Tektronix 7834

VERTICAL MODES .
When the LEFT or RIGHT button of
the VERTICAL
MODE switch is pressed, only the signal
from
the plug-in unit in the selected compartment is
displayed .
Alternate
Mode . The ALT position of the VERTICAL
MODE switch produces a display which alternates between
the LEFT VERT and RIGHT VERT compartments
with
each sweep of the crt . Although the ALT mode
can be used
at all sweep rates, the CHOP mode provides a
more
satis-
factory display at sweep rates below
about
20
milliseconds/
division . At these slower sweep rates, alternate-mode
switching becomes perceptible .
Alternate Mode displays have three types of triggering
available . When the A and
B
TRIGGER SOURCE
switches
are set to the VERT MODE positions, each
sweep is trig-
gered by the signal
being
displayed on
the crt . This provides
a stable display of two unrelated signals,
but does not
indicate the time relationship between the
signals . In either
the LEFT VERT or the RIGHT VERT positions of
the
TRIGGER SOURCE switches, the two signals
are
displayed
showing true time relationship
. However, if the signals are
not time
related, the display from the plug-in that is not
providing a trigger signal will be unstable on the crt .
When
the ALT vertical mode is selected and either the
ALT
or CHOP
button
of
the HORIZONTAL MODE switch
is
selected, the instrument operates in the independent-
pairs
mode . Under
this
condition, the signal from the
LEFT VERT unit is always displayed at
the sweep rate of
the B HORIZ time-base
unit,
and the
signal from the
RIGHT VERT unit is displayed at the sweep rate of the A
HORIZ time-base unit (non-delayed sweep only) . This
results in two displays that are completely independent as
to vertical deflection and sweep rate . This display is equiv-
alent to the display obtainable with a dual-beam oscilloscope
for most repetitive-display combinations .
If delayed-sweep operation is used with this Mode, a
different sequence is displayed . First, the LEFT VERT unit
signal is displayed at the sweep rate of the A HORIZ time-
base unit (delaying sweep) and then at the sweep rate of the
B HORIZ time-base unit (delayed sweep) . The vertical
display then shifts to the RIGHT VERT unit and its signal
is displayed consecutively at the delaying and delayed
sweep rates .
Chopped Mode .
The
CHOP position of the VERTICAL
MODE switch produces a display which is electronically
switched between channels at about a one-megahertz rate .
In general, the CHOP mode provides the best display at
sweep rates slower than about 20 milliseconds/division or
Operating Instructions--834
whenever dual-trace,
single-shot phenomena are to be
displayed . At faster sweep rates
the chopped switching
becomes apparent and
may interfere with the display .
When the A or B TRIGGER SOURCE
switches are set to
VERT MODE, internal trigger
signals from the vertical plug-
ins are algebraically
added and the time-base units are trig-
gered from the resultant signal . The LEFT VERT or
RIGHT VERT trigger-source positions provide trigger
signals to the time-base units on the internal trigger signal
from the selected vertical unit only . This allows two
time-
related signals to be displayed
showing true time relation-
ship . (If the signals are
not time-related, the display from
the
channel
that
is not providing the trigger signal will
appear unstable .)
The CHOP mode can be used to compare two
single-shot,
transient, or random signals that occur within the time
interval determined by the time-base unit (ten
times
selected sweep rate) . To provide correct triggering,
the
displayed signal which provides the trigger signal must
precede the second display in time . Since the signals show
true time relationship, time-difference measurements
can be
made from the display .
Algebraic Addition . The ADD position of the VERTICAL
MODE switch can be used (1) to display
the sum or
difference of two signals, (2) for common-mode
rejection
to remove an undesired signal, or (3) for do offset (applying
a do voltage to one channel to offset the do component of a
signal on the other channel) . The common-mode rejection
ratio between the vertical plug-in compartments is at least
100 :1 from do to 150 megahertz . The rejection ratio
decreases to 30 :1 from 150 to 400 megahertz
.
The overall deflection on the crt in the ADD mode is the
algebraic sum of the signals from the two vertical plug-in
units . It is difficult to determine the voltage amplitude of
the resultant display unless the amplitude of the signal
applied to one of the plug-ins is known . This is particularly
true when the vertical units are set to different deflection
factors, since it is not obvious which portion of
the display
results
from
the signal
applied to a
given plug-in unit . The
polarity
and
repetition rate
of
the applied signals will also
affect the ADD display .
The following precautions should be observed when using
the ADD mode :
1 .
Do not
exceed the input-voltage ratings of the plug-in
units .