No_v. 2, 1943., N. BOTSFORD 2,333,148 INDUCTANCE APPARATUS Filed June 28, 1941
LEAKAGE MUCH/WE ‘
LEAKAG! _J MGM'TIC INDUCDINCE CORE ,45
A
A l 44 4/
LEAKAGE
LEA/(46C _ INDUCTZNCE ‘
57 TRANSMISSION L INE'
INVENTOR N. BOTSFORD
AT TORNEV Patented Nov. 2, 1943 r 2,333,148
‘UNITED STATES PATENT OFFICE
Nelson Botsi'ord, Rutherford, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application June 28, 1941, Serial No. 400,339 10 Claims. (01. 178-44) ’ ‘This invention relates to inductance appara- . A further object is to simplify the manufac~ tus, ‘and more particularly to inductance appa ture of: inductance apparatus. ratus for transmitting signaling waves extend ing over, a relatively broad band of frequencies ' . A further object is to compensate‘for the leak with substantially uniform attenuation and rel ageinductance of inductance apparatus in so atively low re?ection. . . v far as such inductance affects re?ection and Carrier current transmission systems are be ' transmission. ‘ ing presently designed withvv higher frequencies Another object is to provide in a system proper to provide a larger number of discrete carrier terminations for apparatus which functions most channels. This means that certain inductance effectively, only when terminated in the imped ance out of and into which such apparatus is apparatus, such as repeating coils and:trans-/ designed to ‘Operate. formers, is 'also being designed to transmit a '; Another'object is to minimize between adja wider band of frequencies. In the design of’ ' such inductance apparatus, one vfactor involves cent transmission lines crosstalk caused by re controlling the re?ection characteristic. This ?ected waves thereon. , characteristic is among others a function of leak Onetype of well-known inductance apparatus, age inductance, which inductance isthe effective such as a repeating, coil, comprises a pairv of series inductance caused by an imperfect cou- ‘ windings wound on a magnetic core and between pling of the windings of the inductance appa which a certain amount of leakage inductance exists, that is, inductance due to magnetic flux ratus.‘ leakage inductance may be partially an 20 which is not mutual to the pairof ‘windings. nulled by the effective shunt capacitance of the One winding of this'pair may be applied, for inductance apparatus. However, in line repeat example, to central o?lce equipment while the ing coils and transformers where impedance other winding maybev connected to a carrier levels are relative low, the amount of leakage currentline transmitting signaling waves extend inductance may be found to be intolerable. In 25 ing overa certain range of frequencies. As an this connection it has also been found that the uncertain amount of leakage inductance may be amount of leakage inductance is further in introduced in the inductance apparatus due to creased because of design, features which tend normal manufacturing variations, it has been to minimize modulation effects in the inductance found Vdii?cult to compensate for the latter apparatus; ' 30 Heretofore, the amount of leakage inductance, amount of leakage inductance without providing not annulled by the effective capacitance of the ‘ for such compensation on the bases of individual . inductance apparatus, has been partially neu inductance apparatus. Unless due care is ob tralized by connecting individual ?xed capaci served to compensate for the leakage inductance tors in shunt of the input and output terminals of of the inductance apparatus, it may happen that I - the inductance apparatus. These capacitors an intolerable impedance mismatch occurs be served to function together with the leakage in tween the inductance apparatus and the carrier ductance as a low-pass-?lter having a charac-_ current line or between the inductance appara teristic impedance of the same order of magni tus and the central office equipment. Such im ‘ pedance mismatch, depending on the amount, may tude as the winding terminations of'the induct 40 ' ance apparatus so as to transmit therethrough increase the reflection characteristic of the induc with tolerable reflection and attenuation signal tance apparatus to such extent that transmission ing waves extending over a certain range of in ‘the carrier current system is deleteriously frequencies. a?ected. , ' I v . In some ‘cases, adjustable’ capac-j In a speci?c embodiment of this invention, an ' itors may be required to obtain a finer control impedance, network comprising a tertiary wind of the re?ection characteristic of the inductance apparatus. These neutralizing capacitors are ing and a capacitor in shunt thereof is coupled expensive as their serviceability involvesuni to the pair of 'windingsof the inductance appa formity ‘with regard to time‘ and temperature, ratus. The magnitude of the capacity ‘of the capacitor is initially selected at a value suitable and, in some cases, high voltage operation. 50 withrespect to capacitance, physical dimensions This invention contemplates facile means for and commercial availability, and thereafter the controlling the re?ection characteristic of in- ‘ number of turns of the tertiary winding adjusted ductance apparatus. . t ‘ ‘ to neutralizevsubstantially whatever amount of The main object of the invention is to provide leakage inductance is then present in the induct inexpensive, high quality, inductance apparatus. 55 ance apparatus. Thus, the impedance of ’the 2 2,336,148 inductance apparatus looking 'into the other stantially in accordance with their design re winding with the one winding applied to the quirements, it is imperative that such equipment central office equipment, is substantially matched be connected to the impedance out of and into to the impedance of the carrier current line;' and which it is designed to operate. Furthermore, the impedance of the inductance apparatus, look in order to minimize the effects of reflection and ing into the one winding with the other winding . crosstalk on carrier current transmission lines, it is imperative that individual lines be termi connected to the carrier current line, is substan nated in their characteristic impedance. Conse tially matched to the impedance of the central quently, it is necessary to construct inductance of?ce equipment. ' > ‘ - apparatus ‘connecting such central of?ce equip A feature of the invention is that ‘it may be 10. ment and the transmission lines so that when the expeditiously utilized in various types of induct central o?ice winding of the inductance appara ance apparatus, such as repeating coils, trans tus is terminated in central office equipment, the formers and hybrid coils. , The invention will be readily understood from line winding is terminated in an impedance the following description taken together with the 15 which is substantially equal to the impedance of the line; and when the line winding of the in accompanying drawing in which: ' - ‘ Fig. 1 is a schematic circuit showing a speci?c _ ductance apparatus is terminated in the line, the central office winding is terminated in an imped~ ' embodiment of the invention applied to a repeat ance which is substantially equal to the imped ing coil; and 20 ance of the central oi?ce equipment. There Figs. 2 and 3 are schematic circuits illustrat fore, the impedance looking into either the line ing the speci?c embodiment of the invention em or central of?ce winding of the inductance appa bodied in hybrid coils. Fig. 1 shows a repeating coil‘lll comprising a ratus I0 must, to a tolerable degree, hold the match to the respective line B or central office winding II whose terminals 9, 9 are applied to a 25 equipment I2 over the entire frequency range load I2, which, for example, may comprise cen of the signaling waves being transmitted in the tral office equipment, and a winding I3 whose system. terminals I4, I4 are applied to a source 8 of alter In accordance with this invention, the imped nating current waves and a resistor ‘I, both of ance looking into winding I3, when the winding which, for example, may simulate a suitable car 30 II is applied to the load I2, is adjusted for sig rier current transmission line 6. The windings II naling waves extending over a certain range of and I3 are wound on a magnetic core I5, and also frequencies‘so as to be substantially equal to the may have interposed therebetween a shield IS. impedance of the carrier current line 6 connected The coil I0 may also be enclosed in a casing I1 thereto and transmitting said signaling waves which together with the shield I6 is connected 35 extending over said certain range of frequencies to a ground I8. An amount of leakage induct-i with substantially uniform attenuation; and the ance will be present between the windings II impedance looking into the winding II,. when and I3, and may be represented for the purpose" the winding I3 is connected to the carrier current I of illustration as inductance I9 in series with line 6, is adjusted so as to be substantially equal one terminal I4. The coil I0 is theoretically designed to have a 40 to the impedance of‘ the load I2 for the same range of signaling‘frequencies. ‘ substantially ?at impedance-frequency charac-' Referring to Fig. l, the foregoing is accom teristic that conforms substantially with sub-v plished by a tertiary winding 20 coupled to the stantially ?at impedance-frequency characteris windings II and I3 and across which is connected tics of the central office equipment and the car 45 a capacitor 2I. The capacity of the capacitor rier current line to transmit all signaling waves 2I is initially selected at a value suitable with extending over a certain range of frequencies respect to capacitance, physical ‘proportions and with substantially uniform attenuation. This commercial availability, and thereafter the num means that, withithe winding II terminated in ber of turns of the tertiary winding 20 is ad the load I2, the impedance termination of the 50 justed to neutralize substantially the leakage coil Ill, looking into the winding I3 ought to inductance present between the windings II and match substantially the impedance termination - I3, that is, the leakage inductance I9, thereby of the carrier current line 6; and with the wind providing substantially ?at effective resistive and ing I3 terminated in the carrier current line 6, minimum reactive-frequency characteristics for the impedance termination of the coil I0 looking the coil I0 either looking into the winding I3 from into the winding I I ought to match substantially the carrier current line 6, or looking into the the impedance termination of the load I2. winding II from the load I2, when the other of However, leakage inductance present in the these two windings is properly terminated in the coil I U, as previously mentioned, will have the manner previously mentioned. Hence, the at effect of upsetting such impedance match, that tenuation-frequency characteristic of the coil I0 is, causing a mismatch between the impedance j tends to conform substantially with the attenu looking into the windings II and I3 and the im ation-frequency characteristics of the respective pedance of the respective carrier current line 6' carrier current line 6 and load I2. and the load i2. Such impedance mismatch, Maintaining the impedance match between the controlled by the magnitude of the leakage in terminated windings II and I3 in the manner ductance, tends to vary the re?ection character ' pointed out above serves (1) to control the effec istic of the coil ID, thereby exerting a deleterious tive capacity measured across the terminals of effect on transmission in the entire carrier cur--v the individual windings II and I2, which capac rent system of Fig. 1 from the standpoint of both ity consists not only of the capacity between e?iciency and ?delity, as will be hereinafter 70 turns and layers of the windings II and I3 but pointed out. Control of the re?ection‘ charac also the value of the ?xed capacitor 2I trans teristic in inductance apparatus is therefore an formed through from the tertiary winding 20 to important factor in the over-all design of carrier the individual winding II or I3 being measured; current systems. ‘ - (2) to minimize between adjacent transmission Thus, in order to operate ?lters and hybrid lines crosstalk occasioned by re?ected signaling coils embodied in central office equipment sub—' 75 2,333,148 3 waves; (3) to provide proper terminations for ?l . In accordance with the inventionas applied ters or other electrical apparatus which functions to Fig. 2, winding 50 adjustable as to the num-. most effectively, only when terminated in the im ber of turns and embodied in the coil 26 and pedance out of and into which such ?lter or ap shunted by capacitor 5| selected similarly to ca paratus is designed to operate; and (4) to con pacitor 2| of Fig. 1 neutralizes substantially the trol the reflection characteristic of the coil 10 portion of the leakage inductance 45 occurring such that the former is maintained within a tol in the coil 26 and remaining therein after the erable maximum value. Thus, the use of the ad above-mentioned neutralizing actionv of the ca justable winding 20 and capacitor 2! serves to pacitor 3|]; and winding 52 adjustable as to the provide an inexpensive, high quality, inductance 10 number of turns include-.2 in the coil 21 and coil [0 which is relatively simple ‘to manufacture. bridged by capacitor 53 selected similarly to ca Accordingly. neutralization of leakage induct pacitor 2! of Fig. 1 neutralizes substantially the ance enables a control of the re?ection charac- portion of the leakage inductance 46 occurring in teristic of the coil ill so as to promote‘both high the coil 21 and remaining therein after the pre e?iciency and high quality in the operation of 15 viously pointed out neutralizing action of the the entire carrier current system of ‘Fig. 1. capacitor 31. Consequently, the conjugate In connection with Fig. 1, it was found that, branches of the hybrid coil 25 are individually for a speci?c embodiment of the inventionna provided with substantially flat effective resistive tertiary winding 20 comprising‘ a‘number of turns and minimum reactive-frequency characteristics of the order of 32 and a capacitor 2! having a 20 that are substantially identical with those of the capacity of the order of 0.075 microfarad pro respective line 54 and loads 29, 36 and 43, when vided for the coil ID a substantially ?at impedance the remaining windings are properly terminated, frequency characteristic over: ‘approximately a looking ('1) into windings 3i and 38 from the car 0.5-90 kilocycle range of frequencies. Thesim rier current line 54; or (2) into the winding 28 plicity of this embodiment was found to reside in 5 from the load 29; or (3) into the winding 35 from the fact that an inexpensive and yet stable ca the load 36; and (4) into the windings 32 and pacitor meeting relatively lenient minimum and 38 from the load 43. maximum capacity requirements could be initially ‘ Thus, the attenuation-frequency characteris- . selected, and thereafter the number of turns of tics of the conjugate branches of the hybrid coil. the tertiary winding 28 varied in order to obtain 30 25 tend'to conform substantially with the corre the neutralization of leakage inductance l 8 men- ‘ sponding attenuation-frequency characteristics of tioned hereinbefore. the carrier current line 54, and loads 29, 36 and Fig. 2 shows the invention applied to a ‘hybrid 43, respectively. In other words, such neutralize» coil 25 comprising individual coils 26. and 21. The tion of leakage inductance serves to balance the coil 26 wound on a magnetic core 23 embodies a hybrid coil 25 like a bridge by providing similar winding 28 terminated in a suitable load 29 and impedances at the conjugate branches. shunted by a capacitor 38. Coupled to thewind Accordingly, the neutralization of leakage in ing 28 are windings 31 and 32. Interposed be ductance controls the re?ection characteristic of tween the two latter windings and the windingv the hybrid coil 25 so as to promote the operation of the entire carrier current system of Fig. 2 28 is a shield 33. The coil 21 wound on a mag. 40 netic core 24 comprises a winding 35 terminated in the manner pointed out above in connection in a suitable load 36 and shunted by a capacitor ‘ ‘ with Fig. 1. It is to be understood that winding, 31. Coupled to the winding 35 are windings 38 50 and capacitor 5| may also include the ac~ and 39. Disposed intermediate the latter two tion of the capacitor 30 on the coil 26; and that windings and the winding ‘35 is a shield 40. A 45 the winding 52 and capacitor 53 may also include link 4| serves to connect both shields 33 and 40 the action of the capacitor 31 on the coil 21, if to ground 42. The windings 32 and 39 on the re desired. The advantage of splitting the capacity on each side of the leakage inductance is that the spective coils 26 and 21 are terminated in a load or balancing network 43. The windings 3| and range of the hybrid coil is extended upwards in 50 frequency. 38 on the respective coils 26 and 21 are applied Fig. 3 shows the invention applied to a hybrid to terminals 44, 44 which are connected to a coil 60 comprising a winding 6| shunted by a source 55 of alternating current waves and re capacitor 62 and terminated in a load 63. Con sistor 56 both of which simulate a carrier cur pled to the winding Si is a pair of windings 64 rent line 54. ‘This line together with the loads and 65 and load 66 applied in series across a pair 29, 36 and 43 possess substantially flat effective of terminals 61, 61. Across one of the latter resistive and minimum reactive-frequency char terminals and the midpoint of the windings 64 . acteristics for transmitting signaling waves ex and 65 is connected a load 68. Across the termi tending'over a certain range of frequencies with nals 61, 61 may be connected a source 51 of substantially uniform attenuation. alternating current -v Wes and a resistor 58 both A certain amount of leakage inductance occurs of which simulate a carrier current line This between the winding 28. and the windings 3| and line together with the loads 63, 66 and B8 ipos~ 32, all of whichcomprise the coil 26, and may be sesses substantially ?at effective resistive and represented for the purpose of this illustration minimum reactive frequency characteristics for as inductance 45 of Fig. 2. The capacitor 30 ' transmitting signaling waves extending over a shunting the winding 28 serves t-'. neutralize sub certain range of frequencies ‘with substantially stantially one-half of the total amount of the uniform attenuation. Intermediate the winding leakage inductance 45. Also, a certain amount BI and the windings 64 and 65 is a shield 69 one of leakage inductance occurs between the wind end of which is applied to ground 10. A certain ing 35 and the windings 38 and 39, all of which amount of leakage inductance occurs between the constitute the coil 21, and may be represented for winding 6| and the windings 64 and 65, and may the purpose of this illustration v‘as inductance 45 be represented for the purpose of this illustra in Fig. 2. The capacitor 31 bridging the winding tion as leakage inductance 1|. The capacitor 62 38 serves to neutralize substantially one-half of shunting the winding 63 tends to neutralize sub the total amount of the'leakage inductance 46. 75 stantially one-half of the total amount of the 4 2,333,148 ' , leakage inductance ‘I I. The several windings are identical with the attenuation-frequency charac wound' on a magnetic core 15. teristic of said one load circuit to which said one In accordance with the invention as applied to pair of winding termina is connected. Fig. 3, 'vvinding 12 adjustable as to the number of 2. In the combination n broad band inductance turns and shunted by'capacitor 13 selected simi - apparatus according to claim 1, in which said larly tov capacitor 2| neutralizes the portion of impedance network comprises at least one further the leakage ‘H occurring in the hybrid coil 60 inductance winding adjusted as to the number of and remaining therein after the aforedescribed turns and coupled to said plurality of windings, neutralizing eifectt-of the capacitor 62. Accord and a capacitor applied across said further ingly, the conjugate branches of the hybrid coil 60 winding. are individually provided with substantially?at ef- ‘ 3. A broad band inductanceapparatus, com fective resistive and minimum reactive-frequency prising a pair of coupled inductance windings characteristics that are substantially identical between which leakage inductance occurs, and with those of the respective line 59 and loads 63, means comprising a tertiary inductance winding 66 and 68, when the remaining windings are prop coupled to said pair of windingsand a capacitor erly terminated, looking (1) into the network in shunt of said tertiary winding to control the from the carrier current line 59, or (2) into the reflection characteristic of said pair of windings network from the load 68, (3) into the network such that said leakage-inductance is substantially from the load 66, and (4) into the winding 6! neutralized'tojprovide said pair of windings for from the ‘load 63. \ signaling waves extending over a certain range Thus, the attenuation-frequency 'characteris- ’ of frequencies,