Phase Error Compensation (Graph Settings)

Default: 1% span

Range: 0.01% to 100% span

Phase Error Compensation can be used to correct for close-in phase differences that remain after aligning the stimulus and response signals.

To use the default compensation filter (29 points wide), select the Auto check box.

The Auto setting has a fairly wide filter bandwidth and should only be used when the signal distortion is already very low.

To specify a different compensation filter bandwidth, clear the Auto check box and type the desired compensation filter bandwidth in the Compensator BW text box. The compensator bandwidth is specified in percentage of the frequency span.

Phase Error Compensation

After the signals have been aligned for magnitude, delay, and phase, the remaining error can be further reduced by compensating for the phase differences that remain due to close-in phase noise or small residual frequency errors.

Phase noise will generally not be a problem when the stimulus and response signals are measured simultaneously from Ch1 and Ch2 of the same instrument. In this case, the phase noise is common (coherent LO's) between the two channels and cancels. In other words, the phase noise in the stimulus channel measurement also shows up in the response channel measurement.

However, phase noise can introduce error when the stimulus and response signals are acquired at different times, or when the stimulus signal (reference) is an ideal waveform. The phase compensation algorithm will detect the phase drift between the input and output signals and will compensate the output signal accordingly.

Phase noise isn't the only contributor to phase error. Additive noise, spurious, and distortion can also introduce short-duration phase error. For this reason, the best results are generally obtained when the compensating bandwidth is narrow relative to the span. As the bandwidth is increased, the compensation algorithm will begin to compensate for the shorter duration events, such as a large peak amplitude with AM Amplitude Modulation - CW modulation using amplitude variation in proportion to the amplitude of the modulating signal. Usually taken as DSB-LC for commercial broadcast transmissions and DSB-SC for multiplexed systems./PM distortion, and may actually reduce overall accuracy.