A receiver and method for using the same to generate phase spectra that are independent of the starting time of the sequence of digital measurements used to generate the phase spectra are disclosed. The receiver includes a first signal port adapted to receive a first test signal that includes a plurality of tones and a first ADC that generates one digital value from the first test signal in response to each clock pulse from an ADC clock. The first receiver also includes a phase clock register that includes a time stamp value that is incremented on each clock pulse from the ADC clock, and a processor that records a sequence of the digital values starting at a first time and the time stamp value at the first time.