System performance issues are seen in two ways: excessive reflections (more common) caused by impedance mismatches or excessive insertion losses (less common) caused by energy dissipated in the connectors or cables.
The two measurements used to determine communication system performance are:
• Return Loss or Voltage Standing Wave Ratio (VSWR) for reflections
• Cable Loss (Insertion Loss) for insertion losses
It is important to remember that return loss and VSWR are typically Pass/Fail tests. They both measure reflection but display the results in different ways. For either measurement, set a limit line to the specification determined by the carrier and make the measurement. If the entire frequency range swept is below the line, the test passes. If any part of the sweep is at or above the limit line, the test fails. With a failed test, one or more components is at fault. Distance-to-fault mode is used to find the problem.
The second common line sweeping measurement is cable loss. Generally, cable loss measurements determine how less the output signal power is compared to the input power. The loss comes from heat and leakage. Cable manufacturers will specify the loss per foot or meter at different frequencies and may call it attenuation. The Field Master Series and Site Master Series instruments have pre-installed loss specifications for several cable types.
The cable loss measurement is also typically a Pass/Fail measurement and requires a short or open at the cable end. This is a typical measurement specified on new installations or main transmission line replacement but is not typically tested on existing systems.
Note
Anritsu recommends connecting directly to the RF port. If this is not possible, using a phase-stable test port cable attached to the RF port to extend the range. When using an extension cable, calibrate at the open end of the cable. Refer to Calibration.