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pg643e
Figure 6-63. A Reflection Measurement of Two Cables
The ripples in reflection
coefficient
versus frequency in the frequency domain measurement are
caused by the reflections at each connector “beating” against each other.
One at a time, loosen the connectors at each end of the cable and observe the response in both
the frequency domain and the time domain. The frequency domain ripples increase as each
connector is loosened, corresponding to a larger reflection adding in and out of phase with
the other reflections The time domain responses increase as you loosen the connector that
corresponds to each response.
Interpreting the bandpass reflection response horizontal
axis. In
bandpass
reflection
measurements, the horizontal axis represents the time it takes for an impulse launched at the
test port to reach a discontinuity and return to the test port (the two-way travel time). In
Figure 6-62, each connector is a discontinuity.
Interpreting the bandpass reflection response vertical
axis. The quantity displayed on the
vertical axis depends on the selected format. The common formats are listed in lhble 6-10. The
default format is LOG MAG (logarithmic magnitude), which displays the return loss in decibels
(dB).
LIN MAG (linear magnitude) is a format that displays the response as reflection coefficient
(p).
This can be thought of as an average reflection coefficient of the discontinuity over the
frequency range of the measurement. Use the REAL format only in low pass mode.
6-126
Application and Operation Concepts
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