Agilent Technologies 8614 B Series, Руководство пользователя, Страница: 49 / 272

2-9
Using the Instrument
Setting Up Measurements
Triggering a Measurement
Triggering a measurement synchronizes the start of the sweep to an internally generated trigger
signal. Internal triggering ensures continuously triggered sweeps with the shortest delay between
sweeps.
Refer to “Trigger Mode, Internal” on page 3-88 .
In some measurements, the spectrum at a particular time within the modulation period is more
important than the average spectrum. Gated triggering can be used to synchronize the data
acquisition portion of the OSA to a gating trigger connected to the rear-panel EXT TRIG IN con-
nector. Gated triggering requires a TTL-compatible signal with a minimum of 0 Vdc and a maxi-
mum of +5 V.
Gated triggering ignores the spectrum when the trigger input is low. It usually is used in conjunc-
tion with the Max Hold function during several sweeps.
Gated triggering is used to select data samples containing valid information. When the gating
signal is high, the data sample is accepted. When the gating signal is low, the data sample is
replaced by a data point with a value of –200 dBm. Processing continues according to the func-
tions selected, such as, video bandwidth, max hold, and so forth.
If the low level exists for longer that the time needed for the grating to move from one trace point
to the next, then the trace will have “gaps”. There are two ways to eliminate the gaps. You can
increase the sweep time to at least:
(1.2–2 times the product trace length) ¥ (the longest “low level” period)