Patent ID: 8327409

Claim:
A method for measuring the frequency response of a transmission link, having a noise floor level, in an active CATV network transmitting signal traffic, having occupied wavelengths, to and from customers over the transmission link, the method comprising: a) generating a first test signal; b) modulating the first test signal using direct sequence spread spectrum with a chip rate, a data rate, and a spreading code length forming a direct sequence spread spectrum test signal; c) transmitting the direct sequence spread spectrum test data signal into the transmission link at a transmitted power level below the noise floor level to limit interference with the signal traffic; during step b) or c), selecting a shorter spreading code length for a wavelength of the direct sequence spread spectrum test signal that will not overlap with an occupied wavelength of the signal traffic than the spreading code length selected for a wavelength of the direct sequence spread spectrum test signal that will overlap with an occupied wavelength of the signal traffic; d) demodulating the direct sequence spread spectrum test signal at a receiver in accordance with the selected shorter and longer spreading code lengths in order to measure the signal level of the first test signal; and e) monitoring the received data signal power level at a receiver, thereby measuring a frequency response of the transmission link.