QAM Marker
Signal Source
rev1.0.5 August 15, 2017
16
The instructions contained in this document for the spectrum analyzer control are specifically
for the Agilent N9342, shown below, however many of the menu/command structures from spectrum to
spectrum are similar.
The key functions used for the measurements in this document are as follows:
SPAN controls the amount of bandwidth shown on the display indicated and/or set by the start,
center, and stop frequency.
RBW (Resolution Bandwidth) is an important function. It is a band pass filter before the power
measurement is taken. It impacts the measurement in three important ways:
1) The measured power at the marker point is constrained to the band pass limits,
2) the noise floor decreases as the band pass range is narrowed, and
3) frequency signals close together (the QAM Marker is a good example) cannot be
resolved unless the RBW is set low enough to discriminate between them.
VBW (Video Bandwidth) determines the capability to discriminate between two different power
levels. A narrower VBW setting removes more noise in the detector output and ‘smooths’ the
envelope display. Set the VBW to be 3x RBW for QAM Marker measurements.
Sweep mode has a lower RBW of 1 kHz. For a lower RBW, set the sweep mode to ‘FFT’ or ‘Auto’.
Auto mode changes settings as needed.
Span:
Start
Center
Stop
BW:
RBW
VBW
Amptd:
Y-Axis
Ref. Level
Scale
dB/Division
Peak
Marker
Sweep:
Auto
Sweep
FFT
