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alter the central frequency, but just set the SPAN to the max permitted value
with the current central frequency.
3.1.4 Amplitude setting
LEV is used to set various parameters related to amplitude, such as
reference level, vertical scale, attenuation, gain and reference offset.
The level value represented by the inscribed line at the top of the
spectrum chart is called the reference level (REF), a name inherited from the
analog era of oscilloscope display spectrometers, which requires counting the
squares from top to bottom to read the chart. In short, it determines the
maximum amplitude that a spectrum map can fit. In principle, the REF is linked
to the instrument's attenuator, amplifier, and the larger the REF, the greater
the attenuation and the smaller the gain. A high REF must be set for
measuring large signals or the signal may overload or even damage the
equipment; a low REF should be set for measuring small signals to obtain a
high signal-to-noise ratio. Modifying the REF allows the spectrum line to move
up and down. No spectral lines are allowed to go beyond the top of the frame
throughout the spectral chart.
Attenuation and amplification are set automatically by default, and the
parameters and characteristics of the settings are described in the next section.
If you are not satisfied with the automatic selection, you can change it to
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