Agilent Technologies E4406A, Руководство пользователя

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Chapter 4 93
Making Measurements
Making the Spectrum (Frequency Domain) Measurement
NOTE
Parameters under the
Advanced
key seldom need to be changed. Any
changes from the default advanced values may result in invalid
measurement data.
Make sure the
Spectrum (Freq Domain)
measurement is selected under
the
Measure
menu. Press the
Meas Setup
key to access a menu which
allows you to modify the averaging, and trigger source for this
measurement (as described in the “Measurement Setup” section). In
addition, the following parameters can be modified:
•
Span
- This key allows you to modify the frequency span. Changing
the span causes the bandwidth to change automatically, and will
affect data acquisition time.
•
Res BW
- This feature sets the resolution bandwidth for the FFT, and
allows manual or automatic settings. A narrower bandwidth will
result in a longer data acquisition time. In Auto mode the resolution
bandwidth is set to Span/50 (2% of the span).
•
Advanced
- The following FFT advanced features should be used only
if you are familiar with their operation. Changes from the default
values may result in invalid data.
Pre-ADC BPF - This key allows you to toggle the pre-ADC
bandpass filter to On or Off states. The pre-ADC bandpass filter
is useful for rejecting nearby signals, so that sensitivity within
the span range can be improved by increasing the ADC range
gain.
Pre-FFT Fltr - Allows you to toggle between
Flat
(flat top) and
Gaussian
. The pre-FFT filter defaults to a flat top filter which has
better amplitude accuracy. The Gaussian filter has better pulse
response.
Pre-FFT BW - The Pre-FFT bandwidth allows you to select
between a manual or an automatic setting. The pre FFT-
bandwidth filter can be set between 1 Hz and 10 MHz. In Auto
mode this bandwidth is nominally 50% wider than the span. This
bandwidth determines the ADC sampling rate.
FFT Window - Allows you to access the following selection
menu. Unless you are familiar with FFT windows, use the flat top
filter (the default filter).
• Flat Top - Selects a filter for best amplitude accuracy, by
reducing scalloping error.
• Uniform - You can select to have no window active by using
the uniform setting.
• Hanning
• Hamming
• Gaussian - Selects a gaussian filter with an alpha of 3.5.