TM 11-6625-1559-12
line established in b above by adjusting the
PREAMPLIFIER DC LEVEL control.
(3) Procedure for desired type of operation
d. Turn the PREAMPLIFIER GAIN control
fully clockwise. If the trace moves, return it to
the reference line by adjusting the coarse pream-
plifier balance potentiometer, a screwdriver ad-
justment accessible through the center of the
a. Preliminary.
e. Turn the PREAMPLIFIER GAIN control
(1) Set the front panel controls as follows
fully counterclockwise. If the trace moves, return
it to the reference line by adjusting the PRE-
AMPLIFIER DC LEVEL control.
Control
Position
PREAMPLIFIER controls:
f. Repeat the instructions in d and e above un-
AC-DC switch ---------- DC.
til the PREAMPLIFIER GAIN control can be
BALANCE control ---- Midrange.
rotated throughout its entire range without
GAIN control --------- Fully counterclockwise
changing the position of the trace by more than
(minimum gain).
2 centimeters (cm). Use the front panel PRE-
BAND SELECTOR switch -- UHF.
SWEEP WIDTH
WIDE.
amplifier BALANCE (fine) control for finer
switch.
adjustment.
Fully clockwise (maximum
SWEEP WIDTH
sweep width).
g. Remove the connection to the oscilloscope
control.
RF OUTPUT control --- Fully clockwise (maximum
vertical input. If the trace moves, adjust the PRE-
output).
ATTENUATOR db 20.
remains in position whether or not the vertical
switch.
input connection is made.
(2) Insert shorting plug into EXT WOBB
DRIVE socket on the rear panel of the main
i. Pull the PHASING TURN-BLANKING
PULL switch.
switch at ON, and turn on the oscilloscope. Al-
to one input jack on the D-50 detector; use a
low a minimum 30-minute warmup period.
short piece of high-quality, 50-ohm coaxial cable
(RG-55/U, or equivalent). Terminate the un-
Note. It is important that no evaluation of sweep
width be made before the 30-minute, warmup period, be-
used input jack on the detector with the 50-ohm
cause the wobbulator diaphragm is too stiff to make its
termination Adapter-Connector UG-1640/U sup-
maximum excursion while in the cold state. If the wobb-
plied with the sweep generator.
ulator chatters at any time, by the WOBB DRIVE LIMIT
control (fig. 2-2) counterclockwise until the noise stops.
k. Pull the 100 MHz MARKER GAIN switch.
This control is a screwdriver adjustment located on top
of the main chassis and is accessible by opening the top
l. Set the MARKER MASTER GAIN control
cover of the sweep generator cabinet. Chattering does not
for maximum gain (fully clockwise).
indicate a malfunction and no harm will result unless the
chattering is permitted to continue for prolonged periods.
m. Turn the 100 MHz MARKER GAIN con-
trol clockwise until markers appear.
3-4 Initial Check of Equipment
PULL switch in and observe the forward and
return traces, each with a set of markers. Adjust
b. Set the oscilloscope vertical sensitivity to
the PHASING TURN-BLANKING PULL con-
0.1 volt per centimeter and the horizontal sensi-
trol so that the traces and markers approach co-
tivity to 2 volts/cm. Center the trace on the
incidence.
screen.
o. Pull the PHASING TURN-BLANKING
c. Connect the SCOPE VERT jack on the rear
PULL switch.
p. Adjust the RF OUTPUT control to flatten
If the trace disappears, return it to the reference
the oscilloscope trace.