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TYPE 1391-B PULSE, SWEEP, AND TIME-DELAY GENERATOR
n. S e t the SWEEP DURATION pSEC control to 12 and the
SWEEP MULTIPLIER to 10 to produce a 120-psec sweep. The
sweep recurrence rate i s now 5 kc. If the SWEEPMONITORlamp
goes out, flip the RESET switch.
o. Reset the sweep controls for60 p s e c (SWEEP DURATION
pSEC to 6, SWEEP MULTIPLIER to lo), and vary the input tim-
ing frequency from 10 kc a t the audio generator. Note that a s
the frequency is increased toward 16 kc, the sweep becomes in-
stable. The vernier control can be s e t to either
f
or
-
10% to
restore stability.
2.7 PULSE-GENERATING CIRCUIT.
a. Set all controls to the positions listed in paragraph 2.3.
b. Connect the oscilloscope vertical amplifier input t o the
PULSE POS terminals. If either brief pulses or a fast rise time
is desired, use a coaxial cable for this connection.
c. Connect the oscilloscope ext sync to the Type 1391-B
DIRECT SYNC terminals.
d. Observe the output positive 50-psec pulse. Experiment
with the DELAY and DURATION controls, setting DELAY to 20,
DURATION to 20. The negative pulse should appear a s in Fig-
ure 2.2D.
e. Move the oscilloscope connection to the PULSE POS ter-
minals and observe the positive 40-psec pulse.
f.
Reduce the pulse duration from 50 to 25 p s e c by switch-
ing the SWEEP DURATION pSEC control to
3.
Observe the
pulse duration and delay and return the SWEEP DURATION pSEC
switch to
6.
g. Reduce the pulse duration to 25 p s e c by resetting the
PULSE DURATION (inner) dial.
h. Reposition this 25-psec pulse to start 25 p s e c after the
sweep by rotating the PULSE DELAY dial counterclockwise.
Note that the three rings of numbers on the PULSE DURATION
-
and PULSE DELAY dials correspond to the three settings of the
PULSE SCALE switch.
i. Now pulses of 2.5 p s e c can be obtained with the SWEEP
MULTIPLIER switch s e t a t 1. Various other pulse durations and
delays can be s e t by means of the sweep switches, PULSE DU-
RATION, and PULSE DELAY controls.
j.
Short Pulses: Decrease the sweep duration to 3 p s e c .
Then decrease the PULSE DURATION setting until
sl
pulse of
minimum duration is produced. Note that this pulse can be re-
duced even beyond the usual amplitude, and that the pulse polar-
ity will reverse suddenly a t a DURATION setting below zero.
This is characteristic, since i t is not possible toproduce a me-
chanical stop of sufficient accuracy to stop the motion of the
DURATION dial a t exactly zero.
DIRECT
SYNC
2 0 W f
i 1 - 0
START
DELAYED
SYNC
2 ? r ~ f
J
I I
*
STOP
Figure 2.8. Adding Network
for
Multiple Pulsing.
k. Set up a I - p s e c pulse and experiment with the OUTPUT
IMPEDANCE and PULSE AMPLITUDE controls. Some defects
might appear in the pulse due to impedance mismatch a s the
OUTPUT IMPEDANCE setting is varied. Note also that the
PULSE AMPLITUDE control adversely affects the pulse shape
when the pulse is s e t to greatly reduced values. The PULSE AM-
PLITUDE control i s generally satisfactory for pulses of long
duration and over a 10- or 20-db range, but for best pulse shape
an attenuator or a pad of the proper impedance is recommended.
2.8 USE OF THE PULSE START STOP TRIGGERS SWITCH.
2.8.1
INTERNAL (NORMAL) POSITION.
a. Set all controls to the positions listed in paragraph 2.3.
b. Set the oscilloscope horizontal controls for a writing rate
of 20 p s e c per division.
c. Connect the oscilloscope vertical amplifier input to the
PULSE NEG terminals.
d. Connect the oscilloscope sync to the Type 1391-B DI-
RECT SYNC terminals.
e. Observe the 50-psec negative pulse on the oscilloscope.
I t should appear a s shown in Figure 2.6B.
f. Now move the oscilloscope vertical input connection to
the START terminal. Note the presence of a 5-volt positive
start pulse corresponding to the leading edge of the main pulse
(Figure 2.6C).
g. Move the oscilloscope vertical input connection to the
STOP terminal, and note the presence of a 5-volt positive stop
pulse a s shown in Figure 2.6D. Note a t both START and STOP
terminals a negative pulse a t the end of the sweep. Move the
PULSE DURATION dial and note the motion of the
stop pulse
corresponding to the dial reading. The start pulse moves when
the PULSE DELAY dial i s moved.
2.8.2 EXTERNAL POSITION.
a. Move the oscilloscope vertical input connection back to
the PULSE POS terminal, and, if possible, s e t the oscilloscope
for d-c input.
b. Set the PULSE START STOP TRIGGERS switch to the
EXT position.
c. T a p first the START and then the STOP terminal with a
piece of metal held in the hand. The pulse should start andstop
with each tap. In this manner, pulses can be produced by any ex-
ternal trigger generator.
d. To u s e the delay circuit to time the main pulse, proceed
a s directed in s t e p s e through h below.
e. Set the oscilloscope and PULSE START STOP TRIGGERS
switch a s indicated in s t e p s a and b abovz.
f.
Connect a jumper wire from the DIRECT SYNC OUT ter-
minal to the START terminal and another from DELAYED SYNC
to STOP terminal.
g. Note that a 50-psec pulse, corresponding to the 50-psec
delay interval, is produced (Figure 2.5B). Now vary the time
delay settings from 1 p s e c up to about 90 p s e c and note that
pulse duration is controlled by delay.
h. This connection, in which the delay circuit is used to con-
trol pulse duration, permits the production of pulses up to 1.1
seconds in duration. To produce such a pulse, s e t (if possible)
the oscilloscope writing rate a t 0.2 s e c per division. Disconnect
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