User`s guide

Expanding Your Measurement Experience 4
Agilent E5505A User’s Guide 75
Sweep segments
When the system begins measuring noise, it places the noise graph on its
display. As you watch the graph, you see the system plot its measurement
results in frequency segments.
The system measures the noise level across its frequency offset range by
averaging the noise within smaller frequency segments. This technique enables
the system to optimize measurement speed while providing you with the
measurement resolution needed for most test applications.
When the measurement is complete, refer to Chapter 14, “Evaluating Your
Measurement Results for help in evaluating your measurement results. (If the
test system has problems completing the measurement, it informs you by
placing a message on the computer display.
Checking the beatnote
While the Connect Diagram is still displayed, Agilent recommends that you use
an oscilloscope (connected to the Monitor port on the test set) or a counter to
check the beatnote being created between the reference source and your DUT.
The objective of checking the beatnote is to ensure that the center frequencies
of the two sources are close enough in frequency to create a beatnote that is
within the Capture Range of the system.
The phase lock loop (PLL) Capture Range is 5% of the peak tuning range of the
VCO source you are using. (The peak tuning range for your VCO can be
estimated by multiplying the VCO tuning constant by the tune range of VCO.
Refer to Chapter 14, “Evaluating Your Measurement Results” if you are not
familiar with the relationship between the PLL capture range and the peak
tuning range of the VCO.)
The beatnote frequency is set by the relative frequency difference between the
two sources. If you have two very accurate sources set at the same frequency,
the resulting beatnote is very close to 0 Hz.
Searching for the beatnote requires that you adjust the center frequency of one
of the sources above and below the frequency of the other source until the
beatnote appears on the oscilloscope’s display. See Figure 44 on page 76.
If incrementing the frequency of one of the sources does not produce a
beatnote, you need to verify the presence of an output signal from each source
before proceeding.
NOTE
If the center frequencies of the sources are not close enough to create a beatnote within
the capture range, the system is not able to complete its measurement.