Patent GB-151140-A (GB)
Title: Improvements in telephonic transmission systems
IPC: H04B3/14
Filed: 1919-08-05
Abstract: 151,140. Western Electric Co., (Western Electric Co.). Aug. 5, 1919. Telephone systems; repeating and amplifying systems.-In telephonic transmission systems, attenuation equalizers comprising inductance and capacity, inductance and resistance, capacity and resistance, or capacity, inductance and resistance are included in the system, and the elements are so proportioned that the attenuations of the waves of frequencies within a pre-determined range, due to the equalizers and to the line, are substantially uniform. The attenuation equalizers are associated with repeater systems, and formulµ are given for determinating the values of the elements of the equalizer in terms of the constants of the system. A series impedance type of equalizer consisting of a resistance R, inductance L and a capacity C is shown in a periodically loaded transmission line 100, Fig. 5. A shunt admittance type of equalizer consisting of a resistance R connected in series with a parallelled circuit containing a capacity C and an inductance L is shown in a periodically loaded transmission system 100<1>, Fig. 8. Wave filter types of equalizers of the forms shown in Figs. 9 and 10 may be employed, the filter being so proportioned that the attenuation introduced by it within the range of telephonic frequencies is complementary to the attenuation introduced by the transmission system with which it is associated in order that the resultant attenuation shall be substantially equal over the desired range of frequencies. In the two-way valve-amplifying arrangement shown in Fig. 13, the lines 101, 102 are associated with the repeater circuits through transformers 11 and 11', and are balanced with respect to the repeater circuits by means of artificial lines or networks N<1> and N<2>. In order to equalize the attenuation due to the lines 101, 102, and other factors such as terminal reflection, to cause the attenuation to vary with the frequency in any desired manner, attenuation equalizers 51 and 51<1> of the series type are provided, and in order to balance these equalizers with respect to the repeater, equalizers 52 and 52<1> are similarly connected upon the artificial line side. In a modification, the equalizers 51 and 51<1> are placed in the primary circuits of the transformers 13 and 13<1> respectively, Fig. 13, and the equalizers 52 and 52<1> are omitted. In a further modification, the equalizers are placed in the primary circuits of the transformers T and T<1>, Fig. 13. The variable impedance of the repeater circuit may be eliminated by placing the equalizer 54, Fig. 16, between the amplifiers A<1> and A<2> of a two-stage amplifier system and similarly connecting an equalizer 54<1> between the amplifiers A<3> and A'. In the four-wire circuit arrangement shown in Fig. 17, the lines 101, 102 terminate at two separated stations and are interconnected by line circuits 103, 104 and a two-stage amplifier system A<1>, A<2> for transmission in one direction and line circuits 105, 106 and a twostage. amplifier system A, A<4> for transmission in the opposite direction. Attenuation equalizers 51 and 51<1> are inserted between the two halves of one of the windings of the transformers 11 and 11', while attenuation equalizers 52 and 52' are similarly connected to the transformers 12 and 12' on the artificial line side. In the modification shown in Fig. 18, the attenuation equalizers 56 and 56' are associated with the transformers 16 and 16<1> of the input circuits of the amplifier systems A<1>, A<2> and A<3>, A<4> respectively. In a modification, the attenuation equalizers are placed in the secondary circuits of the transformers 13 and 13<1>, Fig. 18. In another modification the equalizers are inserted between the amplifiers A<1>, A<2> and the amplifiers A<3>, A<4> respectively. In another modification, the equalizers are placed in the primary circuits of the transformers 15, 15<1>, Fig. 18; while in a further modification the equalizers are placed in the secondary circuits of the transformers 17, 17<1>, Fig. 18.