TIC SDR-OMNI - Measuring Distance to Fault (DTF)

SDR-OMNI Avionics Test Set User Manual
Revision B 6 June 2023 Page 101
NAME
DESCRIPTION
Start Frequency
Enter lowest frequency to sweep.
Stop Frequency
Enter upper frequency to sweep
Back Icon
When selected, the VSWR Calibration screen will display
Menu Icon
Go to Home menu or Global Settings Menu
6.3 MEASURING DISTANCE TO FAULT (DTF)
The SDR-OMNI has the ability to accurately measure the distance along a cable where a significant discontinuity
or anomaly may be located. It does this in the frequency domain, as opposed to the time domain (like a TDR –
Time Domain Reflectometer).
It does this at a specific frequency, which is entered by the operator. For accurate distance results, the operator
must specify the type of coaxial cable being tested so that its Velocity Factor can be used in the distance
computation. The Velocity Factor is the ratio of the RF signal velocity to the velocity of light, expressed as a
percentage. It is typically in the range of 60% to 90%.
Unlike the VSWR measurement, which sweeps the frequency across a specified range, the DTF measurement is
done at a single frequency, which the user can specify. This frequency should be the center of the frequency
range under consideration.
1. The DTF mode requires the same OPEN/SHORT calibration procedure as described in Section 6.1 above. If
that calibration procedure has already been completed, there is no need to recalibrate.
NOTE
DTF will not be selectable until Open Cal and Short Cal have been completed
as indicated by green check marks.
2. Select Distance to Fault from the calibration screen. The SDR-OMNI will begin DTF testing and display the
results (Figure 6-3).
3. Table 6-2 below explains the operation and controls of the DTF screen. Ensure that the proper coaxial cable
type is selected so that the velocity factor is correct. A table of common avionics coaxial cable types is listed
in Table 6-3.
4. Make sure that the desired Center Frequency (10) is correctly set.
5. Set the range to the shortest range that fully spans the length of cable being tested.
6. Press the Peak button (3) to locate the major discontinuity. The exact distance will be displayed below the
graph in green.
NOTE
To switch distance units between feet and meters, the Settings menu can be
accessed by the Home/Settings button at the bottom of the screen. Pressing
the Back button from the Settings screen will return to the DTF screen.