Agilent Technologies FieldFox N9912A, User Manual

Page: 33 / 209

DTF (Distance to Fault) Measurements 33
o
Distance to Fault (dB)
Faults are displayed on the Y-axis in return loss
format, expressed as a positive number in dB.
DTF (VSWR)
Faults are displayed on the Y-axis in SWR. Learn more about
SWR at the FieldFox Supplemental Online Help:
http://na.tm.agilent.com/fieldfox/help/
o
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:
o
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.
o
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
Freq Mode

Choose one of the following:
o
Lowpass Mode
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.
o
Bandpass Mode
(Default setting) The frequency range of a DTF
measurement is set manually. Use Bandpass mode when the DUT contains a
diplexer or other filtering device which does not pass some frequencies.