GB142115A - Electric wave filters - Google Patents

Abstract

142,115. Western Electric Co., (Assignees of Campbell, G. A.). July 15, 1915, [Convention date]. Repeating and amplifying systems; multiplex systems; simultaneous telegraphy and telephony. -Filter circuits for suppressing currents of certain ranges of frequency are composed of a series of similar sections, each including impedance in series and impedance in shunt. In the general form, shown in Fig. 1, each section consists of an inductance L1 and capacicy C1 in series and an inductance L2 and capacity C2 in parallel shunt. A network of this kind transmits two bands of frequencies f0 to f2 and f1 to f3, Fig. 8, with negligible attenuation, but practically extinguishes frequencies outside these limits owing to repeated reactions between the impedance units. The Specification contains a general mathematical investigation for enabling the dimensions of the various impedances to be calculated for any desired values of f0, f2, &c. The frequencies f1, f2 can be made to coincide, so that only a single band of frequencies is transmitted. The network shown in Fig. 1 can be simplified by omitting one or more of the impedances L1, C1, L2, C2 from each section, and by carrying this simplification to an extreme, as shown in Figs. 6 and 7, one of the limiting frequencies can be relegated to zero or infinity. Thus the circuit shown in Fig. 6 transmits all currents above and extinguishes all currents below a certain frequency, while the circuit shown in Fig. 7 has the opposite effect. The invention is applicable to wireless systems, multiplex high-frequency wire telephony, composite telegraph and telephone lines, and telephone repeater circuits. A two-way repeater system is shown in Fig. 10 with a filter in the in-put circuit of each of the thermionic valves 11. To prevent interaction between the two repeaters, the in-put circuit 8, 9 of each valve is connected between the line 3, 4 and an artificial line 20, which are equally and oppositely affected by the output transformer of the other valve. The use of filters in this arrangement renders it unnecessary for the artificial line 20 to simulate the transmission line except over the range of frequencies involved in telephonic speech.