92 Keysight N9923-90001 User’s GuideDTF (Distance to Fault) MeasurementsDTF Measurement Settings—More then DTF (Lin) Faults are displayed on the Y-axis in linear(unitless) format.DTF Start and Stop DistanceIn DTF measurements, you set the physical length of cable or other device tobe tested. The FieldFox calculates the frequency range of the measurementfrom this distance. The longer the cable to be tested, the lower the frequenciesthat are used. You can also set the frequencies manually using the FrequencyMode [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, thearrows, or the rotary knob, then Enter. By default, the Start Distanceis set to 0 Meters. This means that the measurement will displayfaults starting at the point at which calibration standards areconnected.—Stop Distance Enter a value between the start distance and 5 km (or16,404 ft.) using the numeric keypad, the arrows, or the rotaryknob, then Enter.Frequency ModeAll DTF measurements are made with frequency settings and, using InverseFourier Transform (IFT), the time and distance to faults are calculated.How to set Frequency ModeWith a DTF measurement present,— Press Meas Setup 4— Then Frequency Mode— Choose one of the following:—Lowpass Mode The frequency range of a DTF measurement is setautomatically based on the Start and Stop Distances. Use Lowpassmode when the DUT is a cable ONLY.The start and stop frequencies for the measurement are always annotatedon the screen below the start and stop distances.
