or inverted operation, and set the MODE switch to ALT or
CHOP.
In general, use the CHOP position (chopped-mode opera
tion) with sweep rates up to about 10/x.s/cm for display
ing two non-repetitive signals occurring within the sweep-time
interval set by the oscilloscope Time/Cm switch.
Non-
repetitive signals are those which are single-shot, transient,
or random. The CHOP position is also useful for displaying
low-frequency synchronous signals. Synchronous signals are
those which have the same repetition rate or are frequency
related by a whole number multiple.
NOTE
When using chopped-mode operation, be sure
to set the oscilloscope CRT Cathode Selector switch
to a Dual-Trace Chopped Blanking position to
blank out the undesirable chopped-mode switch
ing transients.
Use the ALT position (alternate-mode operation) when
using sweep rates at about 0.5 ms/cm or faster to display
high-frequency synchronous and asynchronous signals. Asyn
chronous signals are those which do not have the same
repetition rate or are not frequency related to each other
by a whole number multiple. Table 2-2 summarizes the
following discussion on dual-trace operation.
Displaying Two Non-Repetitive or Low-Frequency (be
low 10 kHz) Synchronous Signals.
To show true time and
phase relationship between two non-repetitive or low-fre
quency synchronous signals, use chopped-mode operation.
Transients as short as 0.1 ms can be well delineated or re
solved. At 10/x.s/cm a 0.1 ms duration transient, for exam
ple, will contain about 100 segments in its trace. If a
higher sweep rate is used, the number of segments that
make up each of the traces will be less, and, therefore,
resolution will be poorer.
To make the display stable, use either internal triggering
on Channel 1 Only (from pin 5 of interconnecting plug—
see Block Diagram in Section 10) or use the CH 1 TRIG
GER OUT connector as the external trigger source. If your
oscilloscope has provisions for selecting the Channel 1 only
internal trigger as a triggering source, then use this fea
ture by setting the Triggering Source switch on the front
panel of the oscilloscope to the Plug-in position.
NOTE
Use the oscilloscope Plug-In position o f the Trig
gering Source switch in preference to external
patching to obtain optimum bandw idth c a p a b ili
ties from the Channel 1 Trigger O utput Am plifier.
If there is no Plug-In position, then use the signal avail
able at the CH 1 TRIGGER OUT connector as the Chan
nel 1 only trigger source. To use the signal, connect a co
axial cable from the CH 1 TRIGGER OUT connector to the
oscilloscope Trigger Input connector and set the Triggering
Source switch to Ext.
CAUTION
Do not apply external voltages to either the CH
1 TRIGGER OUT or CH 1 SIGNAL OUT connectors
as this may damage the internal associated cir-
Operating Instructions— Type 1A1
cuits. Shorting the connectors to ground, how
ever, w ill not cause any damage.
If asynchronous signals are applied to the Type 1A1
while you are using chopped mode of operation and Chan
nel 1 only triggering, the Channel 1 waveform will remain
stationary while the Channel 2 waveform will appear to be
free running. However, if the frequency of the Channel 2
signal is changed so that it becomes synchronized with the
Channel 1 signal, or vice versa, then the two signals will
appear as stationary displays on the CRT. This is one ap
plication which can be useful for determining the zero-
beat frequencies of the two signals.
Do not set the oscilloscope Triggering Source switch to
Norm Int or Int (oscilloscope vertical amplifier trigger take
off signal) because a stable display is difficult and some
times impossible to obtain. During dual-trace chopped-
mode operation the Norm Int or Int trigger .source is a com
posite signal consisting of the signals applied to both chan
nels superimposed on, but not synchronized with, the free-
running rate of the chopped-mode switching signal. The
switching signal has a square waveshape the same as the
one shown in Fig. 2-1B. Its amplitude is dependent on the
distance that the traces are positioned apart (providing
no DC component is contained in the applied signals) and
its rate is the chopping rate (about 1 MHz).
Since the internal trigger from the oscilloscope vertical
amplifier is a composite trigger during chopped mode of
operation and the trigger contains a non-synchronized
chopped-mode switching signal, internal triggering may
occur first on one of the applied signals and then on the
chopped-mode switching signal, or vice versa, resulting in
an unstable display.
Displaying Two Asynchronous Signals.
To obtain a
stable display of two asynchronous signals which do not
exceed the system bandwidth, use alternate-mode operation
and set the oscilloscope Triggering Source switch to Norm
Int or Int. Set the oscilloscope Triggering Coupling switch
to AC for stable triggering on signals below 1 kHz; set the
Triggering Coupling switch to AC LF Reject or AC Fast for
stable triggering and a bright display on signals above
1 kHz. Since the oscilloscope vertical amplifier internal trig
ger is the trigger source, the applied signals will not be
displayed in their true time relationship because triggering
occurs on the applied signal in each channel as it switches
on.
To obtain a stable display in this mode of operation, it
is very important to set the oscilloscope Triggering Level
control to a point where the time base can trigger on the
signal in one channel as it turns on, and on the signal in
the other channel when it turns on. In addition, both applied
signals must be of sufficient amplitude to meet the internal
trigger signal amplitude requirements of the oscilloscope.
If one displayed signal has a smaller amplitude than the
other, but is of adequate amplitude for internal triggering,
set the Triggering Level control to a point that will assure
triggering on the smaller amplitude signal. To do this, set
the Triggering Level control near the 0 position.
Though it may seem easy to obtain stable triggering on
asynchronous signals, there are certain conditions that may
promote jitter. When using the AC Fast or AC LF Reject
triggering mode, jitter most likely occurs when attempting
® i
2-9
