Spurs On The Graph - Agilent Technologies E5500A User Manual

Spurs on the Graph

Evaluating Your Measurement Results
Problem Solving
Except for marked spurs, all data on the graph is normalized to a 1 Hz
bandwidth. This bandwidth correction factor makes the measurement appear
more sensitive than it really is. Marked spurs are plotted without bandwidth
correction however, to present their true level as measured.
The spur marking criterion is a detected upward change of more than X dB
(where X is the value shown below) within 4 data points (a single data point
noise peak will not be marked as a spur). Note that the effective noise floor
for detecting spurs is above the plotted 1 Hz bandwidth noise by the
bandwidth correction factor.
Table 15-3
Offset Frequency
<
100 kHz
>
100 kHz
To List the Marked Spurs
A list of spurs can be displayed by accessing the Spurs List function in the
View menu.
Forest of Spurs
A so called forest of spurs is a group of closely spaced spurs on the phase
noise plot. A forest of spurs is often caused by improper shielding that
allows stray RF energy to be picked up by the unit-under-test wiring, etc. A
breadboarded or prototype circuit should be well shielded from external RF
fields when phase noise measurements are being made.
15-16 Agilent Technologies E5500 Phase Noise Measurement System
Spurs on the Graph
Upward Change
Number of
Averages
<
4
≥
4
≥
8
≥
30
Any
for Marking
Spurs (dB)
30
17
12
6
4