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How to measure a
Cable/Connector Loss
Cable/Connector Loss
Cables and connectors can have a dramatic effect on the
accuracy and validity of measurements on additional
components. They also wear with time and use. This
wear can show up as an increase in attenuation over
particular frequency ranges.
You can use a spectrum analyzer and a tracking
generator to easily test the insertion loss (loss vs.
frequency) of the cables and adapters.
Required Hardware:
Two N-type to BNC Adapters. Select adapters that
convert N-type (in/out connectors on most spectrum
analyzers) to the cable type you are testing. Also note
that higher quality connectors (Silver plated, Beryllium
Copper pins, etc..) equal better longevity and
repeatability.
Figure 1: N-type to BNC adapter
A short reference cable with terminations that match
your adapters and cable-under-test.
An adapter to go between the reference cable and the
cable-under-test. This experiment will use a BNC “barrel
connector”. Note that higher quality connectors (Silver
plated, Berylium Copper pins, etc..) equal better
longevity and repeatability.
Figure 2: BNC barrel adapter
Alternately, you can use two adapters a short cable as a
reference assembly to normalize the display before
making cable measurements. This removes the need to
have the cable-to-cable adapter.
A Spectrum analyzer with Tracking Generator (TG)
Test Steps:
1. Attach the adapters to the tracking generator
(TG) output and RF Input.
RIGOL – Uncompromised Performance…. Unprecedented Value
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NOTE: Clean the surfaces of the adapters and
input with a lint free cloth to prevent
damage and ensure repeatability.
2. Connect the reference cable to the TG out and RF
In on the analyzer.
Figure 3: Measuring reference cable
3. Adjust Span of scan for frequency range of
interest.
4. Adjust the tracking generator output amplitude
and spectrum analyzer display to view the entire
trace.
5. Enable the tracking generator output.
Figure 4: Reference cable insertion loss before
normalization.
6. Disconnect the reference cable from the RF
input.Place cable-to-cable adapter (BNC barrel or
other) and connect to the cable to test.
7. Connect the cable-under-test to test to RF input
and enable the tracking generator.
Figure 5: Cable-under-test connected and test result
The screen displays the cable-under-test losses plus
the error of the cable-to-cable adapter.