Applications
Measuring Video Signals
in
IRE Units
1. Display a video signal with VOL TS/DIV VAR adjusted out
of
detent for five
divisions
amplitude from the white level to the black level. (The black level
is defined by the front and back "porches.")
2.
Measure the features
of
interest with
~
V cursors. The RATIO readings
in
percent are equivalent
to
IRE units.
A voiding False Displays
with
Multi-Mode Signals
A signal that has
two
characteristic forms on alternate cycles can produce
incomplete displays. With Alt Vertical mode and
two
displayed channels, the
oscilloscope
could show the same one
of
the
two
forms every time a particular
channel
is shown. Also, if a signal's period is less than the total duration
of
the
sweep
plus the trigger holdoff, the display could show only one
of
several signal
modes.
1. You can
display
all
the modes
of
a multi-mode waveform by changing the
setting
of
Trigger HOLDOFF, so the modes are superimposed
in
the
display.
2.
CHOP Vertical Mode often will superimpose the multiple modes
of
waveforms
in
multi-channel displays.
Algebraic Addition
to
Detect Coincidence
or
Cancel
Interference
3-4
With the Add
Vertical mode, the waveform is the algebraic sum
of
the signals
applied
to
Channel 1 and Channel 2. If Channel 2 is Inverted, the Add waveform is
the difference between the
signals applied to Channel 1 and Channel
2.
The
deflection factor
of
the Add trace is the same as
CH
1 and
CH
2 VOL TS/DIV when
they are
equal.
The following general precautions should
be
observed when using Add mode:
1.
Signal peaks should not exceed ± 8 times the VOL TS/DIV setting.
2.
Position both Channel 1 and Channel 2 waveforms near center screen,
when viewed
separately. This ensures the greatest dynamic range for the
Add trace.
3.
To
obtain similar responses from each channel, set Channel 1 and
Channel 2 input couplings the same.
2465A/2455A/2445A Operators
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