Keysight Technologies N5244/5B Service Manual page 218

Theory of Operations
Signal Separation Group Operation
These switches allow the source signal to be routed to or from rear-panel
connectors. The internal source signal can be sent out through a rear-panel
connector to be made available for external use or an external source signal
can be input through a rear-panel connector to be used in place of the internal
source signal.
In the port 1 signal path, there is an additional reference coupler (A54) which,
when switched into the signal path, is used as a combiner to combine two
source signals from the rear panel. These signals typically come from the
analyzer's two internal sources and are jumpered on the rear panel.
5-50 Keysight N5244B/45B Service Guide