TIC SDR-OMNI - Measuring VSWR And;Or Return Loss

SDR-OMNI Avionics Test Set User Manual
Revision B 6 June 2023 Page 99
6.2 MEASURING VSWR AND/OR RETURN LOSS
VSWR (Voltage Standing Wave Ratio) and Return Loss both measure the same parameter i.e., the signal
reflected back in a transmission line. VSWR is defined as the ratio of the maximum to minimum voltage on a loss-
less transmission line (expressed as 3.0:1, 2.0:1). This ratio represented in dB is called Return Loss.
When the test connection is complete, press VSWR. The SDR-OMNI will begin sweeping across the selected
frequency range and display the results. This may take several seconds for the unit to sweep across the selected
frequency range. See Figure 6-2.
NOTE
VSWR will not be selectable until Open Cal and Short Cal have been
completed.
1. The controls for the VSWR screen are explained in Table 6-1. The Return Loss/VSWR button (Figure 6-2)
allows the operator to display the results as either Return Loss in dB or VSWR as a ratio.
2. Enter the desired Start and Stop frequencies for the frequency range of interest. For example, if testing a
transponder antenna, which operates from 1030 to 1090 MHz, the operator may want to enter 1000 to 1120
MHz as a range of interest. If testing a VHF antenna, 100 MHz to 140 MHz might be a good range.
3. Pressing the PEAK button will move the Frequency Indicator to the frequency with the highest VSWR or
Return Loss. Note that the Return Loss scale is inverted – i.e. 0 dB is at the top, with increasing dB loss
moving lower on the left hand scale.
4. Operate the controls as necessary (Table 6-1) to troubleshoot the test article at hand.
5. If an unacceptable VSWR is detected, the operator may wish to switch to the Distance to Fault (DTF) mode
to determine where along the line the problem may be located.