R&S FSH
Distance-to-Fault Mode (R&S FSH-K41)
Performing Cable and Antenna Measurements
Operating Manual 1309.6275.12 - 14
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5.1.2 Distance to Fault Measurements
The distance to fault (DTF) measurement determines the exact location of possible
faults in a transmission system. If you connect the end of the cable to the R&S FSH,
the DTF measurement shows you the exact distance to the fault (in meter or feet),
regardless by what the fault is caused. In addition, the measurement shows the degree
of the fault in dB. From this information, you can determine the component that has the
fault and its seriousness.
In order to determine the distance to a cable fault, the R&S FSH measures the
reflections of the cable under test in the frequency domain. The R&S FSH first
determines the magnitude of the reflections for a particular frequency by comparing the
phase of the reflected signal and a reference signal created by the tracking generator.
It then performs inverse fast fourier transformation (IFFT) on the signal that has been
received. In combination with the characteristics of the cable model, the R&S FSH is
able to determine the distance the reflections have been travelling.
Because of its sensitivity by first measuring in the frequency domain and subsequent
IFFT, the measurement is able to locate faults in a cable accurately. To keep this
accuracy, the R&S FSH also accounts for any attenuation that occurs over distance in
a cable.
If you are measuring the cable only, make sure to terminate the other end into a load.
M
Press the "Meas Mode" softkey.
M
Select the "DTF" menu item.
The R&S FSH calculates the distance to cable faults.
The figure below shows the results of a DTF measurement. The peaks that the trace
shows at the marker positions are possible faults. Depending on the distance, you can
also get an idea of the component that is defective.
Marker 1, for example, shows a defect in the cable. Marker 2 shows a fault at the end
of the cable, probably a bad or loose connection.
