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pressed. So jitter or double-triggering of complex sig¬
nals is avoidable or at least reduced, in particular with
very low input voltages. The trigger threshold increases
above 1 kHz.
Alternate triggering
With
alternate triggering
(ALT. button depressed) it is
possible to use normal triggering from both channels simul¬
taneously (1 and II) in
alternate
DUAL mode. The two signal
frequencies can also be asymc/ironous with respect to one
another when doing so. So that the two signals can be
shifted about independently of one another on the scope
screen, if possible AC input coupling should be used for
both channels. In this case the same trigger threshold of
O.Bdiv. holds. The trigger pulse is derived from the signal
being written at that point in time, i.e. alternately from the
two signals. It is not posible to view a single waveform in
alternate mode with this triggering type
Line triggering
A part of a secondary winding voltage of the power trans¬
former is used as mains/line frequency trigger signal (50 to
60 Hz) in the ~ position of the TRIG, selector switch. This
trigger mode is independent of amplitude and frequency of
the Y signal and is recommended for all mains/line syn¬
chronous signals. This also applies - within certain limits -
to whole number multiples or fractions of the line fre¬
quency. Line triggering can also be useful to display signals
below the trigger threshold (less than 5 mm). It is therefore
particularly suitable for measuring small ripple voltages of
mains/line rectifiers or stray magnetic field in a circuit.
Magnetic leakage (e.g. from a power transformer) can be
investigated for direction and amplitude using a search or
pick-up coil. The coil should be wound on a small former
with a maximum of turns of a thin lacquered wire and con¬
nected to a BNC connector (for scope input) via a shielded
cable. Between cable and BNC center conductor a resistor
of at least 100Q should be series-connected (RF decou¬
pling). Often it is advisable to shield statically the surface of
the coil. However, no shorted turns are permissible.
Maximum, minimum, and direction to the magnetic source
are detectable at the measuring point by turning and shift¬
ing the coil.
Triggering of video signals
The built-in active
TV-Sync-Separator
(separation of the
sync pulses from the video signal and following amplifica¬
tion) even allows the display of noisy, changing in amplitude
or distorted video signals, alternatively triggered with line
(or horizontal) frequency or frame (or vertical) frequency.
The TV SEP. lever switch has three positions. The OFF
position serves to all normal operations; the TRIG, selector
switch is operative. The TV: H position (horizontal ^ line)
and the TV: V position (vertical ^ frame) are used for video
triggering. The TRIG, coupling switch is inoperable in these
both positions. In the TV: V position (frame triggering), a
low-pass filter or integrating network is connected into cir¬
cuit, which forms a trigger pulse sequence with frame fre¬
quency from the vertical sync pulse (incl. pre- and post¬
equalizing pulses).
For accurate function of the sync separator, the slope of the
sync pulses should correctly be adjusted (corresponding to
the position of the sync pulses in the composite color sig¬
nal. If the sync pulses are placed above the picture content,
the -F/— button should be released. The trigger point lies on
the rising front edge of the sync pulse. If they are below the
picture content, the -F/— button should be depressed. The
trigger point lies on a falling (negative) front edge of the sync
pulse. This setting of the slope is valid for line and frame fre¬
quency. An incorrectly set slope results in an unstable dis¬
play. The trigger slope cannot be changed using the
INVERT buttons. The +/— button relates always to the
input signal! Video signals are triggered in the automatic
mode. Therefore the adjustment of the trigger point with
LEVEL knob is superfluous. The internal triggering is virtu¬
ally independent of the display height, which may differ
from 0.8 to 8div.
Depressing the AT/NORM, button results in an incorrect
working of TV triggering.
Aside from the TV SEP. switch and the -F/— button setting,
a time coefficient, adequate to the measuring purpose,
should be selected on the TIME/DIV. switch. The basic
positions for H (horizontal ^ line) and V (vertical ^ frame)
are marked on the scale of the TIME/DIV. switch. How¬
ever, the TIME/DIV. knob may be turned more to the right
(without break down of the triggering), if more details in the
video signal should be required. More adventageous,
because one video field is suppressed, is the use of the 10-
fold expansion with the X-MAG. xIO button and the HOLD-
OFF time setting. Disconnecting the trigger circuit (e.g. by
rapidly pressing and releasing the EXT. button) can result in
triggering the consecutive (odd or even) field.
Setting: TV: V, 2 ms/div.,HOLDOFF knob at the right stop,
X-MAG. xIO button depressed, searching the picture detail
with X-POS. knob. So the International Insertion Test Sig¬
nals including Video Text and VPS etc. in the vertical blank¬
ing interval are fully visible with a 10:1 expansion ratio.
The sync-separator-circuit also operates with external trig¬
gering. It is important that the voltage range (0.3 Vpp to 6 Vpp)
for external triggering should be noted. In addition, the cor¬
rect slope setting is again critical, because the external trig-
M12 203-7
Subject to change without notice
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