Specifications

Chapter 15 151
Concepts
Time Gating Concepts
Concepts
Using the Edge Mode or Level Mode for Triggering
NOTE PSA spectrum analyzers use edge mode triggering. ESA spectrum
analyzers can use edge or level triggering modes.
Depending on the trigger signal that you are working with, you can
trigger the gate in one of two separate modes: edge or level. This
gate-trigger function is separate from the normal external trigger
capability of the spectrum analyzer, which initiates a sweep of a
measurement trace based on an external TTL signal.
Edge Mode
Edge mode lets you position the gate relative to either the rising or
falling edge of a TTL trigger signal. The left diagram of Figure 15-21
shows triggering on the positive edge of the trigger signal while the
right diagram shows negative edge triggering.
Example of key presses to initiate positive edge triggering:
(ESA) Press
Sweep, Gate, Edge Gate, Slope (Pos).
(PSA) Press
Sweep, Gate Setup, Polarity (Pos).
Figure 15-21 Using Positive or Negative Edge Triggering
Level Mode (ESA)
In level gate-control mode, an external trigger signal opens and closes
the gate. Either the TTL high level or TTL low level opens the gate,
depending on the setting of
Level Gate. Gate delay and gate length
control functions are not applicable when using level mode triggering.
Level mode is useful when your trigger signal occurs at exactly the
same time as does the portion of the signal you want to measure.