Frequency Range And Points; Stimulus (Mode); Set Frequency Lowpass; Start/Stop Time - Keysight N9912A User Manual

Frequency Range and Points

Like CAT mode, all Time Domain measurements are made in the frequency domain
and, using Inverse Fourier Transform (IFT), time is calculated. Select the frequency
range from which Time Domain measurements are calculated. Increasing the data
points will improve measurement resolution. However, more data points will usually
result in slower sweep updates.
Set frequency range and points before selecting Stimulus Mode.

Stimulus (Mode)

There are three variations on how the Time Domain transform algorithm is applied to
the frequency domain measurement. Each method has a unique application.


In both Lowpass modes, frequencies down to DC and negative frequencies are
extrapolated. Therefore, when either Lowpass mode is selected, Set Freq.Low Pass is
automatically applied to adjust the start frequency. Learn more about Set Frequency
Lowpass below.
When the Start Frequency or resolution is changed AFTER selecting a Lowpass
mode, then Stimulus mode is set to Band Pass and Transform is disabled.


Set Frequency Lowpass

NOTE This setting is made automatically when either Lowpass mode is selected.
USE ONLY IN LOW PASS MODES. When this setting is made, the start frequency is
adjusted to be harmonics of the start frequency. Start frequency is computed by the
following formula:
Low Pass Start Frequency = Stop Frequency / Number of points.

Start/Stop Time

The following settings adjust the display resolution, allowing you to zoom IN or OUT
on a response. When the start or stop time is updated, they may be automatically
adjusted to limit the display to one alias-free response on either side of zero time.
How to set Start and Stop time
 Press Measure 4
 Then
 Then
 Then choose from:
54
- Highest resolution. Most useful for seeing small responses in
Lowpass Impulse
devices that pass low frequencies, such as cables.
- Easiest to identify inductive and capacitive discontinuities in
Lowpass Step
devices that pass low frequencies such as cables.
pass- Easiest method - can be used with any frequency sweep. Most useful
Band
for measuring band limited devices such as filters and DC blocked cables. This
mode does NOT show capacitive and inductive reactance. For the same frequency
span and number of points, band pass mode has twice the impulse width, which
hides closely spaced responses degrading the response resolution.
Transform
Transform Start Stop
Sets the transform start time that is displayed on the FieldFox screen.
Start
o
Sets the transform stop time that is displayed on the FieldFox screen.
Stop
o
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