Zenith Cable Modem is one of the first proprietary cable modems deployed at limited scale. There are two basic models, one operating at 500 kbit/s, the other at four Mbit/s using BPSK and about a 25% alpha. ==History== The Zenith Cable Modem was originally developed for a mid-split cable network in the mid-1980s, and used as an eight-bit full heig...