Leveling Point PwrMtr
Sets the swept signal generator to
level power at an external power
meter. A power meter’s recorder
output must be connected to the EXT
ALC input.
Pwr Mtr Range
Specifies the operating range of an
external power meter used in an
external leveling setup. This causes
the swept signal generator display to
agree with the power meter’s power
indication.
The following paragraphs explain the power control (leveling)
function of the swept signal generator in detail.
ALC SYSTEM
-
OVERVIEW
The ALC system, referred to as a system because it encompasses
more than one functional area, is shown as a simplified block
diagram in Figure A-l. The purpose of this system is to control the
amplitude or power level of the RF energy generated by the swept
signal generator. It is a feedback control system, in which the output
power is measured and compared to the desired power level. If the
output power does not equal the desired power level, the ALC system
changes the output until they are equal.
Desired power level can be set by either front panel or remote
operation. As shown in Figure A-l, the inputs and calibration data
are processed by the swept signal generator CPU, which uses this
information to set the Level DAC.
In turn, the Level
DAC
sends a controlling voltage to the Level
Control Circuits. In the presence of modulation, voltages appearing
at the AM and/or PULSE inputs contribute to the control of the
Level Control Circuits.
In swept signal generators with optional step attenuators, the power
level at the output connector can be reduced by a maximum of
90 dB, in 10 dB steps. This is in addition to the control capabilities
provided by the Level Control Circuits.
A Feedback Signal to the Level Control Circuits can be provided by
either internal or external detectors. This signal is the comparison
voltage necessary for accurate, stable, power level settings and good
source match at various Leveling Points. Alternatively, the power
level can be set without using feedback. In this mode however, power
level is uncalibrated and is subject to drift with temperature.
The following paragraphs describe the operation of the different
leveling modes and leveling points.
A-4 Operating and Programming Reference
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