R&S FSW Series, Руководство пользователя

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Common Measurement Settings
R&S
®
FSW
416 User Manual 1173.9411.02 ─ 43
played in any of the traces 1 to 3. Unwanted mixer products are suppressed in this cal-
culated trace.
Test sweep and reference sweep traces
Depending on which of the automatic signal identification functions are used, the
traces are used to display either the test sweep (the upper side-band sweep) or the ref-
erence sweep (lower side-band sweep).
Function Trace 1 Trace 2 Trace 3
Signal ID Signal ID upper side-
band Signal ID lower side-
band -
Auto ID Auto ID - -
Signal ID + Auto ID Signal ID upper side-
band Signal ID lower side-
band Auto ID
Tolerance for the comparison of test sweep and reference
Since the LO frequency is displaced downwards in the reference sweep, the conver-
sion loss of the mixer may differ from that of the test sweep. This is due to the fact that
the LO output power of the R&S
FSW varies with the frequency, and also due to the
non-ideal characteristics of the mixer. A certain tolerance should therefore be permitted
for the comparison of the signal levels in the test sweep and reference sweep. A user-
defined threshold is used to determine deviations.
Auto ID detection threshold
Real input signals are displayed at the same frequency in the test and reference
sweeps, i.e. theoretically, identical signal levels are expected at the frequency of the
real mixer product in both sweeps. If the level difference is lower than the user-defined
threshold, the signal obtained in the test sweep is displayed. If a signal occurs only in
the test sweep or reference sweep, it is an unwanted mixer product. The level of this
signal is compared to the noise floor in the other sweep. If the S/N ratio is sufficiently
large, the threshold is exceeded. This means that the signal with the lower level, i.e.
noise in this case, is displayed.
Note that the Auto ID method operates according to the fail-safe principle, i.e. unwan-
ted mixer products may not be detected as such but signals which are in fact real input
signals are not blanked out.
Time-constant spectrum
The automatic comparison of the test sweep and reference sweep with the Auto ID
function can only be applied usefully for signals with a time-constant spectrum since
the two sweeps are always required to determine the actual spectrum.
Mixer products with low S/N ratio
If the S/N ratio of a mixer product is lower than the user-defined threshold, the level
difference between the test sweep and reference sweep at the frequency of this mixer
product is always within limits, even if the signal occurs in one of the sweeps only.
Data Input and Output