Improving Level Performance
R&S
®
SMA100B
146
User Manual 1178.3834.02 ─ 03
6.2 ALC - Automatic Level Control
The R&S
SMA100B 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.
However, if
pulse modulation
is used, the ALC uses table-based level settings with
table values depending on the pulse timing.
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. Based on
incorrect values, ALC would have an impact on the signal to intermodulation ratio.
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. This setting provides the highest level accuracy.
●
"Off (Table)"
Deactivates internal level control loop. The instrument calculates every level setting
using the attenuation values from the internal (ALC) table. Level attenuation
between two table values is done with linear interpolation. This mode enables you
to perform a strictly monotonic, but not quite as precise level adjustment.
●
"Table & On"
Starts with the associated value of the internal level table and then activates the
automatic level control. This mode achieves maximum level accuracy and fast set-
ting times.
If pulse modulation is applied, this mode ensures fast level setting even with nar-
row pulses at low repetition rate.
The R&S
SMA100B displays the level control setting as a status message in the info
line.
ALC - Automatic Level Control
