Plug Compatible Replacement for a Bell 303Modem Using Local Twisted Pair Wire.

摘要

This note describes a low cost ($275 per end) plug replacement for a Bell 303. 50KB serial modem using local twisted pair wire for transmission. The unit contains a 50 KHz crystal clock and appropriate drivers, receivers, and level shifters to convert the unbalanced local terminal interface to balanced DC signalling for transmission over local twisted pair wire. The note contains a description of the operation of the unit as well as an overview of the subassemblies which comprise the unit and detailed diagrams for each. (Author)