Specifications

Special Measurements
OVERSCANNED
DISPLAYS.
For
various
video mea-
surements,
it may
be desirable
to
magnify
the
video
wave-
form vertically
beyond
the
limits
of the
screen.
Under these
circumstances,
the trigger
amplifiers
or
Sync Separator
may
be overloaded,
blocking out
some sync
pulses
in
the
vicinity
of strong
video
transitions,
or losing
sync
pulses
altogether.
To
avoid overload
problems,
use
external
sync
or
use
the
other
vertical
channel
to supply a constant
amplitude
signal
to
the
Sync Separator while
the overscanned
observations
are being
made. Note, however,
that
transient-response
aberrations in
the
main vertical
amplifier
will be increased
when the
signal is driven
offscreen,
becoming relatively
serious
if
the amplifier is
driven
to
saturation and cutoff.
HORZONTAL
SYNC
PULSE
MEASUREMENTS.
Rise
and
fall
times and width
of horizontal
sync
pulses
may
be
measured
while using
the Sync
Separator
to determine
whether
part
or all of the lines
or
groups
of
lines
appear
to
be
abnormal.
A bright display
of all
horizontal
sync
pulses
is obtained
when the A TRIGGER
COUPLING
switch
is
set
to
TV
LINE.
RF
INTERFERENCE.
Operation
in
the
vicinity
of some
FM
and TV
transmitters may
show
objectionable amounts
of rf signal energy
in the
display, even
when coaxial input
connections
are
used.
The
front-panel
20 MHz
BW
LIMIT
switch
will
usually
eliminate
such interference
from
the
display,
but will not
affect
the
signal
reaching
the
Sync
Separator.
Where
the rI
interferes
with
Sync
Separator
operation, external
filters
will
be required.
Use
of
probes
designed
for
10-30 MHz
oscilloscopes
will
provide
6
to
10
dB
attenuation
in
the
50-100
MHz
range
and
may
be
beneficial
in
reducing
interference.
IDENTIFYING
FIELDS,
FRAMES
AND
LINES
tN
52sl60
AND
62sl50
TV
SYSTEMS
NTSC
(CCIR
System
M)
Field
1
is defined
as
the
field
whose first
equalizing
pulse
is
one full H
interval
(63.5
ps)
from
the
preceding
horizontal
sync
pulse.
The
Field
1
picture
starts
wlth a
full
line
of
video.
Field
1 lines
are numbered
I
through
263,
starting with
the leading
edge
of
the
first
equalizing
pulse.
The
first
regular
horizontal
sync
pulse
after
the
second
equalizing
interval
is
the start
of
line
10.
Field
2 starts
with
an equalizing
pulse
a
half-line
interval
from
the
preceding
horizontal
sync
pulse.
The Field
2
picture
starts with
a
half
line
of
video.
Field
2lines
are
numbered
1
through
262,
starting
with
the leading
edge
of
the second
equalizing
pulse.
After
the
second equalizing
interval,
the
first
full line
is
line
g.
@
4658/DM44
Operators
105