Rohde & Schwarz R&S FSP Series, Operating Manual

Page: 350 / 796

R&S FSP Instrument Functions
LO/IF ports for external mixers - Option R&S FSP-B21
4.278 Operating Manual 1164.4556.12 - 06
The reference sweep is performed using a LO setting shifted downwards by 2*IF/
Harmonic#. Input signals in the wanted sideband that are converted by means of the
set 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 in
both traces at different positions.
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 level should only be measured in the test sweep (trace 1).
Mathematical functions with traces and trace copy cannot be used in the SIGNAL ID
menu.
AUTO ID
The AUTO ID softkey activates or deactivates automatic signal identification.
AUTO ID basically functions like SIGNAL ID . 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
SIGNAL
ID is active at the same time. If SIGNAL ID is not active, the result can be displayed
in each of the traces 1 to 3 Unwanted mixer products are suppressed in this calcu-
lated trace.
As described for the function SIGNAL ID , real input signals are displayed at the
same frequency in the test and reference sweeps, i.e. theoretically identical signal
levels are expected in the two sweeps at the frequency of the real mixer product. If
the level difference is lower than the tolerance set with
AUTO ID 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 tolerance limit for the maximum permissible
level difference is exceeded. This means that the signal with the lower level, i.e.
noise in this case, is displayed.
It should be noted that AUTO ID functions according to the fail-safe principle, i.e.
unwanted mixer products may not be detected as such but signals which are in fact
real input signals are not blanked out. See also
“Remarks Concerning Signal Identi-
fication with AUTO ID” on page 4.278 .
AUTO ID
THRESHOLD AUTO ID THRESHOLD allows the maximum permissible level difference to be fixed
between test sweep and reference sweep during automatic comparison (function
AUTO ID ). The input range is between 0.1 dB and 100 dB.
Values of about 10 dB (i.e. default setting) generally yield satisfactory results.
See also “Remarks Concerning Signal Identification with AUTO ID” on page 4.278 .
4.13.4.1 Remarks Concerning Signal Identification with AUTO ID
Type of signal
The automatic comparison of the test sweep and reference sweep with AUTO ID
can only be usefully applied for signals with time-constant spectrum since the two
sweeps are always required to determine the actual spectrum.