Spectral math phase controls
Select the phase controls
You can set the vertical units to Degrees, Radians, or Group Delay in seconds. To do this, click the Math toolbar button, click
Spectral Analysis Setup, and select the Phase tab. Then select the desired scale type from Degrees, Radians, or Group Delay.
Phase reference position
Phase is a relative measurement that must have a time domain reference point. The phase value is specified with respect to this
phase reference position.
For the spectral analyzer, the phase reference position is the 50% position of the gate, that is, the middle of the gate interval of
the data that is input to the spectral analyzer. This is true for all window functions except for the Tek Exponential window. This
window has a reference point at the 20% position of the gate.
Phase unwrap
The spectral analyzer produces phase values from –π to +π radians or –180 to 180 degrees. However, when you perform
impulse response testing and the phase is continuous, then phase values outside these ranges may occur. The spectral analyzer
then wraps the data with discontinuities in the display from +180 to –180 degrees. Phase unwrap will display the correct result by
unwrapping the phase.
Phase unwrap is only valid when the phase spectrum is a continuous function of frequency. Therefore, do not use it when
analyzing the harmonic content of the typical repetitive signal.
Suppression threshold
Random noise in the spectrum may have phase values over the entire range. This could make the phase display unusable.
However, you can set the suppression threshold control to a level in dB. The phase of any complex spectral points with a
magnitude below this threshold is set to zero. See the next figure for an example.
Oscilloscope reference
724 DPO70000SX, MSO/DPO70000DX, MSO/DPO70000C, DPO7000C, and MSO/DPO5000B Series
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