HP 8712C User Manual page 411

10 MHz signal as frequency standard. When on, if signal is not present at
on QFF
EXT REF lN connector, network analyzer will not sweep. Default is off.
N O T E
External reference should be disconnected from EXT REF IN or power reduced when not in use.
(frequency) point when externally triggered through EXT TRIG IN/OUT rear
panel connector, one point per trigger.
sweep when externally triggered.
Access Keys: (jj] Trigger Trigger Source
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