RigExpert AA-650 ZOOM, Руководство пользователя

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RigExpert AA-650 ZOOM
Unlike many other commercially-available reflectometers, RigExpert AA-650 ZOOM
does not send pulses into the cable. Instead, another technique is used. First,
R and
X (the real and the imaginary part of the impedance) are measured over the whole
frequency range (up to 650 MHz). Then, the IFFT (Inverse Fast Fourier Transform) is
applied to the data. As a result, impulse response and step response are calculated.
This method is often called a “
Frequency Domain Reflectometry”, but the “TDR” term
is used in this document since all calculations are made internally and the user can
only see the final result.
The vertical axis of the resulting chart displays the reflection coefficient:
Γ
=-1 for short
load, 0 for matched impedance load (ZLoad=Z0), or +1 for open load. By knowing the
cable velocity factor, the horizontal axis is shown in the units of length.
Single or multiple discontinuities can be displayed on these charts. While the Impulse
Response chart is suitable for measuring distance, the Step Response chart helps in
finding the cause of a fault.
See the examples of typical
Step Response
charts on the next page.
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