32 FieldFox User’s Guide
o 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/FieldFox.htm
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 Frequency 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.
Typically, you will set the frequency range of the measurement to the passband
of the filter. However, you may also want to test the ability of the filter to reject
unwanted frequencies. In this case, set the frequency range to include those
frequencies which the filter may not be adequately rejecting.
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