4
ALC
5
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Leveling Point PwrMtr
Sets the swept signal generator to
level power at an external p ower
meter. A power meter's recorder
output must b e connected to the EXT
ALC input.
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Pwr Mtr Range
Species the op erating range of an
external power meter used in an
external leveling setup. This causes
the swept signal generator displayto
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 b ecause it encompasses
more than one functional area, is shown as a simplied blo ck
diagram in Figure A-1. The purp ose of this system is to con
trol the
amplitude or p ower 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 po
wer level. If the
output p ower do es not equal the desired p ower level, the ALC system
changes the output until they are equal.
Desired p ower level can be set by either front panel or remote
operation. As shown in Figure A-1, the inputs and calibration data
are pro cessed 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 mo dulation, voltages app earing
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 b e 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 b e provided by
either internal or external detectors. This signal is the comparison
voltage necessary for accurate, stable, p ower level settings and go od
source matchat various
Leveling Points
. Alternatively, the p ower
level can be set without using feedback. In this mo de however, p ower
level is uncalibrated and is sub ject to drift with temp erature.
The following paragraphs describe the operation of the dierent
leveling mo des and leveling p oints.
A-4 Operating and Programming Reference
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