Agilent Technologies HP 8719D Service Manual page 345

The full YIG oscillator frequency range is achieved in two bands:
Mid (HP 87221))
High (HP 8722D)
In the low band, the 2.4 to 20 GHz output of YIGl and the lixed 3.8 GHz output
of the A57 fixed oscillator are mixed in the A53 mixer/amplifier assembly. In
this band, S2 and S3 switch A53 into the circuit.
The high band (mid band, HP 87221)) uses the output of YIGl.
The high band (HP 8722D) uses the output of YIGB.
In the A58 M/A/D/S microcircuit, the YIG oscillator signal is modulated by the
ALC OUT signal (explained below) 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.
Theory of Operation
Band
Low
High
Frequency Range
50 MHz to 2.55 GHz
2.55 GHz to 20.0 GHz
20 GHz to 40 GHz