Zenith Cable Modem - “State of The Art” RF Plant Maintenance in 1994/1995

“State of The Art” RF Plant Maintenance in 1994/1995

An HP 8590L (low cost version of 8591c), video out connected to a Cadco channel modulator operating above 550 MHz, with a Radio Shack black and white TV (picture tube) tuned to UHF channels to see the picture. Add to that a comb generator with 4-6 CW tones, an HP Calan 1776 ‘portable’ spectrum analyzer, which is about the size of an igloo cooler for a weekend car camping trip. Not all amplifiers contained a good return path test point, so the repair lab was asked to modify some line extender diplex filters to pass the forward, and divert the return path to an F connector. A pad socket was also converted as well. Any signal entering an amplifier with an amplitude of above -45 dBmV was located and fixed. CLI was reduced to under 5 uV/m. 2 years later, Milo Medin CTO of @Home was reported to have said, “Please show me the fiber receivers that are connected to the outside plant, these don’t have enough noise, so they are certainly not connected or properly aligned.” Later, he was quoted as saying “Cox San Diego return plant is so clean you could eat off it.” San Diego never had serious RF issues when it came to return path after 1995.

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