Agilent Technologies 4395A, Ручное изменение

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Network Measurement Basics
Figure A -10. Rate of Phase Change V ersus Frequency
When deviations from linear phase are present, changing the frequency step can result in
dierent values for group delay . Note that in this case the computed slope varies as the
aperture 1f is increased (Figure A -11 ). A wider aperture results in loss of the ne grain
variations in group delay . This loss of detail is the reason that in any comparison of group delay
data it is important to know the aperture used to make the measurement.
Figure A -11. V ariations in Frequency Aperture
In determining the group delay aperture , there is a tradeo between resolution of ne detail
and the eects of noise . Noise can be reduced by increasing the aperture , but this will tend to
smooth out the ne detail. More detail will become visible as the aperture is decreased, but the
noise will also increase , possibly to the point of obscuring the detail. A good practice is to use a
smaller aperture to assure that small variations are not missed, then increase the aperture to
smooth the trace .
A-18 Basic Measurement Theory