US1734150A - Loaded transmission system - Google Patents

Description

Nv. 5, 1929. r. sHAw LOADED TRANSMISSION SYSTEM INVENTOA Z Shaw ATTORNEY Filed Nov. 1. 1927 tra sanas THOMAS SHAW, OF HACKENSACK, NEW JERSEY, ASSIGNOR TO AMERICAN TELEPHONE AND' TELEGRAPH COMPANY, .A CORPORATION OF NEW YORK LOADED TRANSMISSION SYSTEM Application led November 1, 1927. Serial No. 230,329.`

Thisv invention relates to a loaded transmission system, and particularly toone comprising physical circuits having a phantom superimposed thereon, the said phantom being loaded to transmit a frequency or range of frequencies differing from that for Which the physical circuits are loaded.

Transmission systems have been devised and used heretofore in Which the range of frequencies transmitted by the phantom circuit differs from that transmitted by the physical circuits constituting the sides of the phantom. The patent to Shaw, 1,501,926, which issued on July 22, 1924, discloses a transmission system in Which both the phantom circuit and the physical circuits constituting its sides are loaded, the said phantom circuit being used for the transmission of frequencies Within the voice range, for eX- ample, from 200 to 7500 cycles, and the side circuits for the transmission of carrier frequencies up to, for example, 30,000 cycles. The Wide range of carrier frequencies employed, required the loading of the side circuits to be spaced at relatively short intervals, slightly over 900 feet. On the other hand, since the frequency range of the currents transmitted over the phantom circuit Was relatively much narrower than that of the sides, the spacing of the phantom circuit loading was equal to six times that of the side circuit loading. Thus, at every sixth loading point upon the side circuits, Ya phantom loading coil would also be connected With the circuit. As has been pointed out carefully in detail in the said patent to Shaw and also in the patent to Martin and Shaw, 1,501,959 that issued on July 22, 1924, the connection of the phantom windings With the physical circuits at every siXth loading point upon the side circuits introduces a diculty that can be eliminated only by the use at the phantomside circuit loading point of a special side circuit coil, namely, one that differs from t-he other side circuit coils connected With the same conductors and also of a special phantom coil which differs materially from phantom coils for voice frequency loading Where carrier currents are not employed uponthe side circuits. Briefly stated, Where the range of frequencies transmitted by the side circuits is radically different from the range transmitted by the phantom, itis necessary to employ special loading units at the points Where both the side circuits and the phantom circuit are loaded, the side circuit coils of the said unit being different from other side circuit coils employed,and the phantom coil differing from the type of coil that Would be employed upon the phantom if carrier .currents Were not transmitted over the sides. The necessity for providing special coils is undesirable from a manufacturing as Well as a service standpoint.- 'lt has been foundpossible to produce a system in which not only may the same side circuit coil be employed in the phantom loading unit as is employed at 'other points upon the side circuit, but also the same phantom coil may be'employed as Would be used upon any phantom circuit in `which carrier frequencies Were not transmitted over the side circuits thereof. My invention resides in such a system.

This invention will be clearly understood from the following description when read in connection With the attached drawing, in which Figures 1 and 2 illustrate the description ofthe development of the invention; Fig. 2a represents symbolically the capacities existing in the loaded circuit'shovvn in Fig. 2; F ig. 3 shows a circuit in Which the invention is embodied, and Fig. 3a shovvs symbolically the capacities existing in the circuit of Fig. 3.

ln Fig. 1, L1 and L2 represent tvvo'circuits that may be employed as the side circuits of a phantom. In the system of the prior art, as exemplified by the said patent to Shaw, the frequency range for carrier transmission Was so great that it required lthe spacing of the carrier loadinor coils at a distance `of slightly over 900 fgeet apart. I have found that by reducing the upper limit of the carrier frequency to approximately 13,000 cycles,

the side circuit loading coils may be spaced apart a distance that is approximately three times the spacing for the system employing 30,000 cycles as the upper limit; that is to say, the spacing for a cut-off frequency of 13,000 cycles is approximately 2800 feet. Since the spacing'of phantom loading coils upon toll entrance cables in which carrier frequencies are not employed upon the side circuits is approximately 6,000 feet, it became apparent lthat by 'extending the'loading section ofthe side circuit to 3,000 feet it would be possible to load both the phantom and the side circuits at every other side circuit loading point. By adopting Vthis ratio of spacing of the side 2o circuit coils to the phantom coils, that is to -say,"atwo-to-one ratio, and by arranging the phantom coil windings at the combined phan- ,fitomssideV circuit loading` points in the manner -hereinafter described, it is possible to -wemploy the same side circuit coil at `the phantom-*side loading point and also to employ vthe same phantom loading coil at that point aswould be employed upon the phantom circuit' of a system in which carrier currents 80j are not transmitted over the sides. The features that render this possible will be appar- 1entfrom the consideration of Figs. 1, 2 and 22. Fig. lV shows the disposition of the side Ycircuitloading coils upon physical'circuits :25 which will be assume-d to have no phantom circuit superimposed thereon but which Lcofuld' be so used. These coils 1, 2, 3 and 1, 2 and 3, which comprise the windings enclose-d VVwithin the dotted lines, may be assumed to aobe `spaced approximately 3,000 feet apart.

'If a phantom circuit were superimposed upon thefpairs L1 'and L2, and such phantom were f loaded in the manner shown by the coils It Y 'and 5 of Fig. 2, that is to say, by the conirne'ction ofthe coil windings into the side Y k'.'cilcuits'at every other loading point upon V*tlieside circuit, the distribution of the capacities between the windings of the side Icircuit-coils, of the phantom coils and between 2150 fthe conductors of each side circuit, would be "as shown in Fig. 2". Assuming as a loading section the distance from the midpoint of the windings atpone loading point to the midv point of the windings upon the same circuit :w f iatan' adjacent loading point, the capacity of 'the section A-B wouldbe made up of'I the -fcapacity a between one-half of the coil 1 at Ivthe point A, capacity b representing that between windings 6 and 7 of the phantom load- ?160 ingcoilglt, .the capacity c representing that 'ofthe side' circuit conductors between A and 'Bi and yanotherV capacity a representing that "offene-half of the side circuit coil 2y at the loading point B. The neXt succeeding loadbetween B and C,

vsame action has b'eenitaken with respect vto i. `the phantom coil 5 at theloading point G.

seen, therefore, that the capacity of section AuB differs from that of section B-C by the magnitude of the capacity b. The foregoing statement assumes, of course, that the capacities of the side circuit conductors between A and B and between B and C are equal, which would be substantially so. The introduction of the capacity d into the side circuit A-B causes an impedance irregularity which, through its uniform recurrence, would impair transmission. This"diiiiculty may 'be remedied inthe "manner shown in Fig. 3, in -which the phantom coil windings are split, one-half being located upon that sideoft'heside-circuit loading coil 1 toward the loading point D, and the other half of each ofthephantom coilpwindingsbein'g located upon that side of theside circuit loading coill toward the-loadingpoint B. lThus,

4it will be seen in Fig. 3 that the winding D6 of Fig. 2 has been divided intoequal halves designated 6 vand 6, and,similarly, the other windings of the phantom'loading coil 4 have been divided `and connected upon opposite sides of the side circuit coil-1. rIhe It will be seenfrom Fig.'3.showing the capacity distribution of the coilsand conductors of Fig. 3 that the capacity of each side .circuit is substantially equal to that'of every-:other .i100

side circuit, so that no impedance irregularity occurs 'at any; point thereon. If the capacities of each half of a phantom` coil winding `be represented byy b', the capacity of the loading section A--B comprises the `capacities a, -i 5105 Vfb', c and a. The capacity ofthe loadingisection B-C likewisey c'omprises'the capacities ab, c'and a. Since one-half ofthe'loading -coil capacityl of Ieachiphantom l'oa'di'ng'coil is added to every loading section, it is not. necessary to have side circuit'fcoils-'atthe combined phantom-side floading points that differ from the 'otheriside-circuit coils eniployed at the points where the. phantom is 'not loaded. It will be apparent that in'thesystem just described the capacity 'increment ofthe side circuits due'to lthe vkconnection therein of one-half'fflthe'phantomloading coil winding at each combinedloading point will occur at opposite 'ends ofadjacent'l'oad-s, ing sections, that' is to say, iniv the section A-B, it is at the `left-hand end, whereas in the section B-C' it is at the right-hand end. The position of thecapacity increment wi`thin the limits of the loading section, h'oweven is n-ot a matter vof importance from thestand- -point of impedance irregularity.

It will therefore beapparent that by choosing the ratio' ofv Spacingofftfhe side circuit loading coils v`to f .the f phantom -iloajding` lcoils 1 v130