Tektronix OM4006D, User Manual, Page: 60 / 205

Operating basics
Table 11: OUI: Analysis Parameters window (cont.)
Parameter Description
Apply Gray coding for
QAM If checked then the bit error rate reported with a QAM signal is
the BER after applying Gray decoding. The Gray coded BER is
typically less than the base BER.
Continuous trace points
per symbol Sets the number of samples per symbol for the clock retiming
that is done to create the
fi ne traces in the phase and eye
diagrams.
Tributaries contributing to
average Sets which possible crosstalk contributions are included in the
calculation of impulse response. The average waveforms are
based on
fi nding the symbol impulse response and convolving
with the data pattern.
Number of symbols in
impulse response Sets the number of values calculated for the impulse response.
More values should provide a more accurate average but takes
longer to calculate. This control is also used by the adaptive
fi lter
choices (such as Nyquist), which uses the impulse response
to calculate the needed
fi lter.
Calculate linear average
eye Controls computation of the average eye. Refresh rate is faster
when disabled, but must be enabled for the linear average to be
displayed in an eye diagram.
Calculate linear average
vs. time Controls computation of the average signal vs. time. Refresh
rate is faster when disabled, but must be enabled for the linear
average to be displayed in the X vs. T diagram.
Calculate subsequence
average Controls computation of the subsequence averaging. Refresh
rate is faster when disabled, but must be enabled for the
subsequence average to be displayed in the spectrum plots.
Subsequence average
length Sets the number of symbols in each subsequence.
Calculate transition
average Controls computation of the transition average. Refresh rate is
faster when disabled. However, this must be checked to enable
calculations based on transition average such as risetime.
Filter type Sets the type of front end fi lter, out of Bessel, Butterworth,
square root raised cosine, raised cosine, user-de fi ned fi lter,
matched fi lter or Nyquist fi lter.
Filter order Sets the order of the Bessel and Butterworth fi lter types.
Filter roll-off factor Sets the roll-off factor of the square root raised cosine and raised
cosine
fi lter types.
Cutoff frequency Sets the cutoff point of the fi lter. The cutoff frequency refers to
the lowpass fi lter cutoff point. It is equal to half the width of the
fi lter as an optical (bandpass) fi lter. The cutoff frequency is the
3 dB point of a Bessel, Butterworth or square root raised cosine
fi lter, and the 6 dB point of a raised cosine fi lter.
Auto-center fi lter on
signal
Sets whether to exactly center the fi lter on the signal, or to apply
it at the nominal signal center frequency.
36 OM4000D Series Coherent Lightwave Signal Analyzer