Atek HP 8753D, Руководство пользователя, Страница: 122 / 677

4. T o better view the measurement trace , press:
4 SCALE REF 5
NNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNN
AUTO SCALE
Figure 2-55 shows the frequency domain reection response of the cables under test. The
complex ripple pattern is caused by reections from the adapters interacting with each
other . By transforming this data to the time domain, you can determine the magnitude of
the reections versus distance along the cable .
Figure 2-55. Device Response in the Frequency Domain
5. T o transform the data from the frequency domain to the time domain, press:
4
SYSTEM
5
NNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNN
TRANSFORM MENU
NNNNNNNNNNNNNNNNNNNNNNNNNN
BANDPASS
NNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNN
TRANSFORM ON
6. T o view the time domain over the length (<4 meters) of the cable under test, press:
4 F ORMA T 5
NNNNNNNNNNNNNNNNNNNNNNN
LIN MAG
4 ST ART 5 4 0 5 4 x1 5
4 STOP 5 4 35 5 4 G/n 5
The stop time corresponds to the length of the cable under test. The energy travels about
1 foot per nanosecond, or 0.3 meter/ns , in free space . Most cables have a relative velocity of
about 0.66 the speed in free space . Calculate about 3 ns/foot, or 10 ns/meter , for the stop
time when you are measuring the return trip distance to the cable end.
2-74 Making Measurements