Operating instructions

OPERATING MANUAL 2945A
46882-311D 3-29
trigger point centre screen with pre-trigger levels shown to the left and post-trigger levels shown
to the right while
100 % will cause the display to finish (on the right of the screen) at the time of
trigger.
25 %
and 75 % will produce displays with these proportions of pre-trigger visible. The
trigger point is indicated on the display by a medium pecked line.
Transmitter frequency
The frequency of the transmission to be analysed can either be set manually or transferred from
the previous test mode used.
When the transient analysis function is accessed, the transmitter frequency set in the Tx TEST
mode is taken as the transmitter frequency for analysis.
If the SPEC ANA mode is accessed and the span changed to use a new centre frequency, this will
become the new transmitter frequency for the Tx TEST mode and therefore the transmitter
frequency for the transient analysis function.
Time scale
The time scale of the display is adjustable from 50 µs/division (500 µs full scale), to 5 s/division
(50 s full scale). Repeated presses of the [
] key will progressively increase the time/division
in a 1, 2, 5 sequence. Using the [
] key will similarly cause the time/division to decrease.
Arming, triggering and storing
The transient capture operation has three phases. The current phase is shown in inverse video at
the bottom right of the display.
The phase is active when the transient analysis function is accessed. The level of any
signal entering the selected RF input connector at the set transmitter frequency is displayed on the
screen, if it is within the dynamic range currently being displayed.
Samples of the level of the signal displayed are stored in a circular buffer, configured to be filled
within the time of one display scan.
While in the
phase, the display is re-initialised if a setting is changed which could
otherwise result in an erroneous display being produced. The settings which cause re-initialising
when changed are:-
Reference level
Transmitter frequency
Display time scale
Pre-trigger.
The phase is activated by the RF level passing through the trigger level in the selected
direction.
Writing to the circular buffer is stopped after the elapse of the post-trigger time to be displayed.
When the display is complete, it will show the profile of the transmitter level transient. This
starts the phase. Fig. 3-7, shows transient records of the same signal transient at Time/div
settings of 50 ms, 500 µs and 50 µs.