R&S FSMR3000, User Manual

Page: 110 / 733

Common Measurement Settings
R&S
®
FSMR3000
110 User Manual 1179.0116.02 ─ 02
Input Coupling
The RF input of the R&S FSMR3 can be coupled by alternating current (AC) or direct
current (DC).
AC coupling blocks any DC voltage from the input signal. This is the default setting to
prevent damage to the instrument. Very low frequencies in the input signal may be dis-
torted.
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:
INPut<ip>:COUPling
on page 401
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:
INPut<ip>:DPATh
on page 402
YIG-Preselector
Enables or disables the YIG-preselector, if available on the R&S FSMR3000.
Note: Note that the YIG-preselector is active only on frequencies greater than 8 GHz.
Therefore, switching the YIG-preselector on or off has no effect if the frequency is
below that value.
Remote command:
INPut<ip>:FILTer:YIG[:STATe]
on page 403
7.2.2 Power Sensors
The R&S FSMR3 can also analyze data from a connected power sensor.
● Basics on Power Sensors ......................................................................................111
● Power Sensor Settings ..........................................................................................112
● How to Work With a Power Sensor ....................................................................... 116
Input and Frontend