HP 8360 - Manual (Page 149)

Par Range Specifies the operating range of an
external power meter used in an
external leveling setup. This causes
the synthesizer display to agree with
the power meter’s power indication.
The following paragraphs explain the power control (leveling)
function of the synthesizer 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 synthesizer. 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 synthesizer 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 synthesizers with optional step attenuators, the power level at the
output connector can be reduced by a maximum of 90
in 10
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.
Operating and Programming Reference HP 8360
User’s Handbook