Agilent Technologies PSA Series Service Manual page 198

Hardware Options
Overview and Verification of Option 123, Microwave and Millimeter Preselector Bypass
After the RF input attenuators the RF path is either routed to the
normal preselected path (through SBTX and RYTHM) or to the
unpreselected path using the coax transfer switch. The unpreselected
mixer uses the ~3 to 7 GHz LO from the LO output port of the LO
Multiplying Amplifier (referred to as FELOMA elsewhere). Since the
LO normally used for the external mixing bands is used for the
unpreselected mixer, Option AYZ (External Mixing) is not compatible
with Option 123.
Since the E4446A, E4447A, and E4448A instruments contain an
additional down conversion path, with its own preselection filter,
Option 123 for these models will bypass both sets of preselection filters
present in those instruments i.e. the microwave preselection filter as
well as the millimeter wave preselection filter.
Figure 8-12 shows the block diagram for a configuration that has both
the Preamp Option 110 as well as the Unpreselected Path Option 123.
Figure 8-12 Block Diagram for 50 GHz Option 110 and 123 Instruments
198 Chapter 8