Hardkey and Softkey Reference ESG Family Signal Generators
I/Q
4-42 User’s Guide
I/Q
This front panel hardkey and its menus are only available on ESG-D
and ESG-DP Series Signal Generators. The softkeys in the I/Q menus
are described in this section in alphabetical order.
ALC Off On
Press this softkey to Toggle 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. For narrower
pulses, set the
ALC softkey to Off.
With external I/Q modulation, the ALC loop acts to hold the signal
generator’s average output power constant, in spite of variations in the
I/Q input power (I
2
+Q
2
). Rapid variations of (I
2
+ Q
2
) propagate to the
output, while slow variations are removed by the ALC loop, with a
high-pass corner of 1 kHz. If you do not want this high-pass filtering,
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