Keysight Technologies N5511A, User Manual

Page: 79 / 369

N5511A Phase Noise Test System User’s Guide 79
Absolute Measurement Fundamentals
Inserting a Device
Inserting a Device
An attenuator
You may find that some of your measurement setups require an in-line device
such as an attenuator in one of the signal source paths. (For example, you may
find it necessary to insert an attenuator at the output of a DUT to prevent it
from being injection-locked to the reference source.) The primary consideration
when inserting an attenuator is that the signal source has sufficient output
amplitude to maintain the required signal level at the test set’s phase detector
input port. The signal level required for the measurement depends on the noise
floor level needed to measure the DUT.
Figure 5-17 shows the relationship between the signal level at the R port and
the measurement noise floor.
Figure 5-17 Measurement noise floor relative to R-Port signal level
This is an important consideration in a single channel configuration. For a dual
channel configuration, equal attenuation can be placed in both channels. This
flexibility allows for cross-correlation to remove the effects of the attenuators
and recover the SNR prior to the signal of the DUT being split.