R&S SMA100B - Page 217

Improving level performance
R&S
®
SMA100B
217User Manual 1178.3834.02 ─ 09
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 (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 fast and 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 settings even with nar-
row pulses at low repetition rate.
●
"External ALC"
Activates the external ALC detector mode.
This setting enables you to control the RF signal level at a specific point in the sig-
nal chain following the signal generator output with high accuracy.
The R&S SMA100B displays the level control setting as a status message in the info
line.
About external ALC
Some applications require precise control of the RF signal level at a specific point in
the signal chain following the signal generator output.
For this purpose, the "External ALC" function of the R&S SMA100B enables you to
close the level control loop of the instrument using an external level detector diode with
negative polarity and a coupler device.
The diode rectifies the signal received from the coupler and loops it back to the
R&S SMA100B to control the ALC system.
As shown in Figure 8-1, you must apply the feed back signal at the modulation input
connector Ext1.
Automatic level control (ALC)