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92 Chapter 4
Making Measurements
Preparing for Measurements
Trigger Source
Changing the
Trig Source alters the trigger source for the current
measurement only. Not all of the selections are available for all
measurements. Note that the
RF Burst, Video, Ext Front, and Ext Rear
menu keys found in the
Trigger menu enable you to change settings to
modify the delay, level, and slope for each of these trigger sources (as
described on page 85. Choose one of the following trigger sources:
• Free Run - Triggers at the time the data is requested, completely
asynchronous to the RF or IF signals.
•
Video - Is an internal IF envelope trigger. It triggers on an absolute
threshold level of the signal passed by the IF.
•
RF Burst - Is an internal wideband RF burst trigger that has an
automatic level control for burst signals.
•
Ext Front - Activates the front panel Ext Trigger Input. The external
trigger must be a signal between
−5 and +5 volts.
•
Ext Rear - Activates the rear panel Trigger In. The external trigger
must be a signal between
−5 and +5 volts.
• Frame - Uses the internal frame clock to generate a trigger signal.
The clock parameters are controlled under the
Mode Setup key or the
measurement firmware, not both. See the specific measurement for
details.
• Line - Activates an internal line trigger. Sweep triggers occur at
intervals synchronized to the line frequency.
Rear panel
TRIGGER 1 OUT and TRIGGER 2 OUT connectors are coupled
to the selected trigger source. These trigger outputs are always on the
rising edge with a pulse width of at least 1
µs.