Tektronix 1760 Manuale Utente Scaricare il pdf (Pagina 122)

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 cha nge c onstantly. The subtraction process

is complete (resulting in zero) only when the two compo-

nents are exactl y 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.

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Tektronix 1760 Manuale Utente Pagina 122