Specifications

Chapter 7 51
Measuring Noise
Measuring Noise Using the Noise Marker
Measuring Noise
Increasing the sweep time when the average detector is enabled allows
the trace to average over a longer time interval, thus reducing the
variations in the results (increases measurement repeatability).
Step 5. Move the marker to 50 MHz (left display Figure 7-2):
Press
Marker.
Rotate the front-panel knob until the noise marker reads 50 MHz.
The noise marker value is based on the mean of 5% of the total number
of sweep points centered at the marker. The points that are averaged
span one-half of a division. Notice that the marker does not go to the
peak of the signal because there are not enough points at the peak of
the signal. The noise marker is also averaging points below the peak
due to the narrow RBW.
Step 6. Widen the resolution bandwidth to allow the marker to make a more
accurate peak power measurement using the noise marker:
Press
BW/Avg, Res BW, 10, kHz.
Press
Marker.
Figure 7-2 Noise Marker (Left - ESA 1 kHz RBW, Right - PSA 10 kHz RBW))
Step 7. Set the analyzer to zero span at the marker frequency:
Press
Mkr →, Mkr → CF.
Press
SPAN X Scale, Zero Span.
Press
Marker.
Note that the marker amplitude value is now correct since all points
averaged are at the same frequency and not influenced by the shape of
the bandwidth filter.
Remember that the noise marker calculates a value based on an
average of the points around the frequency of interest. Generally when
making power measurements using the noise marker on discrete
signals, first tune to the frequency of interest and then make your
measurement in zero span (time-domain).