5-21
Hardkey and Softkey Reference
Ampl
Ampl
Pressing the front panel Ampl key reveals a menu of softkeys. These softkeys are
described in this section in alphabetical order.
ALC Off On
This softkey toggles the automatic leveling control (ALC) circuit off and on.
The ALC is normally on. The RF output power of the signal generator is
constantly monitored and controlled by the ALC circuit. Its purpose is to hold
output power at its desired level in spite of drift due to temperature and time.
There are some modulation conditions which the ALC circuit cannot handle
properly which lead to output level errors. In these conditions, better power level
accuracy can be obtained by turning the ALC off and using power search. (Refer
to the
Power Search Manual Auto softkey documented in this section for more
information about power search.) ALC Off is useful with pulse modulation with a
pulse width narrower than 2
µs and with certain external I/Q modulation.
Pulse modulation is accomplished using a modulator which precedes the ALC
detector. The ALC must, therefore, measure a pulsed signal, and it is able to do
this if the pulse width exceeds 2
µs.
When ALC is off, the
ALC OFF display annunciator will turn on.
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