Oscilloscope Reference Set up the spectral vertical axis
NOTE. The reference level offset is used to calculate the log magnitude in dB. Adjusting the reference
level positions the waveform with respect to the top of the screen but does not change the position of the
waveform with respect to the ground reference marker.
Changing the reference level offset moves the waveform with respect to its ground referenc e marker.
Set the Phase Sc ale
Use these controls to specify the vertical scale for spectral phase waveforms.
Click one of the Scale buttons to specify the vertical units in degrees, radians, or as group delay.
Group delay unwraps and differentiates the phase. All phase values out of the spectral transformation
are between p and -p even though the actual phase value m ay be outside this range.
Click Unwrap to work on a continuous phase function to unwrap the phase value and show the true
range. The phase unwrap begins with a phase value obtained at the first spectral sample after DC.
Click in the suppression Threshold entry box and use the multipurpose to set the level. Suppression
prevents random noise from making the display unusable. Any spectral points w ith magnitudes less
than the threshold will have phase val ues set to zero (degrees or radians). To set a dB level for the
suppression threshold, select dB scale from the magnitude tab, and then set a horizontal bar cursor to
the level on the magnitude spectrum. Read the dB value from the cursor and use the m ultipurpose
kn
ob to enter the value as the suppression threshold.
DSA/DPO70000D, MSO/DPO/DSA70000C, DPO7000C, and MSO/DPO5000 Series 919
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