Tektronix WFM 601i, User Manual

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Measurement Theory
WFM 601i Serial Component Monitor
3–25
Figure 3-14: Typical Bowtie display on the WFM 601i.
The bowtie test signal and display method provides better resolution and is easier
to use than the color bar test signal with the waveform or lightning display to
make relative channel timing measurements. Changes in location of the null
indicate a difference in the relative timing. If the null shifts two full time
markers, the relative timing error between channels would be 40 ns. The
direction that the null is offset identifies the signal that is delayed. If the null is
to the left of the center marker, luminance is delayed. When either of the nulls is
shifted to the right, that color difference signal is delayed when compared to
luminance channel timing.
In addition to measuring the interchannel timing differences, the bowtie
measurement provides a method of determining whether the relative channel
gain is correct. If the gains are not equal, the null point will not be a complete
null; instead it will increase in amplitude. If the gain error is in channel 1, both
halves of the display will not produce a “good” null. If channel 2 gain is off, the
first waveform will not null all the way down, but the second one will. If the
gain is off for channel 3, the left waveform will be normal and the right one will
not null as far.