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Патент USA US2408073

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' Sept. 24, 1946.
K. s. JoHNsoN
2,408,072
TELEPHONE REPEATER CIRCUIT
Filed Dec. 31; 1943
-3 Sheets-Sheet 1
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KS. JOHNSON
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Sept. 24,1946»V
»Kr s. JòHNsoN 'A
IÁTEpEPHoNE REFEATE'R CIRCUIT
-
Filed Dec. s1. 194s
`
2,403,072~
_
s 'sheets-sheet 2
IN VEN TOR
ATTORNEY Y'
'
2,408,072
Patented Sept. 24, 1946
UNÍTE
STATES PATENT OFFICE
2,408,072
TELEPHONE REPEATER CIRCUIT
Kenneth S. Johnson, South Grange, N. J., as
signor to-Bell Telephone Laboratories, Incor
porated, New York, N. Y., a corporation of New
York
l
Application December 31, 1943, Serial No. 516,464
16 Claims. (Cl. 179-170)
2
e This application is in part a continuation .of
circuit; and, indeed, any one may be considered
my ccpending application Serial N o. 509,056, ñled
to include one or more interoffice trunks of con
November 5, 1943, for Telephone repeater cir
ample, telephone repeater systems, involving net
siderable lengths (switched in attimes in extend
ing the talking connection from the cord circuit
to a desired subscriber station) so that its im
pedance facing the cord circuit suifers substan
works that include conjugate circuits and have a
tial variation.l
cuits.
’
This invention relates to systems, as for ex
branch subject to impedance variation that dis
turbs the conjugacy.
„
An object of the invention is to maintain con
jlugacy in such networks.
'
f
In one speciñc aspect the invention is a system
comprising a cord circuit repeater for connection.
to any chosen one of a group‘of subscriber loops
'
The cord circuit includes a link 2| connecting
hybrid coil 2 with plug I3, and a link 22 con
10 necting the hybrid coil with plug I8. The link
22 includes supervisory relay 23 and central oiñce
wiring represented by its equivalent resistance 2li.
Two thermistcrs 25 and 2S comprise tempera
ture-dependent resistances T11 and T (which may
of various impedances, and having direct current 15 have negative temperatures coeii'lcients of re
sistance) and heater elements I-I1 and H2 elec
supplied from the cord circuit over the connected
trically insulated from VT11 and T. (Thermistors
loop for talking or supervisory purposes, the cord
are described in an article by G. L. Pearson at
circuit repeater including therrnistor means re
page 106 of the Bell Laboratories Record for
sponsive to the direct current to so adjust the
impedance of a balancing circuit for the loop as 20 December 1940.) The elements H1 and H2 are in
series in the link 22. Resistance T is connected in
to establish impedance balance between the loop
series in the link 2I through an impedance-modi
and the balancing circuit.
Other objects, aspects and features of the in
vention will Ábe apparent from the following de
scription and claims.
Fig. 1 shows a system in which the invention is
, applied to a cord circuit repeater of the 21-type;
Figs. 2 to 6 show four-terminal networks use
ful in systems such, for example, as those of Figs'.
1 and '7; and
.
.
.
'
`
Fig. 7 shows a system in which the invention is
applied to a cord circuit repeater of the 22-type.
In Fig. 1 is shown a cord circuit or connecting
fying network 3I and an impedance transformer
32.
The (variable) resistance of element T is
25 designated T and that of T11 is designated T11.
The resistance presented tc the- transformer 32
by the network 3I terminated rby T is designated
' R. The resistance inserted in the link 2| by the
transformer 32 is designated r. This resistance
30 forms the series arm of a 1r-network in theÍ link 2|,
one ofV the shunt arms including a group of- con
densers 33' adapted to be connected in parallel by
a sliding switch 34, and the other shunt arm in
cluding a group of condensers 35 adapted to be
circuit, comprising a .2l-type repeater including
amplifier I and bridge transformer (hybrid coil) 35 connected in parallel by the switch 34.
The switch 34 is shown drawn to its extreme
2, for connecting any chosen one of a group 3 of a
right-hand position against the tension of the
considerable number of subscribers’ loops such as
spring 36, by action, on its soft iron plunger 3l,
the two indicated at il and 5 with anychosen
of flux due to current in its operating coil 38.
one of a group 6 of a considerable vnumber of
subscribers’ loops such as the two indicated at 'l 40 This crurrent maybe space current of a tube 4I,
controlled by temperature-responsive resistance
and :8. The loops. are shown terminated in sub
T11. As described hereinafter, this current can
station sets 9, I0, I I and I2, which may each have
-be reduced by heating T11. Then spring 3S can
an impedance of 60 ohms, for example.
draw switch 3'11 to the left. The switch in this
Switching means of any suitable type, as for ex
ample plug I3 for cooperation with jacks of loops 45 movement to the left, can remove from _circuit
the condensers 33 successively, and simultane
3 and plug I8 for cooperation with jacks of 'lines
ously remove from circuit the condensers 35 suc
6, may serve to connect the cord circuit with loops
cessively. In the extreme left-hand position of
3 and 6.
Y
The loops 3 have their impedances facing the
the switch, all of the condensers 33 and 35 will
cord circuit approximately equal. For example, 50 be out of circuit.
Y
they may lbe private branch exchange loops of '
Direct current is 'supplied- to the substationY tele
negligible length, or may be loops in a congested
business area, all of substantially the same length.
The loops 6 may have various lengths, or sub
phone sets connected to the cord circuit from bat
tery 45 (of 24 volts, for example) through the
connecting loops. This direct current applied
stantially different impedances facing the cord 55 over the loops to the substations may be either
4
3
for talking and supervisory purposes, if the sub
station is of the common battery type with its
transmitter energized from battery Q5, or for
supervisory purposes only, if the substation is of
the local battery type with common battery super
Vision. For the sets connected to loops 3, this di
rect current can be supplied Via link 2l and the.
z2 is within the limits of tolerance, then the re
'spense of T11, 4I and 34 should be insufficient to
disconnect any of the capacities 33 or 35; where
as, if plug i8 be connected to a loop 6 so short as
to require a given reduction of the capacities 33
and 35 in circuit in order to bring the degree of
balance between Z2 and e2 within the limits of
tolerance, then the response of T11, 4I and 3e
loop 3 to which plug I3 is connected. For the sets
should be such as to eiîect such reduction.
connected to loops 5, the direct current can be'sup-`
Network 3| may be referred to as a shaping net
plied via link 22 and the loop S to which plug IB is 10
work. It controls the shape of the characteristic
connected. This direct current in link 22 flows
(not shown) of R versus T, as discussed herein
through heaters H2 and H1 and is the current for
after. In the speciñc form shown in Fig. l, it ccn
heating them and thereby controlling the> tern
sists of resistances A and B; but other forms may
peratures of T and T11 and consequently the re
be used, as willbe made apparent hereinafter.
sistances of T and T11. (The heating effects of
Any suitable number of condensers 33 and S5
the voice currents or alternating currents ñowing
in link 2lV may be used, to obtain any desired
in H2 and H1 upon T and T11- are negligibly smalll
number of steps in the capacity Variation. The
When plug E8 is disconnected from all ofthe'
individual condensers 33 and 35 may have any
loops 5, no direct current flows through heaters
Hz and H1. rEhen T, R, and 1' have their maxi 20 suitable Values, either the same or different, to
obtain equal or different steps of any desired
magnitudes; or any suitable form of condensers
may be used as for example, well-known types
sistor 5i! has its minimum Value. Consequently,
of ganged air condensers (not shown) with’ sets
the` component of negative grid bias thenfur
nished for tube lll by the voltage drop across re 25 of ñXed-and movable plates shaped to continu
ously vary the capacity as desired upon relative
sistor ëû due to this current in 59,' has its mini
motion of the plates.
'
,
mum Value; and the space current Vof >tube #it
flowing in coil 33 has its maximum value, so
and
Opening
6l (withswitches
switches55B2 and
closed)
closing
replaces
switches
vthe cir
switch 3d is in its extreme right-hand position',
cuit
of
tube
4I
by
a
circuit
comprising
series
in
as shown.
`
30
ductance L and shunt capacity C1, an oscillator
When the kcord circuit is connected between
or other alternating current source 53 or fre
two loops, it is'desired'that before switch El is
quency f, thermistor SS, network 61, and source
closed to complete the repeater circuit, the link
of electromotive force 69. Thermistor 6% com
2l automatically be given'any adjustment re'
prises a temperature-dependent resistance Te
quired for building out the impedance of the con
with temperature coeñicient of resistance of the
nected lcops Btc ‘make the impedance e2’ pre
same sign as that of temperature dependent re
sented to terminals 53 of the hybrid 'coil equal the
sistance T11, and heater H6 electrically insulated
impedance Z2 presented to terminals 52 of the
from resistance Ts. Heater He is in series with
hybrid coil or balance the impedance Z2 sufli
ciently well to prevent the repeater from having 40 source 63 and condenser C1, which is shunted
mum values. T11 also has its maximum Value, so
the current flowing from battery ¿i9 throughA re
any undue singing tendency.
'
This automatic adjustment is eiîected by re
sponse cf thermistor 26 and network' 3l to give
r the proper value, and response of thermistor
25, tube ¿il and switch '3d to properly adjust the
capacities 33 and 35 connected in circuit.
The longer the loop 6 to which plug IB is con
nected, the greater willv be its resistance, the less
will be the current in'Hz, and the 'greater will be
T, R and 1‘; and the shorter the loop, the less will' .
be its resistance, the greater will be the current
in H2, and the'less will be T, R and r. The re
sponsiveness of T and 3l must, by proper de
sign, be made such as to always establish and
maintain lwithin the limits of tolerance the bal- .
ance between the resistance component of Zz and
that of e2.
In some systems, as for example, where the
variation of length of the loops 6, or the range
of impedance variation of the loops 6, does not eX 60
ceed certain limits, the adjustment of resistance
balance may be adequate for preventing singing,
without necessity for‘provision of capacities 33
across elements L and T11 in series. Element Ta
terminates network 61. Network 61 is shown as
a 1r network of resistances A, B and C.
It is
a shaping network for controlling the shape of
the characteristic of Re versus T6, where Re desig
nates the impedance or resistance that coil 3S
faces (with switches 55 open) and Ts designates
the impedance or resistance of thermi'stor ele
ment T6.
'
With L and C1 given such Values that
thermistor 66, source 63 and elements L and C1
make it possible to have the sign of the resist
ance variation of T11 opposite to the sign of the
consequent resistance variation of Te, though ele
ments T11 and Te be alike as regards the signs of
their temperature coeiiicients of resistance. As
suming, for example, that the temperature coef
ñcient of resistance of T11 is negative, as T11 gets
smaller due to increased current in H1
‘211e tout)
and 35; and then switches 55 may be opened, or
capacities 33 and 35 and switch 34 and its con 65
at the oscillator frequency j or lZv] becomes pro
trol circuits may be omitted. However, their pro
portional to the reciprocal of T11. That is, at the
Vision' enables closer `impedance balance between
frequency of anti-resonance the network consist
e2 and Z2 to be obtained, especially in systems in
ing or resistance T11 and inductance L inseries,
which the Variations in length or impedance of
70 shunted by capacity C1, has its impedance in
loops 6 are great.
v
If plug I8 be connected, for example, to a loop - creasein magnitude as the resistance T11 de
creases. Thus, increase of the heating current in
6 that is so long or has such high resistance and
effective shunt capacity (distributed capacity)
H1 -causesdecrease of the resistance T11, with
consequent increase of [Zf/I, decrease of heater
that, with switch 34 inits extreme right-hand
position, the degree of balance between Z2 yand 75 current in Hs, increase of resistance Ts, increase
,
5y
,
The formulae for a ladder> network of the form
shown in Fig.`4 (a `1r-network) are:
of resistance Re, and decrease> ci?v the» current
flowing from'battery 69 through vcoil 38,.v
' ^
Opening switches> 50 and 62 1 and v'closing
switches 1U and 12 replaces the source 6'3 and
the networkv L, C‘i’by a source ,13' with resistance
'I5 and a lattice or bridge network 14 comprising
resistances A, B, C and D proportioned so that
A/B=C/D. Then, as the> heating current in H1
increases, the resistance T11 becomes’smaller-as
compared- with A-and the lattice or bridge net
work 14- becomes more Vnearly balanced, so the
current ñowing from source 13 in heater He
lll
decreases and consequently the resistance T6
increases.
The source 13 may be either a direct
current source or an alternating current source.
The shaping networks 3| and 61 are typical of
1
.
A_w/wy‘z
four-terminal networks designed so that if ter
minated in a, variable resistance, for example aV
varistor or a thermistor, the input resistance hasv
a plurality of preassigned values, (within Vthe 20
limits of physicalrealization), one for each of a
plurality of speciñed values of the terminating
A
=
B
,and
(13)
1
=
1
~1 xfa/T2
Y
resistance. For example, two preassigned Values
of input resistance, which may be designated R1
,
< 4)
,
A
i
(15)
and R2, can be obtained with a two-element lad 254
der network (such for instance as network 3l of
The 1r-network may be replaced by its equiva
Fig. A1 or the network of Fig. 2) or with a lattice
lent T-network with the conversion relations of
network such for instance as that'of Fig. 3, kand '
Figs. 28A and 28B of Appendix D of my book
three preassigned values,- which may be desig
“Transmission Circuits for Telephonie Commu
nated R1, R2 and Rs can be obtained with a three
30' nication/’_ published by the D. Van Nostrand
element ladder network such', for instance, as
Company, New York.
It may be noted that although Formulae Y1 to l5 '
network 61 of Fig. 1 vor the network of Fig. 4. ,
The design formulae for a network of thecon
figuration of network 3| can be shown to be:
were derived on the assumption that all of the _
'
circuit elements involved were pure 'resistances
' these formulae are also Valid if all of the circuit
A-
2
i ( 2
"R112 (l)
t TVT,
and
Y
elements are pure reactances of the same sign.
Consequently, if A, B, C, R. and T in the formulae
were all replaced by corresponding induct'ances,
,
(In, Ln, Lc, LR, and LT) , kor by the reciprocal of
Enna-_Raw
f
capacitances, (I/CA, l/CB, l/Cc, l/C‘R, andi/Cr),
(2,
the formulae would still be valid. For example,
Formulae l@ to 15 would serve if, with a variable
terminating inductance Lr (instead of a variable
resistance T), it were desired to design a network
The formulae for a network ofthe form shown
in Fig. 2 may be given as:
C:
composed of pure inductances LA, LB and Lc
such that the inductance at the input terminals,
LR, would have anyv three desired preassigned
values.
'
Specific numerical examples of designs for net
50 works of the ladder and lattice types shown in
Figs. 5 and 6 are givenfin the following table:
Fig.
Re
Rx
R2
Rs
To Tx
5- _ _ _
5- _ _ _.
48
91
100
133
342
342
642
642
6- _ _ _
101
140
342
642
5- _ _ _
102
142
342
642
0
_., 115
5..-. 227
152
242k
342
342
642
642
O
0
Tn
Ta
A
B
C
55
The formulae for a lattice network of the con
figuration shown in Fig;` 3 are:
`
Y
O
0
43
43
300
300
860
860
43
91
262
1530
-395
°°
0
43
300
860
51
3400
____ _ _
43
300
860
106
4260
2880
43
43
300 860
300 l 860
122
386
œ
'-718
1870
551
60
All the circuits of the table were designed such f
that (1) `when 860 ohms resistance (=Ta) was
connected across the output terminals, the input
resistance
(E123) would be 642 ohms, and (2)
65
when 300 ohms resistance (=T2) was connected
across the output terminals, the input resistance
v(ERz) would be 342 ohms. For the cases v1n
which A, B and C are all ñnite, thev design also
assumed T1==43 ohms and R1 was preassigned to
.70
have the Values indicated. For the other cases,
R1' was calculated for T1=43 ohms, and for all
cases Ro was calculated when the terminal re
sistance Tb wasl 0 ohms.
l
It may be noted that cases ( 1) andv (f6-)f are -not
allegare,
7.
_
tive.
--
-
I
A
g
mayljlave- yaripus lengths or substantially diñer~
I'J'hysicalflyv realizable sinceeither B or C_f is nega
ent impedances facing` the cord circuit.
The. cord circuit includes a balancing ne"
'
Also, it is noted that the value of Ro (=102
ohms), in the case of the three-element physi
work or circuit N> attached to the network ter
minals 53_ of the hybrid coil 2. The network N
cally realizable network, (=Case 4) , lies between
the values of R1 (91 and 115 ohms) -given by the
comprises k_av linkvcircuit. 8i .terminated in a
dummy telephonev set or an ,impedance 88 simu
two-element networks (_-Case 2 and 5); and
likewise «the value of R1 <=142 ohms), in the
lating the impedance of a set such as il or l2.
Case 4, lies between the values of R1 v(133 and 152'
The link 8l .as shown-fis Vlike link 2l of Fig. 1,
ohms) given by the two-element networks (=Case 10 except that fan_¿_optional- blocking condenser 85
and a-resistanceïßû, ,which are referred to here
inafter, are shown in the link 8|.
»
For the circuit of Fig. 2, the table below gives
Zand
5) .
_
_
_
_
_
»The cord'circuit includes alink -82 Vconnecting
the-line terminals 520i the-hybrid coil 2 with the
the calculated values of Rand r-for three values
of T produced by three-values of direct> current I
that flows in heater H2 for three speciñed values
of RIA-34. RL designates the variable direct cur
rent resistance of the'loop-.circuit connected to
link 22 by plug le; Ía’nd'iill is the Value, in ohms,
plug I8.- The link -8_2.as-shown»is like link 22 -of
Fig@ 1¿,A except that the supervisory relay 23 and
centralloiîiceryvirir-ig> resistance 24 are omitted
land aheater element H9 of an additional ther@V
mistor 90, similar> to the thermistors 25 and 26,
assumed for the total direct current resistance
of 4.the elementsâi-LÍ 2li, H1v and H2 in series in the 20 isshown in the link- 82. The-thermistor 80 com
’ prisestemperature-dependent resistance T9 heat
link 22, as indicated by the resistance values
ed vby jI-Ig ¿and --electrically Y» insulated from H9.
appearing in Fig. l. The direct _current resistance
Thev resistance T9 may have a negative temper
of the substation sets is assumed to be 60 ohms
ature coeñicient of resistance, Yfor example. It
as indicated in Fig.V irand I Yis calculated as
'
25
24
154-i-RL
is connected,` across _the input circuit- of- ampliñer
l, either directly or through-a- shaping network
81»shownjas;oi the; same type as network 61,
and controlsthe gain of that amplifier as indi
cated.h`ereinafter._ If desired,- the network 8l
because, as indicated in the Fig. l, the voltage of
battery 45 is Yassumed to be 24 volts, the direct
current resistance of they secondary winding of
the ampliñer output transformer is assumed to
be 20 ohms, and that of the hybrid coil windings
traverseduby I is assumed to be 40 ohms.
maybe as'haping network of the type of net
work 3|v,¿or-may be of any of the types shown
in Figs. 2 tov 6,'¿for example.`
_
y
y
The lowerffhalf _of the cord circuit repeater as
shown in Fig. 7 -isla duplicate -’of the-upper half.
vat The reference__characters____designating the `ele
ments _in_theLfloWer ,halfv-'a-rß'those _designating
the corresponding-elements of the “upper half
primed. In Fig. 7 the dotted lines connecting
thermistor T11 and coil 3_8 are for indicating that
40
the connection maybe as in vlï‘_ìg»..l._ Similarly the
connection betweenTn' and 38’ may include the
It will be noted from the table that the three
values of r closely approach the corresponding
values of RL-i-34.
_
l
-
Below is a similar table for a circuit similar 45
to> that of Fig. l but with network 3i omitted,
the ratio of transformer 32 made 3:1, and the
resistance of heaters H1 and H2 each made‘l
ohm.
RL
R11-F32
I
T
r
0
100
32
132
0. 160
:096
6l
287
20
96
200
232
. 069
615
205
`300v
' 332
.A053 '
1000
333>
400
500
432
532
. 044
. 037
1270
1470
417
490
apparatus shown in Fig. l in the connection
between T11 and 38. Direct currentfrom bat
tery 45 is supplied over theI loop 8 to which plug
I8 is connected, to thesubstation of that loop,
either for talking and supervisory purposes if _the
substation islet the _common battery type, or for
supervisory purposes, only, if ¿the substation is of
the local battery type withV common battery super
vision. Similarly, direct current is supplied over
the loop 6’ to which plug I8' is connected, to .the
substation of that loop. The blocking condenser
85 is of negligible-impedance at voice’îfrequencies.
It prevents direct current flow from battery 45 to
.55
As indicated by the degree toA which)- ap
proaches RL+32 the network 3L may well be 60
omitted as unnecessary in some cases.
Y Fig. 7 illustrates application of the invention
network N. This results in a maximum variation
ofr the resistance T, T11 and T9 as a function of
the loop length. -Similarly, condenser 85’ pre
vents Iiow of direct current from battery G5’ to
network N_’._.
Resistance 8‘6 serves to counterbalance the re
sistance of heaters H1, H2 and H9; and similarly
resistance 88’ counterbalances the resistance of
H1', H2’ and H9’.
l
to a system comprising 'a cord circuit repeater of
The gain which -it is possible to obtain from a
ZZ-type including ampliiiers i and I' and hybrid
coils 2 and 2', for connecting any chosen one'of 65 22-type repeater depends upon»~ the closeness of
lthe impedance balances between (a) the line in
a group 6 of Subscribers’ loops or trunk circuits
one direction and its balancing network, and (b)
such as the two indicated at 1 and 8 with any
the line in the other direction and its balancing
chosen one of a group 6’ of subscribers’ loop or
trunk circuits such as the two indicated at 1’
and 8'. To make such a connection, a plug I8
_at one end of the cord circuit is inserted in the
cooperating jack of the chosen one of lines 6 and 8
and plug I8’ at the other end of the cord circuit
is inserted in the cooperating jack of the chosen
network. In the case of each of the two balanc
ing networks of a 22-type repeater such as a
cord circuit repeater, the impedance of the net
Work ordinarily is given some value representing
an average of the impedances of the lines it is
to balance, since _thenA lengths of the loops or
one ofulines 6’. The linesvß and also the lines G' 75 trunks differ and-.consequently the impedance
2,408,072
10
Eig. 1), in cases in which the variation of length
of the line to bev balanced by the vnetwork varies.
of the lines connected to the repeater, or the range
This variation may be considerableand cons/e
of impedance Variation of the lines, does not ex- „
quently the ratios of the line impedances to the
impedances of the two balancing networks may
Aceed certain limits,v the adjustment of the vre
depart so far from unity that the gain of the Cl sistance balance may be adequate for reducing
singing tendency and permitting the desired
repeater must be limited toa relatively low value
amount of repeater gain, Without necessity for
(for example, 6 or 7 decibels) in order to pre
`provision ofv capacities 33 and 35 and capacities
vent singing.
Y33’ and 35'.; and then theseA capacities and their
By yproper use_,of thermistors, .balancing .net
works can be so constructed that'they are effec-n 10 control circuits may` be omitted. However, (as
in the case of the capacities33 and 35 of Fig. 1),
tively duplicate copies of the actual lines that
the provision of thecapacities 33 and 35 enables
they must balance, regardless of the lengths of
closer impedance balance between Z2 vand z2 to be
these lines. Hence, as the repeater `is employed
obtained, and similarly the provision .of capacitiesv
between lines of different lengths whose imped
ances vary, the impedances of the correspond 15 33' and 35" enables closer'impedance balance be
tween Z2» and 'zz' to be obtained.
„
ying networks will vary in the same way, thereby
If plug .I8 be connected, for example,v to a line
maintaining a close balance between the imped
ance of the lines and that of their corresponding
balancing networks. ' This 'makes it possible to
obtain much greater -gains from such a repeater`
than would be possible if the networks were fixed,
i. e., not variable.
,.
20
that is so longor has such high capacity that,
A,with switch 34 in its extreme right-hand position
the degree of balance between Z2 .and .z2 is within
the limits of tolerance, then the response of Tn,
s4 and the circuit connecting them (as described ‘
_
in connection with'Fig. 1) should be insuii‘icient
v In the system of Fig. '7 this automatic balanc
ing is done by means-of thermistors 25, 26, v25’v „ to disconnect any ofthe capacities 33 and 35.;
Whereas,v if plug |8Abe connected to 'a line so short
as to require a given reduction of the capacities
33'and 35 in circuit in order to bring the degree
of balance between Z2 and z2 within the limits of
of the line varies, the current, or power dissipated
tolerance, then the response of Tn, 34 and their
in these heaters varies 4and the resistance values
of their corresponding temperature-dependent re 30 connecting circuit should be such as to effect such
reduction. As indicated above, control of capaci
sistance elements T11, T, T11' and T' also vary,
ties 33’ and 35’ is similar to the control of the
these resistance values (with the usual type of
capacities 33 and 35.
'
'
»
thermistor) becoming rapidly larger as the cur
and 2,6', which have .their heater elements H1,
'Ha H1I ‘and H2» inserted in .series with the »lines
and a. battery such as V155 and 45’. As .the length
When the line 6 to which plug >|8 is connected
is comparatively short, the direct current from
battery 45 through heater H9k will be relatively
large and the resistance of the heated element T9
rent through the heaters becomes less or as the
length of the loop or trunk becomes greater.
When the cord circuit is connected between two
lines, it is desired that before switches 5| and
5l’v are Aclosed to complete the repeaterr circuit,
the link 8| automatically be giveny any adjust
ment required for building out the impedance of 1
the connected set Bßtoznake the Vimpedance ez
presented to terminals 53 of hybrid coil `2 by net
work N equal the .impedance Z2 presented to ter
will -be its attenuation and the greater will be the
gain required from the amplifier in order to olîset
this greater attenuation and stabilize the trans
missionequivalent of the circuit and the levels at
pedance Zz sufficiently closely, and the link 8|’
automatically be given any adjustmentrequired
for building out the impedance of theconnected
set 8B’ to -make the impedance z2» presented to
the terminals 53’ of hybrid coil 2’ by network N’
equal the impedance Z2’ presented to terminals
the terminals. If network 81 be omitted, then
52’ of the hybrid coil 2’ or balance the impedance
Z2» suiiiciently closely, so the repeater will be pre
vented from having any undue singing tendency
or any undue limitation on its permissible gain.
The automatic adjustment of the link 8| is ef
fected by response of thermistor 26 and network
3| to give r the proper value, and response of ther
mistor 25, switch 34 and the circuit `therebetween
(as described in connection with Fig. 1) to prop
erly adjust the capacities 33 and 35 connected in 60
circuit, so the 1r network formed by the resistance
r and the capacities 33 and 35 will represent close
ly the actual loop or trunk to which plug IB has
f
~
,
The longer the line 6 to which plug I8 is con
fier will be reduced and the ampliñer gain will
be smaller than were the line longer and the re
sistance of T9 correspondingly higher. This is
desirable because the longer the line the greater
minals 52 of the hybrid coil 2 or balance 'the im
been connected.
will be comparatively small.l Since T9 is connect
ed across the input circuit of ampliñer `|, through
network 87, if desired, the output of this ampli
65
when the lines 6 to which plug I8 may be connect
ed are long, the simple `shunt bridging loss of T1
may be not such as to give the required shape
to the characteristic of the variation of ampliñer
gain as a function of the line length. In this case
the required shaping can be obtained with a shap
ing network such as 81, and if desired a trans
former such as the transformer 32 shown in con
nection with shaping network 3|, (as the proper
variation of 1' as a function of the resistance of
T is obtained with network 3| and transformer
32, and as the proper variation of the current
through coil 3S as a function of the resistance of
Te is obtained with the aid of network 61, for eX
ample). As indicated above, the control of the
gain of amplifier |’ by thermistor 90' is similar
to the control of the .gain of amplifier | by ther- K
mistor 95.
will be the current in H2 and the greater will be
In the systems of Figs. 1 and 7, the substations
T, Rand r. The responsiveness of >T and 3| must,
or telephone sets may be of any suitable type.
by proper design, be made such asalways to estab
lish and maintain within the limits of tolerance 70 If desired, ||, I2, ||’ and I2’ may be anti-side
tone telephone sets of any of the types disclosed
the balance between thev resistance component
in my copending application Serial No. 463,184,
of Z2 and that of z2.
ñled October 24, 1942, entitled Telephone system,
The automatic adjustment of the link 8|’ is
having the balancing network in the set automati
similar to that of link 8|.
With the system of Fig. '7, (as with `that ofV 75 cally adjusted in accordance with the length or
nected, the greater will be its resistance, the less
2,408,072
11
12
impedance of the line to which the set is con
nected.
What is claimed is:
l. A wave translating system comprising a line
impedance which may have different values, two
circuits, electric wave amplifying means having
means providing a balancing circuit and a line
circuit for two-way communication with any se
lected one of said lines through said two iirst
mentioned circuits and said amplifying means,
said balancing circuit being adapted to balance
an ampliñer input circuit connected to >one of
said two circuits and an amplifier output circuit
connected to the other, means providing a bal
ancing circuit for said line impedance and a line 10
circuit for two-way communication with said
line impedance through said two first-mentioned
circuits and said amplifying means, means com
the impedance of the selected line, means com
prising said balancing circuit for connecting said
two first-mentioned circuits in energy transmit
ting relation to the selected line and in conjugate
relation to each other, means in one of said two
first-mentioned circuits for supplying direct cur
rent to the selected line, and means responsive to
said current for controlling the resistance of said
prising said »balancing circuit for said line im
balancing circuit.
pedance for connecting saidv two first-mentioned
5. A wave translating system comprising lines
of different resistance, two circuits, wave ampli
fying means having an amplifier input circuit
circuits in energy transmitting relation to said
line impedance and in conjugate relation to each
other, and thermistor means responsive to
change in the value of said line impedance for
changing the impedance of said balancing cir
cuit in substantially the same ratio to maintain
conjugacy of said two first-mentioned circuits.
_ 2. Awave translating system comprising a line
impedance which may have different values, two
circuits, wave amplifying means having an arn
connected to one of said two circuits and an am
plifier output circuit connected to the other,
means providing a balancing circuit and a line
circuit for two-way communication with any se
lected one of said lines through said two first
mentioned circuits and said amplifying means,
said balancing circuit being adapted tobalance
25 the impedance of the selected line, means com
prising said balancing circuit for connecting said
plifier input circuit connected to one of said two
two iirst-mentioned circuits in energy transmit
circuits and an amplifier output circuit connected
ting relation to the selected line and in conjugate
to the other, means providing a balancing circuit
relation to each other, said balancing circuit corn
for said line impedance and a line circuit for two
>way communication with said line impedance 30 prising a four-terminal network having shunt
capacity and series resistance, means for pro
through said two iirst-mentioned circuits and
ducing direct current in the selected line depend
said amplifying means, means comprising said
ent in magnitude on its resistance, and means
balancing circuit for said line impedance for
responsive to said current for varying said ca
connecting said two first-mentioned circuits in
,
energy transmitting relation to said line imped 35 pacity and said resistance.
6. A telephone transmission system compris
ance and in conjugate relation to each other,
ing a group of subscribers’ circuits of different re
impedances comprising a temperature-dependent
sistances, a group of subscribers’ circuits of ap
resistance in said balancing circuit adjustable for
proximately a given resistance, a 21-type repeater
producing changes of the impedance of said bal
ancing circuit corresponding to changes occur 40 having two pairs of terminals, a 7r-network com
prising adjustable shunt capacities and a tem
ring in said line impedance to maintain balance
perature-dependent resistancen for connecting one
of said line impedance by said balancing circuit,
of said pairs to any chosen one of said second
and means comprising a heating element for
group of circuits, means for adjusting said ca
said temperature-dependent resistance respon
sive to said changes in said line impedance for 45 pacities, temperature-dependent resistance for
controlling said adjusting means, a source of
effecting said adjustment of said adjustable im~
direct current for energizing said subscribers’
circuits to condition them for operation, current
3. A wave translating system comprising lines
responsive heating means for said temperature
of different resistance, two circuits, wave ampli
fying means having an amplifier input circuit 50 dependent resistances, and a circuit comprising
said heating means for connecting said other
connected to one of said two first-mentioned cir
pair of terminals to any chosen one of said i'lrst
cuits and an ampliñer output circuit connected to
group of circuits with said heating means in series
the other of said two ñrst-mentioned circuits,
with that chosen circuit and said source.
means providing a balancing circuit and a line
circuit for two-way communications with any 55 7. A wave translating system comprising a line
impedance whose resistance component may have
selected one of said lines through said two ñrst
diiîerent magnitudes, two circuits, wave ampli
mentioned circuits and said amplifying means,
i‘ying meanshaving an amplifier input circuit
said balancing circuit being adapted to balance
pedances.
the impedance of the selected line, means com
connected to one of said two circuits and an
prising said balancing circuit for connecting said
amplifier output circuit connected to the other,
two ñrst-mentioned circuits in energy transmit
ting relation to the selected line and in conjugate
relation to each other, means for producing di
rect current dependent in magnitude on the mag
nitude of the resistance of the selected line, and
means providing a balancing circuit for said line
impedance and a line circuit for two-way com
means comprising a variable resistance in said
balancing circuit responsive to said direct cur
rent for rendering the magnitude of said variable
munication lwith said line impedance through
said two first-mentioned circuits and said ampli
fying means, means comprising said balancing
circuit for said line impedance for connecting
said two first-mentioned circuits in energy trans
mitting relation to said line impedance and in
conjugate relation to each other, means for pro
resistance a function of the magnitude of said
direct current.
70 ducing direct current dependent in magnitude
on the magnitude of the resistance component of
4. A wave translating system comprising lines
said line impedance, said balancing circuit com
of different resistance, two circuits, wave ampli
fying means having an amplifier input circuit
prising a four-terminal network terminated in
a variable resistance, and means comprising said
connected to one of said two circuits and an am
plifier output circuit connected to the other, 75 variable resistance `responsive t0V variation of
2,408,072
14
said direct current for producing variation of
said variable resistance, said network consisting
'
transmitted from saidï 'other' line to the Yselected
line, a source of electromotive force in said link
circuit for supplying direct current .to the se
of a plurality of resistances of such values and
lected line, and means responsive to said direct
circuit coniiguration that -the ratio of said vari
current for increasing and decreasing-the trans
able resistance to the' input resistance ofr said C1 mission efliciency of one of said paths upon in
network has different preassigned values-'for y
crease anddecrease, respectively, ci the resist
given values of said variable resistance.
ance of the selected line by change of the line
8. A wave translating system comprising a line
' impedance whose
resistance
component may
selection.
Y
v
`
»
=
i
~ 11. In a telephone system, a plurality of sub
have different magnitudes, two circuits, wave am 10 scriber lines of different resist-ences, a connecting
plifying means having an amplifier input circuit
circuit for establishing connections with said
vconnected to one of said two circuits and an
lines, a two-way repeater invsaid connecting cir
amplifier output circuit connected to the other,
cut having an amplifying path for receiving and ,
means providing a balancing circuit for said line
amplifying waves i’rcm'said lines and an ampli
impedance and a line circuit for two-way com
fying path for amplifying waves and‘transmit
munication with said line vimpedance through
ting the waves so amplified to said lines, a source
said two first-mentioned circuits and said am
of electromotive force in said connecting circuit
plifying means, means comprising said balanc
for supplying direct current to the line with
ing circuit for said line impedance for connect
vwhich connection is established, means compris
ing said two first-mentioned circuits in energy
ing a resistance of high temperature coefficient
transmitting relation to said line impedance and
in said first path, and av heating element there
in conjugate relation to each other, means for
for electrically insulated therefrom included in
producing in said line impedance a current de
said connecting circuit and responsive to the di
pending in magnitude on its resistance `compo
current supplied to the line.
Y t
nent, said balancing circuit comprising a four 25 rect
12. A wave translating system comprising a
terminal network terminated in a temperature
line, two circuits, means comprising a balancing
dependent resistance, and a heating element for
circuit for said line fo-r connecting said two cir
said temperature-dependent resistance respon
cuits in energy transmitting relation to said line
sive to said current in said line impedance, said
and>
in conjugate’relation to each other, said bal
30
network consisting of a plurality of resistances
Aancing circuit comprising an adjustable imped
of such values and circuit configuration that the
ance, means for adjusting said impedance, a> cir
ratio of said temperature-dependent resistance
to the input resistance of said network has dif
ferent preassigned values for given Values of said
temperature-dependent resistance.
9. A wave translating system comprising a line
impedance whose resistance component may have
different magnitudes, two circuits, wave ampli
fying means having an amplifier input circuit
connected to one of said two circuits and an am
plifier output circuit connected to the other,
means providing a balancing circuit for Said line
impedance and a line circuit for two-way com
munication with said line impedance through
said two first-mentioned circuits and said am
plifying means, means comprising said balanc
ing circuit for said line impedance for connect
ing said two first-mentioned circuits in energy
transmitting relation to said line impedance and
' cuit connected to said adjusting means and com
prising a resistance of negative temperature co
35 eincient for controlling said adjusting means, a
heating element for said resistance electrically
insulated therefrom, a second resistance of nega
tive temperature coeiîicient, means for producing
decreasing current in said heating element in
40 response to decrease of said second resistance,
and a heating element for said second resistance
electrically insulated therefrom and responsive
to current in said line for controlling said sec
ond resistance.
13. A system for'transrnitting current changes
comprising an input circuit, an output circuit,
in conjugate relation to each other, means for
producing in said line impedance a current de
pending in magnitude on its resistance compo
nent, said balancing circuit comprising an ad
justable impedance, means for adjusting said ad
means for producing variable input current in
said input circuit and means for producing cor
respondingly variable output current in said
output circuit, said last means comprising a re
sistance of high temperature coefñcient connected
in said output circuit, a heating element there
for electrically insulated therefrom, a second re
sistance of high temperature coeñicient of the
same sign as the ñrst coefficient, a heating ele
justable impedance, a four-terminal network 55 ment
for said second resistance connected in
connected to said adjusting means and termi
said input circuit, a source of constant voltage
nated in a temperature-dependent resistance for
for supplying heating energy to said first heat
controlling said adjusting means, and means re
ing element, and a circuit comprising said second
sponsive to said current in said line impedance
connecting said source to said first
for controlling said temperature-dependent re 60 resistance
heating element to supply energy of said source
sistance, said network consisting o-f a plurality of
thereto and responsive to magnitude change of
resistances 0f such values and circuit conñgura
one sign in current in said second heating ele
tion that the ratio of said temperature-depend
ment for producing magnitude change of oppo
ent resistance to the resistance of said network
site sign in current in said ñrst heatingelement.
facing said adjusting means has different pre
14. A control circuit comprising a resistance of
assigned values for given values of said tempera
high
temperature coefficient, a heating element
ture-dependent resistance.
10, A
wave translating system comprising
therefor electrically insulated therefrom, a sec
ond resistance of high temperature coeiiicient of
lines of diiïerent resistance, another line, _a link
circuit for establishing connections of said other 70 the same sign as the first coefñcient, a heating
line with any selected one of said first-mentioned
lines, a two-way repeater in said link circuit hav
ing an amplifying path for amplifying waves
transmitted from the selected line to said other
line and an amplifying path for amplifying waves 75
element for said secondvresistance electrically
insulated therefrom, a source of electromotive
force for supplying energy to heat said first heat
ing element, and means comprising said second
resistance connecting said source to supply heat
15
2,408,072
16
>ing energy to said first heating element and re
sponsive to change of current of one sense in
said second heating element for producing cur
rent change of opposite sense in said iirst heat
‘means comprising a second source of electrome
ing element.
perature change of said first resistance large
l5. A system comprising a temperature-,de
pendent resistance, a heating element therefor
electrically insulated therefrom, a second tem
perature-dependent resistance having its tem
perature coeñîcient of resistance of the same sign
as that of said ñrst resistance, a heating element
for said second resistance electrically insulated
therefrom, a source of electromotive force for
tive force in circuit with said second heating
element adapted to produce therein current
change of magnitude sufficient to produce tem
compared to its maximum temperature Change
produced by ambient temperature.
16. In combination, a resistance of high tem
perature coefficient, a heating element therefor
electrically insulated therefrom, a second resist
ance of high temperature coeflicient of the same
sign as the ñrst coeflicient, a heating element
for said second resistance electrically insulated
supplying energy to heat said first heating ele
therefrom, av source of electronic-tive force of
ment, means comprising said second resistance 15 given frequency, and a circuit comprising in
and having variable transmission eñiciency con
series said source, said first heating element and
necting said source to said ñrst heating element
a network Vtuned to approximately said fre
to supply energy of said source thereto and ren
quency, said network comprising a capacity and
sponsive t0 change of current of one sign in said
in parallel therewith said second resistance and
second heating element for sov varying said trans 20 an inductance in series.
mission efficiency as to produce current change
of opposite sign in said ñrst heating element, and
KENNETH S. JOHNSON.
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