MFJ-269C Testing coax cable faults and length

Introduction

This tutorial will guide you through using the MFJ-269C SWR analyzer for testing coax cable faults and measuring cable length. This method is particularly useful for identifying issues in coaxial cables, such as LMR400, without the need to cut or modify the cable unnecessarily. By following these steps, you can ensure your coaxial connections are in good condition, which is crucial for optimal radio performance.

Step 1: Prepare Your Equipment

• Gather the following tools:
  • MFJ-269C SWR analyzer
  • Coaxial cable to test (e.g., LMR400)
  • Appropriate connectors (if needed)
• Ensure your analyzer is fully charged or connected to power.
• Familiarize yourself with the MFJ-269C controls, especially the frequency and measurement settings.

Step 2: Connect the Coaxial Cable

• Connect one end of the coaxial cable to the MFJ-269C.
• If testing a long cable, connect the other end to a dummy load or the radio.
• Ensure all connections are secure to avoid errors in measurements.

Step 3: Select the Frequency Range

• Turn on the MFJ-269C and navigate to the frequency settings.
• Choose a frequency that is commonly used in your application (e.g., 146 MHz for VHF).
• Adjust the range to cover the frequency you will be testing.

Step 4: Measure SWR and Reflective Power

• On the MFJ-269C, select the SWR (Standing Wave Ratio) measurement mode.
• Read the SWR value displayed on the screen:
  • An SWR of 1:1 indicates no issues.
  • An SWR above 1:1 suggests potential problems in the coax or connections.
• Note the reflective power reading, which can indicate how much power is being reflected back.

Step 5: Locate Faults in the Coax

• If the SWR is elevated, use the MFJ-269C to identify the distance to the fault:
  • Use the "Cable Length" measurement feature.
  • The analyzer will calculate the length of the coax and indicate where faults may exist.
• Walk along the cable, inspecting for visible damage or loose connections at the indicated distance.

Step 6: Verify Results

• After locating a suspected fault, check the physical condition of the coax:
  • Look for kinks, cuts, or corrosion.
  • Ensure connectors are tightly secured.
• Re-run the SWR test to confirm if the fault has been resolved.

Conclusion

Using the MFJ-269C SWR analyzer is an effective way to test coaxial cables for faults and measure their lengths. By following these steps, you can quickly diagnose issues without cutting or modifying your cables. Regularly testing your coax will help maintain optimal performance in your radio setup. If you identify any faults, consider replacing the affected sections of coax or repairing connections to ensure reliable operation.