Structural Return Loss measurements

The SARK-110 Antenna Analyzer firmware does not currently have a built-in function for the measurement of cable structural return loss (SRL). However, this measurement is possible with the help of the attached Microsoft Excel spreadsheet.

Structural return loss is defined as the return loss of the cable relative to its own impedance and summarizes the uniformity in cable construction. Cable manufacturing imperfections, defects and faults contribute to degrade cable performance. The extent of these imperfections is characterised by the SRL. Comprehensive definitions and measurement techniques are described in the References below.

For the measurement it is recommended to use the new Deep Sweep Save firmware function or the SARK Plots client software for capturing the data, since it allows to increase the number of measurement points. Structural return loss effects can be very narrow in frequency span, as they are caused by the cumulative effects of small reflections along the entire length of the cable.

Notice that the attached spreadsheet requires 1000-points but can easily adapted to an arbitrary number of frequency points.

The measurement setup is described in the Figure 1. The far end of the cable must be terminated with the matched termination, e.g. 75-ohm for a cable with a characteristic impedance of 75-ohm.

Before starting the measurement, it is necessary to perform the OSL Calibration procedure with the calibration standards connected to the Adaptor.

For capturing the data using the Deep Sweep Save function, you will need first to set the frequency and span range either in the Scalar Chart, Field, or the Smith Chart modes. Then select <File><Deep Sweep><Save>. Then select the file name and the number of points, which by default is set to 1000. Wait for the completion of the measurement and once terminated to can connect the device to the PC and import the data into the spreadsheet.

This data can be then imported into the spreadsheet using the following procedure: open the spreadsheet, select the sheet "CSV", click in A1 cell and with right mouse button select <Update data>. Then the results are plotted in the sheets "Graph SRL" (Figure 2) and "Graph SLR-RL" (Figure 3), which plots both SRL and the Return Losses. The plots show also the maximum value of the SRL.

If using SARK Plots, change the number of points in <Settings><Parameters>; e.g. to 1000. Set the Run Control mode to Single, set the desired Start and Stop frequencies, and Run a sweep. Once the sweep is terminated, export the data using <File><Save File> and import the data into the spreadsheet using the procedure described above.

References

• 1. ANSI/SCTE 03 2008 -Test Method for Coaxial Cable Structural Return Loss; https://scte-cms-resource-storage.s3.amazonaws.com/Standards/ANSI_SCTE%2003%202016.pdf

  2. Cable Impedance and Structural Return Loss Measurement Methodologies: https://docplayer.net/15857551-Cable-impedance-and-structural-return-loss-measurement-methodologies.html