FOA Guide

CATV Networks


Most CATV systems are using fiber backbones. CATV companies began using fiber because it gave them greater reliability and the opportunity to offer new services, like Internet connections and phone service.

CATV used to have a terrible reputation for reliability, not really a problem with service but with network topology. CATV uses very high frequency analog signals, up to 1 GHz, which has high attenuation over coax cable. For a city-wide system, CATV needed many amplifiers (repeaters) to reach the users at the end of the system; 15 or more amplifiers in a row were common. Amplifiers failed too often, meaning that any subscriber downstream of the failed amp lost signal. Finding and fixing failed amps was difficult and time consuming, causing subscriber complaints.

 
CATV

 The development of highly linear distributed feedback (DFB) lasers allowed CATV systems to be converted to analog optical systems called HFC - hybrid fiber coax - networks. CATV companies "overbuild" with fiber. They connect their headends with fiber and then take fiber into the neighborhood. They lash the fiber cable onto the aerial "hardline" coax used for the rest of the network or pull it in the same conduit underground.

Fiber allows them to break their network into smaller service areas, typically fewer than 4 amplifiers deep, that prevents large numbers of customers from being affected in an outage, making their network more reliable and easier to troubleshoot, providing better service and customer relations.

The fiber also gives CATV operators a return path which they use for Internet and telephone connections, increasing their revenue potential. Most current CATV systems still use AM (analog) systems which simply convert the electrical TV signals into optical signals. Look for them to convert to more digital transmission in the future.

The development of these hybrid fiber-coax (HFC) networks and the cable modem allowed CATV companies to offer the first real broadband Internet services. The development of the cable modem and the HFC network created a digital network capable of delivering Internet at speeds much higher than digital services over telephone lines, with only fiber to the home (FTTH) being able to exceed cable modem speeds. CATV companies have developed their own FTTH services over passive optical networks called RFOG that allows them to be competitive with FTTH services.


RFOG: CATV's FTTH

CATV operators were the first broadband providers using a HFC (hybrid fiber coax) system with cable modems using RF signals. Today, some CATV operators see a need for a system to provide fiber to the home, which has lead to the development of RFOG (RF over Glass.) CATV standards have looked at PON architectures and the SCTE has proposed a standard for deploying a broadcast architecture of analog signals similar to PONs called RFoG for RF (radio frequency - i.e. FM) over Glass. RFOG is basically nothing more than an all-fiber HFC/cable modem system built with less expensive components now available thanks to the volume pricing of components used in FTTH. It’s designed to operate over a standard telco PON (passive optical network) fiber architecture with short fiber lengths and including the losses of a FTTH PON splitter.

RFOG

 There is one interesting aspect of this approach. Now telcos and CATV companies can deliver the same services over the same cable plant using totally different technologies. But that means that office or apartment building owners, developers or even whole towns that might be considering installing FTTH infrastructure themselves and leasing the fiber to a service provider can have a choice of service providers. One cable network can support either CATV or telco systems – or even someone else for that matter. That opens up a big market for private fiber optic systems.

 Read "What is Broadband" about the development of the cable modem.






Table of Contents: The FOA Reference Guide To Fiber Optics




 


(C) 2025, The Fiber Optic Association, Inc.