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Патент USA US2117698

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May 17, 1938.
H_ T_ BUDENBOM
2,117,698
TRANSMISSION SYSTEM
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Filed Jan. 11. 1936
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BY
Patented May 17, 1938
UNITEDSTATES PATENT OFFWE
'
‘
2,117 ,698
TRANSMISSION SYSTEM
Horace '1‘. Budenbom, Short Hills, N. J., assignor
to Bell Telephone Laboratories, Incorporated,
New York, N. Y., a corporation of New York
Application January 11, 1936, Serial No. 58,727
13 Claims. (Cl. 178-44)
‘This invention relates to transmission sys
tems and particularly to arrangements for con
trolling and regulating the gain in these systems.
The objects of the invention are to regulate the
5 gain in a transmission system in such a manner
as to obtain the most satisfactory transmission
levels consistent with good quality; to utilize the
undesirable signal components present in the sys
tem to regulate and control the transmission lev
10 el; and otherwise to effect improvements in sys
tems of this character.
Systems have been devised inthe past for uti
lizing the signal currents in the output circuit of
an ampli?er for the purpose of controlling the
gain of the ampli?er. And in some cases it has
been suggested to make use of the noise currents,
which frequently accompany the useful signal
currents in a transmission system, to regulate and
maintain the energy level in the system at cer
20 tain desired values.
According to the present invention advantages
are secured over these prior systems by means of
a gain control arrangement in which the noise
currents are selectively separated from the sig
nal currents in the output circuit of an ampli?er
and then applied to the input control circuit of
the ampli?er to control the gain of the ampli?er
and maintain the energy level in the output cir
cuit within certain desired limits. The separa
30 tion of the noise currents is effected by providing
the output transformer with aiding windings in
which the useful signal energy flows to the work
circuit and also with neutralizing windings in
which the signal currents are balanced out but
which do not fully neutralize the noise currents
because of the coupling of the winding and be—
cause of the random nature of said currents.
These unneutralized noise currents are then de
livered by the neutralizing windings of the trans
40 former to a gain control circuit, in which they are
utilized to control the input potential of the am
pli?er.
The foregoing and other advantages of the in
vention will be explained more fully in the fol
lowing detailed speci?cation and will also be set
forth in the appended claims.
In the drawing, which accompanies the speci?
cation and forms a part thereof, Fig. l repre~
sents any stage of translation, such as a detec
50 tor or ampli?er, in a wave transmission system.
More speci?cally it shows two vacuum tubes con~
nected in push-pull relationship for amplifying
signal waves delivered to them from an incom~
ing circuit and for delivering the ampli?ed waves
55 to an outgoing work circuit. And Fig. 2 is a dia
gram showing the coupling of one of the trans
formers.
‘
In wave transmission systems and particularly
where vacuum tube circuits are used for trans
lation purposes, as to obtain ampli?cation of
the signal energy, the noise currents present in
the system have a detrimental effect on the qual
ity of the transmission and must be taken de?
nitely intov account if the best results are to be
had.
These noise currents are a phenomenon "
resulting largely from thermal conditions in the
physical parts of the system; they are of a ran
dom nature and occur to a large extent in ac
cordance with laws that are not readily ascer
tainable.
They are, however, known to be pro- ’
portional to the absolute temperature of the
physical elements of the system, to the resistance
values of the circuit elements, and to the width
of the frequency band being transmitted. Ref
erence may be had to an article by J. B. John
20
son entitled “Thermal agitation of electricity in
conductors” published in Physical Review, vol
ume 32, pages 97 to 109, for a discussion of the
nature and magnitude of thermal noise currents.
These noise currents mingle with the useful sig
nal currents, and it is their presence that deter—
mines and limits the amount of ampli?cation
that can‘be effected at any given stage. As the
gain of the ampli?er is raised, the ampli?ed noise
energy becomes more and more disturbing until ,
a point is reached beyond which it is inadvisable
to increase the gain. And it is because of this
relation between the intensity of the harmful
noise currents and the gain applied to the useful
signals that it is possible to utilize the noise cur- ‘
rents as a measure of the permissible gain for the
signal currents and to maintain the transmission
level at the best values consistent with the quality
required.
Referring now particularly to the drawing,
there is here shown a single translating and am
plifying stage in a transmission system. The am
plifying stage is shown as comprising a pair of
translating devices, each of which may be a
space-discharge tube of any well-known type.
While an amplifying stage is illustrated and de~
scribed herein, it should be understood that the
invention may be applied to a stage where de
modulation occurs or to any other translation
stage in, a transmission system. Likewise, it will
be obvious that the speci?c construction of the
amplifying or translating devices may vary.
The incoming circuit l shown in the drawing
is connected to the primary winding 2 of the in
put transformer T.
The two secondary wind
2
2,117,698
ings 3 and 4 of the transformer T are connected
in series, the free terminals being connected re
spectively to the grid control elements of the
space discharge ampli?ers A and A-i. The mid
point of the connected windings 3 and t is joined
by conductor 5 to a common point between the
cathode elements of the ampli?ers A and A-l.
A condenser 6 is included in the conductor 5.
The plate or anode element of the device A is
10 connected to one terminal of the primary wind
ing 7 of the input transformer T—~i, and the
anode of the other device A—-! is connected to
one terminal of a second primary winding 3 of
said transformer. The other terminals of the
15 windings l and 8 are connected to form a mid
point, and this mid-point is joined by a con
ductor 9 to the common point of the cathodes
of the devices A and A——I. A condenser I0 is in“
cluded in-the conductor 9. A battery I l is con—
20 nected through a choke coil IE or any other
suitable impedance to the conductor 9 for the
purpose of furnishing plate current to the tubes
A and A~i. With the circuit arrangement thus
described the ampli?ers A and A--i are con
25 nected in the well-known push—pull relationship.
The transformer T—i is provided with four sec
ondary windings l3, l4, l5 and It‘.
The wind—
ings i4 and I5 are connected to each other in
series aiding and to the outgoing transmission
30 circuit H.
The other two coils l3 and I6 are
connected to each other in series opposing and
to the auxiliary or control circuit I8. The pri
mary winding 7 is preferably coupled closely to
windings l3 and i4 and loosely to windings l5
35 and i6, and the primary winding’ 8 in like man
ner is coupled closely to- windings l5 and it and
loosely to windings l3 and M. This coupling
arrangement between the primary and second
ary windings is illustrated schematically in vFig.
2, and its purpose will be discussed more fully
later.
The control circuit l8, which includes the op
posing windings l3 and I6, is connected to the
input side of any suitable ampli?er I 9. A fre
45 quency selective device 25 of any suitable kind,
such as a ?lter, is included in the control circuit
H3. The output circuit of the ampli?er H! in
cludes a resistance 2% and a rectifying device 2!.
The poling of the rectifier 2! is such that the
50 ampli?ed current in the output circuit of the
ampli?er i9 always flows in the same direction,
namely, the direction in which the right-hand
grounded terminal 2!! of the resistance 29 is posi
tive with respect to the other terminal 23 of the
55 resistance. The terminals of the resistance 29
are also connected across the condenser 6, and
a choke coil 22 or other suitable impedance is
included in the connection as shown.
The operation of the system will now be de
60 scribed. Assume that signal currents are ?owing
over the transmission line i. These currents
pass through the primary Winding 2 of the trans
former T and induce potentials in the secondary
windings 3 and 4. These induced potentials cause
65 in the well-known manner changes of potential
on the grid elements of the tubes A and A—!,
resulting in turn in the flow of signal currents
through the windings 1 and 8 in the output cir
cuits of said tubes. The signal current ?owing
70 in the winding '5 bears a de?nite phase relation
to the signal current ?owing in the winding 8,
and these currents cause equal potentials to be
induced in those secondary windings of the
transformer which have the same degree of cou
75 pling with respect to said primary windings l’
and 8. For example, the potential induced in
the winding M from the closely coupled winding
7 is equal to the potential induced simultaneously
in the winding [5 from the closely coupled wind
ing 8. Similarly, the signal current induced in
the winding 15 from the loosely coupled primary
winding '5 is equal to the signal current induced
in the winding M from the loosely coupled pri
mary winding 8. ‘These induced potentials in
windings l4 and [5 add to cause a resultant sig
10
nal current ?ow in the outgoing transmission
line H. Also, since equal currents are ?owing
in windings ‘I and 8, the potential induced in the
winding Hi from the closely coupled winding l
is equal to the potential induced in the winding 15
is from the closely coupled winding 8, and the
potential induced in the winding 53 from the
loosely coupled winding 8 is equal to the poten
tial induced in the winding it from the loosely
coupled winding 1. These equal potentials in 20
the windings I 3 and It being of opposite phase
completely neutralize each other and no signal
current ?ows in the auxiliary circuit i8. There
are also present in the output circuit of the am
pli?er tubes, as was explained hereinbefore, dis 25
turbing currents which result from different
causes and which are usually referred to as noise
currents. Because of their random nature, the
noise currents ?owing in the primary winding 7
of‘ the transformer are not in phase with the 30
noise currents ?owing in the other primary wind~
ing 8. Since the winding ‘I is coupled closely to
winding i 3 and loosely to winding IS, the poten
tial induced in the winding i3 as a result of the
noise current in winding 3' is greater than the 35
opposing potential induced in the winding Hi
from the winding ’1.' Accordingly, there is as a
result of the noise currents ?owing in winding
1, a certain voltage across windings l3 and it
which is obtained by subtracting from the greater 40
potential in the winding l3 the lesser potential in
the winding Hi.
In a similar manner the noise
currents ?owing in the winding 8 at the same
instant induce a greater potential in the winding
l6 and a lesser potential in the winding I3, and
45
the resultant of these two last-mentioned poten
tials is a voltage which is out of phase with the
voltage resulting from the primary winding 'l.
Therefore, there appears across the conductors of
the control circuit IS a resultant voltage which
causes a corresponding current to ?ow toward 50
the input circuit of the ampli?er !9. This cur
rent is ampli?ed by the device 19 to produce a
voltage across the resistance 29 which varies in
magnitude with the intensity of the noise cur
56
rent ?owing in circuit it. As the noise currents
in the system increase in intensity, the terminal
23 of the resistance 26 becomes more and more
negative with respect to the other terminal 24
of said resistance. This increases the negative
potential on the grid elements of the tubes with
respect to their cathodes and correspondingly re
duces the gain of the ampli?ers.
Since even harmonic currents, should they ap
pear in the output circuits of the ampli?ers, bear
a phase relationship for the two ampli?ers, oper 65
ating in a push-pull manner, opposite the phase
relation of the fundamentals and odd-order cur
cents for the two ampli?ers, these even-order
currents may appear in the circuit l8. That is,
if the odd-order terms are in opposing phase in 70
the common circuit 9 and coils l3 and I6 are
wound to exclude these components from cir
cuit l8, the even-order components are in phase
in circuit 9 and would then appear in circuit I8. 75
2,117,698
These even-order‘ currents may be effectively
eliminated from circuit 18 by means of the ?lter
25. The ?lter 25 may be designed to exclude the
first even-order component and all higher fre
quency components, leaving in the circuit “3 all
noise currents having frequencies under that of
the second harmonic. Or, to obtain a greater
range of noise currents, the ?lter may be of the
well—known multi-peak type so designed that it
10 eliminates the successive even-order components,
allowing all noise currents having frequencies
between these successive components to flow to
the ampli?er l9.
’
What is claimed is:
l. The combination in‘ a transmission system
15
of a transmission line having a translating de
vice therein, input and output circuits for said
device, coupling transformer in the output cir
cuit having its windings arranged to selectively
20 separate the thermally produced noise currents
signal currents in said‘output circuit, and
.neans for utilizing said selected noise currents
to control the voltage in the input circuit of said
translating device.
2. The combination in a transmission system
25
of an ampli?er having input and output circuits,
an incoming transmission line coupled to said
input circuit, an outgoing transmission line, a
3
nected in said output circuit, a work circuit, a
control circuit, a pair of windings for said trans
former connected in aiding relation for deliver
ing to said work circuit currents induced from
said output circuit, a second pair of windings
for said transformer connected in opposition for
neutralizing all currents induced with equal in
tensities in both windings and for partially neu
tralizing currents induced in said windings in
unequal intensities, said second pair of windings 10
serving to deliver to said control circuit all un
neutralized currents induced therein, and means
for utilizing the currents in said control circuit
to control the operation of said ampli?er.
6. In combination an ampli?er comprising two 15
space~discharge devices, a combined output cir
cuit for said devices having signal currents and
random noise currents therein, a transformer
having its primary ‘windings connected in said
output circuit, a control circuit, secondary wind
ings for said transformer arranged to deliver to
said control circuit a portion of the noise currents
induced therein from said primary windings and
to ‘fully neutralize all signal currents induced
therein from said primary windings, and means 25
responsive to said noise currents in said control‘
circuit for controlling the gain of said ampli?er.
and outgoing line and having its windings ar
'7. The combination in a transmission system
of. means for transferring energy from one part
of the system to another comprising a trans 80
ranged to separate the thermally produced noise
former having a. plurality of secondary windings,
currents from the signal currents in said out
put circuit, a control circuit for receiving the
two of which are connected in opposition, a pri
coupling transformer between said output circuit
separated noise currents from said transformer,
35 and means responsive to the noise currents in
said control circuit for applying control poten
tials to the input circuit of said ampli?er.
3. The combination in a transmission system
of an ampli?er having input and output circuits,
4 0 an incoming transmission line coupled to said
input circuit, an outgoing transmission line, a
control circuit, a transformer having a primary
winding in said output circuit, a secondary wind
:‘or said transformer connected in said out
- going transmission line, other secondary wind
ings for said transformer connected in said con
trol circuit, said other secondary windings ar
ranged to deliver to said control circuit the noise
currents induced therein from said output cir
cuit and to effectively neutralize all signal cur
50
rents induced therein, and means for amplifying
the noise currents in said control circuit and
utilizing them to control the gain of said am
pli?er.
4. The combination in a transmission system
of an ampli?er having input and output circuits,
an incoming transmission line coupled to said in
put circuit, an outgoing transmission line, a con
trol circuit, a transformer having a primary
winding in said output circuit, a secondary wind
ing for said transformer for delivering to said
outgoing transmission line currents induced
therein from said primary winding, a pair of op
posing secondary windings for said transformer
_, connected to said control circuit, said latter wind
ings serving to neutralize all signal currents in
duced therein from said primary winding and
to deliver to said control circuit the unneutralized
components of. the random noise currents induced
Ti) iih ,rein from said primary winding, and means in
said control circuit for utilizing said noise cur
rents to control the output signal level of said
ampli?er.
In combination an ampli?er having input
and output circuits, a coupling transformer con
mary winding coupled closely to one and loosely
to the other of said opposing secondary windings
and a second primary winding likewise coupled 85
closely to one and loosely to the other of said
opposing secondary windings, and circuit means
for delivering the currents in said system to said
primary windings.
8. The combination in a transmission system 40
of an incoming circuit, two outgoing circuits,
means for transferring energy from said incom
ing circuit to said outgoing circuits comprising
a transformer having a pair of secondary wind
ings connected in the ?rst outgoing circuit, a sec
45
ond pair of secondary windings connected to
the second .outgoingcircuit, a primary winding
closely coupled to one of the windings connected
to said ?rst outgoing circuit and to one of the
windings connected to said second outgoing cir 50
cuit and loosely coupled to the remaining two
secondary windings, and a second primary wind
ing closely coupled to said remaining two sec
ondary windings and loosely coupled to the other
two secondary windings.
65
9. The combination in a transmission system,
an incoming circuit, an outgoing‘ circuit, a cou
pling transformer between said circuits compris
ing a pair of secondary windings wound in oppos
ing relation, a primary winding closely coupled 60
to the first and loosely coupled to the second of
said secondary windings, a second primary wind
ing closely coupled to the second and loosely
coupled tothe ?rst of said secondary windings,
an ampli?er serving to deliver to said primary 65
windings currents having both useful and harm
ful components, the useful currents appearing
in phase in said primary windings and the harm
ful currents appearing out of phase in said pri
mary windings, and means for utilizing the un 70
neutralized currents induced in said secondary
windings for controlling the operation of said
ampli?er.
10. The combination in a transmission system
of a transmission line having a translating de
4
2,117,698
vice-therein, input and output circuits for said
device, a coupling transformer in the output
circuit having its windings arranged to select
thermally produced noise currents and means
for ‘utilizing said selected noise currents for con
trolling the voltage in said input circuit.
11. The combination in a signal transmission
of a transmission line having a translating de
vice therein, input and output circuits for said
10 device, a transformer having a primary winding
connected in said output circuit, and a control
circuit for controlling the voltage in said input
circuit, the primary and secondary windings of
said transformer being so arranged that noise
currents existing in said output circuit as a
result of noise currents thermally produced in
said input circuit are impressed on Said control
circuit while signaling currents have no eifect
on said control circuit.
12. In a transmission system, a transformer
20
having two primary windings and a plurality of
secondary windings, said primary windings being
energized by currents some components of which
are at all times of' substantially equal intensity
25 in both windings and some components of which
areof random intensity and occurence in the two
windings, one of the secondary windings being
closely coupled to one of the primary windings
and loosely coupled to the other of the primary
windings, and another secondary winding being
closely coupled to said other primary winding
and loosely coupled to said one primary winding,
said secondary windings being connected in op
position.
13. In a transmission system, a transformer
having two primary windings and a plurality of 1O
secondary windings, said primary windings being
energized by currents, some components of which
are at all times of substantially equal intensity in
both windings and some components of which
are of random intensity and occurrence in the 15
two windings, one of the secondary windings
being closely coupled to both of said primary
windings, another secondary Winding being
closely coupled to one of the primary windings
and loosely coupled to the other of the primary 20
windings, and another secondary Winding being
closely coupled to said other primary winding
and loosely coupled to said one primary winding,
said other secondary windings being connected
in opposition.
'
HORACE T. BUDENBOM.
25
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