Spectrum Analyzer Measurements 3-4 Setting Amplitude Parameters
Spectrum Analyzer MG PN: 10580-00447 Rev. H 3-9
Setting Amplitude Reference Level
The amplitude reference level is typically an absolute reference level set at the top of the graticule for the
power level being measured. Signal levels above this set value will be outside of the display range and may
overdrive and saturate the input circuit (refer to “Indications of Excessive Signal Level” on page 3-11). To set
the current amplitude reference level:
1. To automatically set an optimum reference level, press AMPLITUDE > AUTO REF LEVEL.
2. To manually set the reference level, press AMPLITUDE > REF LEVEL, then enter the desired reference
level.
Setting Amplitude Range and Scale
This setting applies to most analyzer modes of operation and allows you to set the y-axis graticule scale for
log-based units only.
1. Select AMPLITUDE > SCALE/DIV.
2. Enter the desired number of units per division.
Reference Level Offset for External Loss or External Gain
To obtain accurate measurements, you can compensate for any external attenuation or gain by using a
reference level offset. The compensation factor is always in dB, even if linear amplitude units are selected.
External attenuation can be created by using an external cable or an external high power attenuator. External
gain is typically from an amplifier.
To adjust the reference or amplitude level for either gain or loss:
1. Select AMPLITUDE > REF LEVEL OFFSET.
2. Enter a positive dB value to account for gain or enter a negative dB value to account for loss.
3. The new reference level offset value will be displayed on the instrument and the y-axis and trace
amplitude is adjusted accordingly.
Attenuator Functions
The spectrum analyzer includes a step attenuator at the RF input. This attenuator is used to reduce large
signals to levels that make best use of the analyzer’s dynamic range. By default, the auto attenuation
automatically adjusts the attenuator as a function of the reference level. In the AMPLITUDE menu, the
ATTEN LEVEL allows manual adjustment of the input attenuation. When auto attenuation is selected, both
the reference level and the attenuation are increased. The following actions, listed in decreasing order of
effectiveness, can facilitate the detection of low-level CW signals:
• Decrease the reference level and attenuation. Refer to “AMPLITUDE Menu” on page 3-12.
• Turn on the preamplifier.
• Reduce RBW and or VBW (RBW/VBW = 10 is often optimal for this purpose). Refer to “Field Strength”
on page 3-14.
• Use trace averaging if VBW is already set to 1 Hz. Refer to “Setting Trace Parameters” on page 3-21.
Note
Select AUTO ATTEN coupling of the attenuator setting and AUTO REF LEVEL to help ensure that
harmonics and spurs are not introduced into the measurements.
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