Distance to Fault and Time Domain Reflectometry with FieldFox | Keysight
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Distance to Fault and Time Domain Reflectometry with FieldFox | Keysight


Hi, I’m Tom Hoppin, application specialist. Our customers have told us that transmission
line failure is their single top concern for complex communication systems. The FieldFox Cable Test Suite is the best
tool to help you pinpoint the location and nature of the transmission line faults. Let’s see how this done. FieldFox is the only handheld RF and Microwave
Analyzer offering line sweeping, distance to fault and TDR in a single instrument. With that range of measurement flexibility
it allows users to not only determine if their system transmission lines have faults, but
where they are and the nature of the fault with a single connection. That means efficiency. What I’m showing here is a simple set of
cables connectors in a 50 Ohm load as an example of a transmission line. The first step in analyzing the cable’s
performance is the line sweep. We’ll be looking at return loss and distance
to fault. We see a reasonable return loss of about 30
dB for the functional cable, and a distance to the end of the cable assembly at about
2 meters. You’ll also see the initial FieldFox-to-cable
connection and the cable-to-cable connections as reflections. Now, I’ll introduce a fault by loosening
this adapter. You can see that we have almost all of the
incident power reflected back in the return loss screen and then we have a large reflection
down the line. But we don’t know the nature of the fault. Let’s tighten the adapters. By switching measurements to TDR we can see
that we have a good 50-Ohm cable out to 2 meters. Then we see a short. After all, the short doesn’t support voltage
across its conductions, so by definition it’s zero Ohms. If we change the short to an open, the impedance
moves to infinite. In the case shown here, we have a damaged
cable with bend radius exceeding specification, and a nick in the outer shielding and dielectric. The distance to fault function shows exactly
where the faults are, and the TDR function shows the bend fault as capacitive and the
nick as inductive, helping the technicians figure out what the faults are. If you consider that transmission lines can
be hundreds of meters long, these functions are essential in efficient system diagnosis
and repair. Keysight’s FieldFox Analyzer now offers
industry’s most comprehensive cable test suite. Learn more with Keysight’s app note, Advanced
Cable Testing using FieldFox Handheld Analyzers. Thanks for watching.

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