Rohde & Schwarz SMC100A - Automatic Level Control - ALC

Instrument Function
R&S
®
SMC100A
134Operating Manual 1411.4060.32 ─ 09
Note: This setting is not affected by an instrument preset (PRESET key), *RST) or the
"Save/Recall" function. Only the Chapter 5.2.3.17, "Factory Preset", on page 105
resets the setting.
Remote command:
[:SOURce<hw>]:POWer:EMF:STATe on page 314
5.3.5.4 Automatic Level Control - ALC
Your signal generator is equipped with an automatic level control unit to obtain best RF
level accuracy.
Automatic Level Control (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, the Pulse Modulation
mode excludes ALC, as the control loop would detect incorrect values 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 SMC offers the ALC states:
●
AUTO
automatically adjusts the output level to the operating conditions.
●
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 State -
ALC .
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 Block