HP 8591C User Manual page 291

Test Descriptions
Color Test Descriptions (Chromalluma Delay Inequality, Differential Gain, Differential Phase)
Differential Phase Test
The differential phase test measures the change in phase of the chrominance
Description
subcarrier as the luminance changes from a blanking level towards white
level.
The five-step riser portion of the test signal is used to perform this
measurement. The test signal is selected automatically.
Again a Fast Fourier transform is performed on the reference burst and
each step in the five-step riser. Each step is normalized to the reference
burst. The differential phase test can be configured for each of the two
common definitions for this test. For the NTC definition, the largest phase
difference between any two riser steps (including the reference) is calculated
and displayed. For the FCC (NCTA) definition, the largest phase difference
between the reference and any riser step is calculated and displayed.
If 5th PKT YES NO is set to NO, then the calculation is based on the first
four steps in the five-step riser in channel measurement mode. The 5th
packet is never used in system measurement mode. MORE INFO shows the
normalized values for each packet. This is useful for relative measurements.
See Figure 8-15.
The FCC differential phase is equal to the largest packet value in degrees
from the phase of the reference packet.
The NTC differential phase calculation is as follows: (where max = largest
packet value in degrees and min = smallest packet value in degrees)
8-38
DP = max - min