LOCAL OPERATION RF LEVEL
SIG
GEN
B5196
...
B5621
3-29
Carrier/RF
ALC Mode POW:ALC page 4-148
Use the numeric keypad to specify the automatic level control mode:
0
Auto The leveling mode is selected automatically, depending on modulation type.
The instrument selects Normal mode for CW, FM, ΦM and IQ, and AM
mode when AM modulation is needed.
1
Normal RF output power is controlled such that average power is leveled. IQ
modulation can be applied as long as there is no slow variation of
modulation with time (for example, QAM), where Scaled mode is the
correct choice.
2
AM Carrier power is leveled independently of the level of the modulation
sidebands; leveling to average voltage.
3
Frozen In this mode, the leveling loop is frozen and the RF output scales directly
with IQ input power. The output power is ‘frozen’ at the gain setting
determined previously from the ALC average power mode. The output
power varies with temperature or applied modulation level.
This mode is useful where burst profile information is included in the IQ
baseband signals.
4
Scaled Output power scales directly with IQ input power, but is leveled against
temperature change. Useful where applied I and Q baseband signals contain
slow time-varying information that must not be removed by the leveling
loop (for example, QAM).
Note: For Frozen and Scaled modes, external IQ inputs must be 0.5 V RMS to produce the nominal
output power.
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