CATV Tap and Splitter Linearity Improvement for Broadband Information Networks

Broadband CATV Information Networks must be designed such that analog and digital transmissions coexist. These networks require upstream as well as downstream transmission, and in the past have used a frequency plan that allocated 5 to 30 MHz to the upstream and 50 MHz and above to the downstream. Typical converter upstream channels operate in the 5 to 20 MHz range. Due to pressure for more capacity the upstream in recently constructed networks has been expanded to 5 to 40 MHz. Simultaneously, new services are demanding highly reliable upstream transmission, which translates to high upstream transmit power. Since the second harmonic of signals in the 27 MHz to 40 MHz band fall into channels 2 through 5, these two changes taken together require improved linearity in CATV taps and splitter/combiners to limit interference between upstream transmissions and down-stream analog video services. This paper describes the factors limiting linearity in existing CATV taps and splitter/combiners, and a method for linearity improvement.