3 Spectrum Analyzer Mode
3.2 Swept SA Measurement
Options
The Band Functions are Marker Noise, Band Power, and Band Density, only one of
which can be on for a given marker.
Value SCPI Notes
Marker
Noise
NOISe
When Marker Noise is on, the marker’s Y Axis Result is the average noise level,
normalized to a 1 Hz noise power bandwidth, in the band specified under the Band Adjust
key
To guarantee accurate data for noise-like signals, a correction for equivalent noise
bandwidth is made by the instrument
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 tradeoff
between sweep time and variance of the result is best when Average Type is set to Power
Averaging. Therefore, Auto coupling chooses the Average detector and Power Averaging
when Marker Noise is on. Though the Marker Noise function works with all settings of
detector and Average Type, using the positive or negative peak detector gives less
accurate measurement results
Noise Markers assume that the signal to be measured is noise-like. Based on this
assumption, we can actually make reasonable measurements under very non-ideal
conditions: any detector may be used, any averaging type, any VBW. In contrast, the
Band Power and Band Density markers make no assumption about the statistics of the
signal
Band
Power
BPOWer
Computes the total power within a span in a nonzero span. The results computation must
include the RBW
In Zero Span, measures the average power across a time interval. This is sometimes
referred to as the interval power
Band
Density
BDENsity
On frequency domain traces, the band density across a band is the total band power
divided by the bandwidth over which it is measured
In Zero Span, measures the average power across a time interval, divided by Bn. Bn is the
noise bandwidth of the RBW filter, as noted and used within the Band Power
computation. This is sometimes referred to as the interval density
It may seem like the band density marker function is exactly like a function of a noise
marker with variable width. But they are somewhat different. The Noise marker assumes
that the signal to be measured is noise-like and applies a correction based on that
assumption. The Band Density markers make no assumption about the statistics of the
signal
Off
OFF
Turns off all Band Functions
Turning off the marker function has no effect on the band span, nor does it turn the
marker Off
The unit to be used for displaying Band Function results is automatically chosen
based on the control mode (Normal, Delta, Fixed) of the marker and the reference
marker. For example, dB/Hz is used when the marker is a noise marker, and the
reference marker is a band power marker.If the selected marker is Off, pressing
Marker Function sets it to Normal and places it at the center of the display on the
344 Spectrum Analyzer Mode User's &Programmer's Reference
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