151 VIDEO SIGNAL OBSERVATION
The
TV
FRAME/LINE
switch permits selection of vertical or
horizontal
sync
pulse for sweep
triggering
when viewing
composite video waveforms. In the
LINE
position, horizon-
tal
sync
pulses are selected as triggers to permit viewing
of horizontal line of video. In the
FRAME
position, vertical
sync
pulses are selected as triggers to permit viewing of ver-
tical fields and frames of video. When observing the video
waveforms,
stable display is obtained on the screen regard-
less
the
TRIG
LEVEL
© control.
At most points of measurement, a composite video signal
is
of the (-) polarity, that is, the
sync
pulses are negative
and the video is positive. In this
case,
use " - "
SLOPE.
If the waveform is taken at a circuit
point
where the video
waveform is inverted, the
sync
pulses are positive and the
video is negative. In this
case,
use " + "
SLOPE.
(6)
SINGLE
SWEEP
OPERATION
This
mode of display is useful for looking at non-
synchronous
or one time events.
Procedure:
1.
Set the A
TRIG
MODE © to either AUTO or NORM. Ap-
ply a signal of approximately the same amplitude and fre-
quency as the signal that is to be observed as the trigger
signal
and set the trigger level.
2.
Set A
TRIG
MODE to
RESET
- observe that the
READY
indicator LED lights to indicate the reset condition.
This
LED
goes out when the A sweep period is completed.
3.
After the above set-up is completed the scope is ready
to operate in the
SINGLE
sweep mode of operation after
resetting the instrument using the
RESET
switch. Input
of the trigger signal results in one and only one sweep
and
READY
indicator LED goes out.
, CAUTION: ,
With the
HORIZ
MODE set to ALT the simultaneous
observation of the A sweep and B sweep waveforms
at
SINGLE
sweep mode is not possible. Also for
DUAL
or TRI operation simultaneous observation is
not possible using ALT mode. Set the
unit
to the
CHOP
mode in this
case.
18
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