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MKNOISE Marker Noise
Description
The marker value is normalized to a l-Hz bandwidth. Use “MKA?;
”
to read the noise marker
value.
The noise marker averages 32 trace data values about the location of the marker on the
frequency or time scale. The 32 values averaged, except for the first 15 or last 14 values in the
trace, commence with the 16th point to the left of the marker, and end with the 15th point to
the right of the marker. Note that the data values averaged are not exactly symmetrical with
respect to marker position. At the trace end points, the spectrum analyzer uses the nearest 32
data values. So while the marker may be moved to trace position 1 to 15, the actual amplitude
value returned will be the same value for any marker position from 1 to 15. A similar situation
applies for markers at the end of the trace.
A nominal correction for equivalent noise bandwidths is made by the firmware based on a
nominal 3
dB
resolution bandwidth. The firmware assumes the noise bandwidth is 1.12 times
the resolution bandwidth. This means the shape of the resolution bandwidth filters cause the
noise power to be overstated by 1.12 times. The detection mode also affects the measurement.
If in log mode, the log detector understates the noise response. lb compensate, 2.5
dB
is
added to the measurement. If the detector is in linear mode, the firmware uses 1.05
dB
as a
correction value.
In log detector mode, the final reported value will then be, with the result reported in
dBm
in a
l-Hz bandwidth:
(Averaged value over 32 values)
-
10 x
(log[1.12
x Resolution bandwidth]) + 2.5
dB
In linear detector mode
(dBm)
units, the final reported value will then be, with the result
reported in
dBm
in a l-Hz bandwidth:
(Averaged value over 32 values)
-
10 x
(log[1.12
x Resolution bandwidth]) + 1.05
dB
In linear detector mode with the normal display of voltage units, the noise marker voltage
value will be related to the present marker voltage by this relation.
(V-noise-marker)2
= (V-average)’ x 1.12 x Resolution bandwidth x 0.7824
V-noise-marker = V-average/( 1.12 x Resolution bandwidth x
0.7824)“.5
V-noise-marker = V-average x
l.O6633/(Resolution
bandwidth)0.5
Query Response
ON
output
termination
+
OFF
002
Programming Commands
5.345