Technical data

Marker Fctn 12
Agilent N8201A Performance Downconverter Synthetic Instrument Module, 250 kHz to 26.5 GHz 221
Marker Noise
Activates a noise marker for the selected marker. If the selected marker is off it is turned on
and located at the center of the display. Reads out the average noise level, normalized to a 1
Hz noise power bandwidth, around the active marker. The noise marker averages 5% of the
trace data values, centered on the location of the marker.
The data displayed (if the marker is in Normal mode) is the noise density around the marker.
The value readout is followed by “(1 Hz)” to remind you that display is normalized to a one
Hz bandwidth.
To measure carrier to noise ratio, be sure that the Marker Fctn is not Marker Noise. Select a
Marker, Normal type marker. Place the marker on the signal peak, then select Delta marker.
Now place the active (D) marker on the noise, and select Marker Noise to change the
marker type. In this case, the reference marker has units of amplitude and the data
displayed is the ratio of the noise density at the delta marker to the reference marker power.
The value readout is dB/Hz if the Y-axis units are logarithmic, and % if the Y-axis units are
linear. It is understood, in this case, that % stands for the units for volts units and
%/Hz for watts units.
To measure the ratio of the noise densities at two locations, be sure that the Marker Fctn is
Marker Noise. (The noise is averaged over a region that is 5% of the span, centered at the
marker location.) Select Marker, Normal before selecting Delta marker. Then move the
active (D) marker to the second noise location. In this case both markers have units of noise
density (for example, dBm/Hz), so the data displayed represents the ratio of the noise
density at the delta marker to the noise density at the reference marker. The value readout
is displayed as a ratio (dB or %).
To guarantee accurate data for noise-like signals, a correction for equivalent noise
bandwidth is made by the N8201A. The Marker Noise function accuracy is best when the
detector is set to Average or Sample, because neither of these detectors will peak-bias the
noise. The trade off between sweep time and variance of the result is best when Avg/VBW
Type is set to Power Averaging. Auto coupling, therefore, normally chooses the Average
detector and Power Averaging. Though the Marker Noise function works with all settings of
detector and Avg/VBW Type, using the positive or negative peak detectors gives less
accurate measurement results.
Key Path: Marker Fctn
Dependencies/Couplings: Video triggering is not available when the detector is
Average, therefore marker functions that would set the detector to Average, and thus
conflict with video triggering, are not available when the Video trigger is On.
Positive or negative peak detection is not recommended for use when measuring noise-like
signals. Though the Marker Noise function allows you to select these detector types, the
average noise measurement results will not be as accurate using peak detection as when
using sample or average detection.
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