Non-Linear Behavior Characterization Methods for HFC Networks Return Path Devices and Their Relationship

This paper presents a measurement methodology to characterize the non-linear behavior of HFC (Hybrid Fiber Coax) return path components and sub-systems. The measurement method, based on NPR (Noise Power Ratio), takes into account the spectral and statistical nature of return path signals, those being different from downstream signals. The paper describes a reliable measurement set-up based on a filtered white noise source and a spectrum analyzer. Correction figures to apply to spectrum analyzer measurements, experimental best practices and measurement uncertainty are developed. The automation of the set-up is presented as well as some results concerning an electric return path amplifier and an optical return path system. The temperature behavior of those devices is compared by the way of the NPR. Also, a theoretical analysis of the relationship between tones distortions characterization and the NPR method is established and experimentally demonstrated. Therefrom, an alternative measurement method for return path systems is proposed to the attention of laboratories which do not possess NPR measurement capabilities.