Keysight N9938-90003 User’s Guide 55
DTF (Distance to Fault) Measurements
DTF Measurement Settings
— More then DTF (Lin) Faults are displayed on the Y-axis in linear
(unitless) format.
DTF Start and Stop Distance
In DTF measurements, you set the physical length of cable or other device to
be tested. The FieldFox calculates the frequency range of the measurement
from this distance. The longer the cable to be tested, the lower the frequencies
that are used. You can also set the frequencies manually using the Frequency
Mode [Bandpass] setting.
How to set Start and Stop Distance
— With a DTF measurement present, press Freq/Dist.
— Then choose from the following:
— Start Distance
Enter a value using the numeric keypad, the
arrows, or the rotary knob, then Enter
. By default, the Start Distance
is set to 0 Meters. This means that the measurement will display
faults starting at the point at which calibration standards are
connected.
— Stop Distance
Enter a value between the start distance and 5 km (or
16,404 ft.) using the numeric keypad, the arrows, or the rotary
knob, then Enter
.
Frequency Mode
All DTF measurements are made with frequency settings and, using Inverse
Fourier Transform (IFT), the time and distance to faults are calculated.
How to set Frequency Mode
With a DTF measurement present,
—Press Meas Setup 4
—Then Frequency Mode
— Choose one of the following:
— Lowpass
The frequency range of a DTF measurement is set
automatically based on the Start and Stop Distances. Use Lowpass
mode when the DUT is a cable ONLY.
The start and stop frequencies for the measurement are always annotated
on the screen below the start and stop distances.
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