Agilent Technologies N9010A - Manual (Page 44)

44 Chapter 1
Agilent EXA Signal Analyzer
Dynamic Range
c. Reference level and off-screen performance: The reference level (RL) behavior differs from some ear-
lier analyzers in a way that makes this analyzer more flexible. In other analyzers, the RL controlled
how the measurement was performed as well as how it was displayed. Because the logarithmic ampli-
fier in these analyzers had both range and resolution limitations, this behavior was necessary for opti-
mum measurement accuracy. The logarithmic amplifier in this signal analyzer, however, is
implemented digitally such that the range and resolution greatly exceed other instrument limitations.
Because of this, the analyzer can make measurements largely independent of the setting of the RL
without compromising accuracy. Because the RL becomes a display function, not a measurement func-
tion, a marker can read out results that are off-screen, either above or below, without any change in
accuracy. The only exception to the independence of RL and the way in which the measurement is per-
formed is in the input attenuation setting: When the input attenuation is set to auto, the rules for the
determination of the input attenuation include dependence on the reference level. Because the input
attenuation setting controls the tradeoff between large signal behaviors (third-order intermodulation,
compression, and display scale fidelity) and small signal effects (noise), the measurement results can
change with RL changes when the input attenuation is set to auto.
d. The ADC clipping level declines at low frequencies (below 50 MHz) when the LO feedthrough (the
signal that appears at 0 Hz) is within 5 times the prefilter bandwidth (see table) and must be handled by
the ADC. For example, with a 300 kHz RBW and prefilter bandwidth at 966 kHz, the clipping level
reduces for signal frequencies below 4.83 MHz. For signal frequencies below 2.5 times the prefilter
bandwidth, there will be additional reduction due to the presence of the image signal (the signal that
appears at the negative of the input signal frequency) at the ADC.