Trigger Source; Basic Applications - Tektronix 1S1 Instruction Manual

sensitivity can be used only if the signal source impedance is
50 ohms. Passive sampling probes or cathode - follower
probes, with 10X minimum attenuation, may be used if the
source impedance is other than 50 ohms. Another advantage
of real-time sampling with the Type 1S1 is that the passive
probes may be conveniently extended from the oscilloscope
by relatively long lengths of 50-ohm coax cable without
changing the input characteristics of the Type 1S1.
Sweep Rates
The range of sweep rates available for use in real-time
sampling is from the slowest rate available with the oscillo-
scope to about 0.1 msec/cm. At the crossover point from
real-time to equivalent-time sampling, the display dots begin
to have significant horizontal dimension, due to their dura-
tion in real time. This may be seen in Fig. 2-16 which shows
a 5-kc square wave in equivalent-time sampling and real-
time sampling displays. (This is one sweep rate beyond the
practical limit of real-time sampling.) At sweep rates of 2
msec/cm and slower, the display dots are essentially con-
tinuous and provide a presentation that can be compared
quite favorably with that obtained with a non-sampling
plug-in unit.
Fig. 2-16. Crt display of a 5-kc square wave showing comp-
arison between equivalent-time sampling (A) and real-time
sampling (B), just past the sweep-rate limit of real-time
sampling (see text).
Signal Coupling
The input signal may be applied to SIGNAL IN connector
through 50-ohm coaxial cables and attenuators, passive
Operating Instructions – Type 1S1
sampling probes or cathode-follower probes. For input
signals with amplitudes above approximately 16 volts, a
cathode-fol lower probe should be used, since dc-coupled
passive sampling probes cannot be used above this voltage
level, and ac-coupling of the probes does not pass signals at
these frequencies.
Triggering Sources
Since the oscilloscope triggering circuitry is used, the
normal triggering sources available through the oscilloscope
are used. The triggering signal may be obtained either in-
ternally from the oscilloscope vertical amplifier or power-
line signal, or externally through the oscilloscope external
trigger input.
Procedure
To set up the Type 1S1 and oscilloscope for displaying sig-
nals with the real time method of operation:
1. Set the Type 1S1 controls as follows:

TRIGGER SOURCE

TIME/CM
SAMPLES/CM
mVOLTS/CM and
VARIABLE
VERT POSITION and
DC OFFSET
2. Set the oscilloscope Horizontal Display switch to one
of the internal time-base positions (e.g. Time Base A).
3. Apply an input signal within the amplitude limits of
the SIGNAL IN connector (maximum ±2 volts). Use an at-
tenuator probe or coaxial attenuators if the signal amplitude
is greater than this.
4. Trigger the display with the oscilloscope triggering
controls. For very low frequencies, use dc trigger coupling,
as selected by the oscilloscope Trigger Mode or Coupling
switch. For power-line frequency input signals, use line
triggering.
Fig. 2-17 shows a comparison between a real-time sam-
pling display of a line frequency signal obtained with the
Type 1S1 and a conventional display of the same signal
obtained with a non-sampling plug-in unit. (The signal was
taken from the lead supplying power to the graticule lights
of the oscilloscope.)

BASIC APPLICATIONS

General Information
The displayed waveform on the oscilloscope screen is
normally a plot of voltage per unit equivalent time. The
calibrated deflection factors of the Type 1S1 permit the sam-
pling system to be used for making accurate voltage and
time measurements of the input signal.
FREE RUN
Any position utilizing
the 50 nS or 500 nS
time position range
SWEEP OFF
Adjust for adequate
display amplitude
Adjust to position
trace on crt
2-23