A correction scheme for measurement accuracy improvement in multichannel CATV systems

Many commercially-available oscilloscopes offer the FFT-based spectral analysis capability and it is one of the most economical ways to perform spectral measurement. However, the measurement accuracy is always degraded by the incomplete-cycle sampling present in the FFT. Such degradation in the FFT-based measurement of multichannel CATV systems is investigated. It severely degrades the spectral amplitude accuracy as well as the frequency resolution, both of which are important in deriving the system parameters such as the composite-second-order (CSO), composite-triple-beat (CTB), and carrier-to-noise ratio (CNR). The undesirable effect is formulated mathematically for multichannel systems and the result is used to obtain more accurate spectral values. Windowing and a proposed correction method are used to alleviate such detrimental effects, and an improvement of 3-5 dB in the CTB measurement is achieved with the proposed correction scheme. A procedure for achieving better spectrum analysis for multichannel CATV systems is also presented. The analysis and the proposed schemes can improve the accuracy of the FFT-based measurements of multichannel CATV systems than the traditional windowing method.