Leader LBO-516 Instruction Manual - page 15
and a vertically-deflected but non-synchronized display when
vertical signal is present but the trigger controls improperly
set. This immediately indicates what is wrong. The only
problems with AUTO operation are that signals below 20 Hz
cannot, and complex signals of any frequency may · not,
reliably trigger the timebase. Therefore, the usual practice is
to leave the AUTO pushbutton pushed in, but press NORM if
any signal (particularly one below 20 Hz) fails to produce a
stable display.
The third sweep mode, obtained by pressing the
SINGLE pushbutton, produces a nonrepetitive sweep. Its use
is described in
2-3-10 Single-shot Operation.
Trigger Source Options. Trigger signal can be
obtained from the signal applied to the vertical inputs, or
from a separate source of the same or a harmonically-related
frequency. The SOURCE switch (34) offers several choices.
The CH-1 and CH-2 positions offer a choice of which of
the two input channels the trigger signal is derived. The
choice of channels remains even if the trigger channel is not
displayed; the only requirements are that signal be applied to
the trigger-source channel and the associated VOLTS/DIV
switch be set to provide sufficient signal amplitude. The min-
imum trigger amplitude is around half a division below 10
MHz, and increases to 1 1/2 divisions at 100 MHz. For insur-
ance, use at least a full division below 10 MHz, and two divi-
sions above 10 MHz.
If both channels are displayed, and the two signals are
different but harmonically-related frequencies, trigger from
the low-frequency channel if possible. This will ensure that
traces are stable.
Select the ALT position when you want to display two
signals not harmonically related (720 Hz and 939 Hz, for
example). The ALT SOURCE position must be used in
conjunction with the ALT V MODE (21) pushbutton for this
type of dual-trace display.
The LINE position provides trigger signal at the local
power-line frequency. This is of great use when you wish to
observe a low-level ripple component imposed on a large DC
voltage, or within a mixture of other AC voltages. The line-
frequency trigger will sync signal at any reasonable multiple
of the power-line frequency.
The 0.2 V/DIV and 2 V/DIV positions both select
external trigger signal applied to the EXT TRIG IN
connector (35). Use 0.2 V/DIV position when the external
trigger amplitude is between 100 mV and 2000 mV peak-to-
peak. Use the 2 V/ DIV position when the signal amplitude is
between 2 V and 20 V peak-to-peak.
CAUTION: Do not apply a signal greater than 400
V (DC + AC peak).
Using a trigger source not derived from the channel you
are watching has the advantage that changes in the amplitude
of the signal under observation will not cause the display to
lose sync, even if the amplitude of the observed signal falls
below a half graticule division. External trigger also has the
advantage that complex and/or noisy signals can be stably
displayed, providing the trigger signal is free of noise.
Trigger Coupling Options. The various trigger
coupling options for the main (A) and delayed (B) timebases
increase the probability of stable triggering on difficult
signals, such as those containing several frequencies and/or
hum and noise.
The first two COUPLING positions (36) are frequency-
selective filters that pass certain frequencies on to the trigger
circuitry and reject others. The AC position removes any DC
component in the trigger signal.
The HF-REJ position cuts off frequencies higher than
35 kHz, passing only signals in the 10 Hz to 35 kHz region.
Select this position if high-frequency noise (the CHOP
switching pulses for example) is mixed with a low-frequency
signal.
The DC position removes all filters from the trigger
chain, so everything in the trigger signal from DC to the
upper bandwidth limit of the oscilloscope is passed to the
trigger circuits. Select DC COUPLING if the trigger signal is
below 10 Hz, or may be expected to be below this frequency
at some time during a series of measurements.
The TV-V and TV-H positions insert a TV sync
separator into the trigger chain, so a clean trigger signal at
either the vertical or horizontal repetition rates can be
removed from a composite video signal. The TV-V position
is also effective in securing stable triggering at the low fre-
quency (60 or 70 Hz) of an audio intermodulation distortion
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