Configuring the RF signal
R&S
®
SMM100A
390
User Manual 1179.1341.02 ─ 05
rupts the internal connection to the RF output. This condition is indicated in the status
bar by the "Overload" status message.
Overload
If an "Overload" status message is indicated in the status bar, perform the following:
●
Remove the cause for the overload
●
Press the [RF on/off] key to reset the overload protection
The RF input is activated when the overload protection is reset.
Remote command:
:OUTPut<hw>:PROTection:TRIPped?
7.12.2
ALC - automatic level control
The R&S
SMM100A is equipped with an automatic level control (ALC) unit to obtain
best RF level accuracy.
About ALC
ALC is an adaptive control system to stabilize the RF output level. It continuously moni-
tors the current level and adjusts it to keep a steady state over temperature and time.
ALC is active in almost all applications by default. It is not active for frequencies below
200
kHz and if the optimization mode (IQ modulation) is different than "FAST".
Also note that ALC can detect incorrect values in
multi-transmitter
test setups. If mul-
tiple generators are coupled, reverse power can affect the ALC readings, which leads
to an incorrect RF output power.
ALC states and their effects
The following description basically explains the ALC states and their principle of opera-
tion:
●
"Auto"
Adjusts the output level to the operating conditions automatically. ALC is active in
almost all operating modes.
●
"On"
Activates the internal level control permanently, regardless of the operating condi-
tions.
Note:
This mode is not useful for pulse modulation with narrow pulses and low rep-
etition rates, since the automatic level control cannot settle in time. Set ALC
"Table
&
On" instead.
●
"Off (Sample & Hold)"
Deactivates ALC, but still allows you to maintain a constant output level.
The R&S
SMM100A switches briefly in the CW mode and enables ALC to adjust
the level to the set target value. The instrument freezes this setting, turns off ALC
again, and switches back to the operating mode.
●
"Sample & On"
Improving level performance
