HP 8566B Installation And Verification Manual page 50

Note
Cable W15 is normally connected between the FREQ REFERENCE
EXT and INT BNC ports, providing the HP 8566B with its own internal
10 MHz frequency reference. W15 is removed when an external
frequency reference is used. Cables W37 and W38 are removed for
connection of the IF and VIDEO ports to the HP 85650A Quasi-Peak
Adapter. If the instrument is used without the HP 85650A Quasi-Peak
Adapter, W37 and W38 must be connected for the instrument to
operate.
Installation 2-l 7