User guide

The performance of a transmission feed line system may be affected by excessive signal re
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flection and cable loss. Signal reflection occurs when the RF signal reflects back due to an
impedance mismatch or change in impedance caused by excessive kinking or bending of
the transmission line. Cable loss is caused by attenuation of the signal as it passes through
the transmission line and connectors.
To verify the performance of the transmission feed line system and analyze these problems,
three types of line sweeps are required:
Return Loss Measurement¾Measures the reflected power of the system in decibels (dB).
This measurement can also be taken in the Standing Wave Ratio (SWR) mode, which is the
ratio of the transmitted power to the reflected power.
Cable Loss Measurement¾Measures the energy absorbed, or lost, by the transmission line
in dB/meter or dB/ft. Different transmission lines have different losses, and the loss is fre-
quency and distance specific. The higher the frequency or longer the distance, the greater
the loss.
Distance-To-Fault (DTF) Measurement¾Reveals the precise fault location of compo-
nents in the transmission line system. This test helps to identify specific problems in the
system, such as connector transitions, jumpers, kinks in the cable or moisture intrusion.
The different measurements are defined as:
Return Loss - System Sweep¾A measurement made when the antenna is connected at the
end of the transmission line. This measurement provides an analysis of how the various
components of the system are interacting and provides an aggregate return loss of the entire
system.
Distance To Fault - Load Sweep¾A measurement is made with the antenna disconnected
and replaced with a 50W precision load at the end of the transmission line. This measure-
ment allows analysis of the various components of the transmission feed line system in the
DTF mode.
Cable Loss Sweep¾A measurement made when a short is connected at the end of the
transmission line. This condition allows analysis of the signal loss through the transmission
line and identifies the problems in the system. High insertion loss in the feed line or jump-
ers can contribute to poor system performance and loss of coverage.
This whole process of measurements and testing the transmission line system is called Line
Sweeping.
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Chapter 4 Cable & Antenna Measurements