HP HP 8753E, User Manual, Page: 411 / 699

Time domain low pass
This mode is used to simulate a traditional time domain reflectometry (TDR) measurement. It
provides information to determine the type of discontinuity (resistive, capacitive, or inductive)
that is present. Low pass provides the best resolution for a given bandwidth in the frequency
domain. It may be used to give either the step or impulse response of the test device.
The low pass mode is less general-purpose than the mode because it places strict
limitations on the measurement frequency range. The low pass mode requires that the
frequency domain data points are harmonically related from dc to the stop frequency. That is,
stop = n x start, where n = number of points For example, with a start frequency of 30
and 101 points, the stop frequency would be 3.03 MHz. Since the analyzer frequency range
starts at 30 the dc frequency response is extrapolated from the lower frequency data. The
requirement to pass dc is the same limitation that exists for traditional TDR.
Setting frequency range for time
domain low
pass
Before a low pass measurement is made, the measurement frequency range must meet the
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this function automatically: the stop frequency is set close to the entered stop frequency, and
the start frequency is set equal to stop/n.
If the low end of the measurement frequency range is critical, it is best to calculate
and calibrating. This avoids distortion of the measurement results. see an example,
select the preset values of 201 points and a 300 to 3 frequency range. Now press
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to 2.999 and the start frequency changes to 14.925 MHz. This would cause a distortion of
measurement results for frequencies from 300 to 14.925 MHz.
Note
If the start and stop frequencies do not conform to the low pass requirement
before a low pass mode (step or impulse) is selected and transform is turned
on, the analyzer resets the start and stop frequencies. If error correction is on
when the frequency range is changed, this turns it off.
6-11. Minimum Frequency Ranges for Time Domain Low Pass
Number of
3
11
26
51
101 MHz
201 30 6.03 MHz
401
30 MHz
1601
Application and Operation Concepts