereto,
to said channel, a secondsignal channeltopera
1tive to reproduce signal voltages from said waves,
but I contemplate by the appended claims to
means responsive to the voltages in said'second
channel for chargingsaid capacitor to a thresh
old limiting level, and means for disabling said
?rst channel in response to a transient "noise im
cover any‘ modi?cations as ‘fall within the true
spirit and scope of my invention.
What I claim as new and desire to secure by
"10 pulse therein which increases the voltage across
Letters Patent of the United States is:
said shunt ,circuit to a value greater than said
‘1. In combination, in an ampli?er for signal
modulated waves, a‘translating circuit 'for said '
waves and means including means responsive to
the averagelevel of said waves and meansvre
sponsive to the amplitude of inward peaks of
said modulating signal for preventing the ltrans
lation of noise impulses by said circuit.
2. In a receiver for signal modulated carrier
waves and subject to undesired noise impulses,
the combination with means including a thresh
old bias for interrupting the output of "said re
level.
.
l
.
8. In a receiving system 'for signal modulated
carrier Waves, a ?rst signal channel normally
operative for the translation of signal voltages,
‘a shunt circuit including a capacitor connected
to said channel, a second signal channel operative
to reproduce signal voltages from said waves,
means in said second channel for rectifying said
wave andifo'rproducing a voltage varying in ac
cordance with the intensity thereof, means re
sponsive‘to the ‘sum of the voltages in said second
channel for charging said capacitor to a thresh
pulse, of means for adjusting saidbias ‘and the
operation of said interrupting means in accord
old limiting level, and means for disabling said
ance with the magnitude of inward‘pealrs of said 25 ?rst channel in response vto a transient noise-‘im
pulse therein which increases the voltage across
ceiver upon the occurrence of an undesired im
modulating signal.
'
'
'
'
3. In a receiver for signal modulated carrier
waves, the combination of means for interrupt
said shunt circuit to a value greater than said
level.v
'
’
1
'
9. In apparatus for receiving a signal modu
ing the output of said receiver upon the occurence
of a noise impulse therein, means establishing a 30 lated carrier wave a noise suppression circuit
threshold bias for said interrupting means, and
means for adjusting said bias in accordance with
the intensity of said wave and the magnitude of
comprising, a ?rst signal channel normally oper
ative for‘ the translation of said wave, means for
disabling said channel when the intensity of said
wave is greater than a predetermined threshold
4. A noise suppression circuit for a receiver of 35 level and for restoring said channel to operative
condition when said intensity is less than said
modulated waves comprising, in combination, a
level, and means for adjusting said level in ac
?rst signal channel normally operative for the
cordance with the per cent modulation of said
translation of an oscillation comprising a signal
wave, said last means including a second. signal
modulated carrier wave and subject to transient
noise impulses having a duration shorter than a 40 channel and means for rectifying inward modu
lation peaks of waves in said second channel.
wave length of said modulating signal, means for
10. In combination with a source of signalv
disabling said channel when the intensity of said
modulated high frequency‘carrier potentials sub
oscillation is greater than a predetermined
ject to interfering noise impulses, a ?rst signal
threshold level and for restoring said channel to '
operative condition when said intensity is less 45 channel comprising a unilaterally conducting dis“
charge device and an output impedance adapted
than said level, and means including a second
to have'demodulated signal potentials developed
signal channel for adjusting said level in ac
thereon, a second signal channel comprising a
cordance with the per cent modulation of said
inward peaks of said modulating signal.
wave.
unilaterally conducting discharge device, an im
5. A noise suppression circuit for a radio re 50 pedance adapted to have demodulated signal po
tentials developed thereon, and an impedance
ceiver comprising, in combination. a first signal
adapted to have potentials varying in accordance
1 channel normally operative for the translation
with the level of the lmmodulated carrier devel
of an oscillation comprising a signal modulated
oped thereon, means for interrupting said ?rst
carrier wave subject to transient noise impulses,
means for disabling said channel when the in 55. channel upon the occurrence of a noise impulse,
and means responsive to the potentials developed
tensity of said oscillation is greater than a pre
determined threshold level and for restoring‘said
channel to operative condition when said in
in said second channel for controlling the opera
tion of said interrupting means.
‘
11. In combination with a source of signal
tensity is less than said level. and means includ
ing a second signal channel for adjusting said 60 modulated high frequency carrier potentials sub
ject to interfering noise impulses, a ?rst signal
level in accordance with both the intensity of said
channel comprising a unilaterally conducting dis
wave and the per cent modulation thereof.
charge device and an output impedance adapted
6. A noise suppression circuit for a radio re~
to have demodulated signal potentials developed .
ceiver comprising, in combination, a signal chan~
nel normally operative for the translation of an 65 thereon, a second signal channel comprising a _,
unilaterally conducting discharge device, an im
oscillation comprising a signal modulated carrier
pedance adapted to have demodulated signa1po
wave subject to transient noise impulses, means
tentials developed thereon, means for rectifying
for disabling said channel when the intensity oi
inward peaks of said signal potentials, and an
said oscillation is greater than a predetermined
threshold level and for restoring said channel to 70 impedance adapted to have potentials varying
operative condition ‘when said intensity is less
in accordance with the level of the unmodulated
carrier developed thereon, means for interrupting
than said level, and means for adjusting said level
in accordance with the magnitude of inward
modulation peaks of said wave.
said ?rst channel upon the occurrence'of a noise
impulse, and means responsive to said recti?ed
'7. In a receiving system for signal modulated 75 peaks and said carrier level varying potential for
72,404,626
12
11
controlling the operation of said interrupting
,
means.
,
I
r
.
12. In areceiving system for signal modulated
carrier waves, a -?rst signal channel normally
operative for the translation of signal voltages‘,
5
pedance and adapted-to produce a voltage re
sponsive to the level of said carrier wave, a recti
?er diode reversely coupled to saidsignal detec
tion diode and adapted" to rectify inward peaks
of said modulating signal, an output impedance
a second signal channel comprising means for
of suitable time constant ‘for . reproduction, of
producing a ?rst voltage varying in accordance
with the level of said carrier waves, means ‘for
reproducing said modulating signal from said
waves, means connected to said reproducing in
means for producing a second voltage varying, in
accordance with syllabic variations of the inward
peaks of said modulating signal, said ?rst and
second voltages being connected in series in said
syllabic voltage variations of said signal con
nected across said recti?er diode, saidrsyllabic
second channel, and means responsive to the sum
of said ?rst and ‘second voltages for establishing ~
a threshold limiting level in said ?rst channel.
13. In a receiving system for signal modulated
carrier waves subject to interfering noise im
pulses,"a signal detection circuit comprising an
input impedance, a signal diode and an output
impedance network of suitable time constant for
through a capacitor, a control circuit comprising
an output impedance network, a voltage divider
connected across a portion of said output im
having a control electrode and an output circuit
ada’ptedto charge said capacitor to a threshold
limiting level, and means for supplying said series
connected voltages to said control electrode,
thereby to make said‘ series connected voltages
effective torcontrol said threshold level.
14. In radio receiving apparatus for translat
ing signal modulated carrier waves and subject
to undesired noise impulses, the combination of a
signal channeLa control channel, means respon
sive to the intensity of said Waves in said control
channel for establishing a threshold level to limit
the
' detection of said signals, a noise suppression diode
' reversely connected across said signal diode
‘ an input impedance, a signal detection diode and
voltage and said carrier responsive voltage being
connected in series, an electron discharge device
25
magnitude
of
said
impulses . transmitted
through said signal channel, and means whereby
the limiting of said impulses in said signal chan
nel is effective to limit the magnitude of impulses
in said control channel.
GEORGE W; FYLER.
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