User`s guide

3-17
Making Time Domain Measurements
Time Domain Low Pass Mode
Interpreting the Low Pass Response Vertical Axis
The vertical axis depends on the chosen format. In the low pass mode, the frequency
domain data is taken at harmonically related frequencies and extrapolated to dc. Because
this results in the inverse Fourier transform having only a real part (the imaginary part is
zero), the most useful low pass step mode format in this application is the real format. It
displays the response in reflection coefficient units. This mode is similar to the traditional
TDR response, which displays the reflected signal in a real format (volts) versus time (or
distance) on the horizontal axis.
The real format can also be used in the low pass impulse mode, but for the best dynamic
range for simultaneously viewing large and small discontinuities, use the log magnitude
format.