Improving level performance
R&S
®
SMA100B
216User Manual 1178.3834.02 ─ 09
"Unchanged"
Freezes the setting of the step attenuator.
Use this mode if a constant VSWR (Voltage Standing Wave Ratio) is
required.
"Full Attenuation"
Switches to the maximum attenuation.
Use this mode for applications that require a high level of noise sup-
pression.
Remote command:
[:SOURce<hw>]:POWer:ATTenuation:RFOFf:MODE on page 685
8.1.2 Reverse power protection
The R&S SMA100B is equipped with a reverse power protection circuit.
The reverse power protection is tripped when the power of signals reflected from the
load or external signals applied to the RF output get too high. A relay opens and inter-
rupts the internal connection to the RF output. This condition is indicated in the status
bar by the "Overload" status message.
Overload
If an "Overload" status message is indicated in the status bar, perform the following:
●
Remove the cause for the overload
●
Press the [RF on/off] key to reset the overload protection
The RF input is activated when the overload protection is reset.
Remote command:
:OUTPut<hw>:PROTection:TRIPped? on page 493
:OUTPut<hw>:PROTection:CLEar on page 492
8.2 Automatic level control (ALC)
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, when pulse modulation
with short pulses is used, the ALC uses table-based level settings with table values
depending on the pulse width.
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, which leads
to an incorrect RF output power.
Automatic level control (ALC)
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