Common Measurement Settings
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417User Manual 1173.9411.02 ─ 43
Such mixer products cannot be identified by the Auto ID function. It is therefore recom-
mended that you perform a visual comparison of the test sweep and reference sweep
using the Signal ID function.
Examining unwanted mixer products with small span
With large spans in which non-modulated sine-wave signals are represented as single
lines, unwanted mixer products are generally completely blanked out. However, if you
examine the frequency range containing a blanked signal in detail using a small span,
e.g. an image-frequency response, part of the signal may nevertheless be displayed.
This happens when the displayed components of a blanked signal have a level differ-
ence which is smaller than the user-defined threshold when compared with the noise
floor. These components are therefore not blanked out.
An unwanted signal with an S/N ratio that corresponds approximately to the user-
defined threshold may not be blanked out permanently. Due to the fact that the noise
display varies from one sweep to another, the S/N ratio changes and thus the level dif-
ference between the test sweep and reference sweep measured at a frequency
changes as well. As a result, the criterion for detecting unwanted signals is not fulfilled.
To blank out unwanted signals permanently, an almost constant noise indication is
therefore required. This can be achieved by reducing the video bandwidth. Since the
average noise indication lies well below the generated noise peak values, the minimum
level diminishes. For identification using the Auto ID function, signals should have this
minimum noise level.
Display of mixer products at the same frequency
If the input signal consists of a very large number of spectral components, it will
become more and more probable that two different unwanted mixer products will be
displayed at the same frequency in the test sweep and reference sweep.
Data Input and Output
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