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O P E R A T I N G P R O C E D U R E
3.2 NORMAL INTERNAL OPERATION.
3.2.1 PRF ADJUSTMENT.
P u l s e repetition frequency is adjusted by t h e
P R F controls ( 1 and 2, Figure 1-I), over a range of
2.5 c / s t o 1.2 Mc/s. T h e P R F s w i t c h is calibrated t o
indicate prf correctly only when t h e A F control is fully
clockwise. When t h e A F control is fully counterclock-
w i s e , t h e prf is lowered well below t h e next lower P R F
switch setting. T h e range of adjustment of t h e OF con-
trol is more than enough t o s p a n any one of t h e ranges
s e t by t h e P R F s w i t c h and t h u s affords continuous
coverage of the prf range of 2.5 c / s t o 1.2 Mc/s. It is
important t o remember, however, that t h e only calibrated
frequencies a r e t h o s e indicated by t h e P R F s w i t c h
positions, and that t h e s e a r e a c c u r a t e only when t h e A F
control is fully clockwise.
3.2.2 PULSE-DURATION ADJUSTMENT.
Duration of t h e main pulse is adjusted by t h e
PULSE DURATION controls (3 and 4 , Figure 1-1).
T h e RANGE switch (4) s e l e c t s one of s e v e n d e c a d e
ranges and t h e range s e l e c t e d is covered by t h e PULSE
DURATION d i a l (3). T h i s control c o n s i s t s of a knob
linked by
a
slow-motion drive t o
a
d i a l that is calibrat-
e d from 1 t o 11 in t e n t h s of a unit. T h e overlap beyond
the decade s p a n e n s u r e s continuous coverage of a l l
durations.
3.2.3 AMPLITUDE ADJUSTMENT.
Amplitude of the main pulse is adjusted by t h e
large AMPLITUDE switch, which v a r i e s t h e amplitude
from zero t o maximum in t e n s t e p s , and by the s m a l l
amplitude control (concentric with the switch
)
which
f a c i l i t a t e s continuous adjustment between s t e p s . T h e
positions of the larger switch corresponds t o c h a n g e s in
in output impedance in 100-ohm s t e p s . T h u s a s e t t i n g of
five i n d i c a t e s that t h e output impedance is about 5 0 0
ohms. When both controls a r e fully c l o c k w i s e , t h e am-
plitude is 6 0 volts and t h e output impedance is one
kilohm.
3.2.4 FAMILIARIZATION PROCEDURE.
T h e b e s t way t o become familiar with t h e p u l s e
generator is t o connect i t t o a n o s c i l l o s c o p e and watch
t h e p u l s e s themselves. T h e procedure is a s follows:
a . Connect t h e OUTPUT PULSE
t
binding post t o
the oscilloscope vertical input by means of open
l e a d s or a probe.
b. Connect t h e SYNC + b i n d i n g p o s t t o t h e oscillo-
s c o p e s y n c or trigger input.
c . Connect any of the ground binding p o s t s t o t h e
oscilloscope ground.
d. Be s u r e that the link a c r o s s t h e E X T O F F S E T
binding post is firmly connected t o both p o s t s .
e . Adjust t h e oscilloscope trigger controls t o trigger
on t h e %volt, 1 0 0 - n s , positive prepulse of t h e T y p e
1398-A.
f. S e t t h e oscilloscope s w e e p rate controls for a
2-ms/div s w e e p rate.
g. Set the o s c i l l o s c o p e v e r t i c a l gain controls for
about 4 0 volts/cm s e n s i t i v i t y .
h. Set t h e P R F switch t o 1 kc/s.
i. S e t t h e AF control fully clockwise.
j. S e t t h e PULSE DURATION d i a l t o 5.
k. S e t t h e PULSE DURATION RANGE s w i t c h t o
1 0 0
ps-1
ms.
1. S e t t h e AMPLITUDE control fully clockwise.
T h e o s c i l l o s c o p e should now d i s p l a y a 1-kc
square-wave from the p u l s e generator. U s e t h e PULSE
DURATION d i a l t o shorten and t o lengthen t h e p u l s e and
then s e t t h e PULSE DURATION RANGE s w i t c h t o t h e
next lower range D e c r e a s e t h e prf f i r s t by turning the OF
control counterclockwise and t h e n by s e t t i n g t h e P R F
s w i t c h t o t h e next lower position. Adjust the o s c i l l o -
s c o p e s w e e p r a t e control t o k e e p both t h e p u l s e duration
and frequency under observation. T o d e c r e a s e p u l s e am-
plitude, turn t h e AMPLITUDE control counterclockwise.
If t h e o s c i l l o s c o p e h a s a dc-coupled v e r t i c a l am-
plifier, s e t i t for d c , disconnect t h e p u l s e , a n d e s t a b -
l i s h t h e ground reference trace. Now reconnect the pos-
itive main pulse and vary i t s amplitude. T h e n move t h e
connector from t h e
+
O U T P U T PULSE t o t h e
-
OUT-
P U T PULSE binding p o s t and vary t h e amplitude a g a i n .
Note that the p u l s e contains a d c component that is
negative with r e s p e c t t o ground. T h e positive pulse
s t a r t s from -60 volts and r i s e s t o ground during its
a c t i v e interval. T h e negative p u l s e s t a r t s from ground
and fal!s t o - 6 0 volts during i t s a c t i v e interval.
If, during any of t h e above procedures, t h e p u l s e
is defective or t h e pattern becomes confused, c h e c k t o
make s u r e that t h e p u l s e duration h a s not b e e n made
too long for t h e p u l s e repetition frequency and t h a t a n
o s c i l l o s c o p e with a dc-coupled v e r t i c a l amplifier is
u s e d t o observe p u l s e s of very long duration.
3.3 NORMAL EXTERNAL OPERATION.
3.3.1 DRIVING-SIGNAL REQUIREMENTS.
T h e T y p e 1398-A w i l l produce externally triggered
p u l s e s a t frequencies from d c t o 2.4 Mc/s. T h e driving
s i g n a l should be applied t o t h e E X T DRIVE terminals,
and should b e a t l e a s t
0.5
volt,rms, u p t o 500 k c / s and
a t l e a s t 1 v o l t , r m s , from 500 k c / s t o 2.4
MC/S.
E x c e s -
s i v e driving voltages a t frequencies above 1.5 Mc/s
may overload t h e triggering c i r c u i t s . If t h e unit f a i l s t o
trigger, reduce t h e driving voltage. With optimum driving
voltage t h e unit will trigger t o frequencies typically a s
high a s 2.5 Mc/s.
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