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the driving oscillator from the PRF DRIVE terminals. Set the
TIME DELAY MICROSECONDS dial to 11.00, and the TIME
DELAY RANGE switch to 100 p s e c
-
1 sec. Now either flip
the RESET switch or tap the P R F DRIVE terminal quickly, and
note the production of the long pulse.
2.8.3 INTERNAL
f
EXTERNAL POSITION. This position per-
mits externally produced trigger pulses to be added to the start
and stop triggers generated in the pulse timing circuits. To test
the operation of this switch position, generate a double pulse a s
follows:
a. Build and connect the adder circuit shown in Figure 2.8.
b. Set the SWEEP TRIGGER switch to DELAYED.
c. Connect the oscilloscope vertical deflection input to the
PULSE POS terminals.
d. Connect the oscilloscope synchronizing terminal to the
DIRECT SYNC OUT terminals.
e. Set the PULSE START STOP TRIGGERS switch to EX-
TERNAL and move the DELAY MICROSECONDS dial from i t s
standard position, noting that the delay circuit controls the dura-
tion of the pulse.
f. Set the PULSE START STOP TRIGGERS switch to IN-
TERNAL
f
EXTERNAL, with the pulse timing controls in stan-
dard positions. Note the presence of a double pulse. The delay
and duration of the second pulse can be varied by means of the
PULSE DELAY and DURATION controls.
Section
3
CALIBRATION PROCEDURE
3.1 INTRODUCTION.
Calibration and readjustment procedures
are given in the order of signal progression through the instru-
ment. Paragraph 3.2 l i s t s the t e s t equipment necessary to carry
out the calibration of the various circuits, and paragraphs 3.3
through 3.6 discuss the calibration and readjustment procedures
necessary in each circuit.
It i s hardly likely that a complete calibration, such a s that
given every new instrument in the General Radio laboratory, will
ever be necessary. Usually few, if any, adjustments are neces-
sary when a tube or circuit component
is
replaced because of
failure. Gradual degradation in tube characteristics with use may
require retouching of the screwdriver adjustment common to all
ranges in the sweep or delay circuit. Also, some unpredictable
shift in the values of resistors or capacitors in range timing cir-
cuits will generally appear a s a change in the calibration of one
range. Only the adjustment for thatrange must be s e t , and onlythe
relevant paragraph must be consulted, along with paragraph 3.2.
A common adjustment i s the range minimum adjustment
(R238) in the delay circuit, which may require readjustment when
V203 is replaced. This adjustment, discussed in paragraph 3.4,
is common to a l l delay ranges. An equivalent adjustment may be
necessary in the sweep circuits to restore the calibration of the
pulse-delay dial when either V303 or V307 is replaced. The con-
trols requiring readjustment are the pulse duration and delay
minimums R412 and R411. (Refer to paragraph 3.5.2.) Other ad-
justments are those used t o correct for component tolerances in
the R-C time constants. Such adjustments must be made only
when the components themselves drift (unlikely) or are replaced.
3.2 TEST EQUIPMENT.
The type and quantity of auxiliary
t e s t equipment necessary for recalibration depend entirely on
the accuracy desired, the complexity of the recalibration, and,
t o some extent, on the range being recalibrated. This equipment
can range from a cathode-ray oscilloscope, audio oscillator, and
ac-dc multirange meter to the full series of time-measuringequip-
ment listed below. The equipment listed below is adequate for
complete recalibration of the instrument.
(1) Oscilloscope
-
Tektronix 530 or 540 series, or equiva-
lent.
(2) Crystal-controlled time-marker generator
-
Tektronix 180,
Dumont 300, or equivalent producing time markers from 1 to
10,000 p s e c . All of these timing markers should be simultane-
ously available a t the panel terminals of the marker generator.
(3) Time-interval measuring system
-
While not an absolute
necessity in the recalibration of the instrument, a time-interval
meter simplifies the calibration of the longer sweeps, delay in-
tervals, and pulse durations. This time-interval meter should
operate from two triggers, one to start and one to stop the time-
interval measurement. Ideally, i t should resolve 1- or 0.1-psec
input pulses. The time-interval meter will facilitate the measure-
ment of the longer delays, sweeps, and pulses, without the ne-
cessity of viewing the very slow transients arising from the long
delays on an oscilloscope. Possible instruments for use in this
application, if available, are the Berkeley 5571 and 5510, Hew-
lett-Packard 521-A, 522-B, or 524-B plus 526-B, or t h e L F E 501.
Additional test equipment includes an audio oscillator
(General Radio Type 1210, 1302, or equivalent) needed to s e t
the prf, and an a-c vacuum-tube voltmeter to measure either the
rms or peak value of the input voltage.
3.3 CALIBRATION AND ADJUSTMENT OF INPUT CIRCUITS.
3.3.1 ADJUSTMENT OF R104.
a. Connect the audio oscillator (set to 10 kc, output atleast
1 volt) to the PRF DRIVE terminals.
b. Connect the oscilloscope vertical amplifier input to the
DIRECT SYNC OUT terminals.
c . Center the TRIGGERING LEVEL control.
d. Set the TRIGGER SELECTOR switch to POS GOING AC,
and observe the direct synchronizing signal a s the audio oscil-
lator gain-control setting is decreased.
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