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102 Chapter 4
Making Measurements
Making the Spectrum (Frequency Domain) Measurement
❏ Auto Peak - Select this to set the ADC range automatically to
the peak signal level. Auto peak is a compromise that works
well for both CW and burst signals.
❏
AutoPeakLock - Select this to hold the ADC range automatically
at the peak signal level. Auto peak lock is more stable than
auto peak for CW signals, but should not be used for “bursty”
signals.
❏
Manual - Allows you to access the selection menu: −6 dB, 0 dB, +6
dB
, +12 dB, +18 dB, +24 dB, to set the ADC range level. Also note
that manual ranging is best for CW signals.
—
Data Packing - Allows you to select Auto (the default) or the Short (16
bit)
, Medium (24 bit) and Long (32 bit) methods of data packing. The
short, medium, and long methods are not compatible with all
settings and should not be used unless you are familiar with data
packing methods.
Auto is the preferred choice.
❏
Auto - The data packing value most appropriate for current
instrument settings is selected automatically.
❏
Short (16 bit) - Select this to pack data every 16 bits.
❏
Medium (24 bit) - Select this to pack data every 24 bits.
❏
Long (32 bit) - Select this to pack data every 32 bits.
—
ADC Dither - Allows you to toggle the ADC dither function between
Auto, On, and Off. When set to Auto (the default), the ADC dither
function will be activated when a narrow bandwidth is being
measured, and deactivated when a wide bandwidth is being
measured. “ADC dither” refers to the introduction of noise to the
digitized steps of the analog-to-digital converter; the result is an
improvement in amplitude accuracy. Use of the ADC dither,
however, reduces dynamic range by approximately 3 dB.
—
Decimation - Allows you to toggle the decimation function between
Auto and Man, and to set the decimation value. Auto is the
preferred setting, and the only setting that guarantees alias-free
FFT spectrum measurements. If you are familiar with the
decimation feature, you can change the decimation value by
setting to
Man, but be aware that aliasing can result in higher
values. Decimation numbers 1 to 4 describe the factor by which
the number of points are reduced. The default setting is 1, which
results in no data point reduction.
—
IF Flatness - Allows you to toggle the IF flatness function between
On and Off. If set to On (the default), the IF flatness feature causes
background amplitude corrections to be performed on the FFT
spectrum. The
Off setting is used for adjustment and
troubleshooting of the test instrument.