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Chapter 4 101
Making Measurements
Making the Spectrum (Frequency Domain) Measurement
❏ Flat Top - Selects this filter for best amplitude accuracy by
reducing scalloping error.
❏
Uniform - Select this filter to have no window active by using
the uniform setting.
❏
Hanning - Press this key to activate the Hanning filter.
❏
Hamming - Press this key to activate the Hamming filter.
❏
Gaussian - Press this key to activate the Gaussian filter with
the roll-off factor (alpha) of 3.5.
❏
Blackman - Press this key to activate the Hamming filter.
❏
Blackman Harris - Press this key to activate the Hamming filter.
❏
K-B 70dB/90dB/110dB (Kaiser-Bessel) - Select one of the
Kaiser-Bessel filters with sidelobes at
−70, −90, or −110 dBc.
—
FFT Size - Allows you to access the menu to change the following
parameters:
❏
Length Ctrl - Allows you to toggle the FFT and window length
setting function between
Auto and Man (manual).
❏
Min Pts in RBW - Allows you to set the minimum number of data
points that will be used inside the resolution bandwidth. The
range is 0.10 to 100.00 points with 0.01 resolution. This key is
grayed out if
Length Ctrl is set to Man.
❏
Window Length - Allows you to enter the FFT window length in
the number of capture samples, ranging from 8 to 1048576.
This length represents the actual quantity of I/Q samples that
are captured for processing by the FFT (“
Capture Time” is the
associated parameter shown on the screen). This key is grayed
out if
Length Control is set to Auto.
❏
FFT Length - Allows you to enter the FFT length in the number
of captured samples, ranging from 8 to 1048576. The FFT
length setting is automatically limited so that it is equal to or
greater than the FFT window length setting. Any amount
greater than the window length is implemented by
zero-padding. This key is grayed out if
Length Control is set to
Auto.
—
ADC Range - Allows you to access the menu to define one of the
following ADC ranging functions:
❏
Auto - Select this to set the ADC range automatically. For most
FFT spectrum measurements, the auto feature should not be
selected. An exception is when measuring a signal which is
“bursty”, in which case auto can maximize the time domain
dynamic range, if FFT results are less important to you than
time domain results.