General Information - Tektronix 1S1 Instruction Manual

Operating Instructions – Type 1S1
its normal position before another single-sweep presentation
can be obtained.)
Fig. 2-15. Typical "false" sampling display showing the means
of detecting and eliminating the "false" presentation. (A) 1-Gc
sine wave viewed at 5 nsec/cm and a low dot density; (B)
same 1-Gc waveform viewed at a high dot density; (C)
waveform viewed at 1 nsec/cm sweep rate, showing true
frequency of signal.
External Sweep and Manual Scan
When the DISPLAY MODE switch is set to either EXT
HORIZ or MAN, the staircase generator no longer provides
a staircase waveform for driving the horizontal deflection.
If an external voltage signal is applied to the EXT HORIZ IN-
PUT jack with the DISPLAY MODE switch at EXT HORIZ,
the external signal will produce horizontal scanning of the
crt display, but the display will still be calibrated in equiv-
alent time as indicated by the TIME/CM switch. Similarly,
if the MANUAL SCAN control is turned while the DISPLAY
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MODE switch is at MAN position, an internal voltage in
the Type 1S1 will provide horizontal scanning of the equiv-
alent-time crt display.
Slow scanning with either an externally-applied signal
or the MANUAL SCAN control is convenient at times for
driving an external recording device or for observing some
particular portion of the waveform at a high dot density.
Since all circuits other than the staircase must still be
operated once for each sample to be displayed, the other
display and triggering controls should be set up in the usual
manner. The dot density of the display is set by the rate of
scanning, rather than by the setting of the SAMPLES/CM
control. Because of this, it is usually best to use a linear
waveform such as a sawtooth or triangle for scanning the
display, in order to provide a uniform dot density. The Sweep
Output or Sawtooth Output jack on the oscilloscope front
panel is a convenient source for the scanning voltage. The
more slowly the display is scanned, the denser the trace will
be.
The EXT HORIZ ATTEN control adjusts the attenuation of
an external ly-applied deflection voltage. The attenuation
factor is variable from 1 volt/cm with the control fully clock-
wise to greater than 16 volts/cm with the control fully
counterclockwise. This permits full scanning of the crt with
signals of from 10 volts to 150 volts in amplitude (150 volts
is the maximum permissible at the EXT HORIZ INPUT).
REAL-TIME SAMPLING OPERATION

General Information

If sweep rates are needed below the slowest equivalent-
time rate provided by the Type 1S1 TIME/CM switch, the
Type 1S1 and the oscilloscope may be operated in such a
way as to produce "real-time" sampling displays. Real-time
sampling is a method of operation in which the samples are
taken at a constant rate from a relatively low frequency
signal (Dc to 5 kc) and displayed at a sweep rate determined
by the oscilloscope Time/Cm switch. Thus, the samples are
taken continuously along the waveform, rather than one
sample from each cycle of the waveform, and the displayed
series of dots follows the actual shape of the input signal
waveform.
In real-time sampling operation, the oscilloscope provides
triggering of the display, in addition to providing the real-
time sweep rate. The triggering circuit of the Type 1S1 is
operated in free run to provide sampling pulses. To provide
the fastest sampling repetition rate, the Type 1S1 TIME POSI-
TION RANGE switch should be set to one of the 500 nS
or 50 nS positions. The staircase generator of the Type 1S1
must be disabled for real-time sampling operation to prevent
periodic blanking during the staircase retrace. This is done
by setting the Type 1S1 SAMPLES/CM control to the SWEEP
OFF position.
Advantages
The primary advantage of real-time sampling is that it
extends the operation of the oscilloscope down to low fre-
quencies without having to use a different plug-in unit. In
addition, the Type 1S1 provides greater vertical sensitivity
than many non-sampling plug-in units, though its maximum