Comparing Against Expected Data - Keysight Technologies N5511A User Manual

Evaluating Your Measurement Results
Evaluating the Results

Comparing against expected data

If none of the problems listed appears on your graph, there still may be
problems or uncertainties that are not obvious at first glance. These
uncertainties can be evaluated by comparing your measurement results
against the following data:
— The noise characteristics expected for your DUT.
— The noise floor and accuracy specifications of the phase noise test system.
— The noise characteristics of the signal source used as the reference source.
The device under test
If you are testing a product for which published specifications exist, compare
the measurement results against the noise and spur characteristics specified
for the product. If the product is operating correctly, the noise graph provided
by the phase noise system should be within the noise limits specified for the
product.
If the device is a prototype or breadboard circuit, it may be possible to estimate
its general noise characteristics using the characteristics of a similar type of
circuit operating in a similar manner.
The reference source
It is important that you know the noise and spur characteristics of your
reference source when you are making phase noise measurements. (The noise
measurement results provided when using this technique reflect the sum of all
contributing noise sources in the system.)
The best way to determine the noise characteristics of the reference source is
to measure them. If three comparable sources are available, the Three Source
Comparison technique can be used to determine the absolute noise level of
each of the three sources. If you are using as your reference source, a source
for which published specifications exist, compare your measurement results
against the noise and spur characteristics specified for that source.
If you have obtained an actual (measured) noise curve for the reference source
you are using, you can use it to determine if your measurement results have
been increased by the noise of the reference source. To do this, determine the
difference (in dB) between the level of the results graph and that of the
reference source. Then use the graph shown in Figure 14-2 to determine if the
measurement results need to be decreased to reflect the actual noise level of
the DUT.
N5511A Phase Noise Test System User's Guide 291