1-14 Option 100 Fault Location and SRL
Introduction and Measurement Theory
Cable Impedance and Structural Return Loss Measurement Theory
SRL and Discrete Cable Faults
In addition to a set of periodic bumps, a cable can also contain one or
more discrete faults. For this discussion, discrete imperfections will be
referred to as “faults,” and periodic imperfections will be referred to as
“bumps.”
Reflections from discrete faults within the cable will also increase the
level of SRL measured. The energy reflected from a fault will sum with
the energy reflected from the individual bumps and provide a higher
reflection level at the measurement interface. Examining the cable for
faults before the SRL measurement is a worthwhile procedure. The time
required to perform the fault location measurement is small compared to
the time spent in performing an SRL measurement scan.
A fault within the cable will provide the same type of effect as a bad
connector. If the fault is present within the end of the cable nearest to the
analyzer, the effect will be noticed throughout the entire frequency
range. As the fault is located further into the cable, the cable attenuation
will reduce the effect at higher frequencies. The reflected energy travels
further through the cable at lower frequencies where the cable
attenuation per unit distance is lower.
Techniques for Removing Connector Effects
Connector Effects on SRL
To remove the unwanted effects of worn connectors, the SRL
measurement uses a built-in connector model. The connector model
consists of compensation for connector length and compensation for
connector capacitance (connector C).
The “connector C” compensation emulates the C trim value of a variable
impedance bridge.
The connector length is used to compensate for the effects of an
electrically long connector and extends the calibration reference plane.
NOTE A calibration reference plane is established at the point where the short,
open, and load standards have been measured.
The analyzer can automatically measure the optimum values for your
connector model, or you may enter them manually.
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