Common Measurement Settings
R&S
®
FSW
363
User Manual 1173.9411.02 ─ 19
The reference sweep is performed using an LO setting shifted downwards by 2*IF/
<Harmonic order>. Input signals in the desired sideband that are converted using the
specified harmonic are displayed in both traces at the same position on the frequency
axis. Image signals and mixer products caused by other harmonics are displayed at
different positions in both traces. The user identifies the signals visually by comparing
the two traces.
Since the LO frequency is displaced downwards in the reference sweep, the conver-
sion loss of the mixer may differ from the test sweep. Therefore the signal
level
should
only be measured in the test sweep (trace 1).
Auto ID function
The Auto ID fucntion basically functions like
. However, the test and
reference sweeps are converted into a single trace by a comparison of maximum peak
values of each sweep point. The result of this comparison is displayed in trace 3 if "Sig-
nal ID" is active at the same time. If "Signal ID" is not active, the result can be dis-
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 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 suffi-
ciently large, the threshold is exceeded. This means that the signal with the lower level,
i.e. noise in this case, is displayed.
Data Input and Output
