MSRA configuration
R&S
®
FSWP-B1
36
User Manual 1177.5862.02 ─ 09
AC coupling blocks any DC voltage from the input signal. AC coupling is activated by
default to prevent damage to the instrument. Very low frequencies in the input signal
can be distorted.
However, some specifications require DC coupling. In this case, you must protect the
instrument from damaging DC input voltages manually. For details, refer to the data
sheet.
Remote command:
Impedance
For some measurements, the reference impedance for the measured levels of the
R&S
FSWP can be set to 50
Ω
or 75
Ω
.
Select 75
Ω
if the 50
Ω
input impedance is transformed to a higher impedance using a
75
Ω
adapter of the RAZ type. (That corresponds to 25
Ω
in series to the input impe-
dance of the instrument.) The correction value in this case is 1.76 dB = 10
log (75
Ω
/
50
Ω
).
This value also affects the unit conversion.
Remote command:
Direct Path
Enables or disables the use of the direct path for small frequencies.
In spectrum analyzers, passive analog mixers are used for the first conversion of the
input signal. In such mixers, the LO signal is coupled into the IF path due to its limited
isolation. The coupled LO signal becomes visible at the RF frequency 0
Hz. This effect
is referred to as LO feedthrough.
To avoid the LO feedthrough the spectrum analyzer provides an alternative signal path
to the A/D converter, referred to as the
direct path
. By default, the direct path is
selected automatically for RF frequencies close to zero. However, this behavior can be
disabled. If "Direct Path" is set to "Off", the spectrum analyzer always uses the analog
mixer path.
"Auto"
(Default) The direct path is used automatically for frequencies close
to zero.
"Off"
The analog mixer path is always used.
Remote command:
High Pass Filter 1 to 3 GHz
Activates an additional internal highpass filter for RF input signals from 1
GHz to
3
GHz. This filter is used to remove the harmonics of the analyzer to measure the har-
monics for a DUT, for example.
This function requires an additional hardware option.
Note:
For RF input signals outside the specified range, the high-pass filter has no
effect. For signals with a frequency of approximately 4
GHz upwards, the harmonics
are suppressed sufficiently by the YIG-preselector, if available.)
Input source settings