GB563417A - Improvements in or relating to the loading of transmission lines for signal currents - Google Patents

Abstract

563,417. Negative resistance loading. WESTERN ELECTRIC CO., Inc. April 27, 1943, Nos. 6626 and 6627. Convention dates, April 25, 1942. [Class 40 (iv)] Thermistors designed and biassed to act as negative resistances at speech frequencies or negative resistances of other types are connected at intervals in a telephone line with attenuation equalizers if necessary and with further slow acting thermistors to compensate for the effect of temperature changes. The Specification comprises a. discussion of the conditions for avoiding instability. Where pure negative resistances, e.g. thermionic tube circuits, are used, they are associated with networks such as 24, Fig. 11, or the network shown in Fig. 15, to cause the negative resistance to decrease with frequency and become positive at the upper edge of the transmitted band. Properly designed thermistors have this property inherently, but may be associated with a similar network to lower the effective cut-off frequency. A series network 23 designed as an attenuation equalizer may be used. An alternative form of equalizer 13<1>, Fig. 12, may be provided with a thermistor and increases the sharpness of the cut-off at high frequencies. A network of the form shown in Fig. 13 having portions tuned to the frequencies at which singing tends to occur may be provided.