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Table 53 Spurs on the graph
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 DUT wiring, etc. A breadboarded or
prototype circuit should be well shielded from external RF fields when phase
noise measurements are being made.
Table 54
Table 54 Actions to eliminate spurs
Spur Sources
Description
Internal
Potential spur sources within the
measurement system include the phase noise
system, the DUT, and the reference source.
Typical system spurs are –120 dBc, and they
occur at the power line and system vibration
frequencies in the range of from 25 Hz to 1
kHz, and above 10 MHz.
External
Spur sources external to the system may be
either mechanical or electrical. When using
the Phase Lock Loop measurement technique,
the system's susceptibility to external spur
sources increases with increases in the Peak
Tuning Range set by the VCO source.
Agilent E5505A User's Guide
Number of Averages
<
4
≥
4
≥
8
≥
30
Any
shows actions to take to eliminate spurs.
Evaluating Your Measurement Results
Upward Change for Marking Spurs (dB)
30
17
12
6
4
Recommended Action
If you do not have a plot of the system's noise and spur
characteristics, perform the system Noise Floor Test. If
you suspect that the DUT or the reference source may
be the spur source, check each source using a spectrum
analyzer or measuring receiver (such as an Agilent
8902A). Also, if additional sources are available, try
exchanging each of the sources and repeating the
measurement.
Shorten coaxial cables as much as possible (particularly
the Tune Voltage Output cable). Make sure all cable
connections are tight. It may be possible to identify an
external spur source using a spectrum analyzer with a
pick-up coil or an antenna connected to it.
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