Leader LBO-516 Instruction Manual - page 16
test signal. To trigger the scope at the vertical (field) rate,
select the TV-V position. To trigger the scope at the horizon-
tal (line) rate, select the TV-H position. When either TV pos-
ition is used, the SLOPE switch (39) must be matched to the
polarity of the video signal. Leave the SLOPE pushbutton out
(+ position) for positive-sync signals (Figure 2-7a), and push
it in (- position) for negative-sync video signals (Figure 2-7b).
Trigger Point Selection. For a stable display, the
timebase must be triggered at the exact same point on the re-
current waveform each time the timebase is swept. This is
sometimes difficult to achieve, so the LBO-516 has three
controls that enable the operator to achieve this condition.
They are the LEVEL control (40), the SLOPE switch (39),
and the HOLDOFF control (42).
The SLOPE switch determines whether the sweep will begin
on a positive-going or negative-going slope of the trigger
signal (see Figure 2-8). In some cases, the choice of slope is
unimportant; in others, it is vitally important to attain a stable
and/or jitter-free display. Always select the steepest and most
stable slope or edge. For example, small changes in the
amplitude of the sawtooth shown in Figure 2.8a will cause
jitter if the timebase is triggered on the positive (ramp) slope,
but have no effect if triggering occurs on the negative slope (a
fast-fall edge). In the example shown in Figure 2-8b, both
leading and trailing edges are very steep (fast rise and fall
times). However, this particular pulse is the output of a
leading-edge triggered monostable, and has pulse-width jitter.
Triggering from the jittering trailing edge will cause the entire
trace to jitter, making observation diffi-
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