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