3 VMA Mode
3.1 Digital Demod Measurement
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Amplitude Ratio is the free decision distance in height of a digital signal and is
calculated as 2B/(A+B). A and B are the maximum and minimum amplitude
difference at the decision point. An ideal signal has a decision height of 100%.
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Time Ratio is the free decision distance in width of a digital signal and is
calculated as 2B’/(A’+B’). A’ and B’ are the maximum and minimum zero-cross
time width. An ideal signal has a decision width of 100%.
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Modulation Index Outer (SCPI only) is defined as the measure of extent of outer
amplitude variation about an un-modulated carrier. It is calculated as (VAmax –
VAmin)/(VAmax + VAmin). VAmax is the largest amplitude at crest. VAmin is the
smallest amplitude at bottom. Maximum amplitude difference A is equal to
VAmax – VAmin.
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Modulation Index Inner (SCPI only) is defined as the measure of extent of inner
amplitude variation about an un-modulated carrier. It is calculated as (VBmax –
VBmin)/(VBmax + VBmin). VBmax is the smallest amplitude at crest. VBmin is
the largest amplitude at bottom. Minimum amplitude difference B is equal to
VBmax – VBmin.
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Modulation On/Off Ratio (SCPI only) is defined as the ratio of 20log10((VAmax +
VBmax)/(VAmin +VBmin)).
Vector Modulation Analyzer Mode User's &Programmer's Reference 224
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