Instrument Function
R&S
®
SMF100A
192
Operating Manual 1167.2319.02 ─ 12
Active Marker - RF Level Marker
Selects the active marker. The active marker is output with an higher voltage than all
other markers.
Remote command:
[:SOURce<hw>]:SWEep:POWer:MARKer:ACTive
5.4.5 Automatic Level Control - ALC
Your signal generator is equipped with an automatic level control unit to obtain best RF
level accuracy.
A
utomatic
L
evel
C
ontrol (ALC) is an adaptive control system to stabilize the RF output
level. It continuously monitors the current level and adjusts it to keep a steady state
over temperature and time.
ALC is active in almost all applications by default. However,
Pulse Modulation
with
very small pulse widths excludes ALC, as the control loop would detect incorrect val-
ues and result in level deviations.
Also note that ALC may detect incorrect values in
multi-transmitter
test setups. If mul-
tiple generators are coupled, reverse power may affect the ALC readings. Based on
incorrect values, ALC would have an impact on the signal to intermodulation ratio.
ALC States
The following description basically explains the ALC states and their principle of opera-
tion. In particular
ALC OFF (Sample & Hold)
gives an overview on the function in
terms of the equipment of the generator.
The R&S
SMF offers the ALC states:
●
On
enables ALC permanently, regardless of the currently selected mode.
●
Off
deactivates ALC.
The instrument switches to
Sample & Hold (S&H)
state, which still allows to main-
tain a constant output level.
The following section explains the functionality of "Sample & Hold", to provide an over-
view and to indicate what is to be considered. "On" and "Auto" require no additional
explanation. Furthermore, find the ALC state settings described in detail in
.
ALC OFF (Sample & Hold)
In "S&H" mode, the signal generator switches for a short period of time into CW mode
and activates ALC. ALC adjusts the level to the set value and the generator holds the
value (freeze). Then, the generator switches ALC off again and back to the operating
mode.
RF Level
