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It
is
not
necessary
to
display Channel 1
or
Channel 2
to
obtain
CH
1 or
CH
2 triggering. Whenever
the
AC-GND-DC
switch for
the
channel
is
not
in
GND,
the
input
amplifier
and trigger channel are active, regardlesss
of
the
selection of
VERT
MODE
pushbuttons.
ADD MODE. A single-channel trigger signal
amplitude
is
not
affected by
the
contribution
of
the
other
channel
to
an
ADD mode display. When
the
ADD
mode
with
CH
2
in-
verted
is
used
to
compare
two
video waveforms by subtrac-
tion,
the
CH
1
or
CH 2 signal
to
the
Sync
Separator
will be
adequate
for stable triggering providing
the
individual
channel signal (when displayed alone) meets
the
signal
requirements.
When
the
ADD mode
is
used
to
display a signal from
two
sides
of
a balanced line,
the
A
TRIGGER
SOURCE
switch NORM (composite vertical) position may be used if
neither Channel signal alone
is
of
sufficient
amplitude
for
stable sync separation
and
triggering.
Typical Operation
In
a typical operating
mode
for
the
Option
05
instru-
ment,
the
A Sweep establishes
the
basic frame
and
field
presentation, and
the
B Sweep allows detailed observa-
tion
and measurement
of
various
portions
of
the
video
waveform.
To
obtain stable displays free
of
interlace
jitter
(for
systems which have 2:1 interlace),
the
A TIME/DIV switch
should be set
to
display an
odd
number
of
fields, plus a
fraction
of
a field,
in
the
unmagnified display. For
50
and
60
Hz
field rates,
the
2 ms/div setting
is
usually
selected. For some PAL system observations, a setting
of
5 ms/div {approximately 2% field display), with
the
A
TRIGGER
HOLDOFF
control
set
to
approximately
the
four
o'clock
position (additional one-field holdoff), may
be desirable
to
maintain a stable display relationship
to
the
four-field PAL burst-blanking sequence.
All
detail measure-
ments are
then
made with B Sweep, using
the
B DLY'D
or
ALT Horizontal Display, with
the
B
TRIGGER
SOURCE
switch set
to
either
STARTS
AFTER
DELAY
(continuously variable B Sweep
start
point)
or
to
TV LINE
(B
Sweep
starts
after
the
leading edge
of
the
next
hori-
zontal sync pulse following
the
delay interval set by
the
DELAY TIME POSITION
control
and
the
A TIME/DIV
switch setting).
Because
the
leading edge
of
the
sync pulse will
not
be
displayed,
the
typical B TIME/DIV setting for width mea-
surements
on
front
porch,
back porch and horizontal
blanking intervals, horizontal sync, serration, and equaliz-
ing pulses will be
10
~-ts/division
to
allow display
of
two
consecutive pulses.
Use
the
1
OX
Magnifier
to
display
the
second pulse
at
1~-ts/division.
For rise
and
fall time measurements
on
blanking
and
sync waveforms, trigger
the
A
or
B Sweep directly from
the
displayed waveform (avoiding
the
processing delay
of
the
sync separator). This permits viewing
the
triggering edge
at
sweep rates from
0.5
to
0.02~-ts/division.
@
465B/DM44
Operators
103
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