Transmission aspects of electronic telephone exchanges

The transmission and other advantages of 4-wire switching with gain available in the 4-wire paths (which electronic exchanges provide) are described in a previous paper. In the present paper, some of the practical problems and possible solutions in the field are investigated, and a more quantitative assessment of the properties of such exchanges is made. It is shown that reference equivalents can be reduced by 4dB to 14dB depending on circumstances, exchange-line loop resistances can be extended to 1800¿ with a substantial amount of attenuation equalisation for the longer lines, echo levels can be reduced by serveral decibels, and fewer-only switching centres are necessary.