ADInstruments AD8000 Series Instruction Manual page 75

AD8000 Series Spectrum Analyzer Instruction
Manual
For the signal with 3MHz as the frequency, it just falls in the 3dB bandwidth
of the second RBW detection envelop. The value currently shown is
accurate. If a 3.5Mhz signal inputs, and also falls in a valid RBW detection
envelop, the value is also accurate. But if a signal with the frequency
between 3.5 and 4.5MHz , it would fall out of the 3dB envelop. The RBW at
that time could not cover it. The measured signal amplitude in sample
detection mode would be lower than the actual value, since it is at the
sideband of the RBW but not the valid 3dB bandwidth.
In this circumstance, it could be avoided with the positive peak detection
mode if the span/RBW is not too large.
(3) Negative-Peak
The function of negative peak is the opposite of the positive peak that it
could measures the minimum envelop of the signal. But it is not that
common in use than the positive peak detection.
(4) Normal
From the wave it could be seen that the signal amplitude remains the same,
but the amplitude of the noise increases. It is because that to estimate the
collected data in this detection mode: the signal uses positive peak
detection, but the noise part adapts random processing method, for
example odd point with positive peak, and negative peak for even point.
Fig. 3-35 Negative Peak Detection Mode
61