Tektronix 1760 series, User Manual

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Basic Measurements
1760 Series Component Waveform/Vector Monitor User Manual
4-22
The Bowtie test signal consists of a 500 kHz sine wave on
Channel 1 and 502 kHz sine waves of the same amplitude on
Channels 2 and 3. The Channel 2 and 3 waveforms are gen-
erated to be exactly in phase with the Channel 1 signal in the
center of the line. The 1760--Series subtracts Channel 2 from
Channel 1 to make the left half of the display, and Channel 3
from Channel 1 for the right half. The 2kHz frequency offset
between luminance and the difference channels causes the
relative phase to change constantly. The subtraction process
is complete (resulting in zero) only when the two compo-
nents are exactly in phase.
Changes of relative timing change the point at which the null
occurs by changing relative phase between the two channels.
If the amplitudes are not equal, the subtraction never yields
zero and the null is broadened.
The Lightning and Diamond displays provide a high resolu-
tion indicator of proper timing when used with the Bowtie
signal. A spiral ellipse is displayed and the width of the el-
lipse reaches its minimum as timing is adjusted to the opti-
mum setting. It is not necessary to adjust the relative
amplitudes to see the minimum ellipse.