Configuring the Signal in the RF Domain
R&S
®
SMW200A
525User Manual 1175.6632.02 ─ 16
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.
If you also set "Attenuator Mode > Fixed", the instrument recalibrates every level
and frequency setting, resulting in high-level accuracy.
●
"Off (Sample & Hold)"
Deactivates ALC, but still allows you to maintain a constant output level.
The R&S SMW 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"
Initially the level control circuit uses a sample process to settle to the current level.
When settled, it continues level control with 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.
This mode achieves fastest setting times, since the output signal is not interrupted
by the measurement, and also not disturbed.
●
"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.
This mode is useful if your goal is to improve the signal/intermodulation ratio in CW
mode for multi-transmitter measurements.
The R&S SMW displays the level control setting as a status message in the info line.
The ALC modes "Off (Sample & Hold)" and "Sample & On" use a short sample pulse to
set the level control. The level of this sample pulse corresponds to the sample level
setting of the full PEP of the R&S SMW. It does not consider any signal headroom, e.g.
applied to a user defined ARB waveform.
Improving Level Performance
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