# Патент USA US2408073

код для вставки' Sept. 24, 1946. K. s. JoHNsoN 2,408,072 TELEPHONE REPEATER CIRCUIT Filed Dec. 31; 1943 -3 Sheets-Sheet 1 @à ì ï QN ,.§58. R „RA ' “NLT lq „LMI "W1 /NvENroR A vBi’ KS. JOHNSON » B. C. @UVA AT TORNEI’ , 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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