12-18 Service Guide
Theory of Operation 8719ET/20ET/22ET
Source Group Theory 8719ES/20ES/22ES
RF Network Analyzers
The high band of the 8722ET/ES uses the output of YIG2.
In the A58 M/A/D/S microcircuit, the YIG oscillator signal is modulated by the ALC OUT
signal (explained in “ALC: Automatic Leveling Control”) to provide power control and
leveling.
ALC: Automatic Leveling Control
A portion of the source output is detected in the M/A/D/S and sent back to the source
interface board ALC circuit. This circuit generates a control signal which is sent to the
modulator in the M/A/D/S to control the power. The tune voltage from the main coil drive is
used to change the source amplitude as a function of frequency, thus compensating the
source for losses in the transfer switch, bias tees, and couplers.
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